Evidence of age-related improvement in the foraging efficiency of Ad\xe9lie penguins

Amélie Lescroël,Annie Pollard,David Ainley,Katie Dugger,Grant Ballard,Elizabeth Porzig,Scott Jennings,David Grémillet,Arvind Varsani,Annie Schmidt,Melanie Massaro

doi:10.1038/s41598-019-39814-x

Abstract

Age variation in reproductive performance is well-documented but the mechanisms underlying this variation remain unclear. Foraging efficiency is likely to be a key source of demographic variation as it determines the amount of energy that can be invested in fitness-related activities. Evidence of age-related changes in the foraging efficiency of adult seabirds is scarce and inconsistent. We investigated the effects of age on the foraging efficiency of breeding Adélie penguins, a relatively short-lived seabird species, in order to gain a broader perspective on the processes driving variation in ageing rates. We found support for a positive effect of age, either linear or levelling off at old ages, on both our proxies for daily catch rate and catch per unit effort. Across all age classes, males were more performant foragers than females. We found no strong evidence for differing ageing patterns between sexes or individual quality levels, and no evidence for senescence. We infer that continuous individual improvement could be responsible for a larger amount of the variation in foraging efficiency with age at our study site, compared with selective disappearance of underperforming phenotypes. The different results reported by other studies highlight the need to conduct longitudinal studies across a range of species in different environments.

Highlights

The precise mechanisms underlying age variation often remain unclear and attempts to identify proximate causes, such as differences in physiology[3,13,14,15,16] and behaviour[17,18,19,20,21,22,23,24,25,26], have only recently been investigated in the wild
We evaluated foraging efficiency as: (1) the total number of undulations per trip divided by trip duration to get undulations per day (Uperday), as an index representing catch per unit time; and (2) the total number of undulations per trip divided by total VeDBA to get undulations per g (Uperg), as the catch per unit effort
For Uperday, the best model based on intrinsic characteristics only (Table 2, model 1) included a pseudo-threshold effect of age (β = 1453.8, SE = 580.3, 85% confidence intervals (CI): 614.6 to 2293.0)

Summary

Introduction

The precise mechanisms underlying age variation often remain unclear and attempts to identify proximate causes, such as differences in physiology[3,13,14,15,16] and behaviour[17,18,19,20,21,22,23,24,25,26], have only recently been investigated in the wild. Studies involving large sample sizes detected no[22] (thick-billed murres Uria lomvia) or very little evidence[23] (wandering albatrosses Diomedea exulans) of age-related variation in foraging behaviour, and no sign of senescence These two studies are the only ones, to our knowledge, to have quantified the effect of continuous age (rather than age or experience categories) on the foraging performance of breeding male and female seabirds in the wild. Some populations range widely at sea[32], though some to a lesser degree[33,34] and spend most of their lives there, yet often raise two chicks, a life-history pattern that is uncommon among pelagic seabirds[31] Given their relatively fast life-history, we would expect to see faster aging rates in Adélie penguins compared to other seabirds. Once we had determined the most competitive models for foraging efficiency based on intrinsic characteristics of the birds (age, sex, quality), we modelled the additional effect of extrinsic variables (day in the season, year) to account for environmental variation

Methods

Results

Conclusion