Linking the availability of cached food to climate change: an experimental test of the hoard-rot hypothesis

Abstract

Understanding how long-term changes in climate influence populations requires knowledge of the mechanisms by which climate influences individual success and population abundance. We explored the implications of warmer falls and winters on a nonmigratory, food-caching bird, the Gray Jay (Perisoreus canadensis (L., 1766)), in Algonquin Park, Ontario, by experimentally examining the influence of temperature on the caloric content and mass of simulated cached food. Using three sites in, north of, and south of Algonquin, we examined the hypothesis that warmer temperatures would negatively influence the preservation of cached food by accelerating decay. Food cached at the highest latitude site retained the greatest mass and caloric content over 180 days of exposure, but there was no difference between the intermediate and the low latitude sites. We also show that Algonquin experienced a winter climate similar to our northernmost site as recently as 1990, and our results suggest that food availability in Algonquin has likely decreased since then, due to a warming climate. Interestingly, this coincides with a decline in territory occupancy by Gray Jays in Algonquin. Our results point to a unique mechanism by which climate warming may influence the persistence of a boreal species through its influence on winter food availability.Résumé : La compréhension de l'influence des changements climatiques à long terme sur les populations nécessite une connaissance des mécanismes par lesquels le climat influence le succès individuel et l'abondance des populations. Nous nous sommes penchés sur les conséquences d'automnes et d'hivers plus chauds sur un oiseau non migrateur qui cache sa nourriture, le mésangeai du Canada (Perisoreus canadensis (L., 1766)) dans le parc Algonquin (Ontario), en examinant de manière expérimen-tale l'influence de la température sur le contenu calorique et la masse de la nourriture cachée simulée. En nous servant de trois sites, à l'intérieur, au nord et au sud du parc, nous avons vérifié l'hypothèse voulant que des températures plus élevées aient une incidence négative sur la préservation des aliments cachés en en accélérant la décomposition. La nourriture cachée au site à la plus grande latitude conservait la plus grande masse et le plus grand contenu calorique durant 180 jours d'exposition, mais il n'y avait aucune différence entre les sites de latitudes intermédiaire et plus faible. Nous démontrons également qu'un climat semblable à celui du site le plus septentrional régnait encore au parc Algonquin en 1990, et nos résultats indiqueraient que la disponibilité de nourriture dans le parc a vraisemblablement diminué depuis en raison du réchauffement climatique. Fait à noter, cela coïncide avec une baisse de l'occupation du territoire par les mésangeais du Canada dans le parc Algonquin. Nos résultats indiquent qu'un mécanisme unique expliquerait l'influence du réchauffement climatique sur la persistance d'une espèce boréale, qui découlerait de l'influence de ce réchauffement sur la disponibilité de nourrit...

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

“…Such studies could take place in the field (e.g. [139]) or in the laboratory by borrowing many of the approaches used in the field of food science (e.g. [16,50,117]).…”

“…Seven percent (7%) stored both high-and low-perishability food and only 2% (four species: the Bull-headed Shrike Lanius busephalus, Gray Jay, Siberian Jay Perisoreus infaustus and Wolverine Gulo gulo) were both long-term cachers and relied exclusively on high-perishability food (susceptibility score of 9). Population declines at the southern edge of ranges have already been documented for both Gray Jays [171] and Wolverines [6] and studies on both of these species also suggest that climate change could be contributing to population declines [62,139,171].…”

“…For example, in a study of the caloric content of simulated Gray Jay caches at three different latitudes in Ontario, Canada, Scheley et al [139] found that the mass loss and caloric content of cached food (mealworms and raisins) was similar between low-and midlatitude sites even though these sites differed in mean fall temperatures. However, food caches from the highlatitude site lost less weight and caloric content, leading Scheley et al [139] to speculate that 'deep freeze' events may be driving this pattern as the high-latitude site was the only site that reached an average of -16°C during the winter. In Finland, bacterial activity was halted in two different decomposer communities in soil at -16°C, suggesting that this may be an important threshold in natural systems [157].…”

“…Using these values, the nutrition gained from caching food at the more southern site is estimated to be >50% lower (0.23 kcal) compared to the more northern site (0.50 kcal). Given temperatures in Algonquin were similar to the Cochrane as early as 1990 [139], this suggests that Gray Jays in Algonquin park have experienced a significant decline in nutritional quality of cached food. Of course, these are crude estimates but they do serve as an example of how this equation can be used to assess the influence of environmental conditions on nutritional benefits of caching.…”

Vulnerability of Subarctic and Arctic breeding birds

“…While some might be able to withstand climate change due to favorable natural history traits, others might not. The increase in freeze-thaw cycles has also been suggested to be related to declines in gray jay at the southern edge of its range in the Canadian boreal forest (Sechley et al 2015). For a species like the Long-tailed Duck (Clangula hyemalis), which is globally assessed as vulnerable (Birdlife International 2012), regionally assessed as endangered (Helcom 2013), predicted to lose part of its breeding range in the study region in future due to climate change, and has several natural history traits that might make it extra vulnerable to climate change, urgent actions are needed.…”