| Popis: |
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. |
