Photo by IDNR.
Observations on Short-eared Owls
Wintering Short-eared Owls in Illinois
Short-eared owls (Asio flammeus) are sometimes called the ghosts of open country and grasslands. I did not quite appreciate the meaning behind this until my collaborators and I started studying the species. Perhaps it has to do with its crepuscular nature or the bird’s low, stealthy cruising above ground. What is clear to me is their nomadic tendencies, and hence the unpredictability of their local presence, have made studying short-eared owls challenging. Not only that, short-ears are very difficult to catch, too, just like ghosts…
Short-eared owls have experienced a steep decline over much of their North American range during the past half-century. Habitat loss and degradation at their wintering grounds, and in places where the owls occur year-round, are considered the most likely major threat for the species. Therefore, we set out to investigate its winter ecology, including their habitat selection for winter roosts, diet and local movement. Our findings were based on field work done before the pandemic at study sites in the Grand Prairie Region of central Illinois, a landscape dominated by row-crop agriculture.
Short-eared owls showed preference to areas of predominantly smooth bromegrass (Bromus inermis) in selecting winter roosts, with 46 percent of roosts found in uniform smooth brome. On average, short-eared owl roosts had taller vegetation than random sites, and vegetation heights found at roosts were more variable than those suggested by previous literature. At the landscape level, grassland area was a significant predictor of short-eared owl presence, with the owls preferring larger grassland parcels. However, neither grassland area nor the land cover within one kilometer of grassland parcels was found to influence the density of short-eared owl roosts at a site. Our findings suggest habitat managers focus efforts on grassland parcels at least 70 acres or larger and encourage the growth of native grasses that would provide similar vegetation structure as smooth brome if smooth brome is considered undesirable at the site.
Little is known about local winter movement and habitat use of short-eared owls. Throughout our study period, we were only able to capture and radio-tag one short-eared owl. We found this owl’s monthly home ranges showed contraction and expansion in accordance with the fall and rise of monthly temperatures, with the smallest monthly home range (2.6 km2) observed in January and the largest (10.9 km2) in March. Throughout the entire tracking period, 81 percent of the owl’s locations were equally divided between agricultural fields and cool-season grass (i.e., smooth brome) areas. In January, when it was the coldest, more than half of its locations were in the cool-season grass areas. On the other hand, when it became warmer in February and March, more than half of the locations were in agricultural fields. Warmer temperatures appeared to allow the owl to forage more in the agricultural fields with little to no cover. Ambient temperatures might affect local winter movements of short-eared owls.
Although the literature on the diet of short-eared owls during the non-breeding season is extensive, relatively little is known about its diet in Illinois where the short-eared owl is a state-endangered species. We asked: Does the short-eared owl appear to be more of a specialist predator or opportunistic predator in Illinois?
We collected and analyzed close to 400 intact pellets of short-eared owls. Based on the skulls found in the pellets, we were able to identify six different species of small mammal, including meadow vole (Microtus pennsylvanicus), prairie vole (Microtus ochrogaster), deer mouse (Peromyscus maniculatus), white-footed mouse (Peromyscus leucopus), northern short-tailed shrew (Blarina brevicauda) and North American least shrew (Cryptotis parva). The meadow vole was the most common prey species, accounting for more than half of total prey items identified. With the exception of meadow vole and northern short-tailed shrew, the other species have a statewide distribution. The distribution of meadow voles is limited to the top third of the state, mainly in the Grand Prairie Division, while northern short-tailed shrews can be found in the northern two thirds of the state. Our findings suggest that meadow voles dominated the winter diet of short-eared owls in the Grand Prairie Division of Illinois, which is different from the prior findings. Based on our own findings and those from the earlier studies, it seems short-eared owls are more of an opportunistic predator that would take any prey of suitable size available to them in Illinois. In addition, we found relative abundance of pellets consistent with relative abundance of owls in our study. Perhaps searching for owl pellets can be used to track the relative abundance of short-eared owls over time.
Tih-Fen Ting received her Ph.D. in Natural Resources and Environment from the University of Michigan. She has a M.S. in Wildlife from Humboldt State University and a B.S. in Biology from Tunghai University. Her research interests include conservation ecology and population-environment interactions. Broadly speaking, Dr. Ting is interested in examining and finding ways to conserve species, habitats, and ecosystems in our human-dominated landscapes. A major focus of her research program has been on the conservation and recovery of threatened and endangered species, including state-listed species such as Franklin’s ground squirrel, osprey, and short-eared owl. Students in her lab investigate population dynamics, occupancy, habitat use, and movement ecology of various wildlife. The research program of Ting Lab builds on the principles of conservation biology, population ecology, population genetics, ecological and spatial modeling, natural resources management, and other disciplines.
Short-Eared Owl: Personal Experiences
The first time you see a short-eared owl hunting a grassy or marshy area at dawn or at dusk, you remember the experience. This owl flies very low over the grass in a sweeping, but irregular motions; appearing like a long, narrow piece of brown wrapping paper; being blown by a gentle, but uncertain wind; as it searches for small rodents and birds.
Now classed as state-endangered, short-eared owls were once one of the most common owls of Illinois. Today, they are an uncommon winter resident and a spring and fall migrant throughout the state. Only rarely do they nest in the state, and then only in expansive grasslands and marshes. Goose Lake Prairie in Grundy County has been a known locale for nesting. Short-eared owls nest on the ground in tall grasses and reeds. Usually, four or more white eggs are laid. And the female incubates them for 21 days, while the male brings her food.
Most of my sightings of them occurred on large, nearly contiguous tracts of CRP land on the Gifford Moraine in northern Champaign County. These fields had been in the CRP program for a number of years. I drove through this area early and late each day; going to and from work; all the while looking for this owl, hunting the gentle slopes of the moraine.
This CRP sanctuary has since been plowed up in hopes of higher soybean and corn prices. No more brown strips of life pulsing over the land.
A good friend was on the alert while driving in darkness, knowing seeing this owl was a real possibility given the extensive grasslands on one side of the road. At dusk or in the early darkness, be very cautious when driving through short-eared owl country. Reduce speed and be keenly aware. Often, there is little or no warning because owls fly low and may come in from the side of the vehicle. Suddenly, one flew just barely over the top of Jim’s pick-up. The radio antenna clipped its wing. Jim stopped and searched but did not find the owl. Returning early the next morning, he found the injured owl in the field just next to the road. He threw his coat over the agitated and aggressive owl and subdued it. Once home, Jim called the University of Illinois College of Veterinary Medicine Wildlife Medical Clinic (vetmed.illinois.edu) as soon as they opened and took the owl to the clinic.
The injured wing was tended to, the owl was placed in rehab for a time and then released back into the wild. A storybook ending! Be very careful when driving through short-eared owl country in the dark. You may have an incident with this owl that may not end as well.
Robert J. Reber is an emeritus faculty member in the Department of Food Science and Human Nutrition of the University of Illinois at Urbana–Champaign. He has been a lifelong student of many aspects of the Natural World, including archaeology. Bob has served as a managing editor and author for publications such as The Illinois Steward magazine and the Illinois Master Naturalist Curriculum Guide.