Data was recorded on a wild great tit population breeding near Sagunto (Valencia, eastern Spain). The 110 ha study area was located within a homogeneous orange plantation. Wooden nest-boxes (125 x 117 mm bottom area) were placed each year in February in the same trees at about 50 cm above the ground (the height at which natural holes occur in this habitat). During the breeding seasons, nest-boxes were inspected at least once a week, and nests as frequently as necessary in order to accurately determine the reproductive parameters.
|Exposure duration||continuous for approx. 40 days|
The electromagnetic field exposure significantly increased the clutch size (7%) and the egg volume (3%), implying a 10% increase in clutch volume. This indicates an increase in reproductive investment from parent birds exposed to electromagnetic fields as compared to the control group in the adjacent reference area. These results cannot be attributed to habitat or quality differences of the adults in the exposed group and control group. Nevertheless, no differences in hatching success or final productivity (fledging and reproductive success or nestling body mass) could be detected in exposed animals.
The study indicates that electromagnetic fields generated by power lines can have biological consequences in wild organisms living close to them.