Download How good are morphological and behavioral indicators in sex

POSTER ABSTRACT
How good are morphological and behavioral indicators in sex determination of
Galápagos and Magellanic penguins?
Caroline D. Cappello1, P. Dee Boersma1,2,3
1
University of Washington, Department of Biology, 2Global Penguin Society, 3Wildlife Conservation Society
Sex determination is essential to many studies of ecology and behavior and can influence conservation
actions. Several techniques have been used to determine the sex of birds with low sexual dimorphism, but
reliable methods are often time consuming or invasive. Numerous studies have evaluated the usefulness of
morphological measurements as quick and minimally invasive means of sexing penguins in the field. Studies
of Magellanic, Humboldt, and African penguins have shown bill depth to be a useful indicator of sex, but
few have included behavioral variables or within-pair comparisons of morphology in their analyses.
Combining morphometric and behavioral indicators may increase accuracy and flexibility in sexing
penguins. Using Galápagos and Magellanic penguins, we aimed to identify sexing methods that were
accurate, reduced intrusiveness and researcher effort, and increased methodological flexibility. We used a
classification tree (CART) analysis to determine the accuracy of sexing Galápagos and Magellanic penguins
using four morphological measurements: bill depth, bill length, flipper length, and foot length. For
Magellanic penguins, we included a within-pair comparison of bill depth and observations of two breeding
behaviors: 1) which member of a pair settled the nest at the beginning of the season and 2) which member
of a pair took the first long incubation stint. We used birds sexed through genetic analysis, cloacal
examination, and dissection as our known-sex sample. Bill depth was the best splitting variable in
Galápagos penguins, correctly classifying the sex of 95% of study penguins. For Magellanic penguins,
within-pair bill-depth comparison, nest settlement, bill depth, and first incubation were the strongest
indicators, correctly classifying the sex of 100%, 99%, 98%, and 98% of study penguins, respectively. These
results suggest that penguins may be effectively sexed with minimally invasive procedures and that
researchers have flexibility in their methodology. Though the discriminating threshold of morphological
measurements may differ between colonies, behavioral indicators, within-pair comparisons of morphology,
and the relative importance of each variable should be useful species wide.
9th International Penguin Congress, Cape Town, South Africa, 5th – 9th September 2016