Coastal Texas black rail population states and survey effort

Abstract

ABSTRACTEastern black rails (Laterallus jamaicensis jamaicensis) are of conservation concern. These birds vocalize infrequently and inhabit dense vegetation, making them difficult to detect. We conducted the first large‐scale study of black rail occupancy and abundance in Texas, USA. We conducted point count surveys that were 6‐minute call‐playback broadcasts and detected rails acoustically. We fit 19 occupancy and 19 abundance models while accounting for imperfect detection. We used the top occupancy model to estimate the required survey effort to precisely estimate black rail occupancy with and without detection correction methods. We found that detection increased with moon phase but decreased with wind speed and ambient noise. Occupancy and abundance increased with cordgrass (Spartina spp.) and intermediate marsh cover. Estimates of mean occupancy (0.27 and 0.26) and abundance (1.08 and 1.00 rails/point) were similar between 2015 and 2016. Estimated survey efforts under mean (wind = 6–10 km/hr, lunar phase = half‐moon) and optimal (wind = 0–5 km/hr, lunar phase = full moon) environmental conditions were less for detection correction methods than for non‐correction methods. We also concluded that efforts to predict black rail presence from naïve occupancy estimates are impractical. Managers and researchers who wish to monitor black rails populations should use detection correction techniques when estimating occupancy and abundance. © 2018 The Wildlife Society.