Vegetative composition of areas with and without breeding red-billed pigeons (Patagioenas flavirostris) in Texas.

摘要

Much of the historic habitat of the red-billed pigeon (Patagioenas flavirostris) in southern Texas has been lost to agriculture, urban expansion, and changes in water flow in the Rio Grande. Populations in Texas have been declining since the 1920s. Our objectives were to quantify vegetational parameters in areas along the Rio Grande where red-billed pigeons were observed breeding and areas where they were not observed breeding. We conducted our study May-September, 2000 and 2001, along 30-km of the Rio Grande below Falcon Lake Dam in southern Texas. We used line-intercept transects to collect vegetational data in three areas where breeding activity was observed and in three areas where breeding activity was not observed. We compared length of transect, height of plants, width of canopy, density of plants, relative density of plants, and percent ground cover among and within areas. We also tested for relationships between height of trees and width of canopy. Height of trees and width of canopy were greater in breeding areas. The riparian zone was wider in breeding areas and there was greater heterogeneity in length of riparian zone within non-breeding areas. Breeding areas had high importance values for Mexican ash (Fraxinus berlandieriana), willow (Salix nigra), and Texas ebony (Pithocellobium ebano), and a low value for honey mesquite (Prosopis glandulosa). Mature stands of riparian habitat appeared to be favored by breeding red-billed pigeons. However, this habitat is declining along the Rio Grande and more information is needed to aid conservation efforts for this species in the United States.