Estimating distributions of two declining aerial insectivorous Nightjars species using passive acoustic monitoring in southern Illinois

Author

Elaine Metz, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2023

Degree Name

Master of Science

Department

Forestry

First Advisor

Pease, Brent

Abstract

Nightjars are a group of nocturnal and aerial insectivorous birds that have experienced long-term decline likely driven primarily by habitat loss and declines in prey populations. Eastern Whip-poor-will (Antrostomus vociferus) and Chuck-will’s-widow (Antrostomus carolinensis), two nightjar species native to Illinois, declined 69% and 58% since 1966, respectively. Although previous survey efforts have documented presence of Chuck-will’s-widow and Whip-poor-will, their current distribution in the state is not well known. Using Autonomous Recording Units (ARUs) deployed in a uniform, systematic grid, I surveyed 142 locations from May – July 2022 on public and private lands across the southern eleven counties of Illinois to assess Whip-poor-will and Chuck-will’s-widow distribution and estimate species occupancy. I estimated species relationships with proportion of landcover types, forest patch configuration, and proximity to other landcover types. Additionally, I quantified disturbances from the past 15 years to estimate species relationships to the severity and duration of disturbances. I deployed ARUs for 710 survey days collecting 170,400 minutes or 3,000 hours of recordings. Acoustic bird call identification software, BirdNet, was highly accurate at detecting focal species and greatly reduced the time spent manually reviewing acoustic data. BirdNet identified 43,922 calls of Whip-poor-will and 31,447 calls of Chuck-will’s-widow. I detected Whip-poor-will on 78 surveys with 100% accuracy and Chuck-will’s-widow on 75 surveys with 76% accuracy. Whip-poor-will were positively associated with forest patches with large core areas that neighbored pastures. Additionally, Whip-poor-will were likely to occupy landscapes that had experienced low to moderate disturbance within the previous 15 years. Covariates used to model Chuck-will’s-widow occupancy explained little variation in detection or occupancy and there were no significant relationships with any covariate. However, examining non-significant trends suggest similar relationships as Whip-poor-will in the area. Results highlight the efficiency of passive acoustic monitoring for these birds and the need for further investigation into Chuck-will’s-widow species-environmental relationships. In southern Illinois, Chuck-will’s-widow populations appears to be consistent with previous estimates from the 1990s while Whip-poor-will follow the broader trend of decline.