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Density and Fledging Success of Grassland Birds in Conservation Reserve Program Fields in North Dakota and West-central Minnesota

by

Rolf R. Koford

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Abstract: The Conservation Reserve Program, initiated in 1985, was designed primarily to reduce soil erosion and crop surpluses. A secondary benefit was the provision of habitat for wildlife. Grassland bird populations, many of which declined in the decades prior to the Conservation Reserve Program, may have benefited from the Conservation Reserve Program if reproduction in this newly available habitat has been at least as high as it would have been in the absence of the Conservation Reserve Program. On study areas in North Dakota and Minnesota, I examined breeding densities and fledging success of grassland birds in Conservation Reserve Program fields and in an alternative habitat of similar structure, idle grassland fields on federal Waterfowl Production Areas. Fields were 10 to 25 hectares in size. The avifaunas of these two habitats were similar, although brush-dependent species were more abundant on Waterfowl Protection Areas. The common species in these habitats included ones whose continental populations have declined, such as Grasshopper Sparrow (Ammodramus savannarum), Savannah Sparrow (Passerculus sandwichensis), and Bobolink (Dolichonyx oryzivorus). These ground-nesting species were pooled with other ground nesters in an analysis of fledging success, which revealed no significant differences between habitats, between states, or among years (1991-1993). Predation was the primary cause of nest failure. I concluded that Conservation Reserve Program fields in this region were suitable breeding habitat for several species whose populations had declined prior to the Conservation Reserve Program era. This habitat appeared to be as secure for nests of ground-nesting birds as another suitable habitat in North Dakota and Minnesota.

Key Words:   Bobolink; Conservation Reserve Program; Grasshopper Sparrow; grassland birds; habitat quality; nest success; North Dakota; Minnesota; productivity; Savanna Sparrow; Waterfowl Production Areas

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This resource is based on the following source (Northern Prairie Publication 1060):

Koford, Rolf R.  1999.  Density and Fledging Success of Grassland Birds 
     in Conservation Reserve Program Fields in North Dakota and West-
     central Minnesota.  Studies in Avian Biology 19:187-195.

This resource should be cited as:

Koford, Rolf R.  1999.  Density and Fledging Success of Grassland Birds 
     in Conservation Reserve Program Fields in North Dakota and West-
     central Minnesota.  Studies in Avian Biology 19:187-195.  
     Jamestown, ND: Northern Prairie Wildlife Research Center Online.  
     http://www.npwrc.usgs.gov/resource/birds/denfled/index.htm 
     (Version 02MAR2000).

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Table of Contents

• Introduction
• Methods
• Results
• Discussion
• Acknowledgments
• Literature Cited

Tables

• Table 1 — Numbers seen, estimated densities, and confidence intervals for density estimates for birds counted on CRP and WPA fields.
• Table 2 — Estimated fledging success of grassland birds on CRP and WPA fields.
• Table 3 — Least squares mean Daily Survival Rates for nests of ground species in CRP and WPA fields.

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