Tail-racket removal increases hematocrit in male Turquoise-browed Motmots (Eumomota superciliosa)
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Graduated avian tails with short outer tail feathers and longer central tail feathers are thought to handicap aerodynamic function. The Turquoise-browed Motmot (Eumomota superciliosa) has a highly graduated tail with a long racket-tip that may impose a substantial aerodynamic cost. Previous research on this species has demonstrated a moderate sexual dimorphism in the tail, and has provided evidence that the racketed tail functions as a sexually selected trait only in males. To explore whether costs are associated with the maintenance of the ornamental male tail, I tested whether tail-racket removal affected hematocrit, a measure of condition and metabolic activity. I removed tail rackets from a manipulated group of males and left the rackets intact among a control group. I then compared change in hematocrit between the two groups over the breeding season. Males with rackets removed experienced a greater increase in hematocrit than did control males. This result suggests that males either experienced an increase in condition after being emancipated from bearing a costly sexually selected ornament, or that a social cost was associated with the loss of an ornament used in communication. This work supports previous research showing that the male tail functions as a sexual signal.
KeywordsAerodynamic costs Hematocrit Tail-plumage Sexual selection Eumomota superciliosa
This research was supported by the National Science Foundation (DDIG-0206584; IRFP-0700953). Steve Emlen, Paul Sherman, Kern Reeve, and David Winkler provided useful comments throughout the study. I am thankful to Chris Egan, Valerie Steen, Erin Macchia, and Jennifer Smith for their help in the field. Bob Montgomerie and anonymous reviewers provided valuable comments on the manuscript. This research was conducted under Cornell University’s Institutional Animal Care and Use Committee protocol 99-23-02.
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