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1 December 2018 Estimating the Breeding Population of Great Blue Herons (Ardea herodias) in Maine, USA, Using Dual-Frame Sampling
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Abstract

The Great Blue Heron (Ardea herodias) is a Species of Special Concern in the State of Maine, USA, due to declines along the Atlantic coast since the mid-1980s. To determine if this decline was statewide, an aerial survey was conducted from 1 May to 18 June 2015 to estimate the breeding population using a stratified dualframe design accounting for imperfect detection of colonies. The strata were based on habitat and known colony densities. The area frame consisted of 10-km x 10-km plots. Stratum samples were searched by air independently by front and rear observers for known and new colonies. The list frame consisted of plots containing known colonies, a sample of which was checked for nesting activity. The dual-frame design combined the strengths of both list- and area-only surveys. Flying directly to known colonies in the list frame was very efficient, and accounting for new colonies in the area frame, allowed unbiased, statistically valid estimation. Estimates were calculated for a Maine statewide total of active Great Blue Heron colonies (n = 243, 90% credible interval (CI) = 193–352), total nests (n = 2,019, CI = 1,778–2,434), and active nests (n = 1,593, CI = 1,416–1,872). Observer detection ranged from 25 to 99%. The percentage of list frame colony coverage in the dual-frame estimate was 63%, but varied by stratum. The percent CV of the dual-frame statewide total active nests was 8.9%, but also varied by stratum. By repeating these methods, strata and statewide population trends could be obtained.

Danielle E. D'Auria and Mark C. Otto "Estimating the Breeding Population of Great Blue Herons (Ardea herodias) in Maine, USA, Using Dual-Frame Sampling," Waterbirds 41(4), 365-375, (1 December 2018). https://doi.org/10.1675/063.041.0413
Received: 31 January 2017; Accepted: 28 July 2017; Published: 1 December 2018
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