Albatrosses respond adaptively to climate variability by changing variance in a foraging trait

International audience; The ability of individuals and populations to adapt to a changing climate is a key determinant ofpopulation dynamics. While changes in mean behaviour are well studied, changes in trait variancehave been largely ignored, despite being assumed to be crucial for adapting to a changingenvironment. As the ability to acquire resources is essential to both reproduction and survival,changes in behaviours that maximise resource acquisition, should be under selection. Here, usingforaging trip duration data collected over 7 years on black-browed albatrosses (Thalassarchemelanophris) on the Kerguelen Islands in the southern Indian Ocean, we examine the importanceof changes in the mean and variance in foraging behaviour, and the associated effects on fitness, inresponse to the El Niño Southern Oscillation. Using double hierarchical models, we find noevidence that individuals change their mean foraging trip duration in response to a changingenvironment, but strong evidence of changes in variance. Younger birds showed greater variabilityin foraging trip duration in poor conditions as did birds with higher fitness. However, duringbrooding, birds showed greater variability in foraging behaviour under good conditions,suggesting that optimal conditions allow the alteration between chick provisioning and selfmaintenancetrips. We found weak correlations between sea-surface temperature and the El NiñoSouthern Oscillation, but stronger links with sea-level pressure. We suggest that variability inbehavioural traits affecting resource acquisition is under selection and offers a mechanism bywhich individuals can adapt to a changing climate. Studies which look only at effects on meanbehaviour may underestimate the effects of climate change and fail to consider variance in traits asa key evolutionary force.