In 2001, border disease virus (BDV) was identified as the cause of a previously unreported disease in Pyrenean chamois (Rupicapra pyrenaica) in Spain. Since then, the disease has caused a dramatic decrease, and in some cases collapse, of chamois populations and has expanded to nearly the entire distribution area in the Pyrenees. Chamois BDV was characterized as BDV-4 genotype and experimental studies confirmed that it was the primary agent of the disease. The infection has become endemic in the Central and Eastern Pyrenees. However, while most Pyrenean chamois populations have been severely affected by the disease, others have not, despite the circulation of BDV in apparently healthy individuals, suggesting the existence of different viral strategies for persisting in the host population. Changes in the interplay of pathogen, host and environmental factors may lead to the formation of different disease patterns. A key factor influencing disease emergence may be pathogen invasiveness through viral mutation. Host factors, such as behavior, immunity at the population level and genetic variability, may also have driven different epidemiological scenarios. Climatic and other ecological factors may have favored secondary infections, such as pneumonia, that under particular circumstances have been major contributing factors in the high mortality observed in some areas.

Rates of increase, survival and reproduction were studied in two re-introduced populations of mountain ungulates, the Pyrenean chamois (also named isard, Rupicapra pyrenaica) and the ibex (Capra ibex) in the French Alps. The populations were monitored from 1983 to 1998 (ibex) or 1984 to 1999 (isard) using capture, marking and resighting of individuals. Population rates of increase were estimated during the colonizing phase from: (1) a time series of estimates of population size; (2) projection matrices based on rates of survival and fecundity. Both populations had exponential rates of increase, with annual multiplication rates of 1.28 for isard and 1.30 for ibex. Age of first reproduction was 2 years in both species, with 77% of females breeding at this age in isard and 43% in ibex. From 3 years of age onwards, 90% of isard and 87% of ibex females bred each year. Survival rates of adult females, estimated using capture–recapture models, equalled 0.94 for isard and 0.98 for ibex, whatever the age and year. The projection matrix led to a slightly lower asymptotic multiplication rate than the time series of population size. Despite adult body size of the ibex being about twice that of the isard, no difference was detected in the intrinsic rate of increase between the two species. This supported the hypotheses of homogeneous life-history traits among ungulates, varying little with body size.