Micrometeorological data were collected during the winter of 1974 in an active blackbird (starlings [Sturnus vulgaris] and several species of icterids [e.g., Agelaius phoeniceus, Quiscalus quiscula, Molothrus ater]) roost in a pine (Pinus spp.) plantation at Fort Campbell, Kentucky [USA], in a nearby area of similar cover where blackbirds were not roosting, in an adjoining area of thinned roosting habitat and in adjacent clearings. The root area provided almost complete protection from direct wind and, when winds were light, slowed the rate of nocturnal temperature decrease so that the roost was as much as 2.degree. C warmer than the surrounding area. Where 2/3 of the trees were removed, little or no protection was provided. Metabolism of the roosting birds appeared to raise roost temperature about 0.5.degree. C except in strong winds which displaced the warmed air rapidly. The data do not suggest a meteorological reason for blackbirds forming dense assemblies in only part of suitable roosting habitat.