Early-life begging effort reduces adult body mass but strengthens behavioural defence of the rate of energy intake in European starlings.

Jonathon Dunn,Melissa Bateson,Clare Andrews,Daniel Nettle

doi:10.1098/rsos.171918

Abstract

Animals require strategies for coping with periods when food is scarce. Such strategies include storing fat as a buffer, and defending the rate of energy intake by changing foraging behaviour when food becomes difficult to obtain. Storage and behavioural defence may constitute alternative strategies for solving the same problem. We would thus expect any developmental influences that limit fat storage in adulthood to also induce a compensatory alteration in adult foraging behaviour, specifically when food is hard to obtain. In a cohort of hand-reared European starlings, we found that higher manipulated early-life begging effort caused individuals to maintain consistently lower adult body mass over a period of two years. Using an operant foraging task in which we systematically varied the costs of obtaining food, we show that higher early-life begging effort also caused stronger behavioural defence of the rate of energy intake when food was more costly to obtain. Among individuals with the same developmental history, however, those individuals who defended their rate of energy intake most strongly were also the heaviest. Our results are relevant to understanding why there are marked differences in body weight and foraging behaviour even among individuals inhabiting the same environment.

Highlights

Animals require strategies for coping with periods when food is scarce
Using an operant foraging task in which we systematically varied the costs of obtaining food, we show that higher early-life begging effort caused stronger behavioural defence of the rate of energy intake when food was more costly to obtain
We investigated whether developmental influences that lead to lower body mass in adulthood lead to stronger behavioural defence of the rate of energy intake, in a cohort of hand-reared European starlings in which we manipulated early-life feeding schedules

Summary

Introduction

Animals require strategies for coping with periods when food is scarce. Such strategies include storing fat as a buffer, and defending the rate of energy intake by changing foraging behaviour when food becomes difficult to obtain. Comparing the same individual across states where it had different levels of stored reserves, we would expect to observe a negative relationship: assuming an animal has a fixed predation risk it is willing to accept, as stored reserves decrease, behavioural defence of the rate of energy intake should become stronger. In support of this claim, within-subjects studies find that food-restricted or lighter animals become more willing to forage in potentially dangerous places [12] and are less food selective [13]

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Conclusion