Buchholz, Richard. (1989) Singing Behavior and Ornamentation in the Yellow-Knobbed Curassow (Crax daubentoni)
Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfilment of the
Requirements for the Degree of Master of Science
SINGING BEHAVIOR AND ORNAMENTATION
IN THE YELLOW-KNOBBED CURASSOW
Chairman: H. Jane Brockmann
Major Department: Zoology
The selective pressures maintaining the puzzling range of sexual dimorphism among the Crax curassows are unknown. My objective was to describe the reproductive behavior of the Yellow-Knobbed Curassow, one of the most sexually dimorphic species, and determine the adaptive significance of male singing behavior and sexual dimorphism in this endangered avian family. I review the ecological and morphological evidence for mating systems in curassows of our genera, and conclude that C. daubentoni may be polygynous.
A study of the singing behavior of this species in the Venezuelan Llanos showed that males sing regularly from mid-April through July, at traditional singing at the forest edge. The singing display consists of three primary action patterns: a long descending whistle, a low frequency “boom,” and wing-flapping. Recorded the singing bout duration, whistle length and frequency, interwhistle interval, boom frequency, wingflap frequency and wingflap number of ten individually identified male Yellow-Knobbed Curassows is most similar to song-types that serve an intrasexual fuction in passerines. Males sang significantly longer when other males were nearby, and wingflapped less intensely when in the presence of females. Females visitation rate, not associated with any of the display variables, is negatively correlated with male whistle frequency. Males were attracted to playbacks of whistle song in their singing areas, suggesting that the “descending whistle display” of this species has an intrasexual function.
Only the singing males on the study site had large, fleshy facial ornaments. Sexual selection theory suggests that extravagant structures sush as these may signal the heritable fitness of male. A study of the correlates of ornament size of 15 captive males of known age and history revealed a significant correlation between knob height and wattle thickness with age. No blood parasites were found despite frequent reports in the literature of hematozoa in this family. Coccidian oocysts in the feces of 5 of 12 males examined had no significant association with ornament size, wing chord or tarsus length. A male’s age demonstrates his ability to survive disease, find food, and compete with conspecifics, and thus should be a criterion of mate choice in long-lived species such as the Yellow-Knobbed Curassow.