NEW FINDINGS IN BODY-MASS REGULATION IN ZEBRA FINCHES (TAENIOPYGIA-GUTTATA) IN RESPONSE TO PHOTOPERIOD AND TEMPERATURE

Small birds in temperate zones increase body mass in winter (Lehikoine n, 1987). We investigated daily and annual variation of body mass and fat reserves of locally-reared Australian zebra finches Taeniopygia gu ttata, by exposing them to different photoperiods, feeding periods, an d temperatures. Experiments with long and short photoperiods and long and short feeding periods, showed that long photoperiods increased bod y mass and fat reserves of the zebra finches, and readiness to breed, independently of the actual feeding period. Furthermore, the zebra fin ches in indoor aviaries with constant temperature (22-24 degrees C) an d in outdoor aviaries with ambient temperature, both exposed to the na tural daylength changes of Bielefeld, Germany (52 degrees N), had high dawn body mass in summer (12.9 and 12.0-12.4 g, respectively) and low in winter (10.7 and 11.1 g, respectively). Thirty to sixty percent of these mass changes were related to changes in fat reserves, so that t he finches had only 0.1-0.2 g of metabolizable fat reserves in short p hotoperiods (or in winter), which increased up to 1.5 g in long photop eriods (or in summer). Indoor finches consumed more seeds in summer th an in winter (3.3 vs. 2.7 g/day), while outdoor finches consumed 4-5 g of seeds per day throughout the year, which probably represented the limit of energy intake for a 11-13 g bird (Kirkwood, 1983). Nightly ma ss loss, increasing from 0.7 g in summer up to 2.0 g in winter, was hi ghly positively correlated with night length, not influenced by ambien t temperature. Foraging before dawn and after dusk, roosting with well -led crops, and decreasing body mass and fat reserves, seem to be adap tations of zebra finches for survival in winter. The summer fattening probably accelerates reproduction in this opportunistic breeder, by al locating more time to reproductive behaviour and more endogenous nutri ents to egg-formation.