Evolutionary demography and conservation lab - Labo de démographie évolutive et conservation

         
 

Caw Ridge Study area

 

Study area and population

 

Caw Ridge is in the foothills of the Rocky Mountains and is the northernmost of the three study areas. Most pictures of mountain goats show them in rugged habitats, often feeding in narrow bands of vegetation above precipitous cliffs. Caw Ridge, however, is a complex of rolling hills with a few short cliff faces and several rockslides. The study area is approximately 28 km2 and includes four major ridge complexes above timberline. Elevations used by goats range from about 1700 m in the lowest sections of the winter range to 2180 m at the summit of Big Ridge. Consequently, compared to many other mountain ungulate populations, the study population has limited opportunities for altitudinal migrations. Mountain goats on Caw Ridge are geographically isolated from other goat populations. The main Rocky Mountains range, with several other goat populations, is about 40 km to the west, but the intervening distance is almost completely covered with boreal forest and does not include many areas of goat habitat. The isolation, however, is not complete as almost every year we documented successful immigration to and emigration from Caw Ridge.

 

The area retains all species of large mammals present at the time of European contact, including grizzly bears, wolves, and cougars that prey on goats of all sex-age classes. Other potential goat predators include black bears, wolverines, coyotes, and golden eagles. The vegetation is mostly alpine tundra, with grasses, sedges, forbs, and prostrate willows. The treeline is at about 1900 m and the forest is mostly made up of spruce and alpine fir, with a few pine trees. The alpine weather is a major factor affecting fieldwork and data collection: it changes rapidly, is generally cold and often windy. Snowfalls of 20 cm or more and temperatures of -4°C or less can occur at any time of the year. Winds strong enough to make walking or even standing difficult are not uncommon. Winters are long, very cold, and windy, with temperatures reaching below -40°C.

 

The field camp is usually open from mid-May to late September, but we have also watched the rut in November in some years. In late spring, fieldwork mainly consists of intensive winter survival and surveys to locate parturient females and newborn kids. We intensively search the entire ridge to find all surviving individuals. We try to locate most adult females every day to evaluate their reproductive status, describe habitats used for parturitions, and to determine the sex and exact age of kids. As snow melts, goats start to be attracted to the traps baited with salt. From then, an intense period of captures begins. We capture goats in remotely controlled Stevenson box traps (Fig.1), and occasionally in self-tripping Clover traps. Because they are aggressive when handled and have dangerous sharp horns, goats are tranquilized with drugs before being marked and measured. We rarely capture goats that are already marked. Kids of the year are not captured therefore most goats are first marked as yearlings, that receive ear tags. We also recapture all 2-year-olds: we fit males with VHF radio-collars to assess dispersal, and females with large visual collars to help identification during behavioural observations. Because of the risk of kid abandonment, we stopped capturing adult females and kids in 1998. Therefore, not many individuals are recaptured and weighed each year. Similarly to Sheep River, however, we started using platform scales baited with salt in 2001. We weigh most individuals (except for some adult males) each year without having to handle them, and often collect repeated measures on the same individuals during the summer. In addition to the longitudinal data on survival and reproductive success of individuals, extensive behavioural observations each summer have provided us with a substantial long-term behavioural database that is quite unique for such a long-lived species. These data are used to answer questions about relation to habitat use, group composition, maternal care, mother-offspring associations, sexual segregation, effects of ATV and helicopter disturbance, social dominance, vigilance, and predation.

History

 

The idea of studying the goats at Caw Ridge developed during a conversation between Marco Festa-Bianchet and Kirby Smith in April 1988. Kirby was the wildlife manager responsible for this area. He had used a drop-net to capture goats on Caw Ridge and was interested in a study of population dynamics. A recent drop in mountain goat numbers in Alberta had led to the closure of hunting over the entire province. Caw Ridge was clearly the best population in Alberta for a study based on monitoring marked individuals. It was accessible and had a large mountain goat population, unhunted since 1969. The study began officially in June 1989, although a few goats were marked and released in 1987 and 1988. During the first few years, the main objectives of our research were to determine which factors affected population dynamics and what selective pressures shaped female reproductive strategies. In 1994, Steeve Côté became involved and is now leading the project. Recently, research has expanded to address questions related to male reproductive success, inbreeding and phylogenetics of mountain goats, in collaboration with Dave Coltman. Many graduate students have been involved with fieldwork on Caw Ridge. Sandra Hamel and Julien Mainguy are currently writing up their theses.

 

Since the beginning of the study, the number of individuals in the population almost doubled (Fig. 2), but so far we have observed few density-dependent effects. In recent years, however, the population seems to have reached a plateau, fluctuating around 150 individuals. The Caw Ridge population may have reached its carrying capacity and thus we may start seeing evidence of density-dependence in future years.

             

     
 
    Figure 1: Traps used to capture mountain goats at Caw Ridge.          
               
   
 
Figure 2: Total number of goats at Caw Ridge between 1989 and 2007.