Determining the status and distribution of the eastern black rail (Laterallus jamaicensis) in coastal Texas
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The black rail (Laterallus jamaicensis) is a small and secretive marsh bird that inhabits coastal high marshes and freshwater wetlands throughout the Americas and is a species of conservation concern. In Texas, winter migrant and breeding populations of the eastern black rail (L. j. jamaicensis) are known to occur in disjunct wetlands along the Gulf Coast. Black rail distribution and life history, however, are poorly studied in Texas. I studied the spatial ecology and habitat requirements of black rails in marshes of the Texas Gulf Coast from 2015 to 2018. Through the application of occupancy models, radio telemetry, capture-recapture studies, and a geographic information system, I provide an evaluation of factors that influence the distribution of black rails at multiple spatial scales in coastal Texas. Using occupancy data, I developed a species distribution model for the black rail in coastal Texas to identify important areas for the bird on a landscape-scale. I found positive associations between black rail occurrence and average annual precipitation as well as herbaceous vegetation density. High-marsh habitats with minimal tidal influence containing >50% herbaceous vegetative cover, especially gulf cordgrass (Spartina spartinae), had the highest predicted occupancy probabilities. Using radio telemetry, I tracked individual black rails during winter to estimate home range size and examine habitat associations at the home-range scale. Home range size of wintering black rails in Texas was somewhat smaller than estimates of those during breeding in Florida, which represents the only other published home range study for the subspecies. Habitat selection within black rail home ranges were similar to occupancy model findings: black rails selected high-marsh habitats with vegetation types that included large amounts of gulf cordgrass and avoided the low tidal marsh. Home ranges also contained an elevational gradient which may allow for rails to seek higher ground during times of increased water levels. I also looked at effects of disturbance from prescribed fire within black rail habitats. Prescribed fire is a common method used to manage the coastal marshes inhabited by black rails. Results from capture studies conducted in multiple burn plots indicated black rails will use habitats within a wide range of burn regimes (27 - 76 months post-burn). I found no strong relationships between black rail density and habitat features measured in study plots. Nevertheless, there might be a minimum cover requirement in that I only detected black rails ≥27 months post-burn. For the closely related yellow rail (Coturnicops novaboracensis), plots with lower herbaceous density were favored more. Yellow rails will also use habitats within a wide range of burn regimes (11 – 84 months post-burn) and may require a shorter return interval post-burn before using the habitat. There was no correlation between months post-burn and density of either species of rail which might be explained by a lack of correlation between herbaceous density and months post-burn. Management of burn regimes for black rails and yellow rails in coastal Texas should maintain a mosaic of seral stages. My studies provide information that is crucial for beginning to understand black rail distribution in coastal Texas as well as for managing habitat for the species.