Short Communication Ventilatory Oxygen Extraction during Cold Exposure in the Pigeon

The respiratory responses to cold ambient temperatures in birds have only rarely been described. Bernstein & Schmidt-Nielsen (1974) studied the fish crow (Corvus ossifragus) during moderate cold exposure, while Bouverot, Hildwein & Oulhen (1976) measured ventilatory variables in pigeons (Columba livia) at near thermoneutral (22°C) and at cold (2°C) ambient temperatures. With respect to the amount of oxygen extracted from the ventilated air, both studies did not show any significant alterations correlated with changes in ambient temperature. However, several recent studies have demonstrated an increased oxygen extraction (EoJ in response to cold exposure in birds [Bucher (1981) in the linneated parakeet (Bolborhynchos lineola), Brent, Rasmussen, Bech & Martini (1983) in the kittiwake (Rissa tridactyla), Brent, Pedersen, Bech & Johansen (1984) in the European coot (Fulica atra) and Bech, Johansen, Brent & Nicol (1984) in the duck (Anas platyrhynchos)]. The significance of such an altered Ec^ is obvious: the resultant decrease in ventilatory requirement will lower the relative loss of heat and water. Thus, together with a low expired air temperature (Schmidt-Nielsen, Hainsworth & Murrish, 1970), the increased oxygen extraction serves to minimize the respiratory heat and water loss in cold environments (Johansen & Bech, 1983). In most of the studies in which changed E ^ values have been described, ventilatory volumes have been measured by pneumotachography (Brent et al. 1983, 1984; Bech et al. 1984). Thus, the birds were wearing a small face-mask and the ventilated air was forced through a Fleisch-tube (Glass, Wood & Johansen, 1978; Bech, Johansen & Maloiy, 1979). Recently, Barnas & Rautenberg (1984) used body plethysmography to measure the respiratory responses to cold in pigeons. Their results revealed a constant oxygen extraction with changed ambient temperature, thus confirming the results of Bouverot et al. (1976). Barnas & Rautenberg (1984) therefore questioned the results obtained in earlier studies using pneumotachography and claimed that 'differences in responses may, . . . , reflect differences in experimental methods rather than in species'.