Nest Integration: a novel form of food acquisition by altricial fledglings

Parental investment in offspring provides fitness benefits for progeny but incurs costs for parents. However, in birds there is a paucity of information on the foraging behaviors of altricial young once they leave the nest. Here we report a novel form of food acquisition in an altricial bird that is driven by a fledgling itself rather than its parents. In a population of densely nesting Red-winged Blackbirds (Agelaius phoeniceus) in Eastern Illinois, USA, we encountered multiple instances of a free-moving fledgling present in a focal nest that also had chicks too young to fly. We observed this behavior six different times in the field and obtained detailed video footage of six total instances at three independent nests, with two of these resulting in an apparent acceptance (i.e., feeding) of the focal fledgling by the attending parental adults. In one of the two nests where the fledgling(s) were accepted, feeding adults provisioned the fledgling as much as the average chick in the nest while at the other nest attending adults fed the fledgling above random expectations. Nest integration appears to be a novel form of food acquisition that is distinct from other fledgling self-maintenance behaviors.