by Carl Strang
One of the classical sources of data in vertebrate wildlife ecology is the Hudson Bay Company fur records in Canada. Those were used, for instance, to establish the dramatic cyclical pattern of lynx relative to showshoe hare populations, inspiring much subsequent research as to the underlying causes. There still are data to be mined from those records, as was demonstrated in a 2011 study [Estay SA, Albornoz AA, Lima M, Boyce MS, Stenseth NC. A Simultaneous Test of Synchrony Causal Factors in Muskrat and Mink Fur Returns at Different Scales across Canada. PLoS ONE 6(11): e27766. doi:10.1371/journal.pone.0027766].
The researchers examined Hudson Bay Company fur records from 81 posts across Canada, looking at muskrat numbers, mink numbers, and bringing in climate data. They concluded that mink had an important impact on muskrats all across Canada, but the greatest and most direct effect was in the west.
In the east, variation in winter precipitation also was important, with drought in particular affecting muskrats. Interactions among these factors could be important here. For instance, drought could force muskrats to disperse longer distances over land, reduce their watery escape space, and concentrate them, exposing them to greater mink predation.