The Ram Mountain study area
Study area and population
Ram Mountain is an isolated mountainous outcrop located ~ 30 km east of the main Canadian Rockies. The range used by the sheep is ranging from 1700 to 2200 meters in altitude and is approximately of 38 km2 . It is characterized by subalpine and alpine vegetation. The weather at Ram Mountain is harsh and unpredictable. Snow cover usually persists from November to May but snowfalls have been recorded in all months of the year. Temperatures under -40°C have been registered in winter months.
The field camp
is usually open from late May to late September. During that period, our
work consists mostly of censusing and capturing sheep. Regular censuses
and captures provide us with detailed information on population size and
composition, and on the survival, weight changes, horn growth and reproduction
of marked individuals. We capture the sheep in a corral trap baited with
salt. Sheep are particularly attracted to salt in late spring. Captured
sheep are weighed and measured. This allows us to document growth over
the entire lifetime of each sheep. Ram Mountain is one of the rare studies
where repeated measurements of the same individual are collected within
a season. This allows us to study the patterns of growth throughout ontogeny,
development of sexual dimorphism and the effects of environmental variations
on these processes.
The Ram Mountain study was initiated in 1971. Research on this population has contributed substantially to bighorn sheep management and is part of a collaborative effort involving marked ungulate populations elsewhere in Alberta and in Europe. Recently, research has expanded to male reproductive success, population genetics and selection on morphology and life-history evolution.
Research on Ram Mountain has undergone three phases. First, from 1972 to 1980, ewes were removed in late summer to simulate a non-trophy hunting season. Second, from 1981 to 1996, the population was allowed to increase, to examine density-dependent effects on life history, population dynamics, and horn and body growth. In collaboration with Jack Hogg and Dave Coltman, we also expanded the scope of the research to include male reproductive success, inbreeding and the genetic basis of growth and reproductive success. We documented the continuing demise of the population, apparently related to low genetic variability and artificial removal of desirable genetic traits. In the last nine years the population underwent a precipitous decline (Fig. 1), due to poor recruitment and very high adult mortality, apparently due in large part to cougar (Puma concolor) predation in 1997-2002. Cougar predation ended in 2002, as suggested by the higher adult survival over the past 4 years. In the third phase of this study, sheep from the Cadomine area have now been translocated to the Ram Mountain population. We are currently monitoring the consequences of this experimental supplementation. The transplant will provide key data for managers interested in the selective impacts of trophy hunting.
Figure 1: Total number of sheep at Ram Mountain between 1974 and 2004, the red bars represents years with cougar predation.
From: Festa-Bianchet et al. 2005 Proc. Roy. Soc. Lond. B