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

Observations and experiments were carried out at 34 four-nestling nests of Arabian babblers (Turdoides squamiceps) and feeding events were analzyed ac cording to hatching order and nestling location in the nest. Nestlings were fed in a negative correlation with hatching order. Nestling locations in r elation to the provisioners were defined as Near, Far, Right, Left, and Cen ter. Feeders fed closer nestlings more often than those further away, and s traight ahead rather than sideways. In the open circular nest, the feeding adults' positions were unpredictable and equally distributed around the nes t. Each peripheral position therefore served equally as Near, Far, Right an d Left positions. The Center was independent of the arrival direction of th e feeders and was advantageous relative to the peripheral positions. The im portance of the central position uas demonstrated by three experiments. (a) Food deprivation for 1 h caused the first-hatched nestling to occupy the c enter position and pain more feedings than its siblings. (b) Introduction o f a Perspex barrier into the neu. 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, resulte d in the first-hatched nestling occupying the near position more often than its nestmates and obtaining 52% of the feedings provisioned to the whole b rood. These findings imply that the architecture of the nest has an importa nt role in food distribution among the nestlings, and contributes to reduci ng inequalities in the siblings' abilities to obtain food.