Treesearch

Non-sustainable land use practices in the state of Michoacan, Mexico, have perturbed endemic bird h~bitats for several decades. Endemic birds have a restricted geographic and ecological distribution. This feature makes them suitable to be used as indicators of biological diversity and environmental perturbation. Forty-one Mexican endemic species have been recorded in 11 temperate and 3 tropical vegetation types in Michoacan (59,000 km2 ). This paper demonstrates the use of a geographic information system to locate and display spatially explicit endemic bird richness areas based on the...

We recommend that managers of forest-associated bird species follow a five-step hierarchy in establishing and implementing management programs. In essence, a manager must evaluate the composition and physiognomy of the landscape mosaic in the context of the regional and subregional goals and objectives. Then he/she can explore alternatives that allow manipulation of the configuration of the land uses within the management area to integrate elements of the surrounding landscape matrix. Wherever possible, spatial relationships within the region should be considered to help maintain connectivi...

The pressures of growing borderland populations, increased land use, and Increased water use are threatening amphibians in the Chihuahuan Desert border area. In this paper, we describe potential direct threats such as loss or contamination of aquatic habitats, and indirect threats such as the sublethal effects of pesticides on developing larvae and tadpoles. More research is needed on amphibians of the Chihuahuan Desert region to develop guidelines for managing the natural resources of the region in ways that benefit both wildlife and humans.

Hubbard (1999) criticizes our paper "Migration of the Willow Flycatcher along the middle Rio Grande" (Yong and Finch 1997), where we reported aspects of stopover ecology of the species including timing, abundance, fat stores, stopover length, and habitat use. Hubbard questions our identification of subspecies of the Willow Flycatcher (Empidonax traillii) and the methods we used to identify them. He also attempts to evaluate the accuracy of our results of subspecies composition by comparing them with data from other researchers. We welcome and applaud this scrutiny in the hope that this...

The large number of Neotropical migratory bird (NTMB) species and their diverse habitat requirements create conflicts and difficulties for land managers and conservationists. We provide examples of assessments or conservation efforts that attempt to address the problem of managing for multiple NTMB species. We advocate approaches at a variety of spatial and geographic scales, and believe that successful NTMB conservation will require a broad "top-down" perspective combined with management actions taken from the "bottom up." A top-down approach is needed to establish priorities or objectives...

The endangered southwestern Willow Flycatcher (Empidonax traillii extimus) is an obligate riparian species that typically nests in willow (Salix spp.) thickets or other dense, shrubby habitats. We report on the first nests in Arizona sycamore (Platanus wrightii) and in a climbing rose vine (Rosa multiflora). Although these nests were located in novel substrates, they were typical for the species in being supported by multiple small stems and in having a dense canopy cover. We suggest that nest substrate preferences of Willow Flycatchers in the Southwest may be broader than generally...

Historic and recent changes in the structure, composition, and distribution of riparian forests have likely influenced populations of bats through their effects on habitat quality for reproductive females. This project seeks to identify natural structures used by maternity colonies, determine criteria used in the selection of these roosts, and interpret how historic and current human activities may positively or negatively impact bat populations in the bosque. This paper reports first season results from this ongoing project. Thirteen reproductive female bats (5 little brown myotis, 5 Yuma...

Expanding human populations in the middle Rio Grande have increased demands on water, land, and other resources, potentially disrupting bird migration activities. From 1994 to 1997, a total of 26,350 birds of 157 species were banded and studied. Results include species composition, timing of migration, and habitat use. Recommendations for managers are included.

In the Southwestern United States, recent degradation of riparian habitats has been linked to decline of the Southwestern subspecies of the Willow Flycatcher. During a 2-year banding effort, migration patterns and bird fat content were analyzed. Recommendations for managers, and outlines for conservation plans, are included.

Although usually considered to be a bird of old growth mixed conifer forests, the Mexican spotted owl historically occurred in a wide range of habitats from lowland cottonwood bosques to montane canyon systems. In a recent study of habitat use in central New Mexico, we found that owls roost primarily in canyon bottoms, and that they select sites that are characterized by deciduous trees and high structural complexity of vegetation, rather than by large diameter conifer trees per se. Intact riparian areas in montane canyons typically have considerable structure, yet, as in the lowlands,...