From the Antillean Crested Hummingbird, through the Blond-crested Woodpecker, and on to the Crested Goshawk, there really do seem to be a lot of birds with feathery crests. In most cases, the bird can choose to lay its crest back, or erect it to best effect. It is fair to assume that birds use their crests as part of a display, but who is the intended recipient of the signal?
Spanish researchers Magdalena Ruiz-Rodríguez, Manuel Martín-Vivaldi, and Jesús Avilés of the Estación Experimental de Zonas Aridas and the Universidad de Granada investigated the use of crest displays by the Eurasian Hoopoe. Beautiful enough when resting quietly, these birds reveal starling black and white banding across the wings, back and tail in flight. When they get excited, both males and females show off their crest composed of long cinnamon/orange-coloured feathers with large black spots. Who are Eurasian Hoopoes showing off to?
Using male Eurasian Hoopoes, born in captivity, Ruiz-Rodríguez and her colleagues documented the displaying of crests when exposed to the playback of four sounds. The first sound was the singing of another male hoopoe, which might represent a rival. The second was a human voice, which could be perceived as a potential predator. As controls, the male hoopoes also heard the playback of background noise, and a blackbird, neither of which represent a threat.
The researchers found that the test subjects were significantly more likely to erect their crests when they heard playback of human voices (60% of trials), and in response to the playback of hoopoe songs (65% of trials), than they were to either of the control sounds (about 20% of trials).
It seems clear that the hoopoe display involving raising of crest feathers is directed at members of its own species, but also in response to potential predators. In terms of response to the playback of songs of its own species, males may perceive other males as rivals in the competition for mates. “The most probably target of the crest display in this situation,” wrote the researchers, “was the rival male.”
The behavioural response by the test hoopoes to the sounds of human voices has at least two possible interpretations. By erecting its crown, a hoopoe may be signaling to the potential predator, indicating that it has already been detected, and so the likelihood of a successful attack is small. Furthermore, hoopoes are thought to be unpalatable, presumably because of chemical secretions of their preen gland. Raptors are known to avoid Eurasian Hoopoes, and by erecting its crest a hoopoe may be making its identity very clear. Alternatively, the display utilizing an erect crown may not be directed at the potential predator per se, but rather at other nearby hoopoes. The display may be a way of saying: “Have you noticed that predator yet?”
In the animal kingdom, signals tend to be very specific. There are not many examples of individuals using a single display in two entirely different contexts. The dual-functionality of the crest display of Eurasian Hoopoes may lead ornithologists to look for more cases.
Ruiz-Rodríguez, M., M. Martín-Vivaldi and J. M. Avilés. 2017. Multi-function crest display in hoopoes Upupa epops. Journal of Avian Biology 48:1425-1431.
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