Adaptive significance of seasonal migrations: whether annual migrations are dangerous for birds themselves

摘要

The monthly distribution of found dead or shot ringed birds was used for the analysis of seasonal differences in the rate of annual mortality. The analysis was based on the published ring recoveries often species belonging to five bird orders. The significant differences were found between the mortality rate in various seasons for all species. However, the pattern of these differences was highly specific for every bird species. No sexual differences in seasonal distribution of mortality in 3 species was found, whereas age differences in seasonal mortality were significant in 2 species out of 5. The mortality during stay at winter quarters was essentially higher than during migrations in 10 cases, whereas the opposite situation occurred-in 3 cases out of 18. On the average, the mortality of birds during seasonal migrations comprises about 1/3 of the total annual mortality. Migrations are adaptive for birds, and the real accidents of their mass death during migrations are of no selective significance.