Autumn Migration of Immature Red Kites Milvus milvus from a Central European Population

Abstract

Post-fledging behaviour and mortality between the place of birth and wintering sites can be crucial to populations of raptors. We studied this phenomenon during the autumn migration of immature Red Kite Milvus milvus using telemetry data on the population breeding in western Poland. In total 34 immatures from 17 nests were ringed and GPS–GSM transmitters were attached, but only half of them survived the post-fledging period and started their first migration to wintering sites. The main mortality factors after fledging were collisions with power lines (6 individuals — 26.1%) and poisoning in wintering grounds (3 individuals — 8.8%). The mean (± SD) duration of migration and the mean distance between the breeding and wintering sites were 91.5 ± 45.2 day (range: 27–236) and 1328.0 ± 442.4 km (range: 690–2070), respectively. The daily mean speed of migration was 17.8 ± 9.4 km/day. On migration kites stopped on average 4.3 ± 3.1 times (range 1–12) for longer than 3 days, and spent a total of 37.5 ± 10.7 days (range 20–51) at stopovers. The migration duration was negatively correlated with the day of beginning of the migration, i.e. birds that started to migrate late in the season reached the wintering grounds faster. However, when the number of days at stopovers was excluded from the migration duration, this relationship was not significant, which means that the total number of days that kites spent at stopover sites significantly influenced the total duration of autumn migration. The wintering sites of birds from western Poland were located in the Iberian Peninsula and southern France and less important was Greece where single bird followed. Regular stopping over of immature Red Kites during their autumn migration indicates the need to focus more on protecting the staging areas.