Tuesday, January 6, 2009

Sheep Capture, Part 5: Past and Future

Group of bighorn sheep a couple hundred yards from Gibson Dam. Photo taken fall 2000.

This article will be slightly longer than normal. Hopefully it is worth the read.

Since the first unsuccessful attempts at capturing sheep in Montana in 1938, the capture efforts have evolved from simple corral and hay set-ups to using helicopters and net gunning, but the need to capture and translocate bighorns has remained constant.

It has been mentioned in previous articles that capture and translocating bighorns is essential. In the overview to this series of articles, Montana Fish, Wildlife & Parks Wildlife Management Bureau Chief Quentin Kujala was quoted, “Translocating is prescribed, almost necessary for sheep management.”

Without pouring over books and manuscripts relating to sheep management or talking to many wildlife biologists, basics reasoning behind Kujala’s statements may not be apparent. To know where Kujala, and other biologists, are coming from we need to take some stair-steps through the building blocks that lay the foundations in bighorn wildlife management.

The first step is that sheep are not elk or whitetail. Obviously. The difference is that sheep act more like sheep than elk or whitetail—they “follow the leader.” A bighorn herd relies on the knowledge base held by the oldest rams and ewes. A knowledge base that is lost—through disease, or over-hunting takes generations to recover.

In further conversations with Kujala, he named a group of sheep that lived in an area he referred to as “Grizzly Basin,” that if lost, would be nearly impossible to replace. (The exact area isn’t important.) What is important is the why.

Studies of bighorns reveal that most sheep are afraid of timber. American (New World) sheep rely on rocks and cliffs, and their powerful muscles to escape predators. (Old World sheep of Asia evolved to be more like America’s pronghorn antelope, using longer leaner bodies and speed to outdistance predators.) Timber is a weakness their capabilities don’t address. But, Grizzly Basin has a lot of timber. How can bighorns that are normally afraid of timber seem to exist where timber exists?

In Montana it takes 120 years for a conifer to grow to a diameter of two- feet. Compare that with the oldest bighorn’s lifespan of about 20-years. While the conifers grow, at least six generations of bighorns have evolved and expanded their knowledge base to include living in, and around timber.

With that in mind, the impossibility of replacing sheep in Grizzly Basin looms large. The only apparent solution to replacing that heard would include: clearing the timber, relocating sheep to the area and letting another six generations of bighorn’s build a knowledge base that includes slow-growing timber.

The second step would answer, “Why are sheep different than elk and whitetail that thrive in habit that is very near and sometimes overlaps?” It is difficult to answer that question directly. There is very little fossil evidence to trace sheep development. In some respects biologists know less about the supposed evolution of sheep than experts on dinosaurs know of the giant reptiles.
Many of the prehistoric reptiles and fish lived where there was mud, silt and other soft deposits that made preservation of bones easy. Sheep lived on and around glaciers, cliffs, rocks and fast moving torrents. As Ice Ages came and went, natural physical processes broke, smashed and ground sheep remains to minute elements of glacial till.

Without fossilized remains biologist look at contemporary sheep patterns and extrapolate from there.

One contemporary pattern is that sheep find a static balance within their ecosystem. In an amazing biological adaptation much like wolves reaching capacity in their ecosystem, when a herd reaches the ecosystem’s limits, reproduction slows. (Although wolves are different in that they do disperse.) In a growing herd, bighorn ewes will begin breeding at two-years, but when the upper limits are reached, ewes don’t breed until they are three or four-years old.

It is believed that the bighorns that survived waves of glaciation during the Ice Ages did so by being “sheep.” Sheep that stayed with the herd and relied on the herd’s knowledge base in relation to winter and summer ranges survived. Sheep that left the herd to seek “greener pastures,” perished.

That is not to say that all sheep that stayed with the herd survived. Hardly. Sheep that died while with the herd actually made room for subsequent sheep to thrive, or at least survive to another day.

Bighorns that survived another day within the somewhat closed yet harsh glacial environment never developed resistance to diseases brought by domestic sheep.

Fragility of bighorns is probably a third step in managing bighorns. FWP biologist Brent Lonner put much of this into perspective in a recent email. In it he said, “Ideally, by translocating wild animals, such as sheep, we are reducing the threat of major disease and die-off events (other instances of relocations can also relate to limiting game damage problems in areas as well). This has occurred several times in recent history, one primary reason being related to too many animals on the landscape. When a disease is introduced or propagated in a population, if animal numbers are too high, it doesn't take much for animals to come into contact and the disease to move through population at a relatively fast rate - especially with sheep due to their susceptibility to disease. I often wonder if one of sheep's primary goals in life is to find a place to die.”

There are more than three steps in bighorn management. As wildlife experts observe sheep living, thriving and dying, management thought, theory and application will evolve with these hardy, and ironically, fragile animals. This four-article series is a thumb-nail of Montana’s, and the west’s, attempts to keep bighorns hardy and thriving in a rocky and changing environment.
I owe thanks to wildlife officials of Montana, Utah, Idaho and Nebraska.

I especially need to thank Quentin Kujala and Brent Lonner for their input; FWP Wildlife Laboratory personnel; and, Dale Toweill from the Idaho Fish and Game. Dr. Dale E. Toweill and Dr. Valerius Geist co-authored Return of Royalty: Wild Sheep of North America. While many books and online resources helped with these articles, Return of Royalty was both a starting point and a tightly packed chest of information. Filled with many high-quality photos it makes a great coffee-table book.

1 comment:

Anonymous said...

I did not know to much about sheep until I read your post. At least now I know a little bit more than I did before.