Population trends for Scripps's murrelet following eradication of black rats

Abstract

ABSTRACTNest monitoring at Anacapa Island, California, USA, in 2001–2010 documented considerable benefits for Scripps's murrelets (Synthliboramphus scrippsi) following the eradication of black rats (Rattus rattus) in 2002. In 2014, post‐eradication monitoring resumed at Anacapa to update the number of occupied nests in monitored plots, count murrelets in nocturnal at‐sea congregations near Anacapa using round‐island spotlight surveys, and compare post‐eradication rates of population change (λ) estimated from nest counts and spotlight surveys. Nest counts and spotlight counts demonstrated increases; the overall number of nests increased 4.45 times from 2001 (11 nests) to 2014 (60 nests) and mean round‐island counts in 2014 (869 ± 592 [SD]) were higher than in 2001–2003 (227 ± 151). Time series regression yielded annual increases that were marginally higher for nests (λ = 1.151) compared to round‐island counts (λ = 1.122). The slight difference may have resulted from inherent differences in the indices used to measure λ, spatial biases in nest plots, data gaps in the regressions, and small sample biases for round‐island counts. The post‐eradication λ for murrelets at Anacapa was slightly higher than the mean response reported for other Alcidae (λ = 1.113). This was the first use of spotlight surveys to estimate λ based on counts of seabirds congregating at‐sea near breeding areas. This study provided vital information needed to better assess the risks and benefits of future island restoration actions, justification for further murrelet conservation efforts, and confirmation of spotlight surveys as a population monitoring tool for Scripps's murrelets. © 2017 The Wildlife Society.