Secretive Marsh Bird Monitoring
The populations of many species of birds that depend on emergent marsh habitat appear to be declining, but basic information on the population status and habitat requirements of many of these species is lacking. This information is necessary to evaluate the impacts of management actions, climate change and sea level rise on marsh bird populations. Clapper rails, Rallus longirostris, in the marshes of the North Inlet-Winyah Bay National Estuarine Research Reserve are being counted using a standardized call broadcast method developed by the U.S. Geological Survey, Arizona Cooperative Fish and Wildlife Research Unit. The effects of habitat type, distance from the marsh/upland edge and the presence of developed upland area on the distribution of rails are being studied using GIS and spatial analysis techniques. The results of this analysis will further our understanding of the habitat requirements of this species and be used to assess the potential effects of land use change and sea level rise on the population status of clapper rails.
Habitat Loss: Coastal development, sea level rise and climate change impact the quantity, distribution and functionality of tidal marsh habitats. Developing a better understanding of the habitat requirements of species that depend upon marshes will guide habitat conservation and restoration efforts.
Species Conservation: The population status of clapper rails is assumed to be stable, but there is little data on their distribution and habitat requirements. Long-term monitoring of marsh bird species is necessary to determine the effects of habitat loss and climate change on species populations and distribution and to develop conservation efforts.
A monitoring training session is head in early March, and monitoring occurs on four dates in March through June. Volunteer monitors travel by boat with reserve staff members to sites in the North Inlet marsh at sunrise to listen for clapper rail calls following a standardized procedure. In the future, the study may be expanded to include sites at Huntington Beach State Park and Pawleys Island.
Please contact Jen Plunket at jen@belle.baruch.sc.edu or 843-904-09033.
Five ‘routes’ have been established in the North Inlet marsh.
LA: The Land route will count rails close to the marsh-upland edge.
CB: The Clambank route represents relatively pristine mid-marsh habitat.
OL: The Oyster Landing route also covers mid-marsh habitat.
DM: The Debidue Marsh route is the only marsh area impacted by upland development.
JC: The Jones Creek area is barrier island marsh and represents the marsh habitat furthest from the upland edge.
Variables such as tide height, daylight, and wind speed may affect call detection, and call-response sampling methodology has not been widely employed in the salt marsh environment of the southeast. Two years of preliminary data for the North Inlet study were examined to evaluate and refine sampling protocols.
The number of birds observed at each survey point in 2009 was tested against air temperature, wind speed, daylight and tide depth measured at the Oyster Landing meteorological station. No correlations were found between the number of birds and these environmental variables, indicating that within the 3 hour morning sampling period chosen, time of day, tide height, and wind and air temperature did not affect the behavior of the birds or the ability to detect bird calls. The monitoring protocols produced by the Arizona Cooperative Fish and Wildlife Research Unit Surveys recommend that surveys should only be conducted when wind speed is less than 20 km/hr, and not during periods of sustained rain or heavy fog. No sample days occurred during rain or fog, and the mean maximum wind speed recorded was 11.6 km/hr with the maximum wind recorded at 23.4 km/hr.
Peak call response is likely to occur during courtship and egg-laying periods. The 2008 sampling period did not begin until the end of May, when it was noted that clapper rail chicks were seen in the marsh, raising concerns that the peak call response period may occur earlier in the spring. The 2009 sampling period extended from the end of March through the end of June to capture the peak response period. The number of birds observed increased from March 27 to April 24, and then there was an overall decrease in the number observed over the remaining May and June sample dates. Based on the 2009 data, the overall peak response period appears to be in late April, however the greatest number of birds were recorded for on the Clambank route 4 weeks prior to the greatest number of birds recorded on the Jones Creek route. Peak nesting periods may occur at different times within subpopulations of an estuarine area.
Update
The 2010 monitoring was finished in May. Special thanks to this year’s volunteer team who made the marsh bird monitoring project both a success and enjoyable way to spend the sunrise. Look for information about training and next year’s monitoring in January 2011.
