Abstract
Fledgling behaviour and movement patterns throughout the post-fledging dependence period (PFDP), especially in relation to changing environmental conditions, have been rarely studied, despite the fact that this period is recognized as of crucial significance in terms of high mortality of juveniles. The PFDP can extend over quite a protracted period, particularly in birds of prey, and a knowledge of the movement patterns of individuals is fundamental for understanding mechanisms underlying survival, habitat use and dispersion. We radiotracked 39 fledglings of the Tengmalm’s owl (Aegolius funereus) in two years with different availability of prey: 2010 (n = 29) and 2011 (n = 10) and obtained 1455 daily locations. Fledglings reached independence on average in 45 days after fledging in 2010 (n = 22) and 57 days in 2011 (n = 6). Within years, the most important measures influencing the distance moved from the nest box were age of fledglings and number of surviving siblings present. Individual home range size and duration of PFDP in particular were dependent on maximal number of siblings seen outside the nest box. In the season with low prey availability fledglings were observed at greater distances from the nest box than in the year with higher prey availability (mean distance: 350 m in 2010 and 650 m in 2011) and occupied larger home ranges (mean: 30.3 ha in 2010 and 57.7 ha in 2011). The main factor causing these differences between years was probably the different availability of prey in these two years, affecting breeding success and post-fledging survivorship of the Tengmalm’s owls.
Highlights
Animal movement is fundamental to many ecological phenomena occurring over a wide range of spatial and temporal scales [1,2]
We found significant differences between the two seasons throughout the post-fledging dependence period (PFDP) in the fledgling distances from the nest box, individual home range sizes throughout the PFDP and individual PFDP duration
We could not test the relationship between the variables measured in this study and prey availability directly, but because we have demonstrated differences between years in all variables analysed, we may speculate that these differences were dependent on prey availability
Summary
Animal movement is fundamental to many ecological phenomena occurring over a wide range of spatial and temporal scales [1,2]. Movements are related to dispersal, migration, and colonization [4,5]. Fledglings of predatory birds are entirely dependent on their parents for food during PFDP and stay within the natal area until the initiation of natal dispersal [11]. This time period is frequently described as most crucial due to incomplete feather growth and inexpert flying skills [12,13,14] and ranges in different species from a few weeks to several months [8]
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