Respiratory and cutaneous water loss in freeflying pigeons

We used a continuous-signal telemetry system to make the first measures of respired air temperature (TJ and respiratory frequency in a free-flying, trained tippler pigeon (body mass = 323 g). T was measured with a micro-bead thermistor, inserted 3 mm into the pigeon's nares, and was attached to an FM transmitter (total mass = 9.5 g) mounted on its back. In a 3 hour flight at an air temperature of 15rC and relative humidify of 50% (water vapor density = 6.42 g-rtv3), steady state respiratory frequency was 5-7 breaths/8, while mean T.x was 32°C. Respiratory water loss (RWL) was calculated as the product of ventilation volume (VJ and the difference between expired (assumed saturated at TJ andinspired water vapor density. V, was calculated using a published computer model for flight energy and water budgets. We estimated respiratory water loss to be 8.45 mg(HjO)-g1(body mass)-h'1. In a separate study, mean total evaporative water loss (TEWL) for 6 tipplers flown under the above conditions was 11.45 mg-(g-h)1 and cutaneous water loss, CWL, is TEWL- RWL = 3 mg-(g-h) . The computer model assumed CWL to be 10% of RWL, i.e. 0.84 mg-(g-h)-1, which is about % of our estimate. Thus, this preliminary result suggests that CWL may be a greater proportion of total evaporative water loss in flying birds than previously assumed. (Supported by US-Israel Binational Science Foundation grant # 93-00232.).