Bathurst Caribou Calving Ground Studies: Influence of Nutrition and
Human Activity on Calving Ground Location; and Influence of
Parasites on Calving Ground Location
Organization / Researcher: University of Alaska, Brad Griffith; GNWT, Anne Gunn; Canadian Wildlife Service, Don Russell
Length of Project: 3 years (1998-2001)
Personnel involved: Seven researchers and five local trainees.
Total Project Expenditures: $428,826 (Nutrition & Human Activity); $5,000 (Parasites)
This project looked at factors affecting Bathurst Caribou calving ground location, reasons why the calving location changes year to year, and possible effects of different calving locations on the health of the herd. It investigated whether climate change is affecting forage production on the calving and post-calving ranges; it estimated the diet, energy and protein intake of the caribou on the various ranges, and predicted the effect of human activity displacing caribou from important ranges. The project built on initial observations made during the study "Habitat Characteristics of the Calving Area of the Bathurst Caribou Herd" by Mueller, also funded by WKSS.
Each spring most of the Bathurst caribou cows group together and calve in one small core area within their overall calving grounds surrounding Bathurst Inlet. Over the years this core area has shifted hundreds of kilometres. In recent years, caribou have calved to the west of Bathurst Inlet, while for most of the previous 20 to 30 years they calved east of Bathurst Inlet. During both years of this study, the caribou calved in almost the same place near the Hood River.
Most of the research looked at food and nutrition. Caribou cows require sufficient quantities of high quality food plants in order to give birth to healthy calves and nurse them adequately; making milk requires extra protein from the cows. By analyzing the food value and protein content of plants eaten by caribou, researchers found that some varieties of lichen are more digestible than others and have differing amounts of protein: one type, Peltigara, was found to contain ten times the protein of most other lichens. Also high in protein are Oxytropis roots and birch leaves. Grasses and sedges have moderate amounts of protein.
Based on studies of the plant remains in caribou droppings, the animals ate mostly lichen on the calving grounds: at the beginning of calving, lichen made up about 50% of the diet, dropping to about 30% with spring green-up (when they could select other plants). Caribou also ate birch, labrador tea, sedges, grasses and moss, and dug for Oxytropis roots. As a general rule, caribou ate the most nutritious plants they could find in the calving area; these vary from year to year according to the weather, temperature and snowcover. It also looks like the caribou calve in areas where there will be a high level of green plants available at the peak of nursing.
Calf growth rates are likely to be lower in the Bathurst herd, because of the lower quality food available to the nursing cows. Researchers think that the relatively low weights of the Bathurst cows (about 10 kg less than other migratory mainland herds) enables them to more easily nurture a calf as they require fewer calories for themselves.
The amount of energy the caribou use to get their food is also important, since this affects how much of the food is used to improve their body condition, feed their young, build up strength and health etc. compared to how much is used up getting more food. Researchers watched how much time caribou spent in different types of activities and recorded over 70,000 observations. They have found the caribou spend about half their time looking for food and about one third lying down.
The researchers noted that the forage quality of the Bathurst herd's calving ground is similar to some other herds during calving, but after green-up is only one-eighth as good as that accessible to the Porcupine Caribou Herd and one-quarter that of the George River herd. Once on the calving grounds, and before greenup, Bathurst cows only ate about one-quarter as much food as the cows in the other herds although they spent a very similar amount of time looking for food.
The researchers believe the cows have better quality range at other times of the year and can make up the difference then. One reason the researchers believe this is because of examinations of caribou antlers found in the field. Caribou antlers grow in layers and are shed annually; the layers show how the nitrogen content of the diet changes through the course of a year - the inside layers will reflect the nitrogen content early in the year, and outer layers will show later diet. The analysis showed that caribou seem to begin eating more grass-like vegetation after calving, although this was not statistically significant.
In general the herd is healthy; however a computer model shows that if the herd was displaced north and west from its usual calving area by development activities, the amount of green plant growth available to the cows would be reduced at the peak time of nursing, when they most need it: as the forage quality of the area is already low compared to that of other mainland herds, this could be a major problem for them.
Satellite information was analyzed to find out if global climate change, since 1984, has affected the calving grounds. The east side of Bathurst Inlet showed no evidence of warming, but the west side is getting warmer, causing an increase in green vegetation that benefits the herd.
A sub-component of the study was a preliminary examination of the possible role of parasitic nematode worms in the movement of the core caribou calving areas. Though the worms do not seem to trouble the caribou or affect their health much, a buildup of parasite eggs on the ground may cause caribou cows to avoid certain calving areas or leave a calving area early. During the time of calving and lactation, hormonal changes temporarily relax the immune system allowing a surge in worm egg production in the intestinal tract of caribou cows. Eggs of the parasite Ostertagia are carried out of the body in fecal pellets; they hatch into larvae on the ground where they are ingested by grazing cows and calves, to begin the life cycle anew. Researchers collected fresh fecal pellets and found that parasite eggs hatched within two weeks, when the cows and calves were still in the area. The Board does not consider this report to be an official report of the Society and its contents are the sole responsibility of the author.
Bathurst Calving Ground Studies
Influence of Nutrition and Human Activity on Calving Ground Location
Prevalence and Intensity of Gastro-Intestinal Nematode Parasitism in the Bathurst Caribou Herd (1998-1999)