Meeting Abstract

P2.17  Sunday, Jan. 5 15:30  Mitigation of Costs Associated with Laying Order in a Cavity Nesting Songbird HANSER, J.T.*; CASTO, J.M.; Illinois State University; Illinois State University jthanse@ilstu.edu

In many avian species, periodic and partial incubation prior to the completion of the clutch causes eggs to hatch in the order they are laid, promoting the establishment of size hierarchies among nestlings within a brood. Since later hatched nestlings are often at a competitive disadvantage, laying order holds significant fitness consequences for nestlings. However, females may be able to mitigate these effects by differentially allocating resources across the laying sequence, such that (1) later laid eggs hatch relatively more quickly than earlier laid eggs or (2), all else being equal, nestlings of later laid eggs are able to outcompete individuals of earlier laid eggs. We experimentally investigated this hypothesis by examining the relationship between laying order and hatching order as well as patterns of nestling growth in European starlings (Sturnus vulgaris). Nest boxes were checked daily and all eggs were marked to indicate the order of laying. Within experimental nests, eggs were removed soon after they were laid, stored in an empty nest box for the duration of the laying period, and placed back into the original nest following the completion of the clutch. Starting on the projected hatch day and continuing until hatching had finished, nests were checked every two hours from 0600 to 2000. While laying order and hatching order were positively correlated within control nests, this pattern was reversed within experimental nests, suggesting that either eggs laid later in the laying sequence require shorter periods of incubation to hatch than earlier laid eggs, or alternatively, delaying incubation lengthens the period of incubation required to hatch. Additional analyses will examine whether patterns of nestling survival and growth across the hatching order differed between treatments.