Migratory birds not so picky about rest areas

A new study has added to a growing body of research showing that that small remnant woodlots can provide important habitat for birds in areas heavily impacted by urbanization and agriculture.

Bay-breasted Warbler.Remnant woodlots as migratory stopover areas... In parts of the United States, the loss and fragmentation of forests have created landscapes of remnant wooded areas surrounded by development and agricultural land. Scientists have given increased attention to these small woodlots as bird habitat of last resort (see Forest bird communities along the urban rural gradient).

A new study by researchers at Purdue University has entered the fray by looking at remnant, woodlots as stopover habitat for migratory birds in northwest Indiana. According to the study authors,

Birds may spend up to one-third of the year in migration, and to arrive at their breeding or wintering grounds in good condition they require networks of stopover sites along their routes where they can rest, refuel, avoid predators, and find shelter from adverse weather.

The scientists wanted to know whether migratory birds selected stopover sites based on proximity to large riparian forests. The researchers looked at woodlots at three distances from Indiana's Wabash River and its tributaries - within half a kilometer, between one and five kilometers and at about 20 kilometers. The woodlots were less than 20 acres and had row crops surrounding them on at least three sides.

The researchers surveyed the sites in September 2005 and 2006, and May 2006 and 2007, the peaks of fall and spring migration in northwest Indiana. They recorded 76 different species of migratory birds in the woodlots and found no statistical differences in the number of species or overall population of birds based on distance from streams. These results suggest that small, isolated woodlots can provide important stopover habitat for birds on par with wooded areas closer to large forests. 

Implications for conservation... According to the study authors, conservation attention has largely focused on larger, contiguous blocks of forest and ignored smaller, remnant woodlots. The researchers warn that in the Midwestern US , these woodlots may become subject to increased conversion to agricultural uses for biofuels and merit greater conservation focus.

This study has received some attention from the popular press who in my opinion have mistakenly interpreted the results to mean that small, remnant woodlots are just as good stopover habitat as larger, contiguous forests. While this study is important, it leaves two big unanswered questions in my mind about the habitat value of these areas:

1) How does the number of migratory species and population abundance compare between small woodlots and larger, contiguous forest? This study only compares woodlot to woodlot.

2) How do the different woodlots compare against each other and against larger forests in terms of providing food and refuge for resting migratory birds? Just because equal numbers of migratory birds selected woodlots as stopover destinations doesn't necessarily mean that all those areas provide equal quality habitat. The researchers realize that this question needs to be answered in future studies.    

Source:	The Auk
Title:	Stopover habitat selection by migrant birds in a fragmented forest-agricultural landscape
Authors:	Dianne Packett and John Dunning
	Purdue University