Habitat associations of red squirrels (Tamiasciurus hudsonicus) and their impact on the gray-cheeked thrush (Catharus minimus minimus) in western Newfoundland

McDermott, Jenna P. B. (2021) Habitat associations of red squirrels (Tamiasciurus hudsonicus) and their impact on the gray-cheeked thrush (Catharus minimus minimus) in western Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Introduced species are known for disrupting ecosystems and affecting endemic species. Red squirrels (Tamiasciurus hudsonicus) were introduced to Newfoundland during the 1960s and by the 1990s the Newfoundland Gray-cheeked Thrush (Catharus minimus minimus) had undergone a steep decline. It is hypothesized that nest predation by squirrels caused the thrush decline so during 2016 and 2017 I undertook point count surveys in the Long Range Mountains of western Newfoundland to compare the contemporary distributions and habitat use of these species. Squirrels and thrushes were strongly segregated, whereby thrushes were restricted to higher elevations (~340-600 m), while squirrels were abundant below 275 m, reaching an upper range limit at ~500 m. Gray-cheeked Thrushes were associated with harvested clearcuts, modified cuts, conifer forest, and tall scrub at the local scale, with only weak negative habitat associations at the landscape scale. Squirrels were associated with second-growth fir/spruce forest and old growth fir, while they avoided water, coniferous scrub, and regenerating fir/spruce forest. Gray-cheeked Thrushes have been historically abundant down to sea level, so this strong altitudinal segregation adds to the growing body of evidence that squirrels played an important role in the decline and range contraction of this species on Newfoundland.

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