Dynamic occupancy models reveal Black-billed and Yellow-billed Cuckoos have high rates of turnover during the breeding season

Abstract

Abstract Understanding the conservation needs of rare and hard-to-detect species becomes even more difficult when a species is highly mobile. Black-billed Cuckoos (Coccyzus erythropthalmus) and Yellow-billed Cuckoos (Coccyzus americanus) have experienced extensive range-wide population declines over the last several decades. Low detection probability has made it hard to determine causes of declines and resulted in poorly supported population and trend estimates. However, given evidence that cuckoos make wide-ranging movements during the breeding season, it may be necessary to address issues of both low vocalization rate and availability for detection to better understand these cryptic species. We performed passive and call-broadcast surveys for cuckoos at 41 sites across northern Illinois in 2019 and 2020. We examined the influence of call broadcast and temporal and environmental covariates on detection probability and how habitat covariates affected occupancy, immigration, and emigration both within and among sites. Individual detection probability increased substantially using call broadcasts (12 and 6 times for Black-billed and Yellow-billed Cuckoos, respectively) and detection increased with temperature. Black-billed Cuckoo detection probability also varied temporally, being lowest in the middle of the breeding season. We found strong support for turnover within sites during the breeding season, indicating maintenance of large home ranges, as well as among sites (average emigration probability of 86% and 47% for Black-billed and Yellow-billed Cuckoos, respectively). Black-billed Cuckoos were more likely to use open, shrubby sites and Yellow-billed Cuckoos to use sites with older successional habitat. While turnover rate was affected by habitat covariates, these species’ reliance on ephemeral insect abundance may ultimately be driving occupancy dynamics. Our results suggest that broadcasts are essential for effectively monitoring these cuckoos, but also imply the need to move towards coordinating management at broader spatial scales for these highly mobile species.