Five replicates of this irradiation chamber were built. Three chambers were operated at 0.1, 1.0 and 10.0 mW/cm2, respectively, from one Cober S6F generator, using topwall couplers of 20 dB and 10 dB for the horn feeds to the first two chambers and a direct waveguide feed to the horn in the third chamber. The two remaining irradiation chambers were energized by a dedicated Cober S6F generator. One of these operated at 25 or 50 mW/cm2 for subchronic exposure studies while the other was used in studies involving acute exposures in conjunction with a wind tunnel. Molt in House Finches Following its introduction to the Northeastern United States in 1940 (5), the house finch has become a year-round resident. The adult prebasic molt is complete and typical of resident passerines (6). In southeastern Massachusetts, the resident, non-migrant house finches have one complete molt between the end of June and December. Adult birds with worn plumage and brood patches (females) or cloacal protruberances (males) were trapped before the onset of prebasic molt with the exception of five birds which had just started to molt. Trapping sites were Chatham, Plymouth, and Rockport, Massachusetts. Individually numbered plastic legbands were applied to each bird. The finches were housed in rectangular microwave transparent cages 1 x 1 x 0.5 m that were divided into four separate cells, each containing one or two birds. Cages were placed in either microwave exposure chambers or in control chambers. Initial experiments concentrated on differentiating responses between the control and 10 mW/cm2 exposure groups in order to provide data of highest relevance to the SPS system. The sample sizes of birds could not be increased beyond ten animals because most of the space in the chamber was already committed to other experiments. These reasons and our inability to obtain adequate numbers of birds at the critical time (before onset of molt) precluded conducting experiments at 0.1 mW/cm2 and reduced the number of birds available for exposure to levels of 1 mW/cm2. We proposed initially to expose representative numbers of birds to 25 mW/cm2 until two problems were encountered. Firstly, there was a delay in completion of the 25 mW/cm2 chamber. Waiting until the chamber was completed would have meant missing the first week or two of molt at the end of June and early July. Secondly, in early July, house finches placed in a nonfunctioning exposure chamber exhibited gaping behavior from hypothermia within an hour when ambient temperatures were greater than 30°C. Additionally, there was small likelihood of birds being exposed to 25 mW/cm2 on a continuous basis at a rectenna site. For these reasons, we chose to use 10 mW/cm2 exposures for the major sample and delayed the 25 mW/cm2 exposures until later in the season (4 September) when ambient temperatures are lower. At this time, two birds that had already started molting were included in the 25 mW/cm2 experiment. The birds were exposed continuously, except for times of cage maintenance, e.g., cleaning, feeding, water replacement, for a period ranging between 110 and 150 days. Artificial lighting was controlled to simulate day length. A balanced diet of water, seeds, fresh fruit, vegetables and mealworms was given daily, perches were provided and cages were cleaned daily. The ambient or room temperature where the controls were kept typically ranged between 21 and 32 °C during a mid-summer day in 1980, between 20 and 24°C during the fall, and was held at 10°C during November and December. All birds acclimated satisfactorily and, with one exception, survived to completion of the experiment.
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