Eurasian brown bears

[Sully]

Environmental and anthropogenic correlates of seasonal
migrations in the Dinaric-Pindos brown bear population

Abstract: 


Seasonal migrations (i.e. seasonal round-trips between disjunct areas) have been

rarely documented for large carnivores. The Dinaric-Pindos brown bear (Ursus arc-

tos) population is the third largest in Europe, but little information is currently

available on individual movement patterns. We studied movement patterns by 12

GPS-collared adult and subadult bears in Croatia and Bosnia Herzegovina during

2004–2017, including migratory movements by some instrumented bears. To inves-

tigate environmental correlates of migrations, we rst used the canonical Outlying

Mean Index analysis, identifying habitat descriptors of summer and fall ranges, and

then applied mixed-effects logistic regression to quantify variation in habitat use

between them. Thirty-seven per cent 37% of the bears (7 bear-years) migrated dur-

ing hyperphagia (i.e. partial migration), and seasonal migration was also facultative,

as it occurred only during mast (i.e. beechnut) poor years. Migrating bears entered

migration during early fall (median = 25 Sept) and returned to their pre-migratory

ranges after about 7 weeks (median = 18 Nov). Net distances between pre-migra-

tory (summer) and post-migratory (fall) averaged (

SD) 26.5  9.7 km, with a

maximum distance of 38.8 km, corresponding to actual distances travelled of

61.1  21.5 km. Summer ranges from which bears migrated were best described

by proximity to supplemental feeding sites and mixed forests, whereas fall ranges

reached by migrants were differentiated by lower elevations, and a higher share of

deciduous forest, grasslands, forest edges and shrublands. Relative to pre-migratory

ranges, bears in post-migratory ones increased their distance to anthropogenic fea-

tures and showed higher use of cover types expectedly richer in berries and other

eshy fruits. Although we lack any causative evidence, we speculate migration in

this bear population is triggered during poor beechnut years by increased social

despotic interference at supplemental feeding sites that elicits redistribution of sub-

ordinate bears. Reply