by Kelsey D’Ewart
The freezing and thawing patterns in the Arctic have been increasingly affected as a result of global temperatures increasing, resulting in earlier later freezing and earlier thawing. This is forcing phenology changes in many Arctic species. Particularly, there has been a change in migration patterns in many species due to the lack of frozen bodies of water. This can lead to longer, more strenuous, and more dangerous migrations that can result in higher mortality rates. Leblond et al. (2016) tracked the ice thawing and freezing times for bodies of water in the migration path of caribou Rangifer tarandus Northern Quebec from 2007−2014, allowing them to determine if the change in ice melt was affecting the caribou’s phenology. Their hypothesis was that the caribou would travel extra distance in order to avoid swimming or water that was not completely frozen. They assessed four different parts of the migration: previous data for freezing trends, the caribou’s response to the change in freezing trends, fine-scale caribou behavior and phenology, and possible future movement using climate change projections.
To study the movements of the caribou herd Leblond et al. used GPS collars on 96 caribou, the majority of which were females because the migration being observed was to breeding grounds. The bodies of water assessed were chosen using the route of the caribou’s migration to determine the lakes, rivers, and reservoirs most encountered. Thawing and freezing patterns were determined using moderate-resolution imaging spectroadiometer (MODIS), which was also used to estimate the proportion of ice to water on bodies of water the caribous would typically cross. Thawing and freezing trends were then extrapolated using linear regression. GPS and turning angle (a metric to determine if the state of bodies of water altered the migration route) were used to study the caribou behavioral patterns. Additionally, future ice freezing and thawing patterns were projected up for the year 2070 to predict how the caribou’s phenology may change.
Leblond et al. found that from 2000−2014 there was no significant change in the thawing and freezing dates of the bodies of water. They found that if there was absolutely no ice available for caribou to cross they would swim distances as long as 25 kilometers. The amount of water crossings remained constant regardless of whether it was a late or early freezing year. However, when ice was not available the caribou would “pause” to either rest or determine if it was safe to cross, which took both extra time and energy. The caribou were able to move more efficiently with ice, and had fewer turning angles on ice than in open water. Future projections showed that only a small amount of spring migrations would not occur if water had thawed 10−15 days sooner. However, projections in 2070 showed that up to 36% of crossings might be greatly hindered if the earlier thawing trend continues.
Although migration patterns were not significantly altered in the small time period of this study, the future projections show the possibility of a much smaller frozen period. This will lead to more caribou swimming or detouring, which could lead to much larger energy expenditure as well as potential drowning. For the moment a slight shift in migration time will be enough to help the caribou, but in the future the global temperature increase and ice thawing could become a serious problem for the caribou and many other species.
Leblond, M., St-Laurent, M., Cote, S. 2016. Caribou, water, and ice- fine-scale movements of a migratory arctic ungulate in the context of climate change. Movement Ecology 4:14.