Abstract
The behaviour of the nestlings of nocturnal cavity-nesting species has relatively rarely been studied in detail because of problems connected with use of the technical devices required to provide long-term monitoring of individuals. However, long-term observation of nestling behaviour is crucial in order to identify different types of behaviour which may be caused by sibling competition at the end of nesting period. We studied behaviour of 43 Tengmalm's owl (Aegolius funereus) nestlings at 14 nests using a camera and a chip system. The nestlings perched at the nest box entrance from an average age of 28 days from hatching (range 24–34 days) until fledging, spending around 2 hours per day here in total, in periods ranging from a few seconds to 147 min (7.6±10.9 min, mean ± SD). We found that individual duration of perching at the nest box entrance was significantly influenced by nestlings' age and wing length and that the duration of perching at the nest box entrance significantly decreased with time of night. However, during daylight hours, time of day had no effect on either probability or duration of nestlings' perching. We suggest daylight perching at the nest box entrance results from nestlings' preparation for fledging, while individuals perching here during the night may gain an advantageous position for obtaining food from the parents; another possibility at all times of day is that nestlings can reaffirm their social dominance status by monopolizing the nest box entrance.
Highlights
In bird species where parents deliver food to dependent young, there is frequently significant competition for resources and evidence is accumulating that parental provisioning behaviour can be influenced by nestlings’ behaviour [2,3,4,5,6]
Length of time spent perching at the nest box entrance decreased with the time of night (Fig. 3a), increased with increasing age (Fig. 4) and wing length (Fig. 5)
Throughout the late nesting period (1– 2 weeks before fledging) Tengmalm’s owl nestlings spend a total of about 8% of their time overall at the nest box entrance
Summary
In bird species where parents deliver food to dependent young, there is frequently significant competition for resources (reviewed for example by [1]) and evidence is accumulating that parental provisioning behaviour can be influenced by nestlings’ behaviour [2,3,4,5,6]. Nestlings of cavity-nesting birds can improve their chances of obtaining food ahead of their siblings by positioning themselves as close as possible to the cavity entrance [16,17,18] Such studies in owl nestlings are, scarce. Hofstetter & Ritchison [5] found out in Eastern Screech-owls (Asio otus) that the nestlings fed first by adults were those which started to beg significantly earlier, extended their beaks higher and closer to the adult, and called at higher rates and with greater volume than did their siblings. During the late nesting period when the nestlings are able to climb the wall from the nest floor to the nest entrance they may be able to perch at the entrance and wait for the parent there Studies on such behaviour, especially in nocturnal birds of prey, are lacking
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