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Warner P. Gorenzel, Ronald A. Ryder, Clait E. Braun, Reproduction and Nest Site Characteristics of American Coots at Different Altitudes in Colorado, The Condor: Ornithological Applications, Volume 84, Issue 1, 1 February 1982, Pages 59–65, https://doi.org/10.2307/1367822
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Abstract
Reproduction and habitat use of American Coots (Fulica americana) were investigated on four study areas in the major elevational areas of Colorado, one in the eastern plains, two in the high mountain valleys, and one west of the Continental Divide. Nests were started from mid-April to mid-July; peak initiation dates ranged from 25 April to 12 June. Coots at high elevations had a shortened territory establishment-to-nest initiation period. Eggs hatched from mid-May through early August with peak hatching from 30 May to 4 July. We found 354 nests, and eggs in 284 nests hatched. Nesting and hatching success, respectively, ranged from 68.6 to 84.9% and 85.2 to 92.4%, with more nest failures and eggs lost per nest than expected at the high altitude areas. Average clutch size was lower at high altitude and decreased at all elevations as the season progressed. Predators caused most nest (64.3%) and egg (45.9%) loss. All nests were over water and most (99.7%) were in cattail (Typha spp.) or tule bulrush (Scirpus acutus). Early-nesting coots (75.6%) used dead, remaining vegetation for nest cover; later nesters used live cover as it became available. Measurements of nest site vegetation height, concealment, water depth, and distance to open water were variable and depended on local conditions. Breeding densities ranged from 10.2 to 33.1 successful nests/ha of cattail and bulrush and were independent of altitude. Intermingling of open water and emergent cover influenced the number of nesting coots.
