Energetic and Fitness Costs of Mismatching Resource Supply and Demand in Seasonally Breeding Birds

Abstract

By advancing spring leaf flush and ensuing food availability, climatic warming results in a mismatch between the timing of peak food supply and nestling demand, shifting the optimal time for reproduction in birds. Two populations of blue tits (Parus caeruleus) that breed at different dates in similar, but spatially distinct, habitat types in Corsica and southern France provide a unique opportunity to quantify the energetic and fitness consequences when breeding is mismatched with local productivity. As food supply and demand become progressively mismatched, the increased cost of rearing young pushes the metabolic effort of adults beyond their apparent sustainable limit, drastically reducing the persistence of adults in the breeding population. We provide evidence that the economics of parental foraging and limits to sustainable metabolic effort are key selective forces underlying synchronized seasonal breeding and long-term shifts in breeding date in response to climatic change.

Resting and daily energy expenditures of free-living field voles are positively correlated but reflect extrinsic rather than intrinsic effects

“…A correlation with RMRt may then emerge either because RMRt is pulled along by DEE or because it is independently determined by similar environmental factors. Similar conclu-sions were reached by Tinbergen and Verhulst (30) in their study of breeding blue tits, and the notion of extrinsic influences on DEE has formed a fundamental component of recent studies that explain links between changes in global climate and animal distributions (31). Interspecific comparisons of RMRt in the genus Peromyscus have also produced similar conclusions (32).…”

“…They are selected, however, to have elevated expenditures because of the fitness benefits this brings. However, an alternative view is that poor environments may lead to greater levels of both DEE and RMRt, because metabolism is forced upwards by the harsh conditions (31). A critical difference between the forcing and enabling processes is that under environmental forcing the animals could not survive if they chose to expend energy at lower levels.…”

Annual rhythms that underlie phenology: biological time-keeping meets environmental change

“…However, this plasticity is limited by the complex mechanisms of avian reproduction, so that their breeding season is progressively delayed with respect to the food peak [84]. Although evidence for large effects on recruitment rates and population density is still scarce, mismatched timing of reproduction has imposed energetic and fitness consequences, including reduced fledging rate, fledging mass and adult survival [90,91].…”

Optimal annual routines: behaviour in the context of physiology and ecology

“…In contrast, the framework for modelling annual routines that we present below handles both these aspects. Thomas et al (2001) compare two populations of blue tits (Parus caeruleus) that differ in terms of the relationship between the timing of breeding and the peak in the availability of food. In the population in which the timing of peak offspring's need for food matches the peak in food, parents work at approximately 3-4 times BMR, whereas if there is a mismatch in timing, parents are forced to work at levels that cannot safely be sustained.…”