Broadcasting regional call dialects has little influence on the effectiveness of call-broadcast surveys for marsh birds

Emergent wetlands have declined in North America and, in response, many wetland-dependent animals have declined in abundance. For example, many species of secretive marsh birds in North America have declined during the last century. However, estimates of population decline and efforts to assess the effects of management actions are hampered because marsh birds are difficult to detect using conventional survey techniques. Call-broadcast surveys can improve detection probability of marsh birds; however, the effectiveness of call-broadcast varies regionally for some marsh birds, which might reflect differential responsiveness to call dialects. Here, we evaluated differential responses by least bitterns (Ixobrychus exilis) and clapper rails (Rallus crepitans) to different call dialects by using 679 paired call-broadcast surveys in Florida and South Carolina. We detected similar numbers of least bitterns and clapper rails responding to the different call dialects, except in Florida, where least bitterns responded more frequently to a more-distant (Louisiana) dialect than a more-local (Florida) dialect. Our results suggest that, at least for clapper rails and least bitterns, it may not be necessary to incorporate regional call dialects into standardized surveys. However, additional research is needed in more regions of North America and with other species.