Environmental relationships, decadal changes, and regional decline of Eastern Whip-poor-will ( Antrostomus vociferus ) and Chuck-will’s-widow ( Antrostomus carolinensis )

Abstract

Nightjars are a family of nocturnal and aerial insectivorous birds that have experienced long-term declines driven primarily by loss of habitat and prey populations. In Illinois, structured survey efforts documented the presence of Eastern Whip-poor-will ( Antrostomus vociferus ) and Chuck-will’s-widow ( Antrostomus carolinensis ) over 30 years ago, but their current distribution in the state is not well known. We deployed autonomous recording units at 142 locations during May–July 2022 to resurvey a uniform sampling grid developed by the Illinois Breeding Bird Atlas during 1986–1991 surveys, with the objective of estimating the current distribution of the species within the state and understanding how their distribution has changed over 30 years. We used a bird call identification algorithm, BirdNet, to detect Nightjars in 4-hour recordings and then manually verified detections where species were reported. We used single-season, single-species occupancy models and a suite of remotely sensed, ecological variables to identify key drivers of their current distribution relating to landcover, forest patch configuration, and forest disturbances. BirdNet was highly accurate at detecting Nightjars and reduced the time spent manually annotating recordings. Eastern Whip-poor-will were positively associated with large core forests and proportion of pastureland within a sampling block. Additionally, Eastern Whip-poor-will were more likely to occupy areas that had experienced low to moderate disturbance in forests. Covariates used to model Chuck-will’s-widow occupancy explained little variation in detection or occupancy. However, examining non-significant trends suggest some similar relationships as documented with Eastern Whip-poor-will. Compared to the 1986–1991 surveys, Chuck-will’s-widow populations remained constant while Eastern Whip-poor-will declined although the spatial distribution of occurrences for both species changed. Our results provide updated knowledge of the current distributions of Nightjars in our region and highlight the need for further studies examining the drivers of distribution particularly in the case of Chuck-will’s-widow.

Keywords

• aerial insectivores
• autonomous recording units
• birdnet
• disturbance
• nightjars
• nocturnal birds
• passive acoustic monitoring
• whip-poor-will