Food-caching dynamics and reproductive performance of gray jays (Perisoreus canadensis) by Talia Heather Sechley A Thesis presented to The University of Guelph In partial fulfillment of requirements for the degree of Master of Science in Integrative Biology Guelph, Ontario, Canada © Talia Heather Sechley September 2013 ABSTRACT Food-caching dynamics and reproductive performance of gray jays (Perisoreus canadensis) Talia Heather Sechley Advisor: University of Guelph, 2013 D. Ryan Norris The influence of climate on resource availability and the subsequent effects on reproductive performance is one of the most important processes driving the responses of populations to climate change. For food-caching species, warmer temperatures may accelerate cached food decay, leading to food limitation during the breeding season. I investigated the influence of warm temperatures on the preservation of cached food, and explored the effect of an interaction between climate and habitat quality on food availability and breeding condition of female gray jays (Perisoreus canadensis). Food cached at a high-latitude site decayed the least compared to two lower-latitude sites, and decay was exacerbated on deciduous trees compared to coniferous trees. Further, the percentage of conifers on territories positively influenced final pre-laying weights of females, which conferred a higher reproductive output. These results suggest that climate warming may accelerate cached food decay and carry-over to influence female reproductive performance via habitat quality. ACKNOWLEDGEMENTS I would first like to thank my advisor, Ryan Norris, for his guidance and support throughout my thesis, from planning and carrying out fieldwork to writing up the final manuscripts. I am also very grateful for the encouragement and mentorship provided by Dan Strickland throughout the process of learning about all things gray jay (and all things Algonquin Park). This research also benefitted greatly from the input of my advisory committee members, Andrew McAdam and Tom Nudds who provided valuable guidance during as well as outside of committee meetings. For their assistance in the field, I would like to thank (in no particular order), Matt Iles, Rory Eckenswiller, Deanna Hergert, Hugo Kitching, Amy Newman, Matt Strickland and Sarah Strickland. Thanks to Dominique Bureau, Arlene Ali and Jamie Hooft in the Fish Nutrition Lab at the University of Guelph for their help with the calorimetry, and for providing access to the bomb calorimetry equipment. I must also thank my lab mates, Rachael Derbyshire, Gustavo Betini, Tyler Flockhart, and Dmitri Kishkinev for their advice throughout this process, and for their friendship. On the same note, I also thank the WIP meeting group for all of their feedback and (constructive) criticism along the way. I am very grateful for the support and encouragement from my parents and sister throughout all of my endeavors, and would like to thank Dayna LeClair, Cayleih Robertson and Kelly Hadfield for their everlasting friendship, and for making Guelph feel like home during these past two years. Finally, I thank the American Ornithologists’ Union, the Explorer’s Club and the Ontario Graduate Scholarship Program for financial support. iii TABLE OF CONTENTS ABSTRACT............................................................................................................................ ii ACKNOWLEDGEMENTS.................................................................................................... iii TABLE OF CONTENTS........................................................................................................ iv LIST OF TABLES.................................................................................................................. v LIST OF FIGURES................................................................................................................ vii PROLOGUE............................................................................................................................ 1 CHAPTER 1 LINKING THE AVAILABILITY OF CACHED FOOD TO CLIMATE CHANGE: AN EXPERIMENTAL TEST OF THE HOARD-ROT HYPOTHESIS Abstract.......................................................................................................................... 7 Introduction.................................................................................................................... 8 Methods.......................................................................................................................... 10 Field methods.......................................................................................................... 10 Statistical methods................................................................................................. 12 Results............................................................................................................................ 13 Discussion...................................................................................................................... 16 Tables and Figures......................................................................................................... 22 CHAPTER 2 CAUSES AND CONSEQUENCES OF PRE-LAYING WEIGHT GAIN IN A FOOD-CACHING BIRD THAT BREEDS IN LATE WINTER Abstract.......................................................................................................................... 32 Introduction.................................................................................................................... 33 Methods.......................................................................................................................... 36 Field methods.......................................................................................................... 36 Statistical methods.................................................................................................. 40 Results............................................................................................................................ 41 Patterns of weight change....................................................................................... 41 Causes of weight gain............................................................................................. 42 Consequences of weight gain.................................................................................. 43 Discussion...................................................................................................................... 43 Tables and Figures.......................................................................................................... 50 EPILOGUE.............................................................................................................................. 57 REFERENCES........................................................................................................................ 62 APPENDIX.............................................................................................................................. 75 iv LIST OF TABLES CHAPTER 1 Table 1. Results from Analysis of Variance (ANOVA) tests examining the influence of site (Guelph, Algonquin, Cochrane), exposure time (‘exposure’; 60, 120, 180 days), tree species (‘tree’; black spruce, jack pine, white birch) and interactions between tree and site and tree and exposure on the mass remaining (‘mass’) and caloric content (‘calories’) of cached raisins and mealworms. Adjusted R2 (for whole model results), F-values, degrees of freedom (‘df’; shown as predictor variable df, residual df) and p-values based on F-values (α = 0.05) are reported. .... 22 CHAPTER 2 Table 1. Results of model selection for explaining the rate of weight gain during the 15 days before first egg (rate of weight gain) and final weight of females on the day prior to first egg (final weight) with respect to female age and the percent of conifers on territories (percent conifers). Within each response variable, models are ranked (best-worst) based on the change in AICc units (ΔAICc) and Akaike weights (w). .......................................................................... 50 APPENDIX: CHAPTER 1 Table A-1: Results of two-way comparisons of means based on three-way Analysis of Variance (ANOVA) tests. ANOVA tests included the effect of site (Guelph, Algonquin, Cochrane), exposure time (‘exposure’; 60, 120, 180 days), tree species (‘tree’; black spruce, jack pine, white birch) as well as tree*site and tree*exposure interactions on (a) raisin mass, (b) raisin caloric content, (c) mealworm mass and (d) mealworm caloric content. Two-way comparisons are based v on Welch’s two-sample t-tests for differences between means; t-values, degrees of freedom (‘df’) and p-values based on t-values (α = 0.05) are reported for each comparison. ........................... 75 vi LIST OF FIGURES CHAPTER 1 Figure 1. (a) Average monthly temperature (oC) from Sep. 2011- Mar 2012 and (b) mean fall temperature (defined as the average of mean daily temperatures in Oct and Nov; Waite and Strickland 2006) in Guelph, Algonquin and Cochrane. Asterisks represent significant differences between sites (α = 0.05) based on Welch’s t-tests; error bars represent standard deviations. .. 24 Figure 2. Freeze-dried mass (% original mass remaining) of (a) mealworms and (b) raisins, and caloric content (kcal) of (c) mealworms and (d) raisins cached on three tree species (black spruce, white birch, jack pine) across a latitudinal gradient in Ontario at the end of 180