Researchers from the National Museum of Natural Sciences have carried out a study, which they have just published in Animal Behaviour, in which they have been able to verify how the Canarian houbara increases its reproductive activity during full moon nights.
The Canarian houbara, Chlamydotis undulata fuertaventurae, is a subspecies of the houbara bustard endemic to the Canary Islands. A diurnal bird that lives in arid areas of the easternmost islands, Fuerteventura, Lanzarote and La Graciosa, whose survival is threatened.
Until now, according to the National Museum of Natural Sciences, it was known that these birds were especially active during twilight, but now it has been documented for the first time how the moon stimulates the reproductive behavior of the Canarian houbara.
Transmitters with GPRS mobile communications technology have made it possible to record the activity of the Canarian houbara at night. This work, financed by Red Eléctrica de España, has been supported by the use of GPRS transmitters equipped with accelerometers that record acceleration waves of the marked individual according to the three axes of space, which allowed to identify and quantify for the first time the movements and activities of the marked houbaras during the night, without the need to observe them. The study, which lasted for five months, three in the breeding season (January-March 2019) and two in the non-breeding season (October-November of the same year), was carried out on a sample of 19 males and 12 females.
As detailed, the display of male houbara in the mating season has two components, one visual, the display run in which they show their showy plumage of heat, and another acoustic, a very low frequency sound barely perceptible to the human ear but easily audible to the houbaras at distances of up to 1 km. “Until now it was known that the vocal display of males reaches its maximum intensity during sunrise and sunset. In this study we have discovered that males also vocalize at night and we have detected that the frequency is highest on full moon nights, when they equal the values recorded during twilight”, explains the MNCN researcher and director of the study, Juan Carlos Alonso. “Males vocalize at night because the sound is transmitted better due to the lower wind intensity, the low temperature and the absence of songs from other birds that during the day mix with the vocalizations of the houbaras making them less audible”, he continues.
These sounds also inform the females of the quality of the male that emits them. “The research has allowed us to verify that the acoustic series are longer than the diurnal ones, which suggests that they contain more information. This fact makes us think that the night allows these birds to perfect the communication they exchange during the day”, says MNCN researcher Inmaculada Abril-Colón.
Beyond the communicative improvement offered by the night, the study suggests that the fact that males increase their activity during the full moon may be because the moonlight allows them to detect the approach of predators, counteracting their greater vulnerability while they are displayed and vocalized. In addition, it is pointed out that lunar illumination is sufficient for the male to display his white nuptial plumage in front of the females that approach them, thus facilitating nocturnal copulation, something that was previously unknown in this species. Finally, it is noted that we must not forget that, by taking advantage of the night, males increase the time they have to display each day, thus increasing their chances of attracting females.
The use of transmitters with accelerometer allowed to detect nocturnal exhibition races on two occasions, both on full moon nights, and starring two of the most sexually active males, one of which came to perform precopulatory movements. The frequency of these movements was six times higher than at dawn, the time of day when the houbaras reach the maximum intensity of heat. “This remarkable frequency of nocturnal reproductive behaviors suggests that houbaras can take advantage of full moon nights to copulate, benefiting from the advantage of not being disturbed by neighboring males who at night fail to see those matings, while in broad daylight they could interrupt the courtship”, clarifies Alonso.
Future studies should determine whether this same nocturnal display behavior, and especially in the light of the moon, also occurs in other birds that have traditionally been classified as diurnal.