Dishonest ‘preemptive’ pursuit-deterrent signal? Why the turquoise-browed motmot wags its tail before feeding nestlings

Both sexes of the turquoise-browed motmot, Eumomota superciliosa, display their long-racketed tail in an exaggerated side-to-side wag display in two contexts. In the first, the wag display is performed in the presence of predators (predator-elicited wag display), and evidence supports the hypothesis that the signal functions as a pursuit-deterrent signal (Murphy 2006, Behavioral Ecology, 17, 547–553). In the second, the wag display is performed in the apparent absence of predators immediately before feeding nestlings (prefeeding wag display). I tested four hypotheses on the adaptive significance of the prefeeding wag display: (1) a dishonest, preemptive, pursuit-deterrent signal given in case predators are present; (2) a nonfunctional misfire of the predator-elicited wag display; (3) a signal that alerts nestlings to the delivery of food; (4) a sexually selected signal that advertises parental quality to potential mates. There was no support for the hypotheses that the prefeeding wag display was directed to nestlings or potential mates. The wag display was generally performed where nestlings could not detect the signal and the display did not vary with the sex of the displaying bird, the presence of the mate, or the size of the food carried in the signaller's bill. Evidence presented in this paper is most consistent with the hypothesis that the predator-elicited wag display and the prefeeding wag display are performed as a response to the presence or the potential presence of a predator. I discuss the possibility that the prefeeding wag display functions as a dishonest, pursuit-deterrent signal.