Interaction between parent body condition and sex affects offspring desertion in response to acute stress

In species where the offspring are naturally deserted by one parent, the experimental stressing of breeding individuals can provide valuable information on the mechanisms underlying desertions and thus the evolution of parental roles. During a study conducted in southern Poland in 2016 and 2017, we investigated factors influencing desertion during the chick-rearing period by male and female Whiskered Terns Chlidonias hybrida (a species in which female desertion occurs) subjected to acute stress. We predicted that stressed females should desert their broods at a higher rate than males because of their smaller contribution to chick feeding and the probable lower cost of female desertion. For the control nests, we released birds immediately after trapping, whereas in the treatment group we temporarily removed birds from their nests, releasing them 9 or 24h after being trapped. Birds deserted significantly more often in the treatment (28%) than in the control (7%) nests. The response to stress depended strongly on the sex-body condition interaction: in males, the probability of return to the nest after release was high and unrelated to condition, while in females the probability of return increased with body condition in both the treatment and the control groups. Breeding success in both categories of nests was not related to desertion or any of the other factors studied. This study suggests that in species where females naturally tend to desert, desertion by females subjected to disturbance may be associated with the level of their body reserves, whereas males desert at a low rate, irrespective of their body condition. More importantly, body condition appears to be an important factor that influences natural desertion.