Continuing Bighorn Sheep Die-Offs

You may have seen Scott Sandsberry’s piece in last Saturday’s Ellensburg Daily Record, or somewhere picked up from a wire service. Scott reports for the Yakima Herald Republic, but our local paper occasionally picks up some of his work. We cross paths from time to time with our outdoor writing interests. The piece was about the California bighorn lambs dying by the numbers in the Yakima Canyon.

You recall that we’ve been here before. The last major die-off was in 2009 and 10, when a significant number of both adults and youngsters were dying of pneumonia. In spite of the hopes expressed a half-dozen years ago, this repeat is largely the pattern which biologists have come to expect over 60 or 70 years of study. Herd recovery can take decades, if it even happens.

These die-offs are hard for me to watch. In the latter part of the last Century, I was president, and a founder, of the Rocky Mountain Bighorn Society, based in Denver. In the mid ‘80s, we were seeing the dreadful end of a worsening situation. The 125 or so bighorns in Waterton Canyon, in the foothills southwest of Denver, had formed a unique, low-elevation herd, representing a highly unique gene pool. They were dying of lungworm and pneumonia, under significant stress from construction activity in the Canyon. While we had been working long and hard to improve their habitat, it was still not up to snuff, and we were very concerned about the bighorns.

Many just died, and others were killed and removed for study. By the end, more habitat work had been done, and there were about 15 sheep. Numbers stayed near that for the better part of a decade, and then began growing a bit. Today, there may be three dozen sheep in Colorado’s Waterton Canyon. (You can take a look at some of the rams in the herd butting heads at www.youtube.com/watch?v=zDCDiL_NA7k.)

Biologists in each of the states with wild sheep have been researching the die-off issues. Mostly, it seems, they learned more about how these illnesses spread, and a bit more about how much – or little – patience ought to be practiced when wild sheep start dying.

In 1995-96, pneumonia almost wiped out wild bighorn herds (both California and Rocky Mountain subspecies) in the Blue Mountains and others in the Hell’s Canyon area of Idaho and Oregon along the Snake River. The Wenaha, Cottonwood Creek, and Black Butte or Joseph Creek herds are still rebuilding from that outbreak. The current outbreak here – several years after our big die-off – may take nearly all the lambs in our Umtanum herd. The pneumonia is apparently related to the Mycoplasma and Pasteurella bacteria confirmed in 2010 by Washington State University. Similar relationships have been found in nearby states.

This is a big concern for the health of the state’s overall bighorn sheep population. There are somewhere around 1,500 wild bighorns in Washington. They are found in 18 herds in central and eastern Washington – more than half of which are along the Yakima River. Other herds are at risk of – or experiencing – pneumonia outbreaks, as well.

It has been shown that bighorn sheep ewes surviving a pneumonia outbreak generally would not produce surviving offspring for up to ten years (most lambs would die in the first six months). For a few years, the sheep in the Canyon have seemed to be overcoming that pattern with lamb survival; now it appears that lamb die-offs may happen as often as two out of three years.

Jeff “Bernie” Bernatowicz is our DFW District Biologist, up to his elbows in the die-off. Genetic analysis of bacteria over the past few years has shed some light on the problem. It appears that the Mycoplasma bacteria sufficiently weaken immune defenses for Pasteurella (and now a variety of other genetically-identified bacteria) to trigger the pneumonia. Each of the various bacteria-caused pneumonias may lead to different outcomes. For example, sheep may survive one type, develop antibodies which last for only a year or two, and be re-infected. Or, some strains may kill so quickly that little evidence remains of the bacteria responsible. Some ewes are “shedders,” not unlike human “carriers” (unaffected by something like a strep throat they carry, but infecting others). Then, too, what if the lambs themselves which survived pneumonia are carrying the bacteria and infecting other lambs? Answers are coming, but it is complicated, and biologists are looking.

Various pneumonia bacteria can be easily transmitted from unaffected domestic sheep to wild sheep where they spread very rapidly. States around us have developed strict rules about the intermingling of domestic and wild sheep. The risk of disease is so great that some states have followed Colorado’s lead in giving carte blanche to the killing of any bighorn (ram, ewe or lamb) found near domestic sheep. Almost any nose contact (a common greeting) will infect a wild sheep with enough bacteria to spread like wildfire through a bighorn herd. DFW biologists have worked with both public and private land managers in the region to avoid interactions with domestic sheep and goats.

A die-off is never easy to watch. Keep a good thought for our icons of the West.