Alaska Science Center
Nestling growth relationships of brown-headed cowbirds and dickcissels
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Product Type: Journal Article
Authors: Hatch, S. A.
Nestling growth relationships between brown-headed cowbirds (Molothrus ater), a brood parasite, and dickcissels (Spiza americana) were studied in the Konza Prairie Research Natural Area of eastern Kansas. The intensity of cowbird parasitism was extremely high--nests containing as many as nine cowbird eggs and three host eggs were found. Fifty-nine of 65 nests (91%) were parsitized, and the mean number of cowbird eggs per parasitized nest was 3.1. Dickcissels raised up to five young in mixed broods of various composition. I used multiple regression to assess the relative effects on nestling growth rates of number of host young, number of brood parasites, and hatching date. The analysis revealed a relative insensitiviy of host growth rates to brood size or composition as compared to parasite responses, suggesting preferential feeding of host young based on species recognition or a tendency to feed the smalleer members of a brood preferentially during the latter part of the nestling period.