Parent-offspring interactions in a long-lived seabird, the Little Auk (Alle alle): begging and provisioning under simulated stress

Long-lived seabirds are good models to study the mechanisms that mediate the parent–offspring interactions. Contrary to studies under natural conditions, experimental manipulations allow us to assess the birds’ reactions in a short time period. We used the stress hormone corticosterone as an independent experimental factor to simulate the stress reaction, to examine changes in the behaviour of Little Auk chicks and parent birds. In the first experiment, we hypothesised that after enhancement of the corticosterone level Little Auk (Alle alle) chicks intensify their begging performance and attain a higher pre-fledging body mass than the control chicks. In the second experiment, we hypothesized that parent Little Auks with an increased corticosterone level feed their chicks less frequently and spend less time at the colony than their untreated partners and the control birds. We also expected that chicks with one parent implanted with corticosterone fledge later and with a lower body mass than chicks of two untreated parents. The obtained results supported the above hypotheses. We demonstrated that modification of begging performance in Little Auks constitutes an adaptive mechanism that guards against the decrease in the chicks’ body condition during stressful periods. Even though the provisioning rate in Little Auks can be regulated according to the chick’s needs (expressed by the intensity of the begging display), it appears that adult birds regulate their provisioning strategy primarily according to their body state. The results suggest that parent Little Auks under stressful conditions will decrease their parental effort and redirect the available energy towards self-maintenance. The study provides novel insights into the behaviour of long-lived alcids using an experimental approach on free-living birds.