Bambi’s Blunder

The return of deer to North American forests may threaten songbirds

The hum of woodland chatter and song has hushed, and deer may be the culprit. Scientists have found more evidence that the return of deer to forests across North America may be silencing some songbird populations.

Deer have made a striking comeback with an estimated hundredfold increase in population since the 1930s. But this success also comes at a cost: the deer nibble away at forest understory, taking away important food and nest resources for many woodland birds. While parallels between deer population success and songbird decline have been reported on a local level, a new analysis published in Diversity and Distributions reveals a downward trend among North American songbirds that rely on the understory. 

The team identified 29 species in decline across North America using survey data from 1966 through 2009, a time of widespread deer rebound.  Of those threatened songbirds, 65 percent had been previously identified as sensitive to deer. These birds experienced steeper declines in states where deer numbers were higher, while at-risk birds thought to be deer tolerant did not show that trend with deer density.

While changing habitat conditions play an important role in sustaining songbirds, deer may be a factor for some species. “Deer alone may not threaten any species with extinction but could locally be the straw breaking the camel’s back for many songbird populations when acting in concert with other stresses,” the authors write. “With respect to species diversity in forest bird communities, another concern is the extent to which deer have already caused continent-wide shifts.”—Caitlin Stier | 7 September 2012 

Source: Chollet, S. and Martin, J. 2012. Declining woodland birds in North America: should we blame Bambi? Diversity and Distributions doi: 10.1111/ddi.12003