Symmetrisk boplacering i högspänningsstolpar hos vit stork Ciconia ciconia

Abstract

The white stork Ciconia ciconia was found to build 24 nests on high-tension poles located in marshy fields near the city of Coimbra, Portugal. The metal poles consist of a central frame with three platforms, which ramifies into two arms in nearly vertical position. These arms are connected by a large horizontal frame. The nests were only situated on the high-tension poles. The number of nests in a single pole was found to be: 1, 2, 5, 6 or 7. In most cases the nests were located at the extreme ends of the metal frames whether these had a horizontal or a nearly vertical position. When two or more nests were present, a symmetrical pattern emerged in all cases observed, irrespective of the different nest locations. Four factors are considered when interpreting these findings: (1) The shape of the poles, (2) the size of the stork’s wings, (3) the presence of a high magnetic field, and (4) the mental behaviour of the birds. The last aspect seems to be the most probable explanation but it demands further study.