Sexual Dimorphism in Brown Pelicans (Pelecanus occidentalis) from Puerto Rico: Biometric Evidence Corroborated by Molecular and Necropsy Techniques

The Brown Pelican (Pelecanus occidentalis) is a protected seabird whose Caribbean populations face conservation challenges despite broader regional recovery. In the Puerto Rico Archipelago, historical declines were driven by habitat loss, food scarcity, and other human pressures. Currently, sex identification requires genetic testing, as the species lacks obvious sexual dimorphism. We evaluated whether morphometric measurements could provide a noninvasive alternative. Seventy-seven rescued pelicans were sampled across Puerto Rico. Biometric data included weight, wing chord, tarsus length, culmen length, and culmen width, with sex confirmed by genetic or necropsy analysis. Males had significantly longer wing chords, tarsi, and culmens than females (P < 0.05), while culmen width and weight did not differ. Culmen length emerged as the most reliable variable for distinguishing sex. With training and experience, culmen length may provide a preliminary field cue for sex estimation, although validation is required. This study presents the first evidence of morphometric sexual dimorphism in Brown Pelicans from Puerto Rico. Field-based biometric sexing, particularly culmen length, may reduce reliance on invasive methods in rehabilitation and demographic studies. Future research should test broader populations and other pelican species. These approaches can strengthen conservation outcomes for this sentinel of coastal health.