Status of the Yellow-billed Cuckoo in Sonora, Mexico

Yellow-billed Cuckoo in upland habitat at Sierra La Madera, Municipality of Huásabas, Sonora (photo courtesy of Gilberto Díaz).

By Alberto Macías-Duarte, Universidad Estatal de Sonora

Yellow-billed Cuckoo’s riparian habitat on the Altar River near Tubutama, in nortwestern Sonora (photo by Alberto Macías-Duarte).

Populations of the Yellow-billed Cuckoo are declining throughout the species range. The continental breeding distribution of the Yellow-billed Cuckoo comprises much of the United States, southeastern Canada, and Mexico, where the species inhabits open woodlands with clearings and low, dense, scrubby vegetation, often associated with water. Population declines and range contractions are more evident west of the Continental Divide, and currently represent a conservation concern that associates to the loss and degradation of riparian habitat. Given that the Continental Divide appears to discriminate not only geographic differences but also subtle morphological and obvious physiological differences, the U.S. Fish and Wildlife Service defined the Western Population Segment of Yellow-billed Cuckoo (Coccyzus americanus occidentalis) as distinct, and listed it as Threatened under the Endangered Species Act in 2014. However, an integral assessment of the population status of the Western Yellow-billed Cuckoo (hereafter cuckoo) must consider the entire species’ range, including Mexico. Abundance and distribution data for cuckoos in Mexico have been generally lacking. Of particular significance for further study are cuckoo populations in Sonora, whose conservation and management could potentially contribute to the recovery of populations in adjacent Arizona.

Yellow-billed Cuckoo’s desert arroyo habitat near La Colorada, in central Sonora (photo by Alberto Macías-Duarte).

To better assess the status of the species’ south of the border, the Universidad Estatal de Sonora and Arizona Game and Fish Department initiated a 5-year monitoring program for cuckoo in Sonora beginning in 2015. Using the same standardized broadcast surveys as in the U.S., the protocol aims to provide consistent estimates of abundance in space and time based on the number of cuckoos detected per route. Starting with the onset of monsoon season in June, we surveyed 13-16 sites throughout Sonora twice annually through mid-August. We surveyed three habitat types including: riparian habitats consisting of forests of cottonwoods, willows, and mesquite trees bordering rivers with permanent or semi-permanent water flow, desert arroyos with large desert trees (mesquites, acacias, and desert ironwoods) along sandy washes with internment flow during summer storms, and upland habitats out of the influence of waterways in mountains. We surveyed 37 unique sites throughout Sonora.

Yellow-billed cuckoo’s upland habitat (mountain oak savannas) in the Municipality of Huásabas, in eastern Sonora (photo by Alberto Macías-Duarte).

During these 5 years of surveys, several patterns of cuckoo abundance became evident. We detected an average of 8.4 cuckoos per transect. We found no trend in cuckoo abundance during 2015-2019, as cuckoo populations seems to be stable. We found that cuckoo counts tend to decline from early July to mid-August in all habitat types. This decline is likely a result of a short breeding season and rapid abandonment of the area for migration to the wintering grounds. We also found that cuckoos occupy a large variety of habitats, and probably can occupy any vegetation type as long as there is sufficient tree ground cover. It is frequently hard to guess the cuckoo abundance by just observing a habitat for the first time. However, aridity and proximity to the coastline seem to restrict the species distribution. The only route with no detections was a desert arroyo site with less than 200 mm of mean annual rainfall and located roughly 36 km from the coastline. Other sites near the coast also had few cuckoos detected. Nevertheless, cuckoos can be relatively abundant out of riparian areas. For example, we recorded our highest count of 22 cuckoos in a semiarid, desert arroyo area with 350 mm of mean annual rainfall. Still, cuckoos are more abundant at riparian habitats, with an average of about 50% more cuckoos than in desert arroyos, and about 40% more cuckoos than in upland habitats.

The continuous loss of riparian forests in Sonora’s rivers due to agriculture and ranching is a significant short- and mid-term threat to the species in this region. Nevertheless, cuckoo inhabiting non-riparian habitats in subtropical Sonora, which occupy a much larger area than riparian habitats, may be an important component of the species’ population dynamics and relevant to the species status. Therefore, it is imperative to investigate the suitability of these non-riparian areas as breeding habitats and their capacity to buffer the continuous loss of habitat riparian habitats in Sonora.