Diversity and Spatial Analysis of Passerine Birds in Relation to Habitat Characteristics of Woods Along the Northern Coast of the Gulf of Mexico.

Abstract

I studied the ecological diversity and spatial patterns of passerine birds during the springs of 1993, 1994, and 1995 at 3 stopover sites on the Chenier Plains of Louisiana and Texas. A "control" stand with dense understory vegetation and a "reduced" stand with modified understory were at each site. Data were collected on the structure and composition of vegetation and on the abundance and location of birds. Species richness, dominance, and diversity indices were computed for both vegetation and birds. Patterns of floristic impoverishment, greater dominance, and greater plant species diversity were found at the "reduced" stands. "Control" vegetation did not have greater bird species richness than the "reduced" stands. Nevertheless, bird species diversity tended to be lower in the "reduced" plots. This difference was consistent at 2 of the study sites in all 11-week observation periods. Between 30--40% of the bird species considered had dispersion patterns that differed from random. More bird species had clumped patterns on the "control" stands than at the "reduced" ones. Therefore, it seems that vegetation composition and structure influenced the spatial use of habitat. A more detailed study of the spatial patterns of 2 target species was carried out with Ripley's K functions. Gray Catbird (Dumetella carolinensis) had clumped patterns at both "control" and "reduced" stands in 2 study sites but only in the "control" stand at the third site; the "reduced" plot was basically not used there. Hooded Warblers (Wilsonia citrina) had the same pattern at the same stand but a tendency to be more clumped in the "control" stands at the other 2 sites. A direct link between clumped patterns and specific vegetation characteristics was not found, yet patchiness in birds on the chenier woods seems to result from environmental factors. In short, in this study I present evidence that birds (particularly Neotropical migrants) tend to respond to the overall structure of their spring stopover habitat in the northern coast of the Gulf of Mexico.