Bridging the gap between pupping and molting phenology: behavioral and ecological drivers in Weddell seals Item Type Thesis Authors Beltran, Roxanne Santina Download date 10/10/2021 22:21:11 Link to Item http://hdl.handle.net/11122/9661 BRIDGING THE GAP BETWEEN PUPPING AND MOLTING PHENOLOGY: BEHAVIORAL AND ECOLOGICAL DRIVERS IN WEDDELL SEALS By Roxanne Santina Beltran, B.Sc., M.Sc. A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Biological Sciences University of Alaska Fairbanks August 2018 APPROVED: Dr. Jennifer Burns, Committee Co-Chair Dr. Greg Breed, Committee Co-Chair Dr. J. Ward Testa, Committee Member Dr. Diane O’Brien, Committee Member Dr. Brian Barnes, Committee Member Dr. Kris Hundertmark, Chair Department o f Biology and Wildlife Dr. Leah Berman, Interim Dean College of Natural Science and Mathematics Dr. Michael Castellini, Dean o f the Graduate School Abstract In Antarctica, the narrow window of favorable conditions constrains the life history phenology of female Weddell seals (Leptonychotes weddellii) such that pupping, breeding, foraging, and molting occur in quick succession during summer; however, the carry-over effects from one life history event to another are unclear. In this dissertation, I characterize the phenological links between molting and pupping, and evaluate feeding behavior and ice dynamics as mechanistic drivers. First, I review the contributions of natural and sexual selection to the evolution of molting strategies in the contexts of energetics, habitat, function, and physiology. Many polar birds and mammals adhere to an analogous biannual molting strategy wherein the thin, brown summer feathers/fur are replaced with thick, white winter feathers/fur. Polar pinnipeds are an exception to the biannual molting paradigm; most rely on blubber for insulation and exhibit a single molt per year. Second, I describe the duration and timing of the Weddell seal molt based on data from 4,000 unique individuals. In adult females, I found that successful reproduction delays the molt by approximately two weeks relative to non- reproductive individuals. Using time-depth recorder data from 59 Weddell seals at the crucial time between pupping and molting, I report a striking mid-summer shallowing of seal dive depths that appears to follow a vertical migration of fishes during the summer phytoplankton bloom. The seals experience higher foraging success during this vertical shift in the prey distribution, which allows them to re-gain mass quickly before the molt. Across four years of study, later ice break-out resulted in later seal dive shallowing and later molt. In combination, the data presented in this dissertation suggest that molting, foraging, and pupping phenology are linked in Weddell seals and are affected by ice break-out timing. iii iv Table of Contents Page Abstract................................................................................................................................................. iii List of Figures .......................................................................................................................................xi List of Tables .......................................................................................................................................xv Preface...............................................................................................................................................xviii Acknowledgments .............................................................................................................................. xxi Dedication .........................................................................................................................................xxiii Chapter 1. General Introduction ...........................................................................................................1 1.2 Literature Cited ......................................................................................................................... 6 Chapter 2. Convergence of biannual moulting strategies across birds and mammals ................... 15 2.1 Abstract...................................................................................................................................... 15 2.2 Introduction ................................................................................................................................16 2.3 Functional roles and forms of pelage and plumage .................................................................17 2.4 Metabolic costs of moult ...........................................................................................................18 2.5 Selection pressures and moulting strategies ............................................................................20 2.6 Special considerations for aquatic species ..............................................................................24 2.7 Physiological mechanics of pelage and plumage replacement ............................................. 27 2.8 Feedbacks between moult and global change .........................................................................29 2.9 Conclusion ..................................................................................................................................30 v 2.10 Acknowledgments ...................................................................................................................31 2.11 Literature Cited ....................................................................................................................... 36 Chapter 3. Reproductive success influences molt phenology and subsequent colony attendance in Weddell seals ......................................................................................................................................53 3.1 Abstract......................................................................................................................................53 3.2 Introduction ................................................................................................................................54 3.3 Methods ......................................................................................................................................56 3.3.1 Fieldwork methods .............................................................................................................56 3.3.2 Analytical methods .............................................................................................................59 3.3.3 Estimating molt stage durations ........................................................................................59 3.3.4 Estimating molt initiation dates .........................................................................................60 3.3.5 Accounting for error propagation ..................................................................................... 61 3.3.6 Drivers of molt phenology .................................................................................................62 3.3.7 Interactions between pupping success/phenology and molt phenology ..........................63 3.4 Results........................................................................................................................................64 3.4.1 Demography of molting animals ...................................................................................... 64 3.4.2 Molt duration ...................................................................................................................... 64 3.4.3 Links between pupping phenology and molting phenology in one season ......................65 3.4.4 Inter-annual variation in ice dynamics, molt phenology, and colony attendance 66 vi 3.4.5 Links between pupping and molting phenology in one season and pupping in the next 67 3.5 Discussion ..................................................................................................................................67 3.5.1 Reproductive history affects molt phenology ...................................................................68 3.5.2 Inter-annual variation in ice dynamics, molt phenology, and colony attendance 70 3.5.3 Cross-year carryover effects between molting and pupping .......................................... 70 3.5.4 Implications of links between pupping and molting phenology .....................................72 3.6 Acknowledgements ...................................................................................................................73 3.7 Literature Cited ......................................................................................................................... 87 Chapter 4. Seal diving behavior suggests shallowing of fish distributions during sea-ice driven phytoplankton bloom s ........................................................................................................................ 97 4.1 Abstract......................................................................................................................................97 4.2 Introduction ................................................................................................................................98 4.3 Methods ......................................................................................................................................99 4.3.1 Field methods ....................................................................................................................