Head and body orientation of the White Stork Ciconia ciconia during incubation: effect of wind, apex predators and power lines

Adam Zbyryt,Łukasz Jankowiak,Piotr Tryjanowski,Leszek Jerzak

doi:10.1007/s10336-021-01920-x

Abstract

Incubation behaviour is essential for understanding the reproductive success in birds. For example, the orientation of the bird is important for reducing incubation costs associated with wind or sun, but on the other hand can be modified by the perceived risk of predation. We studied the body position of incubating White Stork Ciconia ciconia in eastern Poland using a small unmanned aerial vehicle (drone). The head and body orientation of the incubating storks was non-random and modified by natural factors, mainly wind direction and speed, but also by the presence of an apex predator, the White-tailed Eagle Haliaeetus albicilla. However, head orientation during incubation in nests located on electricity poles was also modified by the presence of the power lines, probably due to disturbance in the magnetic field detected by birds. Surprisingly, although the positioning of incubating birds (mainly females) is very important for the detection of predators and for reducing energy costs, these have not previously been studied. New technologies, such as drones, make it possible to collect new, extensive information on the incubation behaviour of birds.

Highlights

Incubation behaviour is central to the reproductive success of birds (Carey 1980; Deeming and Reynolds 2015)
The main aim of the study was to describe the body orientation of incubating birds during the daytime and to establish the influence of external factors, such as wind, predator presence, and nest location on incubation behaviour. We suggest that this information may help in better understanding breeding behaviour, ecology and, in consequence, the population trajectory of the White Stork, which are especially important in light of new nesting sites provided by conservationists, both in this particular area, as well as across the geographical range of the species (Muzinic 1999; Zbyryt et al 2021)
If the wind was blowing from the NWW the mean orientation of the birds was 267° and the mean resultant length (0 indicates that the spread of data points was very large, 1 indicates that the data were aggregated as a single value) was 0.56 (Fig. 2B)

Summary

Introduction

Incubation behaviour is central to the reproductive success of birds (Carey 1980; Deeming and Reynolds 2015). Incubating adults must ensure that eggs are kept within a relatively narrow temperature range to promote the growth of developing embryos (Carey 1980; Deeming and Reynolds 2015). Incubation should be, and is, modified by the behaviour of the adult birds depending on weather conditions (Weller 1958; Gochfeld 1978). Incubation is time-consuming and takes place in a practically stationary position, by adult birds, most often the female, sitting on the nest. Such a permanent, stationary position with limited visibility (Graham 2011) makes the incubating bird relatively safe from attack by a predator (Carey 1980; Bakner et al 2019)

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Conclusion