By Lance Nixon
Until Dakota State University associate professor Kristel Bakker undertook a new project, the best guess anyone had about the population of ground-burrowing owls had in South Dakota was an estimate from years ago that arbitrarily put the number at between 100 and 1,000 breeding pairs.
The good news?
That’s way low.
“We extrapolate there’s more than that based on what we found,” said Bakker, who had a South Dakota Game, Fish and Parks state wildlife grant to do some initial survey work on that population of birds.
“They’re a species of concern in the United States,” Bakker said. “We have more of their populations in the Great Plains so it’s a bigger concern for us. They’re showing declines throughout their range.”
The western burrowing owl – Athene cunicularia hypugaea to ornithologists – was once common across all of South Dakota but has now disappeared from most of East River except in the plateau region called the Missouri Coteau, a short way east of the Missouri River. Most of the state’s ground-burrowing owls now are found west of the Missouri River, usually living in prairie dog towns.
“In western South Dakota or South Dakota in general, probably 99 percent of our burrowing owls are in prairie dog burrows,” Bakker said.
Although most scientists don’t believe burrowing owls eat prairie dogs – they prey instead on insects such as beetles and grasshoppers and small mammals such as mice and voles – they use the burrows as dwellings and they seem to like the visibility that a closely cropped prairie dog town affords.
Bakker, who specializes in grassland bird research, said that close association with prairie dogs makes it easy to look for the owls: Simply visit prairie dog towns.
She and a graduate
student working toward his master’s degree, Jason Thiele, traveled in 25-mile routes all over western South Dakota in 2010 and 2011 to do that.
They surveyed 231 prairie dog colonies and found burrowing owls on most of them.
“We estimated we hit only 25 percent of prairie dog colonies, and we found 600 pairs. We recorded over 1,200 adult burrowing owls,” Bakker said.
If they visited roughly one-fourth of the prairie dog colonies in the state, that would suggest that a number of at least 2,400 breeding pairs of burrowing owls in the state, or two and a half times as many as the best-case scenario in that previous estimate.
The bad news?
As Bakker notes, they have vanished already from much of East River.
“The whole grassland bird suite is in trouble,” Bakker said. “They’re linking it mostly to habitat loss and invasive species such as smooth brome grass and some woody species. All grassland birds are declining. They evolved with seas of grass, no woodland, no cropland anywhere.”
Bakker said the DSU study also looked at differences in colonies where burrowing owls are found compared to those where they are not. They noted that the amount of woodland within 800 meters of a colony negatively affected the likelihood of finding burrowing owls. Bakker suspects that may be for two reasons. Those woodlands, which aren’t native to the grasslands in most cases, may harbor predators. And they might also act as barriers that hinder the owls as they hunt from the air.
Bakker said tall and thick vegetation around a colony had a similar negative affect on whether burrowing owls were found there, perhaps for similar reasons.
“They need to be able to see around for predators and prey,” Bakker said.
Bakker said there may be room for follow-up studies to further find out what makes burrowing owls successful in some locations in western South Dakota.
Bakker – who is just beginning a study involving two other grassland species, Sprague’s pipit and Baird’s sparrow – said the DSU study is reason for cautious optimism about the resilience of grassland birds if only habitat remains available.
“If we can keep our prairie, we’ll keep our birds,” Bakker said.