Comparative ecology and reproductive biology of three species of Amazona parrots in northeastern Mexico

Yellow-headed (Amazona oratrix) and Red-crowned (A. viridigenalis) Parrots are threatened endemic species that occur sympatrically with the Red-lored Parrot (A. autumnalis) in northeast Mexico. They suffer from pressure of habitat loss and harvest for trade. I used a comparative approach to test predictions that sympatric species would differ in use of nest cavities, distribution of nests, clutch size and mortality factors.; The study site was in a disturbed habitat mosaic including cattle pastures with trees (83% by area). The study site was divided into four vegetation patch types that differed in tree density: forest, 44 trees/ha; shelterbelts, 27 trees/ha; wooded pasture, 16 trees/ha and open pasture, 9 trees/ha; but not in proportion of trees with cavities (30-34%). I studied 76 different nest cavities during three breeding seasons, 1992-94. Values for seven characteristics of nest cavities used overlapped almost completely among species, showed ample variability and were different only for length of entrance. The pooled sample of Amazona nests was compared with a random subsample of "suitable" cavities and no significant differences found for diameter at breast height of tree, width of entrance, depth and internal diameter of cavities. Parrots nested successfully in all four vegetation patch types.; Nesting started in late March for the three species. Nest cavities previously successful appeared more likely to be reused by the same pair. There were species differences in conspicuousness around the nest in the order {dollar}A. viridigenalis > A. oratrix > A. autumnalis.{dollar} The smallest species A. viridigenalis had the largest mean clutch size (3.4) and youngest age at fledging (53 days). Chicks were usually fed only twice a day. Fledging was approximately two birds per successful nest, but sources of mortality differed among species. Direct evidence of snake predation on chicks was obtained in five cases. A. oratrix had a large proportion (65%) of non-laying adult pairs.; Roost counts at a single roosting site varied significantly across seasons, species and years. Density estimates of nesting parrots were 8.4, 6.3 and 5.7 birds per 100 ha respectively for A. autumnalis, A. oratrix and A. viridigenalis. Food sources were abundant during the breeding season.