Worldwide Species Action Plans
In western North America, yellow-billed cuckoos (Coccyzus americanus) have undergone catastrophic declines, the eastern subspecies has undergone less rapid declines in most areas since approximately 1980. Direct loss and degradation of low-elevation riparian woodland habitats have been cited as the primary causes for the declines in yellow-billed cuckoos in the western portion of the range. Factors contributing to habitat loss and degradation include alteration of flow schemes in rivers and streams, diversion of water for agricultural and municipal purposes, urban expansion, livestock grazing, which affects understory vegetation and cottonwood/willow recruitment, and pesticide applications which decrease local food supplies and potentially induce toxic accumulations in cuckoos. In the east, the reasons for the now widespread declines are less clear. One potential factor contributing to declines across this species range in North America is the loss of forested habitat on its wintering grounds in South America. However, little is known of its ecology or distribution in South America, and this remains an area in need of further research. While it is clear that western populations of yellow-billed cuckoos have undergone drastic declines in both range and abundance, it is important to note that cuckoos are also declining significantly in the east (from the Great Plains eastward), and that this decline has gone largely unnoticed by most regulatory agencies and conservation organizations (e.g., Partners In Flight). This may partly be explained by the fact that cuckoos are still relatively common in many forested habitats in the east, and thus they have not yet registered as a species of concern. However, given the significant recent declines even in the core of their range (e.g., Oklahoma and Kansas), research into the causes of these declines should be initiated while the species is still tractable. Many populations in the west are now so small and isolated that gaining insight into population declines there will be extremely difficult. The identification of the factor(s) contributing to declines in yellow-billed cuckoos on the Great Plains would be a key piece of information in helping to develop a regional management plan.