Alpine ibex is characterised by a huge sexual dimorphism. The elements that differentiate the two sexes mostly are the body dimensions and the form and dimension of the horns (Couturier, 1962; Nievergelt, 1966, 1978; Ratti e Habermehl, 1977; Ratti, 1981; Lüps et al., 1987; Giacometti, 1988; Giacometti et al., 1997; Michallet et al., 1996).
Measures considered important to characterise the species, and the sex and age of the single individual are: the body weight, the total length (measured from the top of the nose to the base of the first coccygeal vertebra), the circumference of the chest (measured behind the shoulder), the circonference of the neck (measured just behind the jaw), the withers height and the length of the metatarsus (Brüllhardt e Lüps, 1984; Michallet et al., 1996; Bassano et al., in prep.).
The linear measurements, particularly the circumference of the chest, appear to be good elements to estimate indirectly the body weight of Alpine ibex (Bassano et al., in prep).
The maximum body weight is reached by adult males at age 11-12 years when they can weight up to 110 kg (mean weight 87.9 ± 8.5 kg). At this age, males reach a mean length of 160.8 cm and a mean withers height of 87.6 cm. Females weight up to 60 kg (mean weight 42.2 ± 7.3 kg), with a mean length of 134.8 cm and a mean withers height of 73.2 cm (Giacometti et al., 1997). The mean maximum length of the horns in males is about 92 cm while in females it is about 34 cm; the sexual dimorphism in horn length starts to be significant in yearlings. (Giacometti, 1988).
Alpine ibex horns grow during the whole life of the individual, and counting the yearly horn increments (annuli), it is possible to determine with good precision the age of the animal (Couturier, 1962; Nievergelt, 1966; Ratti e Habermehl,1977). Horn dimensions are influenced by the environmental quality, the meteorological conditions, the food availability and thus, by population density (Nievergelt, 1966, 1978; Michallet et al., 1994, 1996; Giacometti et al. 2002).
The mean length of the annuli in male Alpine ibex decreases with age (Bassano et al., 1995) and the growth pattern of the yearly horn increments is correlated to population density and the quality of the habitats inhabited (Buchli & Abderhalden, 1998b). Also the ambient temperature and the plant phenology in spring appear to influence horn growth (Giacometti et al. 2002).