Relative Nest Density, Nest Success, and Site Occupancy of King Rails in Southwestern Louisiana Rice Fields

摘要

King Rail (Rallus elegans) populations are listed as threatened or endangered in 13 states. One remaining area of relative abundance is the rice-growing region of southwestern Louisiana. Rice fields are flooded for much of the year and support thickemergent vegetation, potentially providing high-quality habitat for King Rails. The objectives of this study were to determine: 1) relative nest density of King Rails in rice; 2) which local and landscape factors influence relative nest densities; 3) nest survival of King Rails in rice fields; 4) effectiveness of callback surveys in indicating King Rail breeding activity; and 5) site occupancy of King Rails in rice fields. In the summers of 2004 and 2005, King Rail surveys and nest searches were conducted in Cameron,Jefferson Davis, Vermilion, and Acadia Parishes in southwestern Louisiana. In 2004, 42 fields were searched for nests and 30 of those were surveyed with callback survey techniques. In 2005, 40 fields were searched and 60 were surveyed. A total of 77 King Rail nests was found, and relative nest density was between 3.4 and 4.8 nests/km(2). The highest nest densities were in fields with a high proportion of irrigation canals around the perimeters and a low proportion of trees. Nest survivalwits similar to 50% in both years. Most survey responses were detected in June, and survey detections were correlated with nest abundance. Site occupancy was estimated as 0.35 +/- 0.11 in 2004 (no estimates for 2005) from callback surveys and between 0.4(2004) and 0.5 (2005) from nest searches. Callback surveys were an effective technique for monitoring King Rails in this region. Given high nest survival rates and apparently stable nest densities, rice fields appear to provide high-quality habitat forKing Rails in southwestern Louisiana. Received 21 May 2007, accepted 1 April 2008.