Competition and climate change combine to threaten Bicknell's thrush

Date:December 23, 2015

Source:Central Ornithology Publication Office

Bicknell's Thrush (Catharus bicknelli) is a songbird that breeds in New England mountaintop forests threatened by climate change. Research forthcoming in The Condor: Ornithological Applications shows that this threat could be exacerbated by competition from related birds living downslope. Climate change may cause Bicknell's Thrushes' preferred habitat of spruce-fir forests to shift to even higher elevations, constricting their range, and new data suggests that aggression from related Swainson's Thrushes (Catharus ustulatus) could drive them uphill even faster.

In playback experiments conducted in New York's Adirondack Mountains, Swainson's Thrushes approached a speaker in response to recorded Bicknell's Thrush songs in 9 out of 36 trials, but a Bicknell's Thrush approached the speaker in response to a Swainson's Thrush recording in only 1 out of 16 trials. Swainson's Thrushes were also more likely to be aggressive toward Bicknell's Thrush recordings at higher elevations. This suggests that Swainson's Thrushes may be behaviorally dominant over Bicknell's Thrushes, and a warming climate could allow Swainson's Thrushes to move farther upslope and compete with vulnerable Bicknell's Thrushes.

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