Importance of juvenile mortality in birds population: early post-fledging mortality and causes of death in White Storks Ciconia ciconia

Early post-fledging mortality of White Stork during the period from the first flight to their autumn departure from natal area was described. Data from eight breeding seasons (2005−2012) about 56 cases of death of juvenile White Storks from a study area in Western Poland were collected. For a comparison the data of 55 cases of death from recoveries data deposited in Polish Bird Ringing Centre from entire Poland were included in analysis. Early post-fledgling mortality rate varied from 2 to 11% (mean 4.3%) of all fledglings per year. The main causes of death were collision with power lines and electrocution which in Western Poland constituted 60% and in entire Poland −78% of death cases with known causes. Other anthropogenic causes constituted responsibly 25 and 13% and natural causes −15 and 9%. Mean distance where dead storks were found was 183.3m from natal nests, while 73% were found closer than 100 m from their nests.