Springtime bird use of agricultural landscapes examined by using autonomous recording units

Abstract

Autonomous recording units (ARUs) emerged as a novel technology for avian acoustic monitoring in the 2000s. They have since been primarily used as a substitute for human observers during the breeding season. Autonomous recording units have potential uses in springtime soundscapes, such as to study spring departure or arrival of migratory birds and territory establishment of resident breeding birds. We described springtime bird communities of agricultural landscapes based on data collected between 1 April and 15 May 2015–2019, from ARUs deployed at 32 locations across 13 counties in Iowa, USA. We compared bird communities across site types, analyzed trends in migrant arrival dates and detection rates, and examined springtime occupancy of five species that commonly use grassland cover: Common Yellowthroat ( Geothlypis trichas ), Field Sparrow ( Spizella pusilla ), Grasshopper Sparrow ( Ammodramus savannarum ), Savannah Sparrow ( Passerculus sandwichensis ), and Vesper Sparrow ( Pooecetes gramineus ). We made 4029 detections of 86 bird species. The most frequent detections were of common farmland species, including Red-winged Blackbird ( Agelaius phoeniceus ), American Robin ( Turdus migratorius ), Brown-headed Cowbird ( Molothrus ater ), Ring-necked Pheasant ( Phasianus colchicus ), and Eastern Meadowlark ( Sturnella magna ); however, detections also included 18 species of greatest conservation need. Sites with reconstructed prairie vegetation, conventionally grown corn ( Zea mays ) and soybean crops ( Glycine max ), crops with prairie strips, and crops with terraces had similar species richness. We found that, in addition to documenting species richness and departure/arrival times of migratory species, ARUs generated species-level detection probabilities similar to or higher than existing studies on breeding season occupancy. Detection probabilities of five focal species ranged from 0.36–0.89. Occupancy models revealed significant springtime land cover associations for Common Yellowthroats, Field Sparrows, Savannah Sparrows, and Vesper Sparrows. We conclude that springtime deployment of ARUs can provide valuable information on phenological patterns and springtime habitat use of birds.

Keywords

• acoustic monitoring
• detection probability
• habitat associations
• occupancy
• phenology
• soundscape ecology