Effects of including non-breeding bird species on predicted bird distributions for conservation planning in New Mexico

Abstract

There has been uncertainty in the national gap analysis program about including non-breeding birds in distribution models because of concerns that distributions of migrant and winter birds are difficult to predict and are not necessary to assess biodiversity patterns. New Mexico gap analysis included migrant and non-breeding birds assuming that distributions could be predicted using habitat associations, and that excluding non-breeding bird habitat from avian richness projections potentially underestimates community types important to birds. We compared biodiversity estimates including non-breeding birds (inclusive estimate — 324 species) to estimates including only breeding birds (breeding bird estimate — 257 species) in terms of estimated patterns of species richness. Inclusive and breeding bird richness estimates agreed about general locations of some species-rich areas and the most species-poor areas in the state, but were less comparable for intermediate areas of bird occurrence. We found <50% agreement between the two estimates about areas with highest species richness. When non-breeding birds were included, over 2,000,000 ha of short grass steppe shifted to a higher richness category and another 11,600 ha moved into the highest richness category. Graminoid wetlands, playa lakes, and waters in eastern New Mexico also showed elevated richness levels in the inclusive estimate. Our analyses indicate that only assessing breeding distribution does not reliably predict relative importance of areas used by birds throughout New Mexico and should not be used exclusively to identify potential gaps in conservation for land-use evaluation and planning.