Acoustic Monitoring for Western Yellow-billed Cuckoo in the Grand Valley

Acoustic Monitoring for Western Yellow-billed Cuckoo in the Grand Valley 

Whit Blair, Colorado Parks and Wildlife 

Abstract: The Yellow-billed Cuckoo (Coccyzus americanus) Western Distinct Population Segment (Western Yellow-billed Cuckoo; YBCU) is a federally threatened migratory bird (78 FR 61621 and 79 FR 59992) and State of Colorado Tier 1 Species of Conservation Concern (State Wildlife Action Plan 2025). The YBCU is a riparian nesting bird that winters in Central and South America and breeds annually in North America between June and August. The population west of the continental divide is identified as a distinct population that has experienced significant decline over the past century due to breeding habitat loss, degradation, and fragmentation. Two Western Colorado riparian areas were identified as federally designated Critical Habitat for the species in 2021 (86 FR 20798): the Colorado River from east of Palisade, Colorado to east of Fruita, Colorado, and the North Fork of the Gunnison River from east of Paonia, Colorado to west of Hotchkiss, Colorado. Over the past two decades, biologists in the Grand Valley have documented their surveys of public lands along the Colorado River within the current designated Critical Habitat area to find nesting YBCU. These extensive surveys have yielded few positive detections and little information about habitat use. Very little is known about the species’ contemporary abundance, habitat use, and range in Western Colorado which is the easternmost portion of the population segment’s range. 

Surveys to determine YBCU presence are conducted using the “call-playback” system—where recorded calls of YBCU are broadcast on a speaker to elicit a call response from the species. These surveys can be intensive and require multiple, trained individuals and have infrequently resulted in the detection of YBCU in the Grand Valley. More passively, Autonomous Recording Units (ARUs) are self-reliant recorders that can be deployed within potentially suitable habitat and passively listen for YBCU calls. After the season, the data from the ARU can be processed to determine YBCU presence. 2025 was the second year of ARU use in the Grand Valley by Colorado Parks and Wildlife and resulted in multiple detections of YBCU while requiring less intensive survey man hours. While progress to build a stronger understanding of YBCU presence in the Grand Valley has been slow, the use of ARUs may reveal a path forward to determine the status of the species and track future potential use alongside habitat improvement projects taking place in the Valley.