Influence of heat exchange on foraging behavior of Zonotrichia spp. Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/bz60cz865

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  • The heat exchange of individuals in a foraging mixed population of Zonotrichia leucophrys and Zonotrichia atricapilla in western Oregon is analyzed with respect to the direction of stance and feeding location. Values for heat gain or loss in the field were generated from a model that estimates the equivalent black-body temperature "Te" and from other researchers' laboratory findings for the effect of air temperature, solar radiation, and wind speed on metabolism. Observations were recorded at 1 min intervals throughout the daylight hours with samples at weekly intervals from January to March. A summation of 1,500 observations on direction of stance subjected to a X² test for randomness supports the hypothesis that spatial orientation of individuals is not random. The largest percentage of time for all locations was spent facing south. All wind speeds over 1.0 m.s⁻¹ recorded were from the south yet X² analysis indicated a large difference in stance direction between sites. Also, maximum differences in Te for different stances with respect to the wind direction were only 1°C because of the low values for incoming short wave radiation. More important factors than heat exchange influencing the direction of stance were feeding patterns, social interactions, food availability and the location of the hedge in the area used for cover. Placing a trace line of food perpendicular to the most frequently observed direction of stance caused a significant change in percentage of time spent facing each direction for that location. Individuals were facing the same direction as the majority of their neighbors within a 2 m radius for 68% of the total number of recorded observations for a nonrandom flock orientation. Heat production was affected by the large differences in wind speed among the microhabitats available at the site. Heavy use of an open area for feeding resulted in as much as an 8% increase in daily existence energy (DEE). The intense feeding at this site suggests that possibly the increased caloric intake per unit time at the open site compensates for the greater heat loss and increased susceptibility, to predation. A second possibility relates the circadian feeding pattern to the need for a high rate of caloric intake early in the morning and late in the evening.
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