Biodiversity influences: how deer ultimately affect bird populations

It is well known that the presence of large numbers of deer in an area affects plant species composition.  This is very obvious in eastern Ontario, in places like Rondeau Provincial Park, where deer exclosure experiments showed dramatic differences in species composition inside and outside of exclosures. Depauperate vegetation is common in heavily browsed areas.

 In BC, UBC biodiversity researchers Peter Arcese and Tara Martin studied the influence of deer on vegetation and plant species composition in the Gulf Islands, and noted that, ultimately, deer population density influences bird species composition and abundance.

In their essay on this work, they say: "...in an extensive survey of 18 Gulf and San Juan islands with different deer densities, Martin et al.⁵ showed that many species that rely on understory shrubs for feeding and nesting were much less abundant on islands with high deer densities as compared to those with few or no deer.  Examples include: rufous hummingbirds (9 times more abundant on islands with few versus many deer); song sparrows (4 times more abundant); yellow warblers (5 times more abundant); varied thrush (29 times more abundant); orange-crowned warbler (3.5 times more abundant); spotted towhee (25 times more abundant) and fox sparrows (9 times more abundant).  Only one species, the dark-eyed junco, was significantly more abundant on islands with abundant deer, because juncos prefer open forests with little vegetative cover."

Read more in Peter and Tara's essay on deer and biodiversity on the Gulf Islands.  

Reference:

Arcese, Peter and Tara Martin.  2013. Black-tailed deer, plant and bird populations in the Southern Gulf Islands and Coastal Douglas-fir Zone:  a primer for local communities interested in environmental stewardship. IN Klinkenberg, Brian. (Editor) 2013. Biodiversity of British Columbia [www.biodiversity.bc.ca]. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver.