The Effects of Changing Vegetative Composition on the Abundance, Species Diversity and Activity of Birds in the Chihuahuan Desert

A variety of mechanisms, both anthropogenic and natural, can lead
to changes in the vegetation composition of a community. In semi-
desert grasslands, for example, Schlesinger et al. (1990) suggested
that overgrazing can result in desertification through a shift
from primarily grasses to desert shrubs. Changes in plant
communities can also occur as a result of introduced species,
artificial watering, plant removal for human use, disease,
competition, and prolonged drought. In the future, global
problems, such as the greenhouse effect, could possibly lead to
climate changes (and therefore changes in vegetation) that we can
only attempt to predict.

Changes in plant composition have the potential to cause
disturbances in both structure and function throughout the
ecosystem. One element of the ecosystem that could possibly be
affected is bird diversity and behavior. Several studies such as
Dixon (1959), Raitt and Pimm (1976), Naranjo and Raitt (1993),
MacAurthur et al. (1962), Vander Wall and MacMahon (1984) and
Raitt and Maze (1968), all suggest that certain species of birds
depend more, or entirely, on habitats containing specific
functional groups or species of vegetation. According to Naranjo
and Raitt (1993), habitat preferences in birds develop because of
factors such as availability of food, nesting and perching
locations, and cover.

Birds may utilize some plant species more than other plant
species. Vander Wall and MacMahon (1984) suggest that some
particular plant species are ideally suited to particular bird
species. For example, the northern mockingbird relies on tall
plants for perching and singing sites. Other plant species
provide cover for birds like the Gambel's Quail. Certain species
of birds may also use a wider variety of different plants because
of broad habitat requirements. In this study we examine how
different types of plant types and growth affect bird abundance,
bird species diversity, and bird activity in the Chihuahuan
desert.