A study published today inSciencereveals, for the first time, thatthe black kites ( Milvus migrans ) that place the greatest amount of plastic in their nests are also the ones that best keep their territory safe from intruders, as well as those with the most offspring. Scientists postulate that in this way the owners avoid the intrusion of other younger kites, who seek to steal food or appropriate the area.
The use of decorative waste begins at the birth of the bird andgradually ascends until birds are 10-12 years old, at which point it begins to decrease. In this age group, the black kite “reaches its maximum reproductive success and its greater defense capacity against attacks”, explains Julio Blas, one of those responsible for the research, and a biologist at the Higher Council for Scientific Research (CSIC) . The research has allowed the monitoring of this species in more than 150 nests in the Doñana National Park (Huelva). The results show thatgreater use of decoration is related to higher qualityof the specimen that owns the nest.
This behavior could be compared to “the color codes used on belts in martial arts, which also vary depending on the capabilities of the individual,” says Blas. “The bearer of a white belt would not try to face a black one, both benefit from the use of these codes since the good fighter does not waste his time and the inexperienced does not suffer injuries,” adds the expert.
Researchers have found that the most decorated nests suffer 10% fewer invasive attacks, confirming that the prohibitive meaning of the sign is accepted by the entire community.
You have to show strength
To demonstrate that the kite decorates its nest based on its fighting skills rather than the availability of material, the team artificially increased the decoration of a number of nests. The specimens closest to their physical fullness kept the decoration, while the older and younger ones got rid of it. The level of attacks suffered by raptors that did not reject the waste doubled.
According to Blas, this phenomenon is due to the fact that eThe rest of the community checks the physical capacity of the individual when he changes his signal. A) Yes, “they prevent a weak kite from taking advantage of this signaling and pretending to be a strong one, since the physiological cost of making use of decoration in the nest is very low “, he clarifies. For this reason, the older and younger specimens do not risk going through this test, so they reject the decoration.
The distribution of material has also served to verify that this species feelspredilection for white plastic waste, which were selected 90% of the time. The biologist suggests that this preference is due to “the greater durability of plastic and the high visibility of the target”, which allows it to be detected from very far away and facilitates conflict resolution from a distance.
