Regulation of food provisioning and parental body condition in Leach’s storm-petrels, Oceanodroma leucorhoa: Experimental manipulation of offspring food demand

We examined the effects of offspring food demand on parental regulation of food provisioning and body condition in a small long-lived seabird, Leach’s storm-petrels (Oceanodroma leucorhoa). In one experimental group, food demand of chicks on their parents was increased by removing one parent (‘single’), and in another group these food demands were decreased by supplementary feeding of chicks (‘supplement’). A further unmanipulated group provided a ‘control’. Feeding frequencies by one parent were higher in the single but lower in the supplement than in the control group, in accordance with the food demand of chicks. The size of meals appeared to be not different among the experimental groups. However, as single parents did not compensate perfectly for the increase of chick food demand by food provisioning, single chicks grew at slower rates and fledged at smaller masses than control chicks. Supplement chicks grew at similar rates and fledged at similar masses as control chicks, because parents decreased food provisioning and food processing capacity of the chicks might be limited. The body condition of parents, which was determined by body mass loss and feather regrowth rate, did not differ among the groups. These results indicate that feeding frequency was regulated by parental decision in this storm-petrel species. Parents may adjust their food provisioning to match the food demand of chicks but within a certain range so as not to deteriorate their own body condition.