4.1. Body mass and morphological characteristics of organs

Wild capercaillies tended to be heavier than hand-reared birds, but the difference was not significant (I, Table 2). Grey partridges fed with natural food lost body mass dramatically after the change in diet (III, Fig. 1; V, Fig. 1b). In work III they could regain mass 7–10 days after the change in diet, but not in work V. Tannin added to food had no significant effect on body mass (V, Fig. 1b).

The mean body mass of newly hatched grey partridge chicks was 9.2 ± 0.1 (SE) grams (II, Fig. 1, Table 2). Chicks fed an insect-rich diet were significantly heavier than chicks fed a low-insect diet, from the age of three days until the age of 21 days. Further, they were significantly heavier than the chicks fed a fish diet, from the age of six days until the age of 18 days (II, Fig. 1). No difference was found in body mass between low-insect diet and fish-fed chicks. At the age of one week, wild chicks seemed heavier than chicks fed a low-insect diet, but their body mass was similar to those fed an insect-rich or a fish-diet. At the age of eight weeks chicks fed an insect-rich diet were still heavier than chicks fed a fish diet, but at the age of thirteen week chicks did not differ from each other any more in body mass (II, Table 2).

The gut dimensions of wild capercaillies differed from those of hand-reared birds. Wild birds had heavier gizzards and livers and longer small intestines and caeca (I, Table 2). Hand-reared grey partridges fed natural food had heavier gizzards than birds fed either control or tannin-laced food (III, Table 7; V, Table 1). Tannin-fed grey partridges had longer small intestines than birds fed either control or natural food (V, Table 1).

The hearts of wild capercaillies were heavier than those of the hand-reared birds (I, Table 2). Hand-reared capercaillie males had heavier pectoral muscles than wild males, but in females the result was the opposite.