RESULTS For each power density and behavioral variable an analysis of variance (ANOVA) was computed to determine if there were any significant differences in foraging behavior among pre-exposure, exposure and post-exposure periods. The only significant difference found (ANOVA; p < 0.05) was in profitability for parallel sham control (0.0 mW/cm2; Table 1; p < 0.01). Mean profitability was significantly lower during the pre-exposure period (Duncan’s Multiple Range Test; p < 0.05). For each exposure period and foraging behavior variable ANOVAs were computed to determine if there were any significant differences among power densities within treatment periods. The only significant differences (ANOVAs p < 0.05) were (1) during the exposure period birds that were exposed to power densities of 0.1 and 1.0 mW/cm2 ate a significantly higher number of prey than those birds exposed to a power density of 10 mW/cm2 (Duncan's Multiple Range Test; p < 0.05; Table 1; 8.2 versus 3.8 prey eaten); and (2) birds which had been exposed to a power density of 10 mW/cm2 had significantly (p < 0.05) less ‘search time’ than birds which had been exposed to power densities of 0.1 mW/cm2 (Duncan’s Multiple Range Test; p < 0.05; Table 1; 67 versus 141 sec). No other significant differences in behavior were found. ANOVAs on environmental variables (Table 2) yielded only one significant value. Chamber temperatures varied significantly among periods for birds exposed to power densities of 25.0 mW/cm2 (p < 0.05). Chamber temperatures were significantly higher during the exposure period than during the pre-exposure or postexposure periods (Duncan’s Multiple Range Test; p < 0.05). No other significant differences in temperature or humidity were found. DISCUSSION A number of studies have demonstrated the effect of environmental variables on avian daily and seasonal foraging habits. For instance, ambient humidity greatly affects the thermoregulatory performance of small birds exposed to heat stress, and high humidities can be lethal at temperatures that species could tolerate under more moderate humidity conditions (7). Birds confined where humidity was high (35-40%) could not tolerate temperatures above 42°C, but birds kept at a relative humidity of 20% tolerated higher ambient temperatures (8). Many avian species at photoperiods of 10-12 hr feed most actively during the morning, slightly reduced rates during mid-day and declining rates in late afternoon. These feeding rates correlate with increasing temperatures. Feeding sessions occur during the evening when the temperature is lower (9). In addition, most birds exposed to heat stress become hyperthermic and may minimize metabolic heat production by reduced activity (7). Personal observations during these experiments at power densities of 0.1 mW/cm2 and above during August confirmed that at high temperatures and humidity the birds had reduced activity levels. Exposure to low-level microwave radiation has been shown to affect behavior in some animals (e.g., 10, 11, 12, 13, 14. 15, 16, 17). Foraging behavior of White- throated Sparrows, however, was not affected by seven days of exposure to microwaves at power densities of 0.1, 1.0, 10, or 25 mW/cm2 at the reported temperatures and humidities. The significant differences in foraging behaviors among power densities were probably caused by individual variation among birds. No dose response
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