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Spatial and Temporal Distribution of Rails in Colorado
Herman J. Griese, Ronald A. Ryder and Clait E. Braun
The Wilson Bulletin
Vol. 92, No. 1 (Mar., 1980), pp. 96-102
Published by: Wilson Ornithological Society
Stable URL: http://www.jstor.org/stable/4161297
Page Count: 7
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Distribution, breeding densities, habitats and timing of migration of rails were investigated in Colorado between May 1975 and October 1976. Major study areas in the Arkansas, South Platte, Rio Grande and Yampa river drainages were censused by playback of taped rail calls. Soras bred from 1120-3140 m elevation and Virginia Rails from 1120-2730 m. No other rails bred in Colorado. Statewide, Virginia Rails exhibited higher breeding density indices (2.6 responding rails/ha) than Soras (1.3). Indices for Virginia Rails ranged from 4.7 in southeastern Colorado to 0.2 in northwestern Colorado. Indices for Soras ranged from 2.5 in south central to 0.4 in southeastern Colorado. Mean April air temperatures, a function of topography, influenced species composition. Soras were more abundant than Virginia Rails when mean April air temperatures were 5.6°C, or below. Both species preferred marshes dominated by Typha with water depths less than 15 cm. Short emergents attracted Soras during fall migration. Peak concentrations of migrating rails occurred during May and from mid-August through September. Greatest concentrations (>50 rails/ha) occurred locally in late July as the result of irrigation practices. Virginia Rails and Soras wintered in Colorado in small numbers.
The Wilson Bulletin © 1980 Wilson Ornithological Society