Experimental evidence for a novel mechanism driving variation in habitat quality in a food-caching bird

Abstract

Variation in habitat quality can have important consequences for fitness and population dynamics. For food-caching species, a critical determinant of habitat quality is normally the density of storable food, but it is also possible that quality is driven by the ability of habitats to preserve food items. The food-caching gray jay (Perisoreus canadensis) occupies year-round territories in the coniferous boreal and subalpine forests of North America, but does not use conifer seed crops as a source of food. Over the last 33 years, we found that the occupancy rate of territories in Algonquin Park (ON, Canada) has declined at a higher rate in territories with a lower proportion of conifers compared to those with a higher proportion. Individuals occupying territories with a low proportion of conifers were also less likely to successfully fledge young. Using chambers to simulate food caches, we conducted an experiment to examine the hypothesis that coniferous trees are better able to preserve the perishable food items stored in summer and fall than deciduous trees due to their antibacterial and antifungal properties. Over a 1-4 month exposure period, we found that mealworms, blueberries, and raisins all lost less weight when stored on spruce and pine trees compared to deciduous and other coniferous trees. Our results indicate a novel mechanism to explain how habitat quality may influence the fitness and population dynamics of food-caching animals, and has important implications for understanding range limits for boreal breeding animals.

Continental divide: Predicting climate-mediated fragmentation and biodiversity loss in the boreal forest

“…For instance, white spruce face temperature-induced drought [54] whereas moose may experience heat conditions that exceed thermoregulatory thresholds [79]; both phenomena reflect direct effects of climate change that can lead to variation in the distribution and abundance of climate-sensitive species. In contrast, gray jays require cold temperatures to maintain winter food caches [80] whereas snowshoe hares experience higher predation risk with receding snow cover [64]. In both cases, climate-related effects are indirect through correlated biotic processes (i.e., food availability, predation) that are themselves associated with climate.…”

Food storage in a changing world: implications of climate change for food-caching species

“…), which have been proposed to preserve cached food better than deciduous trees. In Gray Jays, evidence suggests that territory quality at the southern edge of their range is related to the percentage of conifers on their territories [110,155], which appears to be partly due to the superior ability of conifers to preserve food [155]. Willow Tits (Parus montanus) have also been observed to preferentially cache food on conifers rather than deciduous trees [81], which could also be related to the antimicrobial properties of conifers.…”

“…Our motivation for understanding the mechanisms behind environmental degradation of cached food stems from our long-term research on a declining population of Gray Jays (Perisoreus canadensis) at the southern edge of their range [32,110,155,171,176]. Gray Jays cache a wide range of perishable food items during the late summer and fall and use this food for over-winter survival and late-winter breeding [154].…”

When anthropogenic‐related disturbances overwhelm demographic persistence mechanisms

“…This could mean that rarity advantages may sometimes buffer against extinction from anthropogenic disturbances (e.g. coalescence of declining populations to source habitats, resulting in higher per capita fitness – Strickland, Kielstra & Norris ) or that extinction is merely delayed by factors including long generation times (Kuussaari et al . ; Gilbert & Levine ).…”