Ontogenetic stability of inherited migratory directions in a nocturnal bird migrant: comparison between the first and second year of life

Publisher Website
Google Scholar
Abstract
According to current theory young passerine migrants on their first migration are equipped with a genetic programme of duration and direction of migration which enables them to reach their winter quarters independently of adults. The question was investigated whether in birds prevented from gathering migratory experience the genetically determined directional information is expressed only during the first autumn migratory season or whether it is retained as an endogenous directional preference at least throughout the 2nd year of life. One group of Blackcaps Sylvia atricapilla (Linnaeus) each from west and east of the Central European migratory divide was hand-raised, held in captivity for 2 years and its orientation tested in funnel cages during the migration seasons of both years. From mixed pairs of these two parental groups F1-offspring were bred in aviaries, hand-raised and their orientation also tested during the first and second autumn of their lives. In comparison with each other the three groups chose significantly different directions, but for none of them was there any difference in overall mean direction between the first and second autumn. In spring, SW-migrants that had wintered in captivity oriented NNE. A slight increase in the scatter of individual mean vector directions was noticed during the second autumn. Activity levels were similar during both years for the parental groups, but showed a sharp decline among the F1-generation during the second autumn. These are the first data from hand-raised birds demonstrating that genetically encoded information about migratory directions persists at least through the second autumn migration. In birds without migratory experience, endogenous directional preferences are not lost and can be expressed as clearly in orientation tests during the second as during the first autumn season.