title: Effects of Ontogeny, Diel Rhythms, and Environmental Variation on the Adrenocortical Physiology of Semialtricial Black Kites (Milvus migrans).
abstract: We examined whether hypothalamic-pituitary-adrenal axis activity in the nestlings of a semialtricial raptor, the black kite (Milvus migrans), varied with advancing age, throughout the day, and in response to a number of socioecological factors presumed to affect allostatic load. Both baseline corticosterone (CORT) titers and maximum CORT levels during 30 min of handling and restraint augmented across all sampled ages, suggesting that nestlings' energetic demands and capacity to respond to perturbations increase progressively throughout development. CORT secretion also peaked in the early morning, reached minimum levels in the central hours of the day, and increased again before dusk, suggesting a possible role of CORT in the regulation of activity-inactivity patterns. Finally, nestlings raised in a year of low marsh inundation, implying lower food availability and heightened allostatic loads, exhibited higher adrenocortical responsiveness to stress than nestlings raised in years of intermediate or high flooding. The nondetectable effect of other socioecological variables, such as territory quality, temperature, or brood order, suggests that parents may be able to buffer their nestlings from adverse environmental conditions or that the effect of such factors may have been obscured by selective mortality operating before sampling. We propose that future studies increase the simultaneous use of complementary techniques (fecal sampling, feather analysis) to reach firmer and more comprehensive conclusions, especially for planning the management and conservation of sensitive species.
authors.forename: Lidia
authors.initials: L
authors.lastname: López-Jiménez
authors.forename: Julio
authors.initials: J
authors.lastname: Blas
authors.forename: Alessandro
authors.initials: A
authors.lastname: Tanferna
authors.forename: Sonia
authors.initials: S
authors.lastname: Cabezas
authors.forename: Tracy
authors.initials: T
authors.lastname: Marchant
authors.forename: Fernando
authors.initials: F
authors.lastname: Hiraldo
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Sergio
mesh_terms: D000302:Adrenal Cortex / Q000502:physiology*; D000375:Aging / Q000502:physiology; D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D003345:Corticosterone / Q000097:blood; D004777:Environment; D046093:Falconiformes / Q000097:blood / Q000254:growth & development* / Q000502:physiology*; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology; D010913:Pituitary-Adrenal System / Q000502:physiology
chemical_list: D003345:Corticosterone
keywords: allostatic load; corticosterone; developmental hypothesis; marshland inundation levels