Conservation of Marine Birds

Conservation of Marine Birds is the first book to outline and synthesize the myriad of threats faced by one of the most imperiled groups of birds on earth. With more than half of all 346 seabird species worldwide experiencing population declines and 29% of species recognized as globally threatened by the International Union for Conservation of Nature, the timing to determine solutions to threats could not be more urgent. Written by a diverse team of international experts on marine birds, this book explores the environmental and biogeographical factors that influence seabird conservation and provides concrete recommendations for mounting climate change issues.

This book will be an important resource for researchers and conservationists, as well as ecologists and students who want to understand seabirds, the threats they are facing, and tactics to help conserve and protect them.

• Outlines both threats and solutions in the marine and terrestrial realm
• Synthesizes information to provide a comprehensive strategy moving forward, especially considering climate change
• Created by a team of experts with the latest and most comprehensive knowledge of seabird conservation

• Language: English
• Publisher: Academic Press
• Release date: Sep 27, 2022
• ISBN: 9780323885409

Book preview

9780323885409_FC

Conservation of Marine Birds

First Edition

Lindsay Young

Executive Director, Pacific Rim Conservation, Honolulu, Hawai, USA

Eric VanderWerf

Director of Science, Pacific Rim Conservation, Honolulu, Hawai, USA

Table of Contents

Cover

Title page

Copyright

Contributors

About the Editors

Preface

Acknowledgments

Section I: Threats

Chapter 1: Ecology of marine birds

Abstract

Life history and adaptations

Population biology

Breeding ecology

Foraging ecology

Differences between temperate and tropical seabirds

Conclusions

References

Chapter 2: Conservation status and overview of threats to seabirds

Abstract

Seabird status and trends

Threats to seabirds

Conclusions

References

Chapter 3: Interactions between fisheries and seabirds: Prey modification, discards, and bycatch

Abstract

Acknowledgments

Introduction

Forage fisheries

Fisheries for large pelagic and demersal fishes

Discards, offal, and food quality

Bycatch

Disturbance

Aquaculture

Projected trends, emerging threats, and environmental synergisms

Knowledge gaps, future research

Conclusions

References

Chapter 4: Invasive species threats to seabirds

Abstract

Introduction

A short history of invasive species, islands, and why seabirds are threatened

Invasive mammals threaten seabird survival globally

The impacts of non-mammalian invasive species on seabirds

Projected trends in invasive species introductions and emergent threats

Conclusions and future directions in addressing invasive species threats to seabirds

References

Chapter 5: Health and diseases

Abstract

Acknowledgments

Introduction

Which infectious agents and biotoxins are most important?

Case studies

Projected trends and emerging threats

Knowledge gaps

Best practices for biosecurity at seabird colonies

Conclusions

Glossary

References

Chapter 6: Pollution—Lights, plastics, oil, and contaminants

Abstract

Acknowledgments

Introduction: Scope and severity of threats

Species and regions most impacted

Interactions with climate change

Projected trends

Emerging threats, knowledge gaps, and future research

Conclusions

References

Chapter 7: Exploitation and disturbance

Abstract

Acknowledgments

Human history, seabird ecology, and exploitation

Temporal aspects of exploitation

Types of exploitation

Harvesting

Disturbance and nonlethal exploitation

Seabirds as inspiration

The impacts of windfarms on seabirds

Discussion

References

Further reading

Chapter 8: Climate change: The ecological backdrop of seabird conservation

Abstract

Introduction

Seabird responses to climate change

Climate change impacts seabirds through timing, distribution, and biomass of prey

Effects of climate on seabird life history stages

Species’ vulnerabilities to climate change

Challenges in understanding and predicting the influence of climate change on seabirds

References

Section II: Solutions

Chapter 9: Introduction and historical approaches to seabird conservation

Abstract

Introduction

Finding nest sites of critically endangered species

Protecting breeding colonies

Providing and protecting individual nest sites

Mitigating mortality induced by artificial lights and structures

Mitigating the impacts of fisheries

Encouraging seabirds to breed at new or restored sites

Conclusions

References

Chapter 10: Legal and cooperative mechanisms for conserving marine birds

Abstract

Acknowledgments

Introduction

Legal and other tools

Land-based protections

Protections at sea

Discussion and conclusions

Disclaimer

References

Chapter 11: Cultural aspects of seabird conservation

Abstract

Introduction

Indigenous worldviews and perspectives of nature

Biocultural relationships between Indigenous Peoples and seabirds

Biocultural relationships and Indigenous resource management guide conservation and sustainable harvest of seabirds

Local Community perspectives of seabirds

Governance and comanagement

Social and environmental justice in seabird conservation

Conclusions

References

Chapter 12: Managing harvests of seabirds and their eggs

Abstract

Acknowledgments

Introduction

Regional patterns

Tools and effectiveness

Knowledge gaps and future research

Conclusions

References

Chapter 13: Mitigating light attraction

Abstract

Introduction

Tools and effectiveness

Knowledge gaps and future research

References

Chapter 14: Reducing collisions with structures

Abstract

Introduction

Identifying factors that impact seabird collision risk

Infrastructure with similar collision risk characteristics to powerlines

Methods for reducing seabird collisions with powerlines and similar infrastructure

Knowledge gaps and future research

Conclusions

References

Chapter 15: Conservation of marine birds: Biosecurity, control, and eradication of invasive species threats

Abstract

Introduction

Tools and planning considerations

Effectiveness of IAS solutions and seabird recovery

Regional trends in invasive species management

Emerging tools and trends in invasive species solutions for seabirds

Conclusions

References

Chapter 16: Fisheries regulation and conserving prey bases

Abstract

Introduction

Seabirds and prey resources

Prey depletion—Fisheries effects on seabirds

Regulation of forage fish and krill fisheries

Regulation of fisheries for large predatory fish

Discards and offal

Discussion

References

Chapter 17: Bycatch reduction

Abstract

Introduction

Determination of risk posed to seabirds from fisheries

Best practice seabird bycatch mitigation

Research to implementation

Case studies of fisheries successfully reducing seabird bycatch

Measuring success

Future directions

Conclusions

References

Chapter 18: Protecting marine habitats: Spatial conservation measures for seabirds at sea

Abstract

Introduction

Fundamentals of marine protection

Perspectives on Indigenous conservation

Protection measures

What and where to protect

How to protect: Approaches and strategies

Costs and benefits of marine protections

Implementation and effectiveness

Research and policy priorities

Summary and conclusion

References

Chapter 19: Restoration: Social attraction and translocation

Abstract

Introduction

Identifying a seabird restoration project

Selecting seabird restoration sites

Selecting a restoration approach

Social attraction methods

Translocation

Case studies

A global Seabird Restoration Database

Knowledge gaps and future work

References

Further reading

Chapter 20: Conclusions and the future of seabird conservation

Abstract

References

Index

Copyright

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Notices

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.

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Image 1

Cover images, clockwise from the top:

Tufted Puffin, photo credit Eric VanderWerf

Phoenix Petrel, photo credit Eric VanderWerf

Yellow-Eyed Penguin, photo credit Eric VanderWerf

Red-Tailed Tropic Bird, photo credit Eric VanderWerf

Laysan Albatross, photo credit Lindsay Young

Publisher: Nikki P. Levy

Acquisitions Editor: Anna Valutkevich

Editorial Project Manager: Kathrine Esten

Production Project Manager: Maria Bernard

Cover Designer: Matthew Limbert

Typeset by STRAIVE, India

Contributors

Karel A. Allard     Environment and Climate Change Canada, Canadian Wildlife Service, Sackville, NB, Canada

Lisa T. Ballance     Marine Mammal Institute, Oregon State University, Newport, OR, United States of America

Elsa Bonnaud     Écologie, Systématique et Évolution, Université Paris-Saclay, CNRS, AgroParisTech, Gif-sur-Yvette, France

Stephanie Borrelle     BirdLife International, Pacific Secretariat, Suva, Fiji

Rachel T. Buxton     Carleton University, Ottawa, ON, Canada

Rory Crawford     Royal Society for the Protection of Birds, Sandy, Bedfordshire, United Kingdom

Maria P. Dias

Department of Animal Biology, Centre for Ecology, Evolution and Environmental Changes (cE3c), Faculdade de Ciências da Universidade de Lisboa, Lisboa, Portugal

BirdLife International, Cambridge, United Kingdom

D.C. Duffy     University of Hawaii, Honolulu, HI, United States of America

Linda Elliott     Hawaii Wildlife Center, Kapaau, HI, United States of America

Jérôme Fort     Littoral, Environment and Societies (LIENSs), UMR 7266 CNRS/La Rochelle University, La Rochelle, France

Eric Gilman

The Safina Center, Honolulu, HI, United States of America

Heriot-Watt University, Edinburgh, United Kingdom

Morgan Gilmour     Institute for Marine and Antarctic Studies, University of Tasmania, Battery Point, TAS, Australia

Helen Gummer     New Zealand Department of Conservation, Wellington, New Zealand

Yuliana Bedolla Guzmán     Grupo de Ecología y Conservación de Islas, A.C., Ensenada, Baja California, Mexico

Craig S. Harrison     Pacific Seabird Group (Retired), Santa Rosa, CA, United States of America

Nick D. Holmes

The Nature Conservancy

Institute of Marine Sciences, University of California at Santa Cruz, Santa Cruz, CA, United States of America

Holly P. Jones

Institute for the Study of the Environment, Sustainability, and Energy

Department of Biological Sciences, Northern Illinois University, DeKalb, IL, United States of America

Peter Kappes     Mississippi State University – Coastal Research and Extension Center, Biloxi, MS, United States of America

Mi Ae Kim     Office of International Affairs, Trade, and Commerce, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Silver Spring, MD, United States of America

Stephen Kress     Cornell Laboratory of Ornithology, Ithaca, NY, United States of America

Phil O’B. Lyver     Manaaki Whenua Landcare Research, Lincoln, New Zealand

Edward F. Melvin     School of Aquatic and Fishery Sciences, College of the Environment, University of Washington, Seattle, WA, United States of America

Colin M. Miskelly     Museum of New Zealand Te Papa Tongarewa, Wellington, New Zealand

William A. Montevecchi     Psychology Department, Memorial University of Newfoundland and Labrador, St. John's, NL, Canada

Liliana C. Naves     Alaska Department of Fish and Game, Division of Subsistence, Anchorage, AK, United States of America

Rae Okawa     Hawaii Wildlife Center, Kapaau, HI, United States of America

Steffen Oppel     Royal Society for the Protection of Birds, Cambridge, United Kingdom

Florian Orgeret     Marine Apex Predator Research Unit (MAPRU), Department of Zoology, Institute for Coastal and Marine Research, Nelson Mandela University, Port Elizabeth, South Africa

V. Peschko     Research and Technology Centre (FTZ), Kiel University, Büsum, Germany

Richard A. Phillips     British Antarctic Survey, Natural Environment Research Council, Cambridge, United Kingdom

Pierre A. Pistorius     Marine Apex Predator Research Unit (MAPRU), Department of Zoology, Institute for Coastal and Marine Research, Nelson Mandela University, Port Elizabeth, South Africa

Airam Rodríguez

Canary Islands’ Ornithology and Natural History Group (GOHNIC), Buenavista del Norte, Canary Islands

Terrestrial Ecology Group, Department of Ecology

Center for Research on Biodiversity and Global Change, Universidad Autónoma de Madrid, Madrid, Spain

Robert A. Ronconi     Environment and Climate Change Canada, Canadian Wildlife Service, Dartmouth, NS, Canada

Thomas C. Rothe     Alaska Department of Fish and Game, Division of Wildlife Conservation, Anchorage, AK, United States of America

James C. Russell     School of Biological Sciences, University of Auckland, Auckland, New Zealand

Araceli Samaniego     Manaaki Whenua – Landcare Research, Auckland, New Zealand

Federico Méndez Sánchez     Grupo de Ecología y Conservación de Islas, Ensenada, Baja California, Mexico

Joanna L. Smith     The Nature Conservancy, Nature United, Fredericton, NB, Canada

Dena R. Spatz     Pacific Rim Conservation, Honolulu, HI, United States of America

Cristián G. Suazo

Albatross Task Force, BirdLife International, Puerto Montt, Chile

Department of Animal Ecology and Systematics, Justus Liebig University Giessen, Giessen, Germany

William J. Sydeman     Farallon Institute, Petaluma, CA, United States of America

Mark L. Tasker     Joint Nature Conservation Committee and International Council for the Exploration of the Sea (Retired), Banchory, Kincardineshire, Scotland, United Kingdom

Graeme Taylor     New Zealand Department of Conservation, Wellington, New Zealand

Sarah Ann Thompson     Farallon Institute, Petaluma, CA, United States of America

Marc S. Travers     Archipelago Research and Conservation, Hanapepe, HI, United States of America

Marcela M. Uhart     Karen C. Drayer Wildlife Health Center, School of Veterinary Medicine, University of California, Davis, CA, United States of America

Eric A. VanderWerf     Pacific Rim Conservation, Honolulu, HI, United States of America

Ralph E.T. Vanstreels     Karen C. Drayer Wildlife Health Center, School of Veterinary Medicine, University of California, Davis, CA, United States of America

Yutaka Watanuki     Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Japan

Kawika B. Winter

Hawaiʻi Institute of Marine Biology

Natural Resources and Environmental Management, University of Hawaiʻi at Mānoa

Hawaiʻi Conservation Alliance, Honolulu, HI, United States of America

Anton Wolfaardt     Independent Environmental Consultant, The Crags, South Africa

Thierry M. Work     US Geological Survey, National Wildlife Health Center, Honolulu Field Station, Honolulu, HI, United States of America

Lindsay C. Young     Pacific Rim Conservation, Honolulu, HI, United States of America

Rebecca C. Young     North Dakota State University, Fargo, ND, United States of America

About the Editors

Dr. Lindsay Young

Executive Director of Science

Pacific Rim Conservation

Dr. Lindsay Young is the Executive Director of Pacific Rim Conservation, a nonprofit organization dedicated to conserving, and preventing the extinction of, imperiled birds throughout the Pacific. Lindsay’s main focus is on the not net loss initiative, which involves creating and restoring island ecosystems that are resilient to the effects of climate change, matching acre for acre what is being lost to sea level rise throughout the Northwestern Hawaiian Islands. This is done through predator exclusion fencing and the translocation of endangered bird species into newly protected areas. A world expert on seabirds, she is the Chair of the World Seabird Union, a member of the International Union for Conservation of Nature (IUCN) species specialist and IUCN species reintroduction groups; she is also a recipient of the Endangered Species Recovery Champion Award from the U.S. Fish & Wildlife Service, a Special Achievement Award from the Pacific Seabird Group, the Koa Award for Conservation Leadership from the Conservation Council for Hawaii, and the 2022 Ralph Schreiber Conservation Award from the American Ornithological Society. Her work has been featured on media outlets around the world including National Geographic, BBC, the New York Times, and Animal Planet, among others. Originally from Vancouver, Canada, she fell in love with seabirds while completing a semester abroad program on a ship sailing to 11 countries and watching a single albatross follow that ship for more than 1000 miles. She has a BSc in Zoology from the University of British Columbia, and an MS and PhD in Zoology from the University of Hawai‘i. Based in Hawaii, Lindsay spends her time with her own flock of children, chickens, and guinea pigs.

Dr. Eric VanderWerf

Director of Science

Pacific Rim Conservation

Dr. Eric VanderWerf is the founder and Director of Science of Pacific Rim Conservation, a nonprofit organization dedicated to studying and conserving birds throughout the Pacific region. Eric has worked on a variety of ornithological and conservation projects involving seabirds, forest birds, and wetland birds in Hawaii and throughout the Pacific for over 30 years. He earned a Bachelor of Science degree from Cornell University in 1988, a Master of Science degree from the University of Florida in 1992, and a PhD from the University of Hawai‘i at Manoa in 1999. In 2006, he left the U.S. Fish and Wildlife Service to start Pacific Rim Conservation with the goal of pursuing projects with direct, on-the-ground conservation value. He is an expert on seabirds of the world and birds of the Pacific in particular, and a leader in the use of several conservation methods including predator exclusion fencing, social attraction, and translocation. He has authored over 150 peer-reviewed scientific papers, book chapters, and government documents, and has served as an associate editor for several journals. He has received several conservation awards, including the Endangered Species Recovery Champion Award from the U.S. Fish and Wildlife Service, the Schreiber Conservation Award from the American Ornithological Society, and the Koa Award for Conservation Leadership from the Conservation Council for Hawaii. He is an elective member and fellow of the American Ornithological Society. He serves as the chair of the Hawaii Bird Records Committee and on the Palau Bird Records Committee. Eric grew up in Rochester, New York and developed an interest in the natural world, particularly birds, at an early age. In his spare time, he enjoys birding, photography, hiking, traveling, and spending time with his children.

Preface

For those who have been fortunate enough to walk among albatrosses in their breeding colonies, you are walking among many individuals that are likely older than many of us are. They have seen changes in the oceans and on their breeding islands that most of us cannot imagine let alone quantify, and most of those changes are a direct result of the impact that humans have had on the planet. These birds use the stars, wind, and currents to navigate across the world’s oceans; they are birds that spend years at sea traveling tens of thousands of miles over the open ocean waves, and then come back to their nesting colonies with laser-like precision. Once there, they find their mate (typically the same one each year) and raise chicks, often next to the very same nest in which they themselves were raised. Despite the risks both on land and at sea, they persist, and do so with a grace and beauty that is impossible to describe in words.

But while albatrosses, and many marine birds similar to them, are living as they have done for millennia, their environments have changed dramatically in the last century. Marine birds as a group are almost all universally declining, some at alarmingly fast rates. The threats that they face are confounded by the fact that they are some of the few animals that inhabit both terrestrial and marine environments, and thus the number of threats they face is higher than for almost any other taxonomic group. These threats range from invasive species, habitat destruction, pollution, disease, and the impacts of climate change on their breeding habitat, to fisheries bycatch, prey depletion, marine pollution, and the impacts of climate change on their marine environments where they obtain their food. Many of these threats are compounded by their interactions with one another. As a result, as the magnitude of any one threat grows, particularly climate change, it increases the effect that all others have on survival and population trends for marine birds.

As a result of the sheer number and magnitude of the threats facing this unique group of birds, the compilation of all of this information into one volume is long overdue. Our hope is to provide a comprehensive reference that can be used by students, academics, natural resource managers, and any other individuals interested in learning more about the threats facing seabirds and what solutions need to be implemented in order to mitigate those threats.

We have opted to divide the book into two sections: one section introduces the main threats, and another details the solutions. There will be areas that experience some degree of overlap, and there will undoubtedly be areas that are not covered in as much detail because a solution may not exist for that threat. Each chapter is meant to provide a general overview of that topic, and each could be expanded into a book in its own right. We encourage readers to seek out the references presented in each chapter for more in-depth knowledge on any given issue and/or to contact the chapter’s authors directly to learn more. For those looking for future research directions in any topic, we also present knowledge gaps and future directions for each topic at the end of its chapter.

Finally, in the development of this book, care was taken to select experts in each particular field who know both the historical and current status of each threat, and who represent a diversity of regions and marine bird taxa in their approach to any issue. Our authors form a diverse collective—this book was written by 53 authors representing 14 countries from a variety of backgrounds and with a large range of expertise. Despite residing in so many different countries, much like the birds that they study, most of our authors are truly multinational and work in many locations and with multiple species. Thirty-five percent come from academic institutions, 41% from nonprofit nongovernmental organizations (NGOs), 15% from government agencies, and 9% from for-profit organizations/other. Most are mid-career (32%) or established (41%) biologists, but some are early career (15%) or retired (12%). In short, our goal in selecting authors was to try to capture the geographic, taxonomic, and experience-related diversity in the field of marine ornithology. While there is ample room for improvement, our aim was to produce a book that was global in nature and represented a variety of viewpoints, geographies, and taxa. It was truly a pleasure writing and compiling this volume, and we sincerely hope that you will find it useful in your quest to better understand these unique animals.

Acknowledgments

This book would not have been possible without the dedication, knowledge, and willingness of our more than 50 coauthors to contribute their expertise toward the effort. As such, we thank first and foremost all the coauthors of each chapter who have spent countless hours sharing their hard-earned knowledge so that others can benefit. This endeavor ended up being a larger undertaking than we anticipated, due to the rapidly changing landscape of the threats that seabirds face, and writing the book during the height of a pandemic brought its own set of challenges. Thank you to our coauthors for persevering through that process to ensure that readers are presented with the most current, comprehensive data. We thank our editor, Kathrine Esten, at Elsevier for shepherding the manuscript through the process, and for assisting all of us with formatting our chapters.

Chapter 5 is dedicated to the memory of Dr. William Conway, as we acknowledge his essential contributions to seabird conservation in Patagonia. For Chapter 11, we give special thanks to the Māori authorities, elders, and communities from Pare Hauraki, Ngāti Awa, and Rakiura. Phil Lyver was by New Zealand’s Ministry of Business, Innovation and Employment Endeavour Fund (Contract: 2122-28-017-A) and Strategic Science Investment Funding for Crown Research Institutes. This chapter itself is intended to embody an acknowledgment to the indigenous peoples and local communities around the world who continue to maintain relationships with seabirds and engage in seabird conservation. The authors of this chapter thank a few communities in particular for shaping our perspectives on seabird conservation: in Hawaiʻi, the communities in the district of Haleleʻa on the island of Kauaʻi, and in particular, the community of Hāʻena, which continues to be a leader in biocultural conservation. In the Northern Pacific Rim and the Arctic, we thank the people of St. George and St. Paul Islands, the North Pacific Research Board, the University of Alaska Fairbanks, the Institute of Arctic Biology, the Universidad Nacional Autónoma de México, the Instituto de Ecología, and the Baltic Seabird Project. Chapter 16 benefited greatly from Sarah Ann Thompson for her insightful editing of this chapter for clarity and brevity.

Finally, this book would not have been possible without the support of our board of directors at Pacific Rim Conservation, who allowed us the time to complete this project. Christen Mitchell, Alex Wegmann, Dave Johnson, and Dave Duffy create the working environment and flexibility that allows our organization to pursue academic endeavors such as these, which serve to benefit the greater good. We are grateful. And to our children, Robin and Gavin, for listening (with minimal eye rolling) to yet another conversation about the book—thank you.

Section I

Threats

Chapter 1: Ecology of marine birds

Lindsay C. Younga; Lisa T. Ballanceb    a Pacific Rim Conservation, Honolulu, HI, United States of America,

b Marine Mammal Institute, Oregon State University, Newport, OR, United States of America

Abstract

Marine birds form a vital part of marine ecosystems and are among the few species groups (all secondary marine forms) that transcend the boundaries of air and water, bridging terrestrial and marine environments. They are also among the most threatened group of vertebrates worldwide, with up to 70% of the 368 species experiencing population declines and up to a third imminently threatened with extinction. Seabirds have been dramatically impacted by human activities. In their terrestrial breeding habitat, resource extraction, commercial harvest, introductions of invasive species, and anthropogenically influenced increases in predator populations have significant negative impacts. In their marine feeding habitat, fisheries, pollutants, resource extraction, and direct and indirect effects associated with climate change negatively impact their populations. This chapter presents an overview of seabirds, with a focus on breeding and feeding ecology, the associated life history characteristics that make seabirds distinct and unique, and how these traits influence their susceptibility to threats and inform conservation strategies. Other comprehensive references on seabirds include Biology of Marine Birds by Schreiber and Burger and Seabirds: A Natural History by Anthony Gaston.

Keywords

Ecology; Ecosystems; Vertebrates; Environment; Seabirds; Populations

Marine birds form a vital part of marine ecosystems and are among the few species groups (all secondary marine forms) that transcend the boundaries of air and water, bridging terrestrial and marine environments. They are also among the most threatened group of vertebrates worldwide, with up to 70% of the 368 species (BirdLife International, 2021) experiencing population declines and up to a third imminently threatened with extinction (Dias et al., 2019). Seabirds have been dramatically impacted by human activities. In their terrestrial breeding habitat, resource extraction, commercial harvest, introductions of invasive species, and anthropogenically influenced increases in predator populations have significant negative impacts (Cury et al., 2011; Furness, 2003; Jones et al., 2008). In their marine feeding habitat, fisheries, pollutants, resource extraction, and direct and indirect effects associated with climate change negatively impact their populations. This chapter presents an overview of seabirds, with a focus on breeding and feeding ecology, the associated life history characteristics that make seabirds distinct and unique, and how these traits influence their susceptibility to threats and inform conservation strategies. Other comprehensive references on seabirds include Biology of Marine Birds by Schreiber and Burger (2001) and Seabirds: A Natural History by Gaston (2004).

Life history and adaptations

What is a marine bird?

The question of what makes a bird a marine bird, or seabird as they are more commonly referred to, is one that is more difficult to answer than it appears. The two key ecological traits that define seabirds are as follows: (1) they breed on land, and (2) they obtain their food from the sea. From these two elements arise the life history traits that drive seabird biology, ecology, behavior, and vulnerability as outlined below. There are both temporal and regional variations within this definition—such as birds that obtain their caloric needs from marine environments for only part of the year, and birds in which the majority of the population obtains food from the marine environment, but some sub-populations rely on inland bodies of water or other sources. For example, several species of Pelecanidae, Laridae, Sternidae, and Phalacrocoracidae that breed inland or rely on freshwater resources are typically not considered to be seabirds, even though they often winter in marine habitats. Because new research often leads to changes in taxonomy and classification, the list of species considered to be seabirds is constantly changing. In this book, we rely on the taxonomy from the BirdLife Data Zone (BirdLife, 2021) downloaded on October 15, 2021, while recognizing there are alternative classifications (e.g., Gill and Donsker, 2015). Table 1.1 provides the number of marine species contained in each order.

Table 1.1

CR, critically endangered; En, endangered; EW, extinct in the wild; VU, vulnerable.

Data from BirdLife International, 2021. From http://datazone.birdlife.org. (Accessed 15 October 2021) and IUCN, 2021. The IUCN Red List of Threatened Species. Version 2021–3. https://www.iucnredlist.org. (Accessed 15 October 2021).

Morphological and physiological adaptations

The flexibility that seabirds show in transitioning between marine and terrestrial environments necessitates multiple physiological and morphological adaptations. Additionally, seabirds nest in virtually all latitudes on earth, from the harsh cold winters of Antarctica to the exposed baking sand of tropical islands. In addition to adaptations for flight (which unite all birds and have had an overwhelming influence on morphology, physiology, behavior, and other characteristics), seabird adaptations are primarily for swimming, diving, feeding in the marine environment, accommodating their extreme thermoregulatory and water balance needs, and attending their breeding colonies on land.

The most obvious morphological adaptation that all seabirds share is webbed feet that aid in moving through water (or, in the case of Grebes, lobed toes). This can be through paddling on the surface, diving underwater, or using them to take off from the water. For ground-nesting species that nest in thermally extreme environments, such as penguins in Antarctica and boobies on tropical atolls, the webbing is also used in thermoregulation. The one exception to this is found in frigatebirds which have greatly reduced webbing since they rarely enter the water.

A physiological need of all animals is the need for water, which can be ingested through drinking, eating, or oxidative metabolism. While seabirds are surrounded by water, it is saline and the salt must be removed before it is suitable as a water source. In addition, consumption of marine prey that are isosmotic with seawater (e.g., fish, squid, and crustaceans) can result in a doubling of salt load for seabirds (Goldstein, 2001). As a result, all seabird species have a more highly developed salt gland than their terrestrial counterparts, which allows them to meet their fluid needs by drinking seawater and ingesting prey with heavy salt loads, while eliminating the salt from it. Experimental evidence shows that increasing ingested salt loads results in increased salt gland excretion by petrels (Goldstein, 2001; Warham, 1996). Fange et al. (1958) conducted comprehensive early research on seabird salt glands and found, amazingly, that the composition of fluid produced by seabird salt glands can contain up to 5% sodium chloride—twice that of seawater and five times that of blood. Seabirds can produce half their weight as salt solution every minute, and the salt glands excrete ~  90% of a seabird’s salt load with the remaining 10% excreted by the much less efficient kidney. This means that a seabird can drink one-tenth of its body weight in seawater (equivalent to two gallons for a typical human) and excrete the entire associated salt load in 3 h.

Seabirds have a variety of adaptations related to prey capture. Wing morphology is a critical factor in determining flight and diving ability. In general, the more highly pelagic the species, the lower the wing loading to facilitate efficient flight (Hertel and Ballance, 1999). (Here we define pelagic as waters seaward of the shelf break.) For diving species, such as penguins and alcids, there is a positive correlation between body size and maximum dive depths (Watanuki and Burger, 1999). Between these two extremes are the procellarids that are both highly pelagic and dive; in this order, smaller species are able to dive more deeply, presumably because larger wing spans hinder underwater mobility. Foraging mode and morphology are discussed in greater detail below.

Ecological importance

Seabirds play a critical role in both marine and terrestrial environments, particularly by extracting and depositing nutrients. Seabird guano contains essential nutrients (nitrogen, phosphorus) and trace elements (e.g., iron) in sufficient amounts that biochemical functions remain stable after it is deposited (Hargan et al., 2017; Shatova et al., 2016; Wiedenmann et al., 2013). When foraging at sea, seabirds consume marine originating isotopes of less common periodic elements and bring them back to land, providing nutrient inputs for both terrestrial and nearshore marine ecosystems. These marine subsidies enrich above-ground biomass and contribute habitat for other species, such as plants (Ellis et al., 2006). On islands off of California, where seabirds forage in the highly productive California current ecosystem, guano deposits around breeding colonies enhance local productivity in the surrounding terrestrial desert ecosystems (Polis, 1998; Stapp et al., 1999). Guano deposition on islands can also enhance the nearshore environment near breeding colonies via a sea-land-sea transfer. Seabird guano can increase macroalgal production and alter benthic community structure (Bosman and Hockey, 1986).

Seabird-derived nutrients can enrich nitrogen inputs to soil on islands, increase nutrient availability in nearby pelagic and benthic food webs, increase growth of branching corals, and be assimilated by coral endosymbionts (Caut et al., 2012; Honig and Mahoney, 2016; McCauley et al., 2012; Mizota and Naikatini, 2007; Savage, 2019).

Seabirds include top predators in the marine food chain and as such are key components of food webs. Seabirds play important roles in shaping ecological processes and services in a multitude of ways, through trophic (bottom-up or top-down) and non-trophic processes (Signa et al., 2021).

Seabirds are important indicators of marine ecosystems. Because they breed on land and feed in the sea, often covering large distances, they are integrators across habitats and large spatial scales. Because they feed at a variety of trophic levels, they are integrators across food webs. Because they are philopatric, long-term data can be used to integrate across time. And relative to other marine organisms, they are easy to identify and sample, and can be instrumented with various animal-borne devices that can record data not only about the individual that carries them, but about the physical and biological environment itself. All of these characteristics combine to make them cost-effective and informative tools for indirectly sampling other species and oceanographic parameters, providing insights, for example, into the effects of natural and anthropogenic disturbances, on food webs and broader features of the marine environment.

Population biology

Lifespan and age at first breeding

Seabirds are K-selected—they are long-lived, produce few young, have delayed reproductive maturity and reproduction, and have high adult survival (Schreiber and Burger, 2001). The majority of seabirds are long-lived, and even some of the smallest of species can live for up to 20 years. For example, diminutive White Terns (Gygus alba) live at least 36 years (Niethammer and Patrick, 1998), and larger species like Laysan Albatrosses and Great Frigatebirds can live and reproduce for at least 70 years (Juola et al., 2006; USFWS, 2020). Many aspects of seabird life history are shaped by their long lifespans. Factors that increase adult mortality therefore tend to have greater negative effects on population size and growth than factors that decrease reproduction or survival of juveniles (Bakker et al., 2017; Finkelstein et al., 2008; Wilcox and Donlan, 2007; Žydelis et al., 2009). Many seabird populations can withstand several seasons of poor reproduction without experiencing long-term population declines. This is not to suggest that chick mortality is unimportant, but rather that adult mortality typically affects population size more quickly and more severely; therefore, threats that impact the adults of a population are of greater concern than those that exclusively impact chicks.

In addition to being long-lived, many seabirds have delayed reproductive maturity, beginning to breed a number of years after fledging (Table 1.2). This delay is often 3–5 years in smaller species like terns (Niethammer and Patrick, 1998; Schreiber et al., 2002) and can be much longer in larger species, such as 8–9 years in albatrosses, for example (Bradley and Wooller, 1991; Van Ryzin and Fisher, 1976; VanderWerf and Young, 2016). In species that take a longer time to reach breeding age, a greater portion of the total population consisting of young, sub-adult birds often are referred to as prebreeders. Prebreeders may visit breeding colonies sporadically, or not at all, until they are ready to breed. Determining the age at first breeding and counting the number of pre-breeders requires long-term banding and mark-recapture analyses, and can dramatically impact population assessments for species where this period is poorly understood. For example, in Laysan Albatross at Ka’ena Point on O`ahu Hawai`i, in the central Pacific Ocean, long-term mark-recapture data revealed that prebreeders comprised 44% of the total population on average (VanderWerf and Young, 2016). Prebreeders that spend most of their time at sea floating can play an important role in buffering a population against threats that occur on breeding colonies. For example, the Short-tailed Albatross was thought to have been driven to extinction by hunting and disturbance on its breeding colonies, but the species was rescued by a pool of prebreeders that had been at sea and eventually returned to breed (Hasegawa and DeGange, 1982). Age at first breeding may not be fixed in a species; rather, it may vary among years or sites in relation to habitat condition, prey availability, or population trends, and this variation can reveal subtle aspects of population dynamics. An abundance of young breeding birds may signal a growing colony with good food resources, whereas an abundance of older prebreeders may indicate some limit to breeding opportunities, such as a shortage of mates, nest sites, or food. Thus, determining age at first reproduction and the proportion of the population that it represents is important for assessing conservation strategies.

Table 1.2

Population variation

Population size and trend are two of the most fundamental demographic parameters and often are used as primary measures of assessing species status (IUCN, 2001). Knowledge of changes in seabird populations is important because of their important roles in island and marine ecosystem processes, and to document changes related to management actions being implemented to prevent population declines. The life history traits associated with K selection make seabird populations relatively robust to interannual variation in breeding success, but highly sensitive to slight changes in adult survival which is the primary determinant of variation in population growth rate (Crespin et al., 2006). Reproductive success, the proportion of birds breeding, and the timing of breeding can vary with prey availability and ocean climate contingencies (Cairns, 1987). Poor reproductive success must be sustained and extensive to decrease populations, and when such effects occur, they often lag well behind the environmental factors that caused them. In contrast, adult survival tends to be high (usually >  90%), except in extreme circumstances (Schreiber and Schreiber, 1984). Following fledging, mortality is generally above 50% during the first year of life (e.g., Lane et al., 2020), though recruitment is relatively high (e.g., Crespin et al., 2006).

Many seabird populations form metapopulations, populations which influence each other through dispersal and immigration (Hanski, 1994). The methods for describing dispersal, colony formation and growth, and other aspects of metapopulation dynamics are useful for seabird monitoring, particularly in environments that are being modified as a result of human pressure and climate change (Buckley and Downer, 1992; Inchausti and Weimerskirch, 2002; Kildaw et al., 2005; Oro, 2003; Schippers et al., 2011). Ultimately, the goal of monitoring is to understand the status and trends among regional populations. To do so, it is important to understand population dynamics across all breeding sites. In addition, some colonies can act as source populations where high levels of reproductive success lead to population growth and emigration, while other sites act as sinks where lower levels of reproduction cause population decline or emigration. Management requires a broader view than just a single colony because population trends on one island can affect populations on others. For example, VanderWerf and Young (2016) showed that Christmas Shearwaters that hatched on Kure Atoll and Midway Atoll visited both islands, and that most visits were made by young birds, with some birds recruiting to the non-natal island to breed as adults. Obtaining this information was made possible by cooperation and sharing of data from both islands.

Factors that influence population trends vary dramatically by species and location, but generally (in the absence of anthropogenic threats), seabirds are primarily regulated by density dependence through food availability (Ashmole, 1963; Birkhead and Furness, 1985). Anthropogenic threats can magnify density-dependent mechanisms. Broadly defined categories of threats to seabirds include fisheries interactions, invasive species, disease, pollution, disturbance and exploitation, and climate change (treated in detail in subsequent chapters). All can impact populations on terrestrial breeding grounds and in marine foraging locations. All can impact all age classes of birds, but many have age-specific impacts.

Survival

Life history theory predicts a trade-off between survival and reproduction, leading to a balance between current reproductive effort and residual reproductive value (Stearns, 1992; Williams, 1966). In long-lived species such as seabirds, individuals are less likely to compromise their own survival by increasing reproductive effort; this can result in delayed recruitment and intermittent breeding (Curio, 1983; Jouventin and Dobson, 2002; Weimerskirch, 1992). The balance between survival and reproduction may differ between the sexes and age classes, and can be affected by environmental variation (Cubaynes et al., 2011; Erikstad et al., 1998; Oro et al., 2010). In many seabirds, adults adjust their reproductive effort, sometimes foregoing breeding entirely for one or more seasons when breeding conditions are poor, thereby buffering their own survival (Cubaynes et al., 2011; Erikstad et al., 1998; VanderWerf and Young, 2011). Many seabirds can migrate when local conditions become unfavorable and thus buffer against environmental changes. For example, adult Emperor Penguins (Aptenodytes forsteri) appear to adjust survival relative to oceanographic anomalies related to the Antarctic Circumpolar Wave. During warm events (every 4–5 years), adult survival is low (0.75) in contrast to the average survival of 0.92–0.97 (Barbraud and Weimerskirch, 2001). For a more detailed analysis of how environmental variability and climate change impact life history traits of seabirds, see Chapter 8.

Adult survival of most seabird species is high owing to their strongly K-selected life histories, in some cases exceeding 97% (VanderWerf and Young, 2011), and averaging 90% across all species (Gaston, 2004). Most age and survival estimates are based on mark-recapture studies using banding, and thus, the estimates are minimums. While most demographic parameters can be estimated relatively easily for breeding adults (because they regularly return to land to breed), obtaining information about other age classes is more difficult. Estimating survival, recruitment, and population size of juveniles and sub-adults can be particularly problematic, because after leaving their natal area, they can disperse over large areas for long periods of time, making it difficult to obtain data on survival (Crouse et al., 1987; Fay et al., 2015; Witham, 1980). Fledgling and juvenile survival tends to be lower and more variable than for adults, associated with challenges of learning to forage and feed at sea. VanderWerf and Young (2016) documented survival of first-year Laysan Albatross as 76%, as compared with adult survival of 97% (which subadult albatrosses reach after their first year) suggesting that most juvenile mortality occurs in the first year immediately after fledging.

Reproductive success

Reproductive success, defined as the proportion of eggs laid that result in the successful fledging of a chick, can be highly variable, both within and between species. Fortunately, reproductive success can be among the easier parameters to measure in some seabird species. Other metrics used to measure aspects of reproductive success include hatching success (the proportion of eggs laid that hatch) and fledging success (the proportion of chicks hatched that fledge). Closely tied to reproductive success is fecundity—a combination of clutch size, breeding frequency, and reproductive success. While the reproductive success of most seabirds is relatively high, fecundity of seabirds is generally low due to single-egg clutches for most species (Table 1.2). Albatrosses, petrels, and shearwaters lay one egg per breeding attempt and will not re-lay in the same season if their nest fails. Terns, tropicbirds, and boobies may attempt to re-nest following failure, depending on when in the breeding cycle failure occurs. And some species may re-nest even after a successful breeding effort (e.g., Black Noddies; Gauger, 1999). For example, 25% of White Tern pairs raised two chicks per year, and a few pairs even raised three chicks per year even after reproductive failure with the initial attempt (VanderWerf and Downs, 2018). Because breeding frequency may vary among years, it may take several years of monitoring to obtain a reliable estimate.

A trait that is relatively common among several seabird families is the tendency to skip years between breeding cycles. Some of the large-bodied species, such as the great albatrosses, are obligate biennial breeders because their chicks take more than a year to fledge. The frequency with which birds skip breeding varies among species depending on the length of the breeding cycle, and within species depending on previous breeding experience, reproductive outcome in the previous year, food availability, and nutritional condition of individual birds (Fisher, 1976; Ryan et al., 2007; VanderWerf and Young, 2011; Weimerskirch, 1992). In some smaller-bodied seabird species, not all individuals attempt to breed every year, with some birds occasionally skipping a year of breeding. Whether a bird skips breeding in a given year may depend on their individual body condition, their reproductive success in the previous year, and food availability and other environmental factors (Fisher, 1976; Jouventin and Dobson, 2002; Weimerskirch, 1992). For example, Laysan and Black-footed Albatrosses skip breeding about once every 5 years on average (Fisher, 1976; VanderWerf and Young, 2011). For these species, the number of nests observed each year therefore is an underestimate of the breeding population.

Reproductive success is the product of hatching success and fledging success and is often called apparent nest success (Jehle et al., 2004). Larger-bodied species, such as albatrosses, tend to have high annual reproductive success (up to 0.90; Tickell, 2000) in the absence of mammalian predators. Dearborn et al. (2001) showed that reproductive success among species in a foraging guild usually is similar and determined by the same external factors, because in many species of birds, food availability directly affects reproductive output and guild members, by definition, tend to forage on similar prey. Exceptions to this are seabirds depending on schooling predatory fishes and marine mammals, where, for example, both terns and shearwaters are members of the same guild but exhibit very different breeding phenology and synchronicity.

Breeding ecology

Seabirds, as relatively large, K-selected animals, employ a suite of shared characteristics to maximize their reproductive output and thus fitness. Really, the only reason seabirds return to land at all is to breed. The aspects that contribute most to their success and that are present across most species in the group are discussed below.

Coloniality

One of the fundamental similarities that virtually all (~  95%) seabirds share is the tendency to nest in colonies. In a biological context, a colony is where several individuals of the same species live together in close association. This association is presumed to be for mutual benefit, such as a stronger defense against predators, to obtain more food, or to communicate to conspecifics that this nesting location is ideal to raise young. Coloniality in seabirds is initially thought to have evolved primarily as a predator avoidance mechanism since locations free of mammalian predators (i.e., islands) are usually in limited supply (Lack, 1968; Tinbergen, 1959) and thus requires many species to nest in dense aggregations in a smaller number of locations. The carrying capacity of colony size is conversely thought to be limited by local prey availability with increasing prey resources the further they are from the colony, or the smaller the colony is (see Ashmole’s halo; Ashmole, 1963). In some tropical seabirds, such as Sooty Terns (Onychoprion fuscatus), individual colonies are thought to reach up to seven million individuals. And this doesn’t count other species that are usually nesting sympatrically with them.

The information center hypothesis put forth by Ward and Zahavi (1973) suggested that colonialism in seabirds evolved as information centers where birds exchange information on the location of prey. Coloniality itself could result in the evolution of information sharing (as opposed to the other way around) since a high density of birds facilitates faster discovery of prey locations through more efficient information transfer compared to breeding in more dispersed colonies. Buckley (1997) demonstrated that colonial breeding is favored when prey abundance is high- or short‐lived so that competition for food is diminished. Conversely, dispersed nesting is favored when prey patches are limited or long-lived. Either way, it is clear that dense aggregations of nesting seabirds facilitate information sharing.

Seabirds can also nest in multi-species colonies. In some locations, upward of 20 species may nest in dense aggregations in the millions on small islands. This is accomplished by partitioning nesting locations (underground burrows, surface nesters, tree nesting, etc.; see below), and by differences in foraging guilds so as not to exploit all the same resources.

From an evolutionary perspective, coloniality among nesting seabirds provides two advantages—increased access to foraging opportunities and predator avoidance, both of which exert strong selective forces. Unfortunately, coloniality also makes them highly vulnerable to land-based anthropogenic threats. A large number of animals nesting in close proximity facilitate more rapid disease transfer (see Chapter 5 on diseases in marine birds) and also make many more individuals vulnerable to predation if predators are introduced (see Chapter 4 for the impacts on invasive species). As a result, protection of seabirds on their breeding colonies is among the most cost-effective of conservation measures because so many individuals can be protected in a relatively small area. On the positive end of the spectrum, their tendency toward coloniality coupled with high-rate natal philopatry also means that restoration can be done using social attraction and translocation (see Chapter 19).

Nesting habitats

Seabird nesting habitat can be characterized into three broad categories: highly pelagic species (albatrosses, petrels, frigatebirds, tropicbirds, boobies, and some terns) generally nest on oceanic islands. The second are species that nest along the coasts and feed in nearshore environments (such as pelicans, cormorants, gulls, some terns, and alcids) and finally species that nest in inland habitats (such as skuas, jaegers, some gulls and terns, and some petrels and alcids) (Schreiber and Burger, 2001). In terms of the specific habitats most species nest in, the majority of seabirds nest on the ground, often in the open (Table 1.3). Since this leaves them highly vulnerable to predation, by both avian and mammalian predators, they also nest in dense colonies as described above, presumably to reduce this predation risk. In addition to coloniality, many seabirds exhibit high-site fidelity and will return to the same nesting site year after year. This is in addition to the strong natal philopatry (particularly among the Procellariiformes) whereby chicks almost always return to their birth colony to reproduce. Since so few predator-free locations exist for seabirds to breed while on land, they are often constrained to small islands with limited space and as such take advantage of that space by partitioning nesting sites. A consequence of this habitat limitation is that there is competition both within and among species for the best nest sites. This is resolved by temporal and spatial segregation within the colony. Temporally, species that share the same nesting site requirements (i.e., ground vs burrow vs tree) may nest at different times of year and thus avoid competition. For example, Tristrams Storm Petrels (Hydrobates tristrami) and Wedge-tailed Shearwaters (Ardenna pacifica) often use the same burrows on tropical atolls, but have different nesting seasons with little temporal overlap. Thus, the same burrow may be used year round, but by two different species, which is particularly important for the diminutive storm petrel who would be killed by the much larger shearwater if they were to share a burrow at the same time.

Table 1.3

Adapted from Gaston, A.J., 2004. Seabirds: A Natural History.

Spatially, seabird nesting habitat can be broadly defined as surface, burrow, tree/vegetation, cliff, and rock piles/crevices. In this way, colonies can be vertically integrated. For example, tropical seabird colonies may support Wedge-tailed Shearwaters and Bonin Petrels (Pterodroma hypoleuca) in burrows, surface nesting Laysan and Black-footed Albatrosses, storm petrels nesting in adjacent rock piles, and Red-footed Boobies, Brown Noddies and Great Frigatebirds in trees or shrubs. Thus, a mere 2 m × 2 m of space can support 8 species nesting at once.

Surface nests can range from simple scrapes in the ground, such as what boobies and terns often make, to carefully constructed, elevated nest cups made by some of the Southern hemisphere albatross species. Burrows, which are most common among shearwaters and petrels, are typically dug into the ground, sometimes up to several meters, and consist of a tunnel for transit, and a larger, wider chamber where adult and chick can share space together during brooding and incubation. Tree nesters can similarly range in extremes from White Terns who simply lay an egg on a bare branch, to complex, traditional stick nests constructed by other species. Cliff, crevice, and rock-pile nesting species attempt to take cover in natural crevices and on sheer vertical areas to provide protection from the elements as well as predators. It should be noted that some of these categories overlap—that is, a surface nester can also be a cliff nester and that assignment to them is not strict for all species. But generally, all seabird species exhibit these nesting tendencies, with the vast majority either nesting on the surface or in burrows.

Phenology

The timing of breeding, or phenology, in seabirds is thought to be closely linked to food supply, both for the parents to be able to provision for growing chicks, and for a high food supply for the fledglings after they leave the nest and learn to forage independently. Most seabird species breed synchronously. However, a portion of species do not adhere to this norm for reasons discussed below.

In synchronous breeders, most individuals arrive at the colony site over a short period of time and establish their nesting sites. Multiple factors contribute to setting the timing of the breeding cycle: temperature, prey availability, age, experience, and likely other additional factors. Temperature and weather are particularly important in polar, subpolar, and temperate species where breeding may not be able to commence until ice and snow have melted and conversely must be completed before frigid temperatures return. This leaves a narrow window of optimal thermal environments in which to breed; thus, most species nesting in these regions are highly synchronous and vulnerable to changes in weather and climate. While tropical seabirds don’t have the same constraint on their breeding cycle as a result of weather, they are highly susceptible to variations in prey availability which is more pronounced in the less productive tropical waters. For all seabird species, prey availability is also critically important in determining time of breeding.

Prey is not uniformly distributed spatially or temporally and is almost certainly the driving factor in determining breeding phenology for most seabirds. As a general rule, tropical marine ecosystems are less variable seasonally than those in higher latitudes. The largest fluctuation in seasonal food availability occurs in polar regions where many species commence nesting before the boom in spring/summer food availability. This is done to ensure that young birds fledge during the period of highest food availability and thus are successful in learning to forage independently. There are exceptions to these generalizations with species that breed in the tropics, but still forage in temperate and sub-polar locations (such as Laysan and Black-footed Albatrosses) and thus their needs are tied to food availability in more northern regions which cause them to be highly synchronous.

Most temperate, sub-polar, and polar species breed in spring and summer months to maximize food availability for their fledgling offspring. Exceptions to this are found in some of the larger penguins and albatrosses whose breeding seasons are so protracted that they encompass multiple seasons. Tropical seabirds mostly breed in spring and summer as well (with multiple exceptions), but have the flexibility to breed asynchronously as prey availability allows. In summary, the combination of temperature, prey availability, age, and experience all combine to influence the timing and duration of seabird breeding cycles.

Pair formation and incubation

Courtship and pair bond formation is often extremely protracted and can last for several years before copulation occurs. The sequence and variety of courtship behaviors varies between species, but typically begins with territorial defense, followed by mate-attraction displays, and selection of a nest site. Seabirds are mostly socially monogamous and often mate for life, which highlights the importance of selecting a mate who will help maximize reproductive success of both individuals in the pair. Part of the pair formation process involves ritualized dances in their courtship. These dances are complex and can include displays and vocalizations that vary greatly between families and orders. Albatrosses are well known for their intricate mating dances, with many species displaying very similar forms (Tickell, 2000). It is thought that both members of the pair use these dances as a proxy for mate quality, and it is believed to be a very important aspect of mate choice.

Once pairs have been formed, nest site selection occurs usually by the male, but sometimes by both members of the pair. Established pairs frequently return to the same nest site each and wait for their mate to return. Most seabirds have long-term multi-year pair bonds with no apparent trends by order of seabird. It is thought that long-term pair bonds result in more efficient and better coordinated breeding in an established pair. For example, gulls that switched partners between breeding seasons had delayed egg laying and lower clutch sizes likely as a result of their need to spend more time establishing a pair bond, and thus reducing the time available to forage (Chardine, 1987; Mills, 1973). Established pairs have been shown to have better coordinated patterns of activity during incubation and chick rearing (Coulson and Wooller, 1984; Mills et al., 1996; Schreiber and Schreiber, 1993; Wooller and Bradley, 1996).

Most seabirds lay clutches of one to two eggs, and 54% of species lay single-egg clutches which is considerably less than most of the terrestrial cousins. The low clutch size is thought to be related to decreased prey density and increased prey variability in the marine ecosystem (Ashmole, 1963; Lack, 1968). In an analysis done by Schreiber and Burger (2001), across all seabird species, modal clutch size is higher in nearshore feeders (mean = 2.1, n = 113, SD = 0.9) than in pelagic feeders (mean = 1.1, n = 80, SD = 0.4; Mann-Whitney Z = 7.83, n = 174, p < 0.001). They hypothesize that the difference partly reflects phylogeny, since petrels, frigatebirds, and tropicbirds all lay one egg and predominantly feed in pelagic waters, whereas cormorants and Laridae have larger clutches and predominantly feed inshore.

Egg size is also dependent upon body size and foraging distance. Globally, birds that forage far from their colonies, or in low-quality prey environments, have larger eggs. Booby eggs represent about 8% of a female’s body weight, whereas eggs of the smaller terns and noddies can have eggs that approach 20% of their body weight. Once laid, eggs are incubated continuously by both members of the pair in order to maintain a constant thermal environment which is needed for embryonic development. The splitting of incubation equally between the sexes is another difference between marine and terrestrial bird species as well as extremely long incubation periods (79 days in the case of Royal Albatrosses (Diomedea epomophora)—the longest of any bird species). Incubation generally starts as soon as the first egg is laid, with the result that in multiparous species, the eggs hatch asynchronously. Tropical seabirds also have longer incubation periods than their cooler water counterparts (up to 9 weeks) and have eggshells that have evolved with fewer pores than temperate species to counteract water loss with prolonged incubation (Whittow et al., 1985). Across all groups, hatching