American robin nestlings compete by jockeying for position

Abstract

We investigated whether nestling American robins (Turdus migratorius) were capable of influencing food distribution in their nests by perceiving that certain sectors of the nest received a relatively high proportion of feedings and positioning themselves accordingly.Feeding observations were obtained from videotape recordings taken at different stages of the nestling period. Parents generally arrived at a predictable location on the nest rim and allocated proportionally more food to nestlings in the central position. The degree of nestling movement was significantly positively correlated with variation in the predictability of parental arrival locations on the nest rim. Furthermore, nestlings moved more in broods suffering brood reduction. This suggests that when competition for food is intense and the location of parental arrival is predictable, nestlings respond by jockeying for access to the most favorable (i.e., central) position in the nest. We conclude that jockeying for position by nestlings can influence the pattern of food allocation by parents, and that hungry nestlings can improve their competitive standing against nestmates by moving to positions where parents are more likely to feed them.

Host–parasite relatedness shown by protein fingerprinting in a brood parasitic bird

“…This conclusion differs from that for moorhens, where host-parasite relatedness is explained fully by philopatry (8). An important difference is that philopatry was much more precise in the moorhen population, where 82% of the locally recruited breeders nested within two territories of their parents.…”

“…An important difference is that philopatry was much more precise in the moorhen population, where 82% of the locally recruited breeders nested within two territories of their parents. Relatives were therefore likely to be parasitized, simply because brood parasitic moorhens almost exclusively selected neighbors as hosts (8). In the present goldeneye population on the other hand, only 13% (2 of 16) of the recruiting wing-tagged females nested in the birth nest or one of its two nearest neighbor nests (M.Å., unpublished work).…”

“…In the present goldeneye population on the other hand, only 13% (2 of 16) of the recruiting wing-tagged females nested in the birth nest or one of its two nearest neighbor nests (M.Å., unpublished work). Philopatry in goldeneyes therefore is much less precise than in the moorhens, which showed no sign of kin discrimination (8). Its likely occurrence in goldeneyes (and some other ducks; ref.…”

“…Albumen is of strictly maternal origin, with band variation that reflects genotypic differences (see above). Therefore, bandsharing analysis, as with DNA fingerprint studies (e.g., 8,15,[21][22][23][24], can be applied to albumen bands for estimating differences in mean relatedness between categories of individuals. For each egg, presence͞absence of each band was recorded in a matrix.…”

“…This return rate makes it likely that some local females are closely related (mother-daughter or sisters). Propagation of genes through relatives (4) therefore might favor conspecific brood parasitism among females in ducks (5,6) and in certain other birds where females nest close to their birth site (7,8). Relatedness between host and parasite may reduce the fitness cost of being parasitized for the host (5) or even increase its inclusive fitness (6), but the role of female philopatry and relatedness in brood parasitism is still a matter of debate (2,(5)(6)(7)(8)(9)(10)(11)(12)(13).…”