Nesting tricolored blackbird survey: Baja California 2007

Publication Type:

Report

Source:

(2007)

Abstract:

We surveyed 44 potential Tricolored Blackbird nesting sites in Baja California on 23 days from January through August 2007, for a total of 103 site visits. Tricolored Blackbirds were observed at 11 locations south to Rancho El Descanso, but nesting was confirmed (or even suspected) at only one. Single birds were seen in or near the marsh below the dam at Héroes de la Independencia on 30 January and 15 May, 80 birds had formed a colony there by 6 June, and 50 birds on 18 June included adults carrying food into the marsh. At other previously documented nesting sites, birds were observed at Presa Rodriguez, La Misión, and Valle Ojos Negros but none were found at Rancho Tres Posos (northern Sierra Juárez), the Maneadero Plain, or the San Quintín Plain. Maximum counts away from Héroes de la Independencia were recorded in May: 80 at Valle Ojos Negros, 50 at Presa Rodriguez, and 50 at Rancho Japá (northern Sierra Juárez). The region suffered extreme drought conditions throughout the period, depressing prey abundance and consequently reproduction in most terrestrial bird species. Tricolored Blackbird numbers in Baja California appeared to be lower than usual in the fall of 2007 as well.