Bird Population Responses to Converting Chaparral to Grassland and Riparian Habitats

Abstract

Twenty-one years after chaparral was converted to grassland and riparian habitat in central Arizona, bird population density ranged from a high of 321 pairs per 40 ha in the riparian stringer to a low of 24 pairs per 40 ha on the grassland, compared to 103 pairs per 40 ha in the chaparral. However, the conversion of 40 ha of chaparral resulted in 38 ha of grassland and 2 ha of riparian habitat. Bird density on both areas together was 37 pairs per 40 ha. Thus although popula- tion density, species richness, and diversity were higher in the riparian area when contrasted with the chaparral, there was an overall net difference of 66 fewer pairs per 40 ha in the converted area. Birds and other vertebrates are attracted to riparian habitats throughout the Southwest (Anderson and Ohmart, 1977; Carothers et al., 1974; Stevens et al., 1977; Szaro, 1980). Because of their dense vertebrate populations, increasing importance has been placed on preserving and managing riparian habitat for wildlife (Johnson and Jones, 1977). Unfortunately, the amount and quality of these habitats has been decreasing (Davis, 1977; Ohmart et al., 1977; Engel- Wilson and Ohmart, 1978). A study was initiated in the arid Southwest to determine the effects of chaparral conversion on water yield in central Ariz- ona. After a wildfire, shrub regeneration was suppressed and a watershed con- verted to grass. As a result of this conversion in 1959, a small riparian stand has developed below the stream gauging station at the base of the converted grass area. This study was designed to assess the impact of grass conversion and riparian generation on the breeding birds of Arizona chaparral.