2001.Immunity, growth and begging behaviour of nestling Barn Swallows Hirundo rustica in relation to hatching order. -J. Avian Biol. 32: 263 -270.In altricial birds, asynchronous hatching often results in a size hierarchy among nestlings. However, laying order and hatching order may affect components of offspring condition differentially. Since parasites can have a heavy impact on their hosts, strategies may have evolved that allow parents and offspring to allocate critical resources to immunity depending on hatching order. In this study of the Barn Swallow Hirundo rustica we (1) analyse the relationship between laying and hatching order of eggs, (2) compare morphological, serological and immunological traits between early-and late-hatched siblings, and (3) compare the begging behaviour of early-and late-hatched nestlings. Hatching order strictly reflected laying order. Late-hatched chicks begged more for food but had smaller body mass throughout the nestling period. Immunoglobulin concentration and intensity of T cell-mediated immunity were larger in late-hatched nestlings. Large concentration of immunoglobulins in late-hatched nestlings may reflect transfer of immunity from the mother via the egg. Alternatively, in association with larger T cell-mediated immunity, immunoglobulin production may indicate larger investment in immunity by latehatched nestlings. Laying order and hatching order may therefore affect components of nestling condition differentially.

No abstract

Parents are selected to maximize their fitness by allocating care among their progeny in relation to the differential reproductive value of offspring. Nestlings have been hypothesized to signal need for parental care reliably through their begging behavior, but offspring condition as reflected by their reproductive value may likewise affect begging and hence provisioning. We assessed the relative importance of need and condition in determining begging behavior and feeding rate of nestling barn swallows (Hirundo rustica) through short-term starvation, a challenge to their immune system with a foreign antigen negatively affecting condition, and brood size manipulation. Food deprivation but not condition or brood size manipulation increased nestling begging rate. Parents fed offspring depending on both need and condition but only when feeding broods that were reduced or of normal size. In enlarged broods, offspring received less food per capita than in reduced broods, and parents did not discriminate among nestlings relative to their need or condition. Thus, nestlings signal their need by increased solicitation. Parents allocate food to offspring dependent on both need and condition, with these effects depending on parental workload as determined by experimental brood size.