I provide a detailed description of an arthropod sampling technique, “branch clipping,” and evaluate its efficacy in measuring food availability for three foliage-gleaning migratory warbler species wintering in Jamaica. I incorporated foraging observations into the sampling protocol to facilitate a match between the distribution of branch-clip samples and the distribution of warbler foraging attacks over available microhabitats. Where the match was imprecise, I weighted branch clip samples accordingly. Foraging observations indicated that most foraging maneuvers used by the warblers were directed at prey located on foliage, which are likely to be well sampled by branch clipping. Published diet analyses permitted the elimination of prey taxa and sizes that were not eaten by the warblers, and suggested that nearly all of the items eaten were captured by branch clipping. Habitat-specific warbler attack rates, which can be used as independent evaluations of food availability measurements, closely matched prey density as estimated by branch clips across three habitat types (citrus orchard, coffee plantation, and dry limestone forest). These data suggest that branch clipping effectively measured food availability for foliage-gleaning warblers in Jamaica. The method is probably also well suited for other foliage-gleaning species, particularly in habitats and seasons in which birds feed largely on prey residing on or flying near leaf surfaces. Branch clipping is probably ill suited for species that feed heavily on either large, fast flying insects (e.g., Odonata), or on large masses of flies (e.g., Chironomidae) that seldom land on forest foliage.
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Vol. 71 • No. 1