Distribution of King Rails in the Lower Mississippi Flyway
May 2006 - October 2008
- USFWS Region 8
- University of Arkansas
ABSTRACT The migratory population of the king rail (Rallus elegans) has declined dramatically over the last 30 years, and research was needed to determine habitat requirements of king rails for wetland management guidelines. Wetland management for king rails throughout their life cycle is important to the conservation of the species. To assess the distribution and habitat use of king rails along the Upper Mississippi Valley, we conducted repeated call-broadcast surveys at 83 sites in 2006 and 114 sites in 2007. We detected king rails at 8 sites in 2006 and 14 sites in 2007. We found king rails concentrated at Clarence Cannon National Wildlife Refuge, an adjacent private Wetland Reserve Program land, and B. K. Leach Conservation Area; these areas were located in the Mississippi River floodplain in northeast Missouri. Using the program PRESENCE, we estimated detection probability and incorporated habitat covariates into the estimation of site occupancy. We tested the fit of our data across a series of models which included percent cover of tall emergent vegetation (e.g. Typha latifolia, Sparganium americanum), short emergent vegetation (e.g. Eleocharis palustris, Leersia oryzoides), woody vegetation, and interspersion of water and vegetation (2007 only) within 50 m of the survey location. We found that the top occupancy model for 2006 included woody vegetation while the top occupancy model for 2007 included short emergent vegetation, tall emergent vegetation, interspersion, and woody vegetation. Site occupancy was negatively related to woody vegetation cover in both years and was positively related to interspersion (measured in 2007 only). The relationship between site occupancy and cover by short and tall emergents was less clear. To compare the habitat use of nesting and brood-rearing king rails, we randomly sampled 5-m plots within used and unused habitats during the nesting and brood-rearing seasons to measure water depth and determine dominant cover type. We fit logistic regression models to the data and selected among candidate models using AICc. We used the regression coefficient of top models to calculate odds ratios for habitat use. Nesting adults were more likely to use sites dominated by short emergent vegetation and deeper water, while broods were more likely to use sites dominated by short emergent vegetation and shallower water, and avoided areas dominated by tall emergent vegetation. During the nesting season throughout our study area, king rails occupied wetlands that were characterized by high coverage of short emergent vegetation, moderate coverage of tall emergent vegetation, high water-vegetation interspersion, and little or no coverage by woody vegetation. Nesting king rails used areas of deeper water, possibly as protection against mammalian predators, while broods may require shallower water for mobility and prey capture. Broods avoided areas with tall emergents, contrary to findings in other studies, and may have resulted from current management practices in our study area. Stands of tall emergents should be managed to provide small openings of shallow water in which broods can forage. The results presented in our study can be used by refuge managers to improve wetland habitat for breeding king rails.