Sex, landscape diversity and primary productivity shape the seasonal space use of a migratory European raptor

Intrinsic and extrinsic drivers shape the space use of wide-ranging
raptors. A large proportion of raptors are migrants that shift their
activity ranges between summer and winter habitats, where they encounter
different environmental conditions. Analysing the effects of intrinsic and
extrinsic drivers on the space use in summer and winter habitats provides
crucial insights into the ecology of migratory raptors. Here, we
investigated the seasonal space use by 43 red kites (Milvus milvus)
tracked by GPS-transmitters across central and south-western Europe over
seven years. We compared space use patterns, i.e., activity range sizes
and mean daily distances of the birds between summer and winter, and
analysed the influence of extrinsic (landscape diversity, primary
productivity) and intrinsic factors (sex). Within summer, we investigated
the influence of breeding success and sex on activity range sizes. We
further analysed differences in habitat availability and habitat selection
between seasons. We found that space use was smaller in summers than in
winters. When compared to those of males, activity ranges of female red
kites were larger in summers and smaller in winters, with shorter mean
daily distances in both seasons. Within summer, successfully breeding red
kites had smaller activity range sizes in both sexes, but this effect was
stronger in females than in males. Regardless of the season, landscape
diversity was positively correlated with space use, whereas primary
productivity was negatively correlated with it. The habitat use differed
between seasons, with agricultural landscapes being less proportionally
used in summers than in winters. Overall, we showed that both intrinsic
and extrinsic drivers shaped space use in both the seasons, leading to
differences in space use patterns and habitat use in migratory raptors
between their summer and winter habitats. Our findings underline the
importance of consideration of the entire annual cycle of migratory
species for conservation management.