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                   GPS collar tracking of a white-tailed sea eagle
                           (Haliaeetus albicillia) in Germany

last update: January 8, 2004

by Oliver Krone
Institute for Zoo and Wildlife Research

Photo: O. Krone


The Project:

The goal of this pilotproject is testing if eagles can be tracked via GPS collars. Until today the tracking investigations on large  birds of prey are nearly almost done with the Argos system. Depending on the classes of location, the accuracy of the Argos locations is < 150 m and > 1000 m.
Our goal was to get a deeper insight in the seasonal and spatial behaviour of white-tailed eagles.


Fig. 1:  Location of the investigation area in Germany (red symbol)













We used Teflon-treated ribbons to fit the 177 g light weight GPS-device (figure 2) on the back of the eagle (figure 3). The GPS-unit is equiped with activity and temperatur sensors and a traditionall VHF-beacon. The GPS-data can be downloaded via UHF-link by a small Handheld Terminal. The GPS-receiver are programmed to take 3 fixings per day, which results in a 1 year lifetime of the unit.


Fig. 2: The 177 g light GPS-unit with address if it will be lost











Fig. 3: The white-tailed eagle with the GPS-harness.
Photo: O. Krone












The eagle was fitted on July 24, 2003 and the first download of data occured on Sptember 9, 2003. Figure 3 presents the downloaded 3D positions, linked in chronological order.

Fig. 4: 3D Positions of the white-tailed eagle from July 24 until September 6, (n= 126)

The following map shows an enlargement of the yellow rectangle in figure 4. Since the mean accuracy of the GPS is about 15 m for 3D positions, the location cluster probably represents the domicile tree of the eagle.

Fig. 5: Enlargement of the yellow rectangle in figure 4


The second download of GPS data from the collar was realized on January 3, 2004 by Handheld Terminal. The movements of the eagle are presented in figure 6.

Fig. 6: 3D Positions of the white-tailed eagle from July 24 until January 2004, (n= 434)

The fixing efficiency of the collar was very good. 93% of the possible fixings were taken and of that 94% were 3D fixings.

Collar statistics from July 24, 2003 - January 3, 2004, 3 fixings/day

collar statistics


tracking time [days]


fixings possible


fixings taken by GPS

459 (=93%)

         of that:   2D





More about the project:

This pilotstudy is part of  the project “Population development of the white-tailed sea eagle  in Germany” . The goal of this project is to compare the results of the study of causes of death obtained from carcasses of white-tailed sea eagles with a group of eagles equipped with the new GPS-device.

The white-tailed sea eagle was persecuted directly until the beginning of the 20th century. Today indirect anthropogenic factors are often responsible for the death of these eagles. The most important mortality factors are heavy metal intoxications, collisions with railway strains and power lines. Only little is known about the natural causes of death such as diseases and injuries from intraspecific fights. The mortality factors and diseases of the German white-tailed sea eagle population are investigated in an interdisciplinary project, using methods from pathology, parasitology, bacteriology, virology, and toxicology. Toxins (heavy metals, pesticides, PCB´s, flame retardants), zoonoses (ornithosis, salmonellosis, Newcastle disease), and virus (herpes-, circo-, adenovirus) are examined in cooperation with national and international institutes.
The small sea eagle population in the northeast of Germany, which survived the pesticide era has undergone an expansion since the 1960s. This positive development may be explained by the fact that the federal states in northeaster Germany have low human population densities and disturbances of eagles were generally rare. In the course of range expansion towards the southwest the population will find itself confronted with an increased number of human structures such as power lines, traffic, settlements, etc. However, even the population in the northeast has to deal with new challenges. Due to growing hunting activities in the new federal states of East Germany more game animals are shot and therefore more carcasses lead containing become available as prey for the white-tailed sea eagle. The increasing fragmentation of the landscape due to highways, country roads, power lines, wind power plants, and increasing tourist activities may become severe threat to the sea eagle population. Therefore, the current outlook suggests an increase of human induced mortality factors in the future.
As a top predator at the peak of the food chain the sea eagle accumulates toxins taken by its prey and is therefore a reliable bio indicator. A risk assessment of sea eagle populations will be performed by measuring the accumulation of toxins and the infection status on individual birds. To document the illegal persecution all carcasses are checked for foreign bodies (bullets). In addition to studies on the causes of mortality, blood samples of nestlings either in the wild taken during ringing or of those brought to rehabilitation stations will be examined. These results will be used to access whether of post mortem examinations of formal carcasses are representative for mortality factors in the population at large. Especially diseased and weak eagles are extremely shy and hide in less disturbed areas and are therefore rarely observed.

In this project a group of eagles will be intensively observed using telemetry over a period of four years, to get information about the turnover in the population and to compare the causes of death in this group with the results from post mortem examinations. Furthermore the home range of the eagles will be examined. The results will be used for the protection and conservation of this species.

For more information please contact:

Dr Oliver Krone

Institute for Zoo and Wildlife Research
P.O. Box 601103
D-10252 Berlin
fax: +49-30-5126104
phone: +49-30-5168405