Acta Theriologica 41 (1): 83-92,1996. PL ISSN 0001-7051 Horn growth pattern in Cantabrian chamois Rupicapra pyrenaica parva: Influence of sex, location and phaenology Francisco J. PÉREZ-BARBERÍA, Luis ROBLES and Carlos NORES Pérez-Barbería F. J., Robles L. and Ñores C. 1996. Horn growth pattern in Cantabrian chamois Rupicapra pyrenaica parva: Influence of sex, location and phaenology. Acta Theriologica 41: 83-92. Sexual dimorphism in Cantabrian chamois Rupicapra pyrenaica parva (Cabrera, 1911) horn length was recorded annually for the first five years of life. The horns of males were larger than those of females, though horn growth rate in the first two years (ie horn length in the first two years divided by horn length in the first five years) was greater in females than males. Sexual dimorphism in horn length of Cantabrian chamois adults was found to be the highest of genus according to available data. Males and females with faster horn growth in the first two years of life reduced their horn growth rate in the third and fourth year. Chamois' horns from the Eastern Cantabrian Mountains were smaller than those from Western Cantabrian Mountains, although at five years of age these differences were not evident. Total horn length and jaw length showed significant positive correlation (females: r p 2 = 0.75, males: r p 2 = 0.54, p < 0.05 in both cases). This relationship suggests that horn growth dynamics may be used as an estimation of body-size dynamics. Horn growth / jaw length correlation was higher in females than in males. Horn growth was also positively correlated with annual precipitation in the previous year, but not with precipitation in the current year. Winter horn growth was observed in the younger age classes. Post-winter horn growth was recorded in 55% of the animals in March. The use of this information to age Cantabrian chamois is described. Facultad de Biología, Dpto. Biología de Organismos y Sistemas, Universidad de Oviedo, 33071-0viedo, Spain (FJP-B, CN); C/ El Pinar 1, Villaobispo de las Regueras, 22195-Leon, Spain (LR) Key words-. Rupicapra pyrenaica parva, horn growth dynamics, Cantabrian Mountains, Spain Introduction Chamois of both sexes are characterized by hook-like horns derived from epidermal tissue. Horn growth is a continuous process throughout an animals life, although the growth rate can be affected by season, the rut in males, pregnancy, lactation in females, and disease (Niethammer 1957). These factors produce marks along the horn. Often, narrow boundaries represent winter marks, caused by a cessation of horn growth, as Couturier (1938) suggested, or a reduced rate of growth in that season (Schroder 1971, Koubek and Hrabe 1983a). Wide segments between two boundaries correspond to a fast horn growth rate. Throughout an [83]