The State of Red Squirrels
Regionally: Pulsating
The mean (thick, dark brown 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 lighter vertical bars represent the 95% Bayesian credible interval (a measure of the uncertainty around the abundance estimates).
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 >10% in the mountains of our region, but the figure above shows a 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, Balsam Fir (Abies balsamea) and Spruce (Picea species) cones. Red Squirrels collect and store these cones in piles (called middens); the collective size of a squirrel’s piles 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.
