A model of coexistence?

As a general rule, complete competitors in the natural world cannot coexist, unless they divide up the resources somehow, by hunting in different areas or at different times, or specializing on slightly different food items in their diet.

On the wet prairies and marshes at Cheyenne Bottoms and Quivira National al Wildlife Refuge near Great Bend, Kansas, we saw several Short-eared Owls and and as many Northern Harriers, not only hunting in the same areas and habitats, but at the same time of day!

A Short-eared Owl landed in the grass after an unsuccessful prey capture. Some studies show that owls are successful capturing mice in open grasslands about 44% of the time.
Short-eared Owls traverse the fields in short, coursing flights, searching the same area intensively and listening for mouse activity. Long wings make gliding over the habitat seem effortless.
Northern Harriers make rapid flights across longer distances than the owls, turning infrequently and flying quickly. If they detect movement, they may hover over a spot, honing in on the prey.
Short-eared Owls hunt by sound, even though they are usually hunting in daylight. Their facial disks collect the infra-sounds that active animals make like a parabolic reflector and relay it to their ears. The owls consume mostly rodent prey, especially while feeding young.
Head down is the way we usually see Harriers hunting. Unlike other hawks, Harriers use hearing as well as vision to find their prey. Rodents make up a big part of their diet as well, but they also eat large insects, amphibians, and reptiles, as well as birds.

One study of niche overlap of Short-eared Owls and Northern Harriers in Utah found that their home ranges overlapped as much as 70%, but within their home range the two raptors hunted and nested in different parts. In addition, in this particular study, the owls tended to hunt most intensively in the mid-afternoon, while the hawks concentrated their hunting in the evening hours before dusk. So, even though the two raptors seem like complete competitors, they seem to have found a way to share the resources cooperatively…usually.

However, Sean Crane (500 pix) photographed a Harrier and a Short-eared Owl fighting over a vole in Washington — which is evidence that the two don’t always get along.

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