The State of Red Squirrels
Regionally: Pulsating
The mean (thick, dark line) annual estimate of Red Squirrel abundance—calculated as the annual sum of estimated Red Squirrel within the local area (a 4-hectare circle) surrounding all 791 Mountain Birdwatch sampling stations. The thinner, lighter lines represent less probable estimates of the annual abundance.
Since 2010, Mountain Birdwatch protocol has involved recording the number of Red Squirrels at each sampling station with the aim of understanding how this common nest predator’s cyclical population dynamics interact with those of our monitored bird species. Mountain Birdwatch data show a mean annual trend of 8.70% in the mountains of our region, but thinking of Red Squirrel populations as steadily changing from year to year isn’t a helpful way to describe their population dynamics. The figure above shows a much more complex pattern than a single number can convey. The conifers on which Red Squirrels feed produce seeds in approximately 3-5 year cycles causing the population to fluctuate significantly from year to year. Red Squirrels can persist in the spruce-fir zone only during winters with substantial amounts of food: namely, mature Balsam Fir (Abies balsamea) and Spruce (Picea species) cones [which mature in the autumn]. In autumns with abundant cones, Red Squirrels are able to move upslope from the hardwood-spruce-fir ecotone, and collect and store these cones in piles (called middens). The collective size of a squirrel’s middens is directly related to their overwinter survival. Following winters with abundant spruce and fir cones, red squirrels remain at those high elevations through the next autumn. During those summers with squirrels at high elevations, squirrels exhibit a substantial effect on the nest survival patterns of spruce-fir birds. In winters without abundant cones, Red Squirrels remain at relatively lower elevations, especially along the hardwood-spruce-fir transition zone.
VCE biologists Mike Hallworth, Jason Hill and others have a paper describing these population dynamics currently (December, 2023) under review.
