||P.3 5th paragraph: "Estimates of Total Body Water (TBW).This parameter has been determined in a number of species (Table 1.1), either by direct weighing (before and after drying of the carcass to constant weight) or by antipyrine dilution. This drug is assumed to be freely distributed in the body water, thus marking not only extracellular, but also intracellular water. For the determination of TBW a water isotope is also usable. The three methods result in nearly the same values (see Tables 1.1 and 1.2). TBW is usually expressed as a fraction (per cent) of body weight. The problem of
determination of body weight as such has been reviewed by Clark (1979). Regardless of the size of the bird the value determined on adult birds is around 60% of body weight. In several species the change of TBW from hatching to maturity has been measured. The results are identical: TBW was around 85% of body weight at hatching and decreases to about 60% as adult weight is attained. Both absolute values and change during maturation in birds are identical to the mammalian pattern. The young birds of some species grow to a weight greater than normal adult weight, and then decrease before fledging. Ricklefs (1968) has concluded, on the basis of measurements on nestling barn swallows (Hirundo rustica), that this weight recession is due entirely to decrease in water content."