Report from two-year study sheds light on historical factors influencing mule deer fawn production in western N.D.
Weather remains the biggest influence on mule deer production in western North Dakota, but results from a two-year study commissioned by the state Game and Fish Department show coyotes and oil development also play roles in areas where both factors are present.
Absent one or the other, the influence of coyotes or oil on “recruitment” — the addition of new mule deer to the population — is much less pronounced.
Those are among the findings highlighted in a new 83-page report, “An Evaluation of Historical Fawn Recruitment in Western North Dakota,” released this month by the Game and Fish Department.
Simone Ciuti of Freiburg University in Germany and Mark Boyce of the University of Alberta conducted the study, poring through spring mule deer surveys Game and Fish has conducted since 1956 and weather data going back just as far.
Ciuti, who did much of the analysis, was a post-doctoral student at the University of
Alberta while the research was underway. The study focused on more than 25 study sites in western North Dakota mule deer range.
Bill Jensen, big game biologist for Game and Fish in Bismarck, said states that accept Pittman-Robertson funding from taxes on guns and ammo are required to review their wildlife-monitoring programs periodically, a mandate that also played a role in launching the study.
“I’d done some preliminary work looking at this, but it got so cumbersome, so big, that I wanted to have someone who’s really an expert look at the dataset and do it right rather than me playing with it,” Jensen said.
Game and Fish then recruited Boyce, who Jensen describes as one of the “go-to guys on the continent” doing this kind of research. In essence, Jensen supplied the pieces, and Ciuti and Boyce put them in place.
That included everything from research on coyotes and oil wells, to the abundance of woody vegetation in the study areas and the expansion of invasive juniper trees across the Badlands.
“I tried to bolt together all the pertinent data that was available on everything that I could think of, and one of them was all of the survey data we collected,” Jensen said. “Very few states have this source of long-term datasets, and I think it might be the only one in a free-ranging big game species.”
Jensen said Ciuti also was able to compile online data from weather stations in the study areas and compare the conditions with oscillations in Pacific Ocean temperatures caused by influences such as El Nino.
Without getting too technical, the results showed a strong correlation between the Pacific Ocean oscillations and winter conditions in western North Dakota, Jensen said.
For example, high oscillations in the northern Pacific generally translated into very cold winters that same year.
“The biggest surprise to me was how well the ocean oscillation data matched the local weather data,” Jensen said.
Bad winters, of course, have a negative impact on fawn production, and the study showed weather explained 71 percent of the variability in fawn recruitment, Jensen said.
By comparison, the combined effect of oil wells and coyotes accounted for about 14 percent.
“Weather is a key driving force and has by far the highest predictive value for fall fawn recruitment,” Jensen said. “If you have a very cold winter, you’re going to have lower fawn recruitment, which isn’t surprising when you think about it.
“You have a cold spell coming on like we had this winter — that was predicted by looking at oceanic oscillations,” he added. “And now with that information, we can have an idea, anyway, of whether fawn numbers are going to be up or down in the fall.”
Oil and coyotes
Jensen said the study didn’t document notable impacts from oil and coyotes on mule deer fawn production unless both factors were present.
“If you don’t have disturbance on the land as far as oil wells or anything, coyote numbers don’t seem to affect fawn recruitment at all — we’re not able to see it, anyway,” Jensen said. “If you don’t have coyotes, and you have oil wells on the landscape, you don’t necessarily see the effect in (fawn) recruitment. But if you have both simultaneously on the landscape in high numbers, then you see lower fawn recruitment.”
A person looking for a quick solution would be tempted to say incentives such as bounties to kill more coyotes are necessary, Jensen said.
Not so fast. …
“We have the most liberal hunting regulations on coyotes as it is, and what drives people to take coyotes is the Asian and Russian fur markets — it’s not what we do as a management agency,” Jensen said. “Incentive programs and bounty systems have been tried over and over again throughout the U.S. and Canada, and they don’t work.”
Instead, Jensen said, the focus needs to be on trying to maintain mule deer habitat in the largest blocks possible, which is increasingly challenging in the face of ever-growing oil development.
Mule deer generally prefer rougher terrain than whitetails, and North Dakota is on the edge of their range, mostly in the Badlands and the breaks along the Missouri River. Recruitment has slowly but steadily declined during the past 50 years, Jensen said, but Game and Fish was able to maintain or grow populations by adjusting the harvest rate.
In recent years, mule deer numbers and densities have declined to the point where Game and Fish didn’t offer any doe tags last year and likely won’t this year, either.
Roads aren’t necessarily the problem, because many of the roads were in place before the oil play, Jensen said. But when the additional traffic is factored into the equation, the impact becomes more pronounced.
“It came down to the well densities,” he said. “What this implies is if you can provide refuge areas as large as possible, that’s better. What appears to be happening is that you get a certain density of roads, and a deer with a fawn is going to stay a certain distance from the road, but the habitat gets so fragmented that they’re in smaller areas and concentrated.
“Those smaller areas apparently are easier for coyotes to hunt.”
Encouraging oil companies to consolidate roads or spur routes whenever possible could help mitigate the impact on mule deer, Jensen said. Whether that’s realistic is a question Jensen says he can’t answer.
“We didn’t have an agenda when we set out on this project,” he said. “We’re just asking a question: What are the most important variables that affect fawn recruitment?”
Jensen said the study marks the first phase of research on mule deer in western North Dakota. Phase 2, he said, has been underway for about a year and involves a GPS study tracking 130 mule deer in the Badlands and Montana to see how they’re responding to the landscape changes resulting from the oil boom and how large of habitat blocks they need.
Randy Kreil, wildlife section chief for Game and Fish in Bismarck, said the real value of the fawn report won’t be known until the telemetry study is complete in four or five years.
The two studies together will provide better insight into the dynamics of energy development and its influence on mule deer, he said.
It’s also important to look at the data over the long term, Jensen said.
“We’re looking at some changes here, but the important thing to remember is when you look at a dataset like this, you can’t focus on one or two or three years,” Jensen said. “You have to take all of the information into consideration.
“We just did a report. Now, it’s up to others to look at it and say, ‘OK, maybe we can consolidate some roads; maybe we can change the types of operations we have.’ Anytime that you can reduce traffic and disturbance, that’s going to be a good thing.”