In August of 1988, I packed everything I could fit into my Chevy Citation, and I headed across the country to the Rocky Mountains. I’d been accepted into a Master’s program at the University of Idaho to study bighorn sheep. I got teased a little (“What are you going to study? Potatoes?”) but unless you’ve traveled to Idaho, you wouldn’t realize that “Potato Country” is only a very small portion of southern Idaho. Most of the state is very mountainous, containing in fact, the largest contiguous wilderness area in the United States, except for Alaska. The Frank Church River of No Return Wilderness Area was where my sheep spent their summers, and my study area was on the edge of that wilderness area in Challis, Idaho.
Bighorn sheep populations tend to be cyclic, with high population densities preceding a population crash, bringing the population down to very low levels. If the herd survives with enough healthy breeding sheep and the annual weather cycle cooperates with enough precipitation in summer to provide green forage, but not too much snow in winter so they can paw into the snow to uncover forage, it can slowly repopulate itself. Numbers will slowly climb back up until they reach high densities again and the cycle tends to repeat itself.
In the past, some sheep would travel from one herd to another, to spread genetic diversity and to augment smaller populations. But nowadays, with human activity, most herds tend to be somewhat isolated spatially from other herds and traveling between herds is less likely. The most isolated herds may die out when a population cycle reaches its low, if the animals are unable to breed quickly enough to repopulate before other catastrophic events wipe the herd out completely.
Places where the sheep used to travel are now criss-crossed with roads and towns, making it more difficult for these reclusive animals to pass through in their natural migration patterns to other areas. In addition, large areas are fenced off as grazing land for domestic cattle and sheep. These domestic herds can carry diseases that affect bighorn sheep, such as pneumonia (usually caused by Pasteurella haemolytica which has been renamed Mannheimia haemolytica since the years in which I studied it).
Bighorn sheep also suffer from lungworm infections (Protostrongylus spp) which can be spread easily when the herd are concentrated into smaller areas such as in winter when snow depths preclude them from moving far. During this time they tend to congregate on open slopes where they can reach forage more easily. The lungworm larvae are excreted from the body in feces and, similar to deer and elk, bighorn sheep feces come in the form of pellet droppings. As the animals are feeding they can incidentally ingest these larvae which lie in the pellets dropped all over the feeding area and this infects them with lungworm.
Aptly named, the lungworm adults grow in the lungs of its host and at higher levels of infection (called the lungworm load), can make the sheep susceptible to respiratory issues and certainly more apt to have serious outcomes when they come in contact with the pneumonia-causing bacteria, Pasteurella or other diseases. While there are other factors at play in disease outbreaks for bighorn sheep (Brucellosis, which can cause spontaneous abortion of fetuses; Leptospirosis, which is a bacterial disease that can also affect the lungs, and many others), and we did test my sheep population for all of these, our biggest concern at the time was the evidence of high lungworm loads in that entire region of Idaho. During population surveys (done by flying helicopters in transects and physically counting the animals seen), we saw evidence of sheep having coughing fits, a symptom of lungworm infestation.
In 1963, the Morgan Creek herd was at a high of about 300 sheep. By 1970 the population had crashed to around 100 animals and the herd was in very poor health. In 1988, the herd had recovered to 278 sheep and concerns that a population crash was again imminent led the Idaho Fish and Game Department to fund a research project looking at habitat and physiological factors that may help predict an upcoming decline and allow biologists to mitigate the causal factors and help stabilize the herd. This became my thesis research project: Habitat relationships and physiological condition of mountain sheep in Morgan Creek, east-central Idaho Gina L. B. (Gina Lyn Ballard) Karasek 1991
We started by radio-collaring sheep that we captured during a transplant project. The Idaho Fish & Game Department began capturing sheep in the Morgan Creek herd by shooting a net over them with a Cap-Chur gun. The biologist then blindfolded the sheep to keep it as calm as possible, bound its feet and then strapped it into a sling that was attached to the helicopter, which then flew it carefully down to the waiting ground crew.
The wildlife veterinarian took blood and fecal samples, nasal swabs, and took other measurements such as its body temperature, weight, breathing rate and heart rate. Although the blood levels of things like protein and various minerals (calcium, phosphorous and magnesium) were within normal limits, the fecal protein levels were extremely low, leading us to believe that the animals were actually starving and catabolizing muscle. Their poor body condition supported this idea.
Most of the captured sheep were being transplanted to a nearby isolated population that was currently at an all-time low in hopes that we could augment that population, providing new genetic diversity into the herd and provide additional breeding animals to help the population recover. At the same time, this could help the Morgan Creek herd by removing some animals – lessening the pressure on the limited forage in the winter range. We had hopes that it would decrease the chance that the population would crash.
Some of the captured sheep were radio-collared and released on site back into the Morgan Creek herd. These were my study animals. I spent the following two years tracking these sheep throughout their winter range, breeding season, and their forays into their summer range in the wilderness area where many of them (mostly the rams) spent the summer.
Since this post has gotten so long, I’ll share more about my wildlife research in another post.