A project of

Red Squirrel

The State of Red Squirrels

Regionally: Stable but Fluctuating 

A plot of Red Squirrel study area abundance. The x axis show years between 2010 and 2021. The y axis shows local population size. Local population size fluctuates greatly between close to 0 individuals during some years and well over 500 individuals during other years.

The mean (thick, dark red line) annual estimate of the Red Squirrel abundance within the immediate areas surrounding ~750 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 survey 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 3.99% (95% Bayesian credible interval = 0.4% to , 7.48%) in the mountains of our region. The conifers on which they feed produce seeds in approximately 3-5 year cycles causing the population to fluctuate significantly from year to year. When the Red Squirrel population rises during a mast year of a preferred food source, such as Balsam Fir (Abies balsamea), the songbird population will suffer due to increased predation of eggs and nestlings.

The largest effect on apparent survival patterns in Bicknell’s Thrush is directly related to Balsam Fir cone production on their breeding grounds. Red Squirrels store Balsam Fir cones in piles (called middens) over the winter to help them survive at high elevations. When few cones are available, the squirrels remain at lower elevations over the winter and the following summer. If the squirrels are absent from the spruce-fir habitat during summer, then Bicknell’s Thrush nests are much more likely to succeed due to lower depredation from red squirrels.

State of the Mountain Birds