SECRETIVE MARSHBIRDS OF URBAN WETLANDS IN THE WASHINGTON, DC METROPOLITAN AREA

Abstract

Secretive marshbirds are in decline across their range and are species of greatest conservation need in state Wildlife Action Plans. However, their secretive nature means there is relatively sparse information available on their ecology. There is demand for this information in the Washington, DC area for updating conservation plans and guiding wetland restoration. Rapid Wetland Assessment Methods are often used to monitor success of restoration but it is unknown how well they indicate marshbird habitat. Using the Standardized North American Marshbird Monitoring Protocol, I surveyed 51 points in 25 marshes in the DC area in 2013 – 2015. I also collected data on marsh area, buffer width, vegetation/water interspersion, vegetation characteristics, flooding, and invertebrates. At each bird survey point I assessed wetland quality using the Floristic Quality Assessment Index (FQAI) and California Rapid Wetland Assessment (CRAM) methods. I used Program Presence to model detection and occupancy probabilities of secretive marshbirds as a function of habitat variables. I found king rails (Rallus elegans) at five survey sites and least bittern (Ixobrychus exilis) at thirteen survey sites. Secretive marshbirds were using both restored and natural marshes, marshes with and without invasive plant species, and marshes with a variety of dominant vegetation species. King rail occupancy was positively correlated with plant diversity and invertebrate abundance and weakly negatively correlated with persistent vegetation. Least bittern occupancy was strongly negatively correlated woody vegetation and invertebrate abundance and weakly positively correlated with persistent vegetation. Species-specific models provided a better fit for the data than generic marshbird models. A comparison model based on important habitat variables in other regions was a very poor fit for the data in all sets of models tested. FQAI was a better indicator of secretive marshbird presence than CRAM, but neither method had very good predictive ability or goodness of fit. These results underscore the importance of having species- and region-specific models for effective conservation. Based on these findings, decreasing woody vegetation and managing for a variety of co-dominant species to avoid monocultures would improve habitat for marshbirds. Rapid Assessment Method scores should be interpreted with caution when applied to marshbird habitat conservation.