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If we look at a white-browed, male or female sparrow weaver, when he starts his melody we will see that one of his companions is immediately incorporated to sing a duet together. They make them in perfect tune. A team led by researchers from the Max Planck Institute for Ornithology in Seewiesen (Germany) wanted to study this phenomenon and used mobile transmitters to simultaneously record neuronal and acoustic signals from pairs of bird duets in their natural habitat. They found that the activity of nerve cells in the brain of the bird that sings changes to synchronize with its partner when it begins its singing.
They form a perfect and almost exclusive duo
The brains of both animals function as one, achieving a perfect duo. White-browed sparrow weavers (Plocepasser mahali) live together in small groups in trees in southern and eastern Africa. Each bird has a resting nest with an entrance and an exit. The dominant couple will have a breeding nest that is easily recognizable by the fact that a passage is closed to prevent the eggs from falling. In addition to the dominant couple, there are eight other birds in the group that help build nests and raise the young. All members of the group defend their territory against rival groups through duets of the dominant couple and the choirs of the rest.
They are one of the few species of birds that sing in duet. The scientists suspected that they would require some cognitive coordination between individuals to synchronize, however, neural mechanisms were unknown. “White-browed sparrows cannot develop their complex social structure in the laboratory. Therefore, we could only investigate the mechanisms of the duo singing in their natural habitat,” says Cornelia Voigt, one of the three main authors of the study. For this, the Max Planck Institute team developed mobile microphone transmitters to record the song in nature. Its light weight, only 0.6 grams, allowed it to be attached to the bird as a backpack.
Another novel transmitter, of barely one gram, was able to make a synchronous record of brain activity in birds while singing in their natural environment. The antenna placed near the bird tree recorded up to eight of these signals in parallel. With the help of an external sound card and a laptop, the singing and brain signals were recorded synchronously with an accuracy of thousandths of seconds.
The researchers recorded almost 650 duets. The most complicated thing was to achieve a technology capable of withstanding the extreme conditions of Kalahari Savannah in northern South Africa, according to Susanne Hoffmann, a scientist and co-author of the study. Lisa Trost, also a scientist in the department, provides another detail: “Fortunately, the procedure to fix the implants on the bird heads did not last long and they were quickly returned to the group. All the birds sang in the tree immediately after their return.”