GPS tracking of Red Kites (Milvus milvus) reveals fledgling
number is negatively correlated with home range size
Abstract To date, reliable studies on the spatial area use
and home range size of the Red Kite (Milvus milvus) during
the breeding season are lacking. Between 2007 and 2014,
43 adult individuals were fitted with GPS transmitters in
Germany. The home range sizes of 27 males, which successfully
reared 47 broods, ranged between 4.8 and
507.1 km2 based on the 95 % kernel utilization distribution.
The median during the nestling and post-fledging
dependent periods was 63.6 km2. The home ranges of 12
females, with a total of 21 successful broods, ranged between
1.1 and 307.3 km2. Within a single breeding season,
there were considerable differences among home range
sizes. There was also considerable variation in the home
range size of adults during the course of a season. Across
years, the median home range size of all males ranged
between 21 and 186 km2, depending on prey availability.
For individual males at the same nest site, the home range
size varied up to a factor of 28 across years. Kites with very
large home ranges had only one fledgling, which indicates
that resources were scarce. Individuals with more nestlings
had intermediate-sized to small home ranges. The relationship
between the number of fledged young and home
range size was modelled using a cumulative logit model.
Fifty-six, 37, and 26 % of male kite fixes were beyond a 1,
1.5, and 2 km radius around the nest, respectively. Birds
with very small or very large home ranges differed
considerably from these average figures. Adults sometimes
travel very long distances to visit distant grasslands during
and shortly after mowing (up to more than 34 km) from the
nest, due to the increased likelihood of prey availability at
these sites. In conclusion, home rage size serves as a useful
indicator of Red Kite habitat quality, which may provide
key conservation information at the wider ecosystem level.