Density and diversity of overwintering birds in managed field borders in Mississippi.

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ABSTRACT.—Grassland bird populations are sharply declining in North America. Changes in agricultural practices during the past 50 years have been suggested as one of the major causes of this decline. Field-border conservation practices encouraged by the U.S. Department of Agriculture’s National Conservation Buffer Initiative meet many of the needs of sustainable agriculture and offer excellent opportunities to enhance local grassland  bird populations within intensive agricultural production systems. Despite the abundant information on avian use of, and reproductive success in, strip habitats during the breeding season, few studies have examined the  potential value of field borders for wintering birds. We planted 89.0 km of field borders (6.1 m wide) along  agricultural field edges on one-half of each of three row crop and forage production farms in northeastern  Mississippi. We sampled bird communities along these field edges during February–March 2002 and 2003 using  line-transect distance sampling and strip transects to estimate density and community structure, respectively. We used Program DISTANCE to estimate densities of Song (Melospiza melodia), Savannah (Passerculus sandwichensis), and other sparrows along bordered and non-bordered transects while controlling for adjacent plant  community. Greater densities of several sparrow species were observed along most bordered transects. However, effects of field borders differed by species and adjacent plant community types. Diversity, species richness, and relative conservation value (a weighted index derived by multiplying species-specific abundances by their respective Partners in Flight conservation priority scores) were similar between bordered and non-bordered edges.  Field borders are practical conservation tools that can be used to accrue multiple environmental benefits and  enhance wintering farmland bird populations. Provision of wintering habitat at southern latitudes may influence  population trajectories of short-distance migrants of regional conservation concern.

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