Birds

Resumen del Proyecto:

As initially projected, this report would have been considerably larger. Fuller discussion of the systematics of many species would have been desirable and the inclusion of life-history observations and allied subjects would have added considerably to its usefulness. In normal times this would·have been possible, for investigation to fill in the not inconsiderable gaps was definitely on schedule for. 1942 and 1943. During the enforced postponement of such plans the outlook has been altered some- what and activity for the post war years has been greatly enlarged- in prospect.

The pine-oak forests of the Sierra Madre Occidental, a mountain range in NW Mexico, have recently been recognized as an area of high endemism and biodiversity. Selective logging threatens three bird species endemic to this habitat, who depend on standing dead trees (snags). This report is based on an 11 month field survey that aimed to locate old- growth remnants and to assess the status of the endemic birds. Old-growth is defined here as a forest that has never been logged mechanically.

Investigations of processes that drive animal distribution and abundance are often approached at one of two different scales and therefore focus on different processes. At local scales, animals are thought to select home ranges or territory patches in an ideal manner by occupying them in order of their fitness potential, but a variety of processes can decouple choices from their fitness consequences and create non-ideal patterns of distribution.