Forest bird communities along the urban-rural gradient

How do forest bird communities change along the urban-rural gradient?
As we travel from outlying rural areas toward the city, it's clear that there's an urban gradient of increasing roads, buildings, and parking lots. For conservation planners and resource managers working to conserve species, a key question is what happens to the habitat value of undeveloped land as we move along the rural-urban gradient. A new study tackles that question with respect to forest bird communities in the Raleigh-Durham Triangle of North Carolina. Specifically, study authors Emily Minor and Dean Urban wanted to answer three questions about bird communities in undeveloped woodlots in the region:

1) Does community composition of forest birds change across a gradient of urban development?

2) If so, what are the important variables driving these changes?

3) From a management perspective, can urban forests be useful habitat for conservation of native species?

To answer these questions, the researchers collected data from 272 point counts from 2002-2005 in city, county, and state parks, conservation areas, state lands, and private woodlands. They also collected data about the local and landscape scale environmental characteristics for each site.

A pileated woodpecker (Dryocopus pileatus) - a species surveyed in woodlots of the study area.Based on the results the researchers were able to identify 3 distinct bird communities - one much more associated with urban areas, one more with rural areas, and one that was mixed. The urban and rural bird communities boasted fairly distinct species composition - the rural communities had more long-distance migrant species and forest interior birds while edge species were more common in urban communities.

Urban woodlots as forest bird habitat...
Nevertheless, the study results suggest that urban woodlots are still important for habitat conservation. The mean species richness was the same for the urban and rural bird communities and the species composition for both was largely native contradicting past studies which have found species richness for birds to be much less in urban areas. In addition, all communities had small but similar numbers of species on the Partners in Flight watch list. The researchers offered the following conservation recommendations:

"A convenient rule of thumb for conservation planners in the Triangle: if birds common to rural communities (e.g., Neotropical migrants) are a conservation focus, reserves should be created outside of municipal boundaries. [However], our results indicate that forest patches in urban environments can be useful conservation sites for many species, in addition to the recreation and other climate services these forest patches provide to city dwellers… "

Landscape factors drive forest species composition...
Another interesting finding of this study was that landscape scale factors - particularly the density of roads within a 2-km buffer of the woodlot - were most important in predicting community species composition. For example, rural bird communities never occurred in locations with a road density greater than 6.4km/km² at either measured scale. These findings suggest that rural development and road building don't just have an immediate edge effect on bird habitat but also a cumulative edge effect that can influence species composition on areas several kilometers away.

Source:	Urban Ecosystems
Title:	Forest bird communities across a gradient of urban development
Authors:	a) Emily Minor, b) Dean Urban
	a) University of Illinois at Chicago; b) Duke University