Least Bittern (<i>Ixobrychus exilis</i>) Survey Protocol

Abstract

The Least Bittern (Ixobrychus exilis) is at risk in several regions of North America and the effectiveness of multi-species marsh bird surveys to detect this secretive species has been questioned. A species-specific standardized survey protocol for Least Bitterns was developed to increase detection, quantify detection probability and improve knowledge of the species' distribution, abundance and habitat use. The protocol is a modification of the Standardized North American Marsh Bird Monitoring Protocol (Conway 2009), whereby only the Least Bittern call is broadcast repeatedly at fixed point count survey stations, and a second passive listening period is added after the broadcast period to increase detection. Vocalizations and behavior are noted on a minute-by-minute basis for each individual Least Bittern, along with estimated distance at first detection. The protocol has been implemented in Canada since 2006 and has resulted in Least Bitterns being detected in more sites and larger numbers than previously suspected. Adoption of the proposed protocol is recommended across the Least Bittern range when Least Bittern detection is the focus of a survey or monitoring program; therefore allowing direct comparisons of relative abundance and detection probabilities amongst sites.