Caecal decomposition of uric acid in captive and free ranging willow ptarmigan (Lagopus lagopus lagopus).

Urine entering the caeca of birds contains significant amounts of uric acid. The discovery of great numbers of bacteria utilizing uric acid in the caeca has encouraged the discussion about nitrogen recycling in birds. In this work caecal decomposition of uric acid in wild and captive willow ptarmigan has been investigated using radioactively labelled uric acid injected directly into one of the caeca. The appearance of radioactive CO2 in the expired air was taken as an indication of uric acid breakdown. The decomposition occurred at a rate corresponding to a half-life of 26 min (11-36 min). The results are in accordance with the previously reported observations of huge numbers of uric acid utilizing bacteria in the caeca of a variety of birds, and also with the nitrogen recycling theory. However, no conclusion concerning the nitrogen recycling can be drawn.