Sexual differences in energy allocation of Capercailie Tetrao urogallus chicks

Abstract

The energy allocation was studied in captive male and female Capercaillie chicks up to the age of one month. The higher energy requirement of the males was at first mostly due to their greater activity and thermoregulation costs. As the chicks grew older, theproportion of energy devoted to growth and resting metabolism increased. To study the allocation of growth energy in detail, chick bodies were divided into five body component groups (integument, digestive organs, flying muscles, legs and "other body components") . Femalesallocated proportionately more of their growth energy to flying muscles and males to legs and "other body components". The higher activity and thermoregulation costs are supposed to be an indirect consequence of the faster growth of male chicks . To obtain the additional growth energy, males must be more active and areexposed for longer to harsh weather conditions. The legs and "other body components" of adult males are relatively larger than those of adult females. Growing male chicks must invest more in these body components and hence less energy is available for the growth of breast muscles. Male chicks with small breast muscles are probably inferior flyers and more vulnerable to predators.