Doctor of Philosophy
Sherry, David F.
Morbey, Yolanda E.
Food scarce periods pose serious challenges for birds, particularly when those periods coincide with demanding life history stages such as overwintering. For resident birds in the Northern hemisphere, resource scarcity typically occurs simultaneously with winter conditions. In order to combat these compounded stressors, some species cache food to ensure a reliable supply of resources. Food caching is the storing of food items for subsequent retrieval and consumption after some delay. Canada Jays (Perisoreus canadensis) are year-round residents of the North American boreal forest and some high elevation areas in the United States, and cache food to combat resource scarcity. Additionally, Canada Jays use cached food to supplement their offspring, making food caching essential for both adult and offspring survival. This thesis explores the decisions Canada Jays make during both the resource acquisition, what food to cache, and cache deposition, where to cache that food, stages of caching. I addressed four specific questions: 1) Do Canada Jays demonstrate cache-site preferences and if so, what information is used to assess site quality, 2) Do Canada Jays employ context-specific cache defense strategies based on risk of cache pilferage, 3) Can Canada Jays anticipate predictable food shortages and alter their behaviour to account for them, and 4) Do Canada Jays attend to the macronutrient contents of their caches, and do they manipulate these nutrients to improve their current or future state. To answer these questions, I maintained a population of captive Canada Jays, and developed specific foraging paradigms to assess their behaviour. I found that Canada Jays make decisions at both the resource acquisition and cache deposition phases of caching. I provide evidence that Canada Jays identify and exploit conifers as cache locations and suggest an empirical explanation for observed distribution trends. I also show that birds successfully employ context-specific cache defense strategies, and that Canada Jays modulate the macronutrient contents of their caches to meet specific macronutrient targets. Canada Jays did fail, however, to plan for food restriction on a short time scale. Overall, I suggest that Canada Jays employ a variety of behavioural tactics to ensure the security of their cached food.
Summary for Lay Audience
Many birds that spend the winter months in North America are faced with long periods of limited environmental food availability. For many of these species, ensuring a consistent supply of food during these times begins long before the winter. Food caching, or food storing, is the process of storing food throughout the environment so that it can be retrieved at a later time. For species that face food scarce winter conditions, food caching typically occurs in the fall when food is abundant. One species that relies of food caching to endure the winter months is the Canada Jay. Canada Jays live in North America year-round, and thus have to endure food scarce winters. Because cached food is essential to their survival, Canada Jays have likely developed behaviours in order to increase their caching success. That is, Canada Jays should make decisions that favour the future availability of their caches. In this thesis, I examined these decisions at two stages: 1) resource acquisition, or what food to cache, and 2) cache-deposition, or where to cache it. I examined the ability of Canada Jays to select cache sites that have known preservative properties, their ability to hide caches from potential cache-robbers, and their ability to predict future food restriction and to plan for it. I also examined their attentiveness to the nutrient contents of their caches and compared that to the nutrient contents of the food they chose to eat. In general, Canada Jays made decisions that benefited their survival. They readily identified and selected cache-sites known to preserve caches, and successfully hid cached food from potential cache-robbers. They also demonstrated an attentiveness to the nutrients they were both caching and consuming, and demonstrated an ability to ensure appropriate nutrients were being cached for later consumption. Canada Jays failed to plan for food restriction on a short time scale, however. Overall, these decisions and behaviours are a positive indication that Canada Jays are well suited to combat the challenging conditions associated with North American winters.
Martin, Robert J., "Food Caching Decisions in Canada Jays (Perisoreus canadensis)" (2021). Electronic Thesis and Dissertation Repository. 7823.
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