Costs of detoxification of xenobiotics in conifer needles to blue grouse Dendragapus obscurus

Thomas E. Remington & Richard W. Hoffman

Remington, T.E. & Hoffman, R.W. 1997: Costs of detoxification of xenobiotics in conifer needles to blue grouse Dendragapus obscurus. - Wildl. Biol. 3: 289.

Nutrient and energy costs of detoxifying defensive compounds in conifer needle diets were estimated for wild blue grouse Dendragapus obscurus captured and maintained in captivity. Ammonium ion comprised the bulk of excreted nitrogen. Excretion of ammonium ion was greatest (P < 0.05) on unpalatable diets, increased (P < 0.05) with addition of monoterpenes to the diet, and was correlated to glucuronic acid excretion. Nitrogen costs of detoxification were estimated at 9-25% of ingested nitrogen for needles of four conifer species. Glucuronic acid was the principal detoxification conjugate excreted, followed by ornithuric and hippuric acids. Glucuronic acid excretion was highest on the least palatable diets and increased with addition of monoterpenes to the diet. The minimal energy cost of detoxification was estimated at 1-10% of energy metabolized from needles of four conifer species. Intake of defended needles was 15% less than for Douglas-fir Pseudotsuga menziesii needles. Defensive compounds can deter feeding if absorption rates exceed detoxification rates.

Key words: blue grouse, Dendragapus obscurus, Douglas-fir, monoterpenes, nitrogen, Pseudotsuga menziesii

Thomas E. Remington & Richard W. Hoffman, Colorado Division of Wildlife, 317 West Prospect Road, Fort Collins, Colorado 80526, USA