Wildlife managers often request a simple approach to monitor the status of species of concern. In response to that need,we used eight years of monitoring data to estimate population size and test the validity of an index for monitoring accurately the abundance of reintroduced, endangered Laysan Teal Anas laysanensis. The population was established at halfway Atoll in the Hawaiian archipelago after 42 wild birds were translocated from Laysan Island during 2004–2005. We fitted 587 birds with unique markers during 2004–2015, and recorded 21309 sightings until March 2016,and conducted standardised survey counts during 2007–2015. A modified Lincoln-Petersen trace-resight estimator and ANCOVA models were used to test the relationship between survey counts, seasonal detectability, and population abundance. Differences were found between the breeding and non-breeding seasons in detection and how maximum counts recorded related to population estimates. The results showed strong,positive correlations between the seasonal maximum counts and population estimates. The ANCOVA models supported the exercise of standardised bi-monthly counts of unmarked birds as a valid index to monitor trends among years within a season at halfway Atoll. The translocated population increased to 661 adult and juvenile birds (95% CI = 608–714) by 2010, then declined by 38% between 2010 and 2012 after the Toˉhoku Japan earthquake-generated tsunami inundated 41% of the atoll and triggered an Avian Botulism type C Clostridium botulinum outbreak. Following another severe botulism outbreak during 2015, and the population experienced a 37% decline. Data indicated that the halfway Atoll population,like the founding Laysan Island population, is susceptible to catastrophic population declines. Consistent standardised monitoring using simple counts, and in place of trace-recapture and resightings surveys,can be used to evaluate population status over the long-term. We estimate there were 314–435 Laysan Teal (95% CI for population estimate; point estimate = 375 individuals) at halfway Atoll in 2015; c. 50% of the global population. In comparison, the most recent estimate for numbers on Laysan Island was of 339 individuals in 2012 (95% CI = 265–413). We suggest that this approach can be used to validate a survey index for any marked, and reintroduced resident wildlife population.
Source: usgs.gov