Post-fledging dependence period, dispersal movements and temporary settlement areas in saker falcons (Falco cherrug)

Abstract

Information on mortality rates and their causes in raptors and owls during the post-fledging dependency period (PFDP) and subsequent dispersal is essential for their more effective protection, including more efficient use of funds. Despite the importance of the above data, these data are not yet available for most birds of prey. The study aimed to provide and expand the knowledge in this field for saker falcon. We used satellite telemetry to monitor a total of six young birds since they left the nest boxes. All young birds survived the PFDP, but none survived to adulthood and died during the period of dispersal movements. The PFDP lasted 47 days (median value hereinafter), and the distance of individuals from the nest boxes during this period was 3.2 km (maximum distance 9 km). The area of the home range of the PFDP calculated by the 100% minimum convex polygon (MCP) method was 81 km2. During the period of dispersal movements, the monitored individuals set up five temporary settlement areas with an area of 422 km2 according to 100% MCP, where they stayed for 37 days. All individuals’ mean length of movement routes throughout the monitoring period was 3862 km. The main finding of the present study is the fact that none of the monitored individuals survived the dispersal period. At least half of them died due to human activity (electrocution, hunting), which is probably unbearable in the long term for wild populations of most animal species. This shows the need to start eliminating all types of artificial traps (e.g., electrocution, hunting, poisoning, etc.) without delay, thus helping to prevent the decline of populations of many species in the shorter or longer time horizon.

Overview of raptor and owl ringing in Slovakia in 2020

“…This colour ringing programme provides valuable information on the philopatry of nesting individuals (SKB D5825). In addition to that, we were able to identify a young saker falcon in Ukraine (SKB 7103) during the postbreeding dispersal (Prommer et al 2012, Kouba et al 2021. Power lines continue to be a significant factor of mor-tality for this species (Demeter et al 2004, Kovács et al 2014, European Commission, DirectorateGeneral for Environment 2019), the highest mortality being in the case of chicks (Nemček et al 2014).…”

Survival rates and causes of death in Tengmalm’s owl offspring during the post-fledging dependence period in Central and North Europe

“…After predation, the next most commonly reported proximate causes of death among fledglings are starvation, disease, human causes and structures (for example, collisions, artificial traps, electrocution, killing and hunting) and unknown reasons (e.g., Overskaug et al, 1999;S ̌aĺek et al, 2019;Kouba et al, 2021Kouba et al, , 2023, but different variables can affect all of these causes of death. Among the factors most frequently mentioned in studies dealing with offspring survival during the PFDP are prey abundance, offspring sex, the timing of hatching and fledging within the breeding season, clutch and brood size, offspring age at dispersal, body condition at fledging (i.e., body mass and/or wing length), habitat composition and weather conditions (e.g., Tarwater et al, 2011;Maness and Anderson, 2013;Cox et al, 2014;Naef-Daenzer and Grüebler, 2016;Kouba et al, 2023).…”

Post-fledging survival of Tengmalm’s owl offspring in boreal forests: Interactive effects of varying dynamics of main prey and habitat composition

“…Published studies identifying fledgling mortality of different owl and diurnal raptor species have considered predation and starvation the most frequent cause of death (e.g., Sunde, 2005;Wiens et al, 2006). Infections, drowning, electrocution, collisions with vehicles and other or unknown cases were less frequent (e.g., Sunde, 2005;Larrat et al, 2012;Kouba et al, 2021b). Significantly higher mortality was observed in years with low prey availability compared to years with high prey availability (e.g., Todd et al, 2003;Sunde, 2005), indicating the validity of the alternative prey hypothesis (Lack, 1954;Korpimäki et al, 1990).…”