Development of a Survey Protocol for Monitoring Reddish Egrets (Egretta rufescens) in Florida, USA

Abstract

The Reddish Egret (Egretta rufescens) is North America's rarest heron, and roughly 10% of its population resides in Florida. Its dark plumage, subcanopy nesting, and rarity make it difficult to count with aerial surveys, and assessments of ground- and boat-based methods for estimating the abundance of nesting pairs at breeding sites in Florida are lacking. The efficacy of flight-line surveys (boat-based counts of adults flying to and from colonies) and direct counts (ground- or boat-based counts of nests) were compared using data collected by multiple observers during repeated visits to 16 Reddish Egret colonies in three core breeding areas in the State of Florida, USA. Detection rates on direct counts were 77% for a single observer and 89% for two observers combined. Variance between repeated flight-line surveys was high (61%) for 1-hr surveys but substantially lower for 2-hr (18%) and 3-hr (14%) surveys. Estimated nest counts from flight-line surveys were substantially greater than those produced during direct counts, with mean differences of 85% for 1-hr counts, 134% for 2-hr counts, and 133% for 3-hr counts. Overestimates from flight-line surveys may be related to factors that can be mitigated by avoidance of sites for which use of the method is likely inappropriate (e.g., where breeding is substantially asynchronous or when a site includes an interior foraging lagoon). Survey recommendations are presented for monitoring the Reddish Egret on a large spatial scale.