and this large area will be virtually impossible to close off to airborne biota. The average body size of many common avian species (5 cm in length) suggests that these animals would have a maximum microwave absorption efficiency of 2.45 GHz and the rate of energy absorption could double or triple due to resonance (1). Molt was chosen as a sensitive indicator of the possible deleterious effects of microwave irradiation on the endocrine and autonomic nervous systems of birds. Molt is a complex mechanism of cyclic (often annual) ecdysis and endysis of feathers. The timing of molt is related to the seasons of breeding and migration: according to Thomson (2), “the cyclical occurrence of molt is determined by intrinsic (physiological) factors in which the thyroid and hypothalmic-pituitary-gonadal systems are principally concerned, activated also by extrinsic (physical) influences. Of the latter, day length appears to be the most important, but temperature also contributes.” Molt is genetically controlled within a given species or larger taxonomic grouping and normally falls into a rigid time frame. Molt begins a fixed number of days after the breeding activity (for adults) or fledging (for juveniles). It usually ends before fat deposition and fall migration or before winter fat deposition in northern non- migratory species (3). A significant interruption or retardation of molt induced by exposure to microwave fields could have a detrimental effect on the bird’s survival. A delay or failure to molt flight feathers (which is triggered to a great extent by day length) could result in an inability of the bird to participate successfully in long migratory flights. Similarly, non-migrant species without a normal molt would be less well equipped to cope with cold weather during northern winters. Another adaptable factor in avian survival is the loss of brightly colored plumage via the adult postnuptial molt which produces a more cryptic non-breeding plumage that is less obvious to predators. Molt, therefore, is a critical factor affecting a bird’s ability to adapt to its environment and thus serves as a sensitive indicator of altered physiology. It is reasonable to postulate that the proposed rectenna configuration would not provide suitable sites for bird’s nests or roosts above or among the active rectenna elements, i.e., in areas subject to field strengths of greater than 1 mW/cm2. These locations would lack shelter from climatic extremes and airborne predators. We expect that nesting or roosting will more likely occur beneath the active elements, or within and among the support and alignment structures and that only birds in flight over the rectenna would be exposed to power densities greater than 1.0 mW/cm2. Unless faced with strong headwinds, birds flying at 30 km/h should not be exposed to power densities greater than 1.0 mW/cm2 for more than 30 min. Therefore, molting house finches (Carpodacus mexicanus) were initially studied to answer the following question; will microwave exposures alter molting of birds that are exposed while nesting in areas immediately adjacent to the proposed rectenna site? METHODS Exposure Facilities and Microwave Generating Equipment The microwave irradiation facilities were designed to provide planwave illumination with a power density variation of ± 0.5 dB maximum over the cages. The radiating source was a Narda #645 standard-gain horn which provided lineraly polarized radiation. It was a precision cast, one-piece unit which shows great uni-
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