Foraging characteristics of breeding Common Yellowthroats (Geothlypist ichassinuosa) on the central California coast varied between early morning and midday periods, among periods within the nesting season, and between sexes. From early morning to midday, yellowthroats increased their use of vegetation at heights below 1 m and above 3 m, but reduced their use of vegetation at heights of 2-3 m. A midseason increase in the use of vegetation at heights above 3 m occurred after 3 May. Male yellowthroats foraged at significantly greater heights, on average, were more likely to choose flycatching over other maneuvers, and were possibly better adapted, morphologically and behaviorally, to exploit spatiotemporal changes in prey abundance than were females. Singing males occurred at greater heights, on average, than either foraging males or females, but did not differ from foraging birds in their use of substrates or plant species. We evaluated the use of plant species for foraging in comparison with availability within 10 m of foraging individuals and over the entire study area, and found significant diurnal and intraseasonal patterns of selection. Common Yellowthroats actively selected arroyo willow (Salk Zasiolepis) at both spatial scales of availability during all diurnal and seasonal periods. Use of foraging maneuvers varied intraseasonally but was independent of diurnal period. We found no significant interaction between diurnal and intraseasonal patterns of foraging. Our results suggested that Common Yellowthroats alter their foraging behavior in response to changes in foraging conditions associated with diurnal and intraseasonal dynamics of freshwater marsh ecosystems. Pooling of foraging data over diurnal or intraseasonal periods, or between sexes, may mask significant differences that are important in understanding foraging characteristics.
Kelly, J. P., and C. Wood. 1996. Diurnal, intraseasonal, and intersexual variation in foraging behavior of the Common Yellowthroat. Condor 98: 491-500.