Nj. Adams et al., WATER INFLUX AND EFFLUX IN FREE-FLYING PIGEONS, Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology, 167(6), 1997, pp. 444-450
We used tritium-labeled water to measure total body water, water influ
x (which approximated oxidative water production) and water efflux in
free-flying tippler pigeons (Columba livia) during flights that lasted
on average 4.2 h. At experimental air temperatures ranging from 18 to
27 degrees C, mean water efflux by evaporation and excretion [6.3 +/-
1.3 (SD) ml . h(-1), n=14] exceeded water influx from oxidative water
and inspired air (1.4 +/- 0.7 ml . h(-1), n = 14), and the birds dehy
drated at 4.9 +/- 0.9 ml . h(-1). This was not significantly different
from gravimetrically measured mass loss of 6.2 +/- 2.1 g . h(-1) (t =
1.902, n = 14, P > 0.05). This flight-induced dehydration resulted in
an increase in plasma osmolality of 4.3 +/- 3.0 mosmol . kg(-1). h(-1
) during flights of 3-4 h. At 27 degrees C, the increase in plasma osm
olality above pre-flight levels (Delta P-osm = 7.6 +/- 4.29 mosmol . k
g(-1). h(-1), n = 6) was significantly higher than that at 18 degrees
C (Delta P-osm = 0.83 +/- 2.23 mosmol . kg(-1). h(-1), (t = 3.43, n =
6, P < 0.05). Post-flight haematocrit values were on average 1.1% lowe
r than pre-flight levels, suggesting plasma expansion. Water efflux va
lues during free flight were within 9% of those in the one published f
ield study (Gessaman et al. 1991), and within the range of values for
net water loss determined from mass balance during wind tunnel experim
ents (Biesel and Nachtigall 1987). Our net water loss rates were subst
antially higher than those estimated by a simulation model (Carmi ct a
l. 1992) suggesting some re-evaluation of the model assumptions is req
uired.