Age Determination in California Brown Pelican (Pelecanus occidentalis californicus) Chicks in the Gulf of California

Abstract

A rapid and reliable method to age California Brown Pelican (Pelecanus occidentalis californicus) pre-fledged young based on exposed culmen measurements is presented. In 1997, 1998, and 1999, a total of 52 unknown-age young were marked and recaptured one to three times throughout the nesting season on Isla Piojo, Bahia de Los Angeles, Mexico. From culmen growth increments of these young, we developed an age scale. The linear equation that described the age/culmen relationship was: estimated age (week) = exposed culmen length (cm) x 0.378 – 0.565. The accuracy of the model, as calculated by the k-Fold cross validation method, was 0.149. California Brown Pelican chicks can thus be aged by culmen length measurements. The application of this aging technique allows the mass of chicks to be plotted against their ages to obtain an average body mass growth curve for any sampled cohort of young California Brown Pelicans based on less frequent visits to the colony to minimize the potential effects of disturbance.