Correcting for Differential Digestibility in Microhistological Analyses Involving Common Coastal Forages of the Pacific Northwest

Abstract

The accuracy of microhistological techniques to describe herbivore diets can be affected by differential digestibility of ingested forages. Correction factors were developed to adjust for those effects in 17 common forages of coastal, forested ranges of the Pacific Northwest. Two ferns, a moss and a sedge were overestimated by microhistological analysis in all seasons, while most shrubs, forbs and a grass were underestimated. Trees were not consistently over- or underestimated. Phenology significantly affected the degree of over- or underestimation of most forages. Failure to correct for differential digestibility will significantly bias results of microhistological techniques such as fecal analyses.