The importance of nestling location for obtaining food in open cup-nests

Abstract.

Observations and experiments were carried out at 34 four-nestling nests of Arabian babblers (Turdoides squamiceps) and feeding events were analyzed according to hatching order and nestling location in the nest. Nestlings were fed in a negative correlation with hatching order. Nestling locations in relation to the provisioners were defined as Near, Far, Right, Left, and Center. Feeders fed closer nestlings more often than those further away, and straight ahead rather than sideways. In the open circular nest, the feeding adults' positions were unpredictable and equally distributed around the nest. Each peripheral position therefore served equally as Near, Far, Right and Left positions. The Center was independent of the arrival direction of the feeders and was advantageous relative to the peripheral positions. The importance of the central position was demonstrated by three experiments. (a) Food deprivation for 1 h caused the first-hatched nestling to occupy the center position and gain more feedings than its siblings. (b) Introduction of a Perspex barrier into the nest, thus eliminating the central position and preventing the nestlings from changing places, led to a loss of importance of hatching order and equal provisioning of the nestlings. (c) Fencing the nest so that entry was possible from only one permanent direction, resulted in the first-hatched nestling occupying the near position more often than its nestmates and obtaining 52% of the feedings provisioned to the whole brood. These findings imply that the architecture of the nest has an important role in food distribution among the nestlings, and contributes to reducing inequalities in the siblings' abilities to obtain food.