I would love to know how many thousands of years this struggle has been going on. The Short-eared Owl (SEOW) and Northern Harrier (NOHA) are separated genetically by millions of years, currently existing in separate orders. The SEOW belongs to the Strigiformes and the NOHA falls within the Accipitriformes. However, they have evolved to have similar lifestyles that have placed them in similar niches and thus, pushed them into direct competition with each other.
Yes, technically, the SEOH has developed more of a nocturnal habit and the NOHA is more active in the day. However, both species are highly crepuscular (active near dawn and dusk) and the SEOW is one of the most diurnal owl species, routinely hunting during daylight hours. They also use the same prey sources – primarily feeding on small rodents like mice and voles in winter. Additionally, both species have similar hunting strategies of flying low over the prairies, meadows and agricultural fields, using both their keen sight and hearing to locate their favorite scuffling mammals.
On average, harriers are roughly 25% larger than the SEOW but the wingspan of both species is nearly identical. Short-eared Owls use this increased wing area to their advantage with increased maneuverability. They can find themselves on the menu of NOHA but this is a much more challenging prey for the harriers who usually prefer their acts of kleptoparasitism (stealing another’s food).
After spending dozens of hours this season watching these two species forage across these grasslands of Lincoln County, MO I can attest that both species are terrific hunters. However, I think it’s safe to say that the SEOW has the higher success rate. They were not successful every time they plunged into the vegetation but more often than not, we saw these birds rising with a recently departed vole or mouse in their beak or claws.
An observation I found interesting is that when the SEOW made a successful kill, they almost always would fly a short distance and either eat it on the wing or, more often, would land in a new place to consume. I can only speculate that they do this because they think the act of catching the prey may alert would-be kleptoparasites and they move with the prey to get a better idea of who may be watching. On the other hand, it could be argued that this action could make it more obvious that they have had a successful kill and potentially ring the diner bell. Here is another interesting question.
It’s a complicated relationship, for sure. I do not know for certain, but I would anticipate that the NOHA gets a significant portion of their caloric needs from the SEOW – or at least in this particular setting. As I mentioned earlier, the SEOW are so successful, it appears they can take this loss with little significant impact – or at least in a setting such as this with ample rodent populations. It may be a completely different scenario when they find themselves in a less productive area.
On numerous occasions, Miguel and I watched as the SEOW took a much more aggressive and territorial stand. They were much more likely to pick a specific area that they foraged in and defended, often chasing NOHA and other SEOW away from their lands. NOHA, on the other hand, appear to cruise much more at random.
I have read that others have documented the swings in the numbers of SEOW from year to year and location to location based on the availability of prey. It is also well known that the SEOW is one of the most migratory of owl species. In the years we have followed these birds in Lincoln County, we can attest to this. If not already done, it would be really interesting to see the results of an in-depth look at the population dynamics and migration patterns of the SEOW and determine what role, if any, the NOHA may play.
Finally, I tapped into the inner comic writer in me and produced this silly little GIF that personifies the above interaction. I apologize if I offended anyone with my bad attempt at using a Cockney accent for the “villain” of this story… 😉
A Thousand Acres of Silphiums 
This is great, thanks so much for sharing…