Morphology and Ornamentation in Male Magnificent Frigatebirds: Variation with Age Class and Mating Status

Male magnificent frigatebird (Fregata magnificens) ornamentation includes bright iridescent plumage and a red inflatable gular pouch. These signals are displayed during courtship, along with a drumming sound produced through specialized beak clackings resonating in the gular pouch. The extent of whi...

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Bibliographic Details
Published in:The American naturalist 2007-01, Vol.169 (S1), p.S93-S111
Main Authors: Madsen, Vinni, Dabelsteen, Torben, Osorio, Daniel, Osorno, José Luis
Format: Article
Language:English
Subjects:
Age structure
Aging - physiology
Animals
Charadriiformes - physiology
Colors
Feathers
Feathers - physiology
Female
Iridescence
Male
Male animals
Mating behavior
Optical reflection
Pigments, Biological - physiology
Plumage
Reflectance
Sex Characteristics
Sexual Behavior, Animal - physiology
Skin
Spectral reflectance
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Summary:Male magnificent frigatebird (Fregata magnificens) ornamentation includes bright iridescent plumage and a red inflatable gular pouch. These signals are displayed during courtship, along with a drumming sound produced through specialized beak clackings resonating in the gular pouch. The extent of white in the plumage identifies three age classes of nonjuvenile male. Here we investigate how morphological and secondary sexual traits correlate with age class and mating status. Even though several age class–related differences in morphology and visual appearance can be identified, the only features that significantly predict mating success are acoustic components of courtship display. Specifically, males that mate drum at lower fundamental frequencies—that is, they have larger gular pouches—and have a quicker and more constant drumming cadence than unsuccessful males. The fundamental frequency decreases with age class, reflecting an increase in gular pouch size. This implies that females prefer older or possibly more experienced or viable males. Drumming cadence speed and stability might reflect male stamina. Apart from the acoustic differences with mating status, there is a nonsignificant tendency for back‐feather iridescence to be of shorter reflectance wavelength spectra in mated than in unmated males, which, when combined with acoustic variables, improves prediction of age class and mating status.
ISSN:0003-0147
1537-5323
DOI:10.1086/510096