Causes and consequences of pre‐laying weight gain in a food‐caching bird that breeds in late winter

Abstract

Animals that reside at high latitudes and altitudes year-round often use cached food to survive over the winter months, but a few species also rely on stored food to sustain them during the breeding season when the nutritional requirements of females are higher than normal. Gray jays Perisoreus canadensis rely on perishable cached food during the winter and females begin breeding in late winter when fresh food is rarely available. To examine pre-laying patterns of weight gain, as well as the causes and consequences of weight gain among individuals, we weighed females regularly throughout the pre-laying period. Females began increasing their weight approximately nine days prior to their fi rst egg date, and on average increased their body weight by 25%, which is on par with other bird species that rely on non-cached food. Final pre-laying weight was positively infl uenced by the percent of conifers on territories, providing some support for previous results showing that coniferous trees are better able to preserve cached food. We also found that both fi nal pre-laying weight and the rate of weight gain were positively related to female age, supporting the hypothesis that female caching ability improves with age. With increasing fi nal weight, females tended to lay larger clutches and hatched more nestlings, despite the fact that fi nal weight was not infl uenced by weight at the beginning of the weighing period. Our results confi rm that gray jays are able to reach breeding condition while relying primarily on food stored before winter, and suggest a novel mechanism by which habitat-mediated carry-over eff ects and female age may infl uence reproductive performance in a food-caching animal.

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

“…They presented some correlational support for the 'hoard-rot hypothesis' but the effect of fall temperatures on reproductive success was relatively small compared to the steep population declines and there was only weak evidence that fall temperatures increased over the period in which Gray Jays declined. Additionally, a recent experiment using simulated caches did not find a consistent effect of warmer fall temperatures on food quality [140]. Sechley et al [140])) did, however, suggest that temperature thresholds, such as the presence or absence of deep freeze events, could be driving observed differences in the degree of food preservation over a latitudinal gradient.…”

“…Additionally, a recent experiment using simulated caches did not find a consistent effect of warmer fall temperatures on food quality [140]. Sechley et al [140])) did, however, suggest that temperature thresholds, such as the presence or absence of deep freeze events, could be driving observed differences in the degree of food preservation over a latitudinal gradient. These lines of evidence lead us to speculate that (a) the persistence of stored food may be influenced by more than a simple linear relationship with temperature and (b) that a deeper understanding of how climate influences food quality may be gained by drawing upon applied research related to the degradation of food stored by humans.…”

“…To estimate G, we use data from Sechley et al [140] who determined the caloric value of mealworms experimentally cached over a typical storage-retrieval period (fall-winter) at two locations with different climatic conditions. Mealworms are an appropriate food item to use for estimating cached food degradation in Gray Jays because this species only stores perishable food, and arthropods constitute a significant portion of their diet [154].…”

Male experience buffers female laying date plasticity in a winter-breeding, food-storing passerine

“…Females advanced laying date as they aged, and nesting success was higher for older than younger females. An experience-derived increase in foraging efficiency could reduce food limitation and therefore advance female laying date (Sechley et al, 2014) and ability to provision young. Alternatively, advancing laying date over time could be due to changing reproductive investment strategies (Winkler, 1987).…”

“…160 ha) and breed during late winter (Strickland & Ouellet, 2011). They store perishable food on their territory in late summer and autumn (Strickland & Ouellet, 2011) and rely on cached food during the reproductive period (Sechley, Strickland, & Norris, 2014). Nesting typically begins in late February or early March, but breeding is asynchronous and the laying date is broadly variable (annual ranges varied from 16 to 51 days).…”