Prey weights for computing percent biomass in raptor diets

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Abstract:

Researchers have been assessing the relative importance of prey species in raptor diets for many years. Early in this century, biologists attempted to document the number of pest species consumed by raptors. More recently, biologists have studied raptor diets to understand the effects of land use changes and environmental contaminants. Frequency of an individual prey species in the diet is not always directly related to its nutritional importance. Raptors may consume several small items that provide less weight and energy than a single large prey item. To account for this, raptor diets are now usually reported in terms of biomass: frequency of a prey item multiplied by its average weight. Accuracy of a biomass estimate depends on the accuracy of the weight assigned to a prey item. To ensure accuracy, weights for each prey species should be categorized by age and sex when appropriate. An average adult weight will distort relative importance of a prey species if raptors are consuming juveniles. Similarly, an average weight will distort results if one sex of a sexually diomorphic prey species is more vulnerable to raptor predation. Unfortunately, few studies have considered size classes in computing biomass in the diet.

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Reference Code: A83STE03IDUS

Full Citation: Steenhof, K. 1983. Prey weights for computing percent biomass in raptor diets. Raptor Research 17(1): 15-27.

Location: ANIMAL EF: BIRDS