Field Sexing Olrog's Gull (Larus atlanticus) Using Morphometry

PABLO F. PETRACCI; BURGOS J.; LOPEZ GC; DELHEY, J.K.V.; CARRIZO M; SARRIA R; SOTELO M.; SOMOZA GM; LA SALA L.F.

WATERBIRDS (DE LEON SPRINGS, FLA.)

WATERBIRD SOC

Año: 2018

1524-4695

Orog?s Gull (Larus atlanticus) is a vulnerable species; however, no study had addressed the relationship between body measurements and sex. To provide an easy and reliable work tool to identify the sex of individuals, adult Olrog?s Gulls (n = 111) were weighed, several measurements were taken, and the sex determined using DNA analyses. All measurements showed significant differences between sexes, with males being significantly larger (Range: 4-15.1%) in all measurements. Logistic regression models were selected using the Akaike information criterion and were validated using leave-one-out cross validation. The best set included three models. Model 1 (AIC = 25.0) included head-bill length, bill depth, wing length and body mass as independent variables, and was closely followed (AIC = 25.5) by model 2, which contained the same variables with the exception of wing length. Model 3 (AIC = 26.4) included head-bill, body mass and wing length as independent variables. Model 1 was 1.3 and 2.1 times more likely to be the best model than models 2 and 3, respectively. Model 1 correctly assigned the sex in 94.6% of all birds and 93.4% of females. Model 2 performance was marginally better and correctly assigned the sex in 95.5% of all birds and 95.1% of females. The correct classification of males was 96.0% in both models. Results demonstrate the validity of these measurements, which can be easily taken in the field to reliably determine the sex of Olrog?s Gulls.