Status of marsh birds in the wetlands of the Colorado River delta, México

Abstract

Populations of secretive marsh birds (Rallidae and Ardeidae) have declined in North America in the last decades. Despite drastic habitat changes, the Colorado River delta supports four species of protected marsh birds: California Black Rail, Virginia Rail, Least Bittern and Yuma Clapper Rail. Our goal was to assess the status (2010–2011) and detect population changes (1999–2011) of marsh birds in the Colorado River delta. This effort was focused on the Cienega de Santa Clara and the recent disturbance events that occurred in this wetland (changes in inflows, dredging and wildfires), but included other areas of the delta as well. The Cienega provides critical habitat for the four species, with estimated abundance of 405 California Black Rails, 7152 Virginia Rails, 8652 Least Bitterns and 8642 Yuma Clapper Rails. Populations of these species have remained stable since 1999, with no significant trend, although with some fluctuations in some years. Other wetlands in the delta also provide important habitat, especially El Doctor Wetlands for California Black Rails and Virginia Rails, the Hardy and Colorado rivers for Yuma Clapper Rails and Least Bitterns, and Laguna del Indio for Yuma Clapper Rails. The detections of marsh birds in 2011 were amongst the highest since the monitoring program began in 1999. This was probably linked to the disturbance regime that was recreated with a series of events in the Cienega, including the dredging of sediment, variations of inflows, and an extensive wildfire. Wetlands in the Colorado River delta support the majority of breeding Yuma clapper rails and important populations of other marsh birds. As these are shared species by México and the U.S., the conservation and restoration of the delta should be a shared responsibility.