Nesting population assessment of the Yellow-headed Parrot (Amazona oratrix) in central-western Mexico

Abstract

The Yellow-headed Parrot (Amazona oratrix) is considered globally endangered due to intense poaching pressure and extensive tropical forest loss. We examined the relationships among nesting pair density, survey area, tropical forest type, and forest conservation conditions to estimate the potential population size in central-western Mexico. The surveyed areas constitute a representative sample of forest types, property ownership, and land use in the region. We estimated the overall surveyed area and the nesting pairs in general and by each forest type. Data were analyzed in multiple and single linear regression models. We used a high-resolution vegetation model to measure the extent of each forest type and land use in the area with suitable climatic conditions for nesting. We recorded 111 nesting events in 77 distinct nest trees during the 2002–2013 study period in an area of 185.3 km2. Overall nesting density was 0.59 ± 0.28 pairs per km2. Individual areas surveyed showed a broad variation in nest densities (0.14–1.5 per km2). Primary tropical semi-deciduous forest held 64% of the nesting pairs and the highest nesting density (1.98 ± 0.82 per km2). Tropical dry deciduous forest contained 11% of nesting pairs and 0.20 ± 0.19 pairs per km2. Single linear regression models by forest type performed better and are more practical for abundance calculations than multiple regression models. We estimate the size of the nesting population in the region at 701 pairs (95% CI: 526–876), which corresponds to about 1,399–2,330 parrots, using the mature/immature ratio used by the IUCN. The results suggest that central-western Mexico may hold about 27% of the species' global population.