Two groups of kestrels were housed under control and exposure conditions throughout the breeding season in the years 1995 and 1996. Exposure began immediatly after kestrels were paired and lasted for 95 days in 1995 and 91 days in 1996, or one week after the last nestling fledged. Altogether 12 female nestlings (6 control, 6 exposure) and 15 male nestlings (6 control, 9 exposure) were studied.The applied electromagnetic fields were equivalent to those experienced by wild kestrels when nesting within 40 m of a 735 kV transmission line running at peak capacity.
growth: body mass; tarsus and antebrachium length (when birds were 21, 27, 36 days old); start of feather growth, growth rate, length of the ninth primary and central rectrix feathers (when birds were 27 and 36 days old)
Electromagnetic fieldexposure affected the growth of female and male kestrel nestlings. Exposed female and male nestlings (when 21 days old) and fledglings (when 27 and 36 days old) were havier and had longer tarsi than female and male control nestlings and fledglings. The period of maximal weight gain began on average 1.1 days later in exposed males than in control males. Although maximal growth of the antebrachia began also on average 1.1 days later in exposed males than control males, antebrachial lengths and growth rates were similar between exposed and control nestlings. The periods of maximal weight gain, growth of tarsi and antebrachia began earlier for control males (after 7.1 days) than control females (after 8.4 days), but not for exposed males (after 8.1 days) compared to exposed females (after 8.2 days). The growth of the ninth primaries and central rectrices of nestlings were unaffected by exposure. Under exposure the periods of maximal weight gain and bonegrowth did not occur earlier in males than females as it did in the controls.