The period of 22 December 1956 until 9 January 1957 was spent in Costa Rica observing winter behavior of warblers. Although myrtle, black throated green, and blackburnian warblers in clude Costa Rica in their winter range (Skutch,in Bent 1953, and pers. comm.), only black throated green of the five were found during the author's study. However, many other species of warbler were present, and detailed notes were
taken on them for comparison with summer behavior. Measurements of interval between flights were made for each species. These should be comparable with those made in other seasons. No strictly comparable measurement of feeding position could be made, however. In view of the great variety of tree heights in tropical forests, measurements of feeding height could not reasonably be made in terms of distance from the top of the tree.Instead, height above the ground was used, usually gauged by eye and occasionally checked by camera viewfinder. Zones such as base, middle,and tip of branch were not reasonable, but general reference to large limbs or leaves could be made. The actual behavior while gathering food is probably comparable with other seasons; it is
fairly subjective, however, so that the comparison should be confirmed by the various other measurements. A general comparison of winter and summer behavior of warblers wintering in Costa Rica will be given first; this will be followed by a more detailed analysis of two species.