Morphology and ornamentation in male frigatebirds: variation with age-class and mating status

TY - JOUR

T1 - Morphology and ornamentation in male frigatebirds: variation with age-class and mating status

AU - Madsen, Vinni

AU - Dabelsteen, Torben

AU - Osorio, Daniel

AU - Osorno, José L.

N1 - Keywords: acoustic communication, female mate preference, Fregata magnificens, iridescence, secondary sexual trait expression, structural feather coloration.

PY - 2007

Y1 - 2007

N2 - 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.

AB - 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.

U2 - 10.1086/510096

DO - 10.1086/510096

M3 - Journal article

C2 - 19426094

SN - 0003-0147

VL - 169

SP - 93

EP - 111

JO - American Naturalist

JF - American Naturalist

IS - 1

ER -