Surveys of Night Birds Along the Rio Grande in Webb County, Texas

摘要

This project sought to determine species richness and relative abundances of allnocturnal birds at representative wooded riparian (river and stock pond) habitats of the Galvan Ranch, Webb County, Texas. We conducted elicited and non-elicited call count surveys (including 91 ten-minute point counts) at monthly intervals from February-June, 1998. Monthly surveys were conducted over one night, from sunset to moonset, between half and full moon phases, and were completed by 0200 hr. Four owl and five nightjar species were detected on the ranch. No ferruginous pygmy-owls were found during this project, although suitable habitat seemed available. Nightjars, as a group, were five times more abundant than owls (mean number of nightjars per point count was 2.6; mean number of owls per point count was 0.5). Mean number per point count of great horned owl (Bubo virginianus), eastern screech owl (Otus asio), elf owl (Micrathene whitneyi), barn owl (Tyto alba), common poorwill (Phalaenoptilus nuttallii), lesser nighthawk (Chordeiles acutipennis), common pauraque (Nyctidromus albicollis), common nighthawk (Chordeiles minor), and whip-poor-will (Caprimulgus vociferus) was 0.25, 0.17, 0.15, 0.03, 1.22, 1.14, 0.57, 0.07, and 0.01 respectively. The river survey sites supported more species (0 = 2.2) than did upland pond sites (0 = 1.5), however, only one species (common pauraque) showed a preference for the river sites (X 2 = 6.38, d.f. = 1, P = 0.012).