Multi-season site occupancy of Eastern Whip-poor-wills (Antrostomus vociferus) in New York

Abstract

Multi-year monitoring of species distribution is important for conservation planners to understand population trajectories. In New York, USA, the Eastern Whip-poor-will (Antrostomus vociferus) is among several bird species that have been documented to be declining and has been monitored for several years through large-scale surveys such as the Breeding Bird Atlas and Breeding Bird Survey. We implemented a study to assess trends in site occupancy at 19 survey routes during 2014–2018 breeding seasons. We surveyed for Eastern Whip-poor-wills following the Center of Conservation Biology Nightjar Survey Network methodology and used these data to estimate yearly relative abundance, factors that may influence the probability of detection, probability of a site being occupied and potentially important landscape features, and dynamic processes of site colonization and extinction. The mean relative abundance ranged from 0.54 in 2016 to 0.89 in 2014, with all yearly estimates having 95% confidence intervals that overlapped. The probability of detection was negatively affected by the greatest wind speeds recorded (12.87–28.97 kph, [8–18 mph]). Site occupancy was relatively low each year ranging from 26% to 32% across all years. We observed a negative effect on site occupancy with survey sites located in the Adirondack ecozone of New York. We additionally found support for a negative effect of median elevation and a positive effect of area of hay and pasture on site occupancy within 675 m of survey sites. The probability of a site becoming colonized ranged from 0.05 to 0.14 and the probability of a site going extinct ranged from 0.14 to 0.42. Overall, we did not find support for a decreasing trend in site occupancy. The yearly relative abundance estimates and site occupancy estimates were small but did not decrease over time and the dynamic processes did not suggest increasing extinction or decreasing colonization rates. Occupied survey locations may represent some of the most suitable and stable habitat for these birds within the state. Important landscape characteristics of lower elevation and area of hay and pasture may be representative of forest mosaics that include open areas with forest edges at lower elevation, which has been documented in other studies.