Moose Mystery
G&F biologists study puzzling decline
Casper – Biologists don’t yet know whether the decline of moose in northwest Wyoming is due to habitat, predators or climate.
“In the Jackson region the Game and Fish has reduced moose tags to 20 or 40 by now, and with the reduced harvest they still haven’t been able to stem the decline,” says Matthew Kauffman of the Wyoming Cooperative Fish and Wildlife Research Unit.
Studies on the decline began with captures via darting in February for the last three winters and have looked at moose migration and distribution. This year 57 cow moose were collared, out of a population estimated at between 400 and 500 moose.
“One of the first questions is seasonal distribution,” says Kauffman. “There are only four or five areas where moose are summering. One of the interesting results of the study has been a relationship where the animals that summer higher in the Teton wilderness leave the winter range later. We know that moose always go back to the same places, and this suggests they have a sense of what to expect for snow conditions and that they time their migration accordingly.”
Another aspect of the study has looked at home range use in summer and winter. “During the summer moose have much larger home ranges than in the winter, and that is consistent,” he explains. “It’s driven by food availability. In the winter things look pretty bleak and browsing opportunities will be poor, but in the summer they move greater distances to seek out high-quality forage.”
As far as their population decline, Kauffman says these moose don’t have diseases or parasites. “Nothing is jumping out. If habitat were driving this, we would expect rump fat measurements to be lower. At this point we’re tentatively concluding these moose are in good physical condition.”
He says biologists have done a lot of work to estimate female and male survival, which is average. “Adult survival doesn’t appear to be depressed,” says Kauffman.
Overall pregnancy rate in the population is 91 percent, which is normal for moose. One concern is that there is a strong difference between live births from non-handled and handled moose. “Calving rates were 80 percent in the non-handled, and only 22 percent in the handled,” says Kauffman. Nine percent of non-handled cows had twins, while none of the handled cows did.
Although the statistics appear straightforward, the same capture and handling techniques are used in other moose populations in the state with no negative effects.
“Nobody knows why this is happening,” says Kauffman. “The Snowy Range moose study came away with 100 percent live births and high twinning rates from handled cows.”
Kauffman says that maybe the 1988 Yellowstone fires could have initiated the decline.
As the study moves forward, biologists will be evaluating the condition of the habitat and sending samples to the lab to look at nutrient value to see if the animals in those areas are in poorer condition.
“We’re also initiating a phase to look at the influence of predators on neonate losses,” says Kauffman. “One of the ideas is that increasing grizzly populations and wolves are influencing neonates and that’s what’s driving decline, but that’s a difficult question to get at.”
He says in the backcountry they can’t get out to the scene fast enough to look at what’s killed the young moose. “We’re taking neonate survival and looking across a gradient of predator densities to see if we have higher losses where we have more predators.”
Kauffman says black bears and grizzly bears are more likely culprits than wolves.
Regarding the capture dilemma, Kauffman says a new sampling of cows was captured with a net gun with no drugs involved. “The captures were much quicker, and the whole process only takes 15 to 20 minutes, as opposed to 45 with the drugs,” he says.
Christy Hemken is assistant editor of the Wyoming Livestock Roundup. Send comments on this article to christy@wylr.net.
