Movement patterns of the White‐tailed Sea Eagle (Haliaeetus albicilla): post‐fledging behaviour, natal dispersal onset and the role of the natal environment

Abstract

Exploratory movements and natal dispersal form essential processes during early life history stages of raptors, but identifying the factors shaping individual movement decisions is challenging. Global positioning system (GPS) telemetry thereby provides a promising technique to study movement patterns on adequate spatio‐temporal scales. We analysed data of juvenile White‐tailed Sea Eagles Haliaeetus albicilla (WTSE) in north‐east Germany (n = 24) derived from GPS tracking to extensively analyse movements between fledging and emigration from the natal territory. Our goal was to determine the time point of fledging, characterize pre‐emigration movements and the onset of natal dispersal while investigating the influence of the natal environment. WTSE fledged at an average age of 72 days and showed strong excursive behaviour during the post‐fledging period regarding the number, distance and duration of excursions, yet with high individual variability. Excursive behaviour did not differ between sexes. On average, WTSE left the parental territory 93 days after fledging. The quantity of excursive behaviour delayed the timing of emigration and WTSE tended to postpone their emigration when foraging water was accessible within the boundaries of their parental territory. The overall results suggest that young WTSE assess the quality of the natal environment via pre‐emigration movements and stay in their territory of origin for as long as internal and external conditions allow for it. Our study is one of the first to characterize post‐fledging and natal dispersal movements of young WTSE to such an extent and applies modern techniques to understand related movements in relation to the natal environment. The results emphasize the urgent necessity for the extension of currently existing nest protection periods and guaranteeing sustainable management of potential breeding and foraging grounds for WTSE. Ultimately, the results are relevant for all large raptor species sensitive to human‐related disturbance, as they support the increasing importance of regulations with spatio‐temporal specifications for breeding populations of large raptors in densely human‐inhabited areas with increasing alteration of land.

Driving forces behind the fluctuating growth of the number of successful nests in an inland population of white‐tailed eagles in Hokkaido, Japan

“…In the study area, white‐tailed eagles start courtship in January–February, nest in March, and lay eggs from late March to late April (the authors' observation). The incubation period is 37–38 days (Müller, 2010), and a brood is fed in the nest for 70–90 days (Engler & Krone, 2022; Mori, 1980; Müller, 2010). The fledging varies from early July to August (the authors' observation).…”

“…Juveniles are vagrant and search for a breeding site long before maturation. Juveniles leave their parental territory 92 days after fledging and make various excursions from their natal site (Engler & Krone, 2022). Nemesházi et al (2018) reported territory intrusions in seven of 11 territories, and those intrusions were done mainly by juveniles, which were not offspring of resident pairs.…”

Survival, Nest Site Affiliation and Post-Fledging Movements of Danish White-Tailed Eagles (Haliaeetus albicilla)

“…Since 2017, DOF BirdLife and the Natural History Museum of Denmark have monitored Danish WTEs with the use of GPS tracking technology to acquire detailed knowledge of their movements. Other studies of the species using GPS technology have been carried out in other European countries, including Croatia [15], Czech Republic, Hungary, Austria [16], Finland [17], Germany [18][19][20], Ireland [3], and Norway [21].…”

“…We still lack detailed knowledge of natal dispersal movements in Denmark, even though it is a vital process affecting both the dynamics, size, and gene flow of a population [23]. Dispersal is a complex subject, and many factors seem to affect dispersal in raptors, both internal and external such as resource availability, quality of the natal habitat, and sex, and this has been the focus of several studies in recent years [4,16,18,24].…”

Out of Africa: Juvenile Dispersal of Black-Shouldered Kites in the Emerging European Population

“…The study of juvenile dispersal has attracted the interest of ecologists and evolutionary biologists dedicated to biodiversity conservation [ 4 ]. However, the study of dispersal movement may be difficult in those species in which the movement capacity is high, and some individuals may leave the boundaries of the study area [ 5 , 6 , 7 , 8 ]. On many occasions, it is hard to know if marked individuals remain undetected because they have moved outside the investigators’ detection area or because they have not survived [ 9 ].…”