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1 October 2013 Sex Determination and Sexual Size Dimorphism in the Red-billed Tropicbird (Phaethon aethereus) and White-tailed Tropicbird (P. lepturus)
Guilherme Tavares Nunes, Gustavo Da Rosa Leal, Cynthia Campolina, Thales Renato Ochotorena De Freitas, Márcio Amorim Efe, Leandro Bugoni
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Abstract

Tropicbirds (order Phaethontiformes) are a well-studied seabird taxon, but there have been no published studies on sexual size dimorphism. Here, we investigated sexual size dimorphism in the Red-billed Tropicbird (Phaethon aethereus) and the White-tailed Tropicbird (P. lepturus), and evaluated the applicability of using morphometrics and discriminant functions to sex birds in the field. We sampled Red-billed Tropicbirds (n = 160) and White-tailed Tropicbirds (n = 57) in the Atlantic Ocean off the coast of Brazil. Each individual had seven morphometric traits measured and blood sampled for molecular sex determination. Discriminant functions were generated using generalized linear models (GLM). Red-billed Tropicbirds had significant male-biased intersexual differences in bill length, wing chord, nostril-to-bill-tip, and head-plus-bill, and the best GLM included bill length and wing chord. White-tailed Tropicbirds were characterized by significant intersexual differences for wing chord, with females larger than males, and the best GLM for this species included wing chord, bill width, and bill depth. Discriminant functions had accuracy similar to those used for other seabird species with similar body sizes.

Guilherme Tavares Nunes, Gustavo Da Rosa Leal, Cynthia Campolina, Thales Renato Ochotorena De Freitas, Márcio Amorim Efe, and Leandro Bugoni "Sex Determination and Sexual Size Dimorphism in the Red-billed Tropicbird (Phaethon aethereus) and White-tailed Tropicbird (P. lepturus)," Waterbirds 36(3), 348-352, (1 October 2013). https://doi.org/10.1675/063.036.0312
Received: 16 January 2013; Accepted: 1 February 2013; Published: 1 October 2013
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