R. Douglas Slack and Kelly L. Mizell, Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, Texas 77843
Texas coastal wetlands serve as wintering or breeding grounds for 6 species of rails. King rails (Rallus elegans), clapper rails (Rallus longirostris), and black rails (Laterallus jamaicensis) are known to breed and winter in Texas, whereas yellow rails (Coturnicops noveboracensis), soras (Porzana carolina), and Virginia rails (Rallus limicola) are winter residents only. These rails inhabit coastal marshes throughout the western gulf coast as well as freshwater wetlands associated with rice agricultural fields.
Rails are almost entirely associated with wetlands and therefore are likely important indicators of wetland ecosystem quality. Coastal wetlands in Texas have declined by more than 52% during the last 200 years. Remaining wetlands have been fragmented and degraded. Declining rail numbers on wintering grounds are likely related to habitat loss, but also may be an indication of degradation in quality of remaining wetlands. Although the nature of wetland degradation is not fully known; factors which may contribute to changes in wetland quality include: nonpoint source pollution, alterations of hydrology, and declines in food availability.
We report on efforts to monitor local populations on two national wildlife refuges, primarily designed to determine presence, habitat associations and responses to management. We have chosen to focus on king and yellow rails studied at the Attwater Prairie Chicken National Wildlife Refuge and Anahuac National Wildlife Refuge. These two species were selected because of differing periods of residency in Texas. Because the king rail breeds and winters in Texas coastal freshwater marshes, we used both audio techniques and radio telemetry to determine habitat associations. Responses of king rails to taped calls were recorded most frequently from early spring to the onset of summer in freshwater marshes associated with nearby rice agriculture. Audio techniques were supplemented by use of radio-telemetry during the non- breeding season. On the other hand, the yellow rail presents a significant monitoring challenge. Because the yellow rail only winters in Texas, attempts to elicit vocal responses to audio techniques were unsuccessful. Therefore, we used radio-telemetry with a geographic positioning system to determine habitat associations and home range sizes of yellow rails.
Radio telemetry requires capture of individuals and successful attachment of appropriate radio transmitters. Attempts to capture king rails included the unsuccessful use of cloverleaf and havahart traps. We were successful using drop nets in capturing individual king rails foraging in irrigation canals. Back-pack harnesses were used for attachment of transmitters to king rails. Unsuccessful attempts to capture yellow rails included drift lines with funnel traps and mist nets. We were successful in capturing yellow rails by pulling weighted drag lines through the marsh to flush individuals at night. Flushed birds were captured using hand nets. Transmitters were affixed to the bird using a modified synsacrum attachment. This attachment placed the weight of the transmitter in the pelvic region and was used on 38 yellow rails during the winters of 1997 and 1998. Transmitters attached in the scapular region were unsuccessful.
Data from these studies indicated that while present in Texas these species exhibited different habitat associations. King rails were found in freshwater coastal marshes and inland wetlands, including those associated with rice agriculture. King rails were located in marshes with relatively dense vegetation and water ranging in depth from 3-10 cm. Yellow rails were found in marshes characterized by >50% vegetative cover and at sites with < 2.5 cm water depth. In addition, yellow rails have been reported to inhabit dry, mature rice fields. In addition, king and yellow rails were associated with marshes receiving burning and grazing management regimes.
Few studies have been documented on king and yellow rail populations along the western Gulf coast and little is know about their current status. Studying king and yellow rails require large investments of effort. Therefore, it is our opinion that future studies should use available monitoring techniques and investigate new methods. Rails are characteristic of Texas coastal wetlands and are indicative of the condition of these wetlands.