Short-eared Owls

 

A Short-eared Owl (Asio flammeus) watches for prey from atop a Honey Locust sapling. It was in the midst of hundreds of acres of grasslands. At least ten other owls shared its haunts, and at least as many Northern Harriers (Circus cyaneus).

A favored winter activity of birders, your narrator included, is watching Short-eared Owls. The charismatic raptors move southward from their breeding grounds in cyclically varying numbers. Some years, like this, there are lots of short-eareds about (at least in Ohio). In other winters relatively few are to be found.

On December 22, I made a trip to an area in north-central Ohio that is playing host to many owls. They were on the wing by 4 pm, but heavy cloud cover meant the light was poor. So, killer photos were not possible, but I share some documentary images here.

A Short-eared Owl sits atop a road sign. As long as observers are quiet, the owls pay us little mind. I crept up on this bird in the vehicle, was able to get to about 30 feet from it, kill the motor, and watch. It was beyond dusk by this time, and light was extremely poor. Much post-processing was necessary to make the image presentable. But making great owl pictures is at best half the fun. Photos or not, Short-eared Owls are charismatic and always interesting to watch.

I was pleased to see that an owl would habitually return to hunt from that locust sapling in the first photo. It meant that there would be plenty of action. Short-eared Owls are fiercely anti-social when hunting, seem to maintain loose territories, and don't hesitate to scrap with other owls (or other raptors). Several times passing owls would drop down to take a swipe at the bird in the locust. That triggered locust-owl to shoot aloft and engage the other in a dogfight, as above. Such squabbles are an aural treat, as the owls bark like angry terrier dogs, and emit low cat-like screams.

A short-ear on the hunt. Incredibly acute eyesight and hearing enable them to pick up the slightest movements and sounds caused by rodents below.

Quick as a wink, this owl pirouetted on a dime and dropped hard into the grasses. I saw many such hunting attempts this evening, and nary a bird came up with prey. The miss rate is often very high.

This is a Meadow Vole (Microtus pennsylvanicus) runway. The burly little rodents are probably the primary prey source for Short-eared Owls and Northern Harriers, at least in these grassland habitats. Vole runways, or raceways, are tunnels in the grass that mostly are hidden by a grassy roof. Occasional openings, as above, will briefly reveal the rodent to raptors coursing overhead.

But I do not think that the owls need to rely on visual identification of prey items such as voles. They likely hear the rodents scurrying through the tunnels, or perhaps gnawing on vegetation. Even with the fine-tuned senses of a Short-eared Owl, it would still be a tall order to pounce unerringly on a vole, sight unseen, especially if it is moving. This may explain the seemingly high miss rate, although rest assured, the owls get many, many voles.

A Meadow Vole dares to peek from a runway. A dash across open ground when lots of raptors are present is a suicide mission for the chunky rodents. Better to stay in the tunnels to up one's survival potential.

Meadow Voles have marked boom and bust cycles. Peaks can occur anywhere from every other year to every third or fourth year. The reasons for these fluctuations are imperfectly understood, but one thing is for sure: raptors quickly pick up on areas rich in the rodents. It has been claimed that at least some raptor species can detect vole urine trails visually, as their eyes can detect ultraviolet reflections in urinary compounds. Thus, the birds would view urine trails as easily seen purple squiggles, thus allowing vole-hunting raptors to quickly ascertain areas of food abundance and forgo areas with a paucity of prey. Much has been written about vole urine/UV/raptors, such AS THIS.

This all makes for a great story, except it may not be accurate. CLICK HERE for a paper that delineates the ability of select raptor species' ability to see into the reflective range of ultraviolet light, and how that compares with UV reflectance from vole urine. It may just be that avian vole-hunters such as Short-eared Owls, Northern Harriers, American Kestrels, and Rough-legged Hawks simply find troves of voles through their extraordinary vision, abetted in the case of the owl and harrier with highly attuned hearing. I have been in sites experiencing very high vole numbers on several occasions, and it was not difficult to detect voles, so many were racing about. Raptors, with their far sharper vision and ability to get an overhead perspective, undoubtedly quickly assess vole populations.

UV-reflective vole urine aside, Short-eared Owl watching is great fun (except for the voles). I hope you get to experience some of these charismatic hooters this winter.