Together with the Lesser Kestrel (Falco naumanni), the Black Kite (Milvus migrans) is Extremadura's commonest diurnal raptor. The only count ever conducted, back in 2005, threw up an estimate of 3000 pairs in the region, the lion's share in the province of Cáceres (1600-2.000 pairs) and the rest in Badajoz. To this figure must be added about 4700 non-breeding birds and the young that fly each year. There are therefore many Black Kite nests in Extremadura. These birds have a well-known habit of bringing the most varied range of trinkets to add to the nesting material, both natural (fish bones, eggshells) and artificial (pieces of plastic and metal). Up to now no one has come up with an explanation for this behaviour. But now a team of researchers from Doñana Biological Station (Higher Board of Scientific Research: CSIC in Spanish initials) have provided the answer in an article published in the prestigious review Science. They do so to show off their physical prowess. Birds in their physical prime (10-12 years of age) adorn their nests more than the younger, less expert birds or the older birds. This warns off their neighbours and avoids many physical conflicts, rather like the coloured belt system in martial arts. No one tackles a black belt. When more objects were experimentally added to the nests, the mature birds kept them but the younger and older birds got rid of them to avoid giving a show of more physical strength than they actually possessed. Another curiosity is their preference for white plastic as adornment, found in 90% of the nests. The study is based on fieldwork in Doñana involving over 150 nests of ringed Black Kites with known ages.
Photo. From left to right: nest of a 3-year old Black Kite, nest of an 11-year old bird and nest of a 22-year old bird. Photographs: F. Sergio, published on the CSIC website.- Sergio, F.; J. Blas; G. Blanco; A. Tanferna; L. López; J. A. Lemus; F. Hiraldo (2011). Raptor nest decorations are a reliable threat against conspecifics. Science 331: 327-330 [abstract].
- Palomino, D. 2006. El milano negro en España. I censo nacional (2005). SEO/BirdLife. Madrid. [PDF]
