Effects of Broadcasting Conspecific and Heterospecific Calls on Detection of Marsh Birds in North America

Standardized protocols that include the use of call-broadcast have recently been proposed for marsh birds in North America. We used data from point-count surveys collected across North America over eight years to evaluate the extent to which each of 13 focal marsh bird species responded to conspecific and heterospecific call-broadcast relative to passive survey methods. Surveyors detected more individuals during the 1-minute of conspecific call-broadcast compared to each of the five 1-minute passive segments and all of the 1-minute heterospecific call-broadcast segments for all species. Surveyors also detected more individuals during most of the 1-minute heterospecific call-broadcast segments compared to the 1-minute passive segments. Most birds responded to conspecific call-broadcast quickly (within 1 min), but we found some evidence for a lag time in birds' response to conspecific calls. The percent increase in the number of birds detected as a result of conspecific call-broadcast (relative to passive survey methods) varied between 14% (American bitterns [Botaurus lentiginosus]) to 632% (purple gallinules [Porphyrula martinica]). We recommend the use of point-count surveys that include both passive and call-broadcast segments for numerous marsh birds when collecting data to assess occupancy, evaluate the effects of wetland management practices, and estimate population trends of marsh birds.