Caribou, water, and ice - fine-scale movements of a migratory arctic ungulate in the context of climate change.
BACKGROUND
Freshwater lakes and rivers of the Northern Hemisphere have been freezing increasingly later and thawing increasingly earlier during the last century. With reduced temporal periods during which ice conditions are favourable for locomotion, freshwater bodies could become impediments to the inter-patch movements, dispersion, or migration of terrestrial animals that use ice-covered lakes and rivers to move across their range. Studying the fine-scale responses of individuals to broad-scale changes in ice availability and phenology would help to understand how animals react to ongoing climate change, and contribute to the conservation and management of endangered species living in northern environments. Between 2007 and 2014, we equipped 96 migratory caribou Rangifer tarandus caribou from the Rivière-aux-Feuilles herd in northern Québec (Canada) with GPS telemetry collars and studied their space use. We measured contemporary (digital MODIS maps updated every 8 days, 2000-2014) and historical (annual observations, 1947-1985) variations in freshwater-ice availability and evaluated the concurrent responses of caribou to these changes.


RESULTS
Ice had a positive influence on caribou movement rates and directionality, and caribou selected ice and avoided water when moving across or in the vicinity of large water bodies. When ice was unavailable, caribou rarely swam across (6 % of crossings) and frequently circumvented water bodies for several km. Although ice phenology did not change significantly during our study, climate projections indicated that ice availability could decrease considerably before the end of the century, generating a ~28 % increase in distance travelled by caribou during the early spring and fall migrations.


CONCLUSIONS
We demonstrated that ice availability influenced the movements of a migratory arctic ungulate. Warmer air temperatures in the Arctic will undoubtedly modify the phenology of ice forming on freshwater lakes and rivers. If migratory caribou are unable to adjust the timing of their migrations, they could be forced to circumvent unfrozen water bodies more frequently and over broader areas, which may increase the distance, time, and energy they use to reach wintering areas. The long-term conservation of wide-ranging species will ultimately depend on our ability to identify the fine-scale behavioural reactions of individuals to broad-scale changes in climate and land use.
Caribou Ungava, Département de biologie, and Center for Northern Studies, Université Laval, 1045 avenue de la Médecine, Québec, QC G1V 0A6 Canada.
Mathieu
M
Leblond
Caribou Ungava, Département de biologie, chimie et géographie, Center for Northern Studies, and Center for Forest Research, Université du Québec à Rimouski, 300 allée des Ursulines, Rimouski, QC G5L 3A1 Canada.
Martin-Hugues
MH
St-Laurent
Caribou Ungava, Département de biologie, and Center for Northern Studies, Université Laval, 1045 avenue de la Médecine, Québec, QC G1V 0A6 Canada.
Steeve D
SD
Côté
Behaviour; Climate; Global change; Long-distance migration; Migratory caribou; Movements; Phenology; Rangifer tarandus; Scales; Space use; Step selection function