Model estimation of energy flow in northwestern coniferous forest bird communities

A simulation model developed in the Grassland Biome Program of the US/IBPis applied to data gathered in the Coniferous Forest Biome Program to estimate the magnitudesand patterns of energy flow in breeding bird populations in Northwestern coniferous forests.Six stands along a moisture-temperature gradient in the central Oregon Cascades supportedbreeding avifaunas of 7-15 species, with standing crops of 223-526 g/ha. Total energy flowthrough these avifaunas during the April—October breeding season was estimated at roughly10 kcal m-= season' in the low-elevation, moderately xeric stands; 12 kcal m-= season' in thehigh-elevation stands; 17 kcal m-= season' in a mesic floodplain stand; and 21 kcal m' season'in a midelevation "transitional" stand. About 1% of the seasonal energy flow was channeledinto production, while reproduction-related processes accounted for 15%-16% of the totalenergy intake. Thermoregulation required 13%-19% of the seasonal total, with the higherrelative costs associated with the cooler, higher elevation stands. Foliage-gleaning bird speciesaccounted for the greatest proportion of the energy intake at most stands, but within this"guild" the importance of granivorous "opportunistic" species generally increased through thestand sequence as the growing season became shorter and environmental conditions moresevere.
Key words: Bird community; coniferous forest; energy flow; IBP; simulation model.