Effects of electromagnetic fields on photophasic circulating melatonin levels in American kestrels

Birds reproduce within electromagnetic fields (EMFs) from transmission line s. Melatonin influences physiologic and behavioral processes that are criti cal to survival, and melatonin has been equivocally suppressed by EMFs in m ammalian species. We examined whether EMFs affect photophasic plasma melato nin in reproducing adult and fledgling American kestrels (Falco sparverius) , and whether melatonin was correlated with body mass to explain previously reported results. Captive kestrel pairs were bred under control or EMF con ditions for one (short-term) or two (long-term) breeding seasons. EMF expos ure had an overall effect on plasma melatonin in male kestrels, with plasma levels suppressed at 42 days and elevated at 70 days of EMF exposure. The similarity in melatonin levels between EMF males at 42 days and controls at 70 days suggests a seasonal phase-shift of the melatonin profile caused by EMF exposure. Melatonin was also suppressed in long-term fledglings, but n ot in short-term fledglings or adult females. Melatonin levels in adult mal es were higher than in adult females, possibly explaining the sexually dimo rphic response to EMFs. Melatonin and body mass were not associated in Amer ican kestrels. It is likely that the results are relevant to wild raptors n esting within EMFs.