Dutch biologist Paula den Hartog has shown that bastard doves can fend for themselves. Despite having a strange coo, hybrid offspring are still able to defend their territory.
How species are formed and remain separate are crucial questions in evolutionary biology. The offspring of crosses between different animal species are often infertile or die when still in the womb. A mule, for example, cannot reproduce. Sheep-goat hybrids are usually stillborn. Such hybrids can also be dysfunctional, for example, because the sounds they make are a mixture of sounds from both parent species.
hybrid dove, Uganda (Photo: Paula den Hartog)
By coincidence, biologists discovered the existence of a hybrid dove alongside the Ring-necked Dove and the Vinaceous Dove, the two species studied by Den Hartog, in a region of Uganda. The DNA of the hybrid dove has genes from both parental species. In order to mate, a male dove coos to defend his territory and attract females. The coos of the Ring-necked Dove and the Vinaceous Dove are different and the hybrids have their own coo as well. Remarkably, the hybrid offspring are able to thrive and reproduce. Although the hybrid doves make a different sound to their parents, this sound is still functional.
Den Hartog investigated the role of cooing in the process of species formation and hybridisation. She wanted to do this by determining the degree to which male doves of different species react to the coos of their own species, to those of the other species and to the coos of the hybrids. To this end she recorded the coos of the different species of males (for examples see fragments below) and subsequently played these recordings in the wild.
The researcher placed loudspeakers in the territory of a male dove to measure the response of the dove to other doves' coos. On hearing a male from his own species cooing in his territory, a male dove will usually approach the intruder and attempt to chase him away, cooing as he does so. This sometimes leads to fights. The male does this to defend his territory; a male dove cannot reproduce unless he has his own territory. However, a male dove can only chase off intruders from his territory if the intruders can 'understand' his coo and recognise the threatening message. Conversely, the male dove must also be able to recognise the intruders' coos to understand that they are possible rivals. A strange coo can therefore hinder a successful sex life.
As soon as the male doves in the study recognised a coo and noticed the loudspeakers, they started an attack. They recognised the coo as being the call of a rival.
Listen to some examples: