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!
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.