On November 27, 2017, at 10 am, we were birding south along the road at Parker River NWR and after enjoying a Cooper's Hawk hunting low, we stopped at the Salt Pannes Wildlife Observation Area to check out the ducks and geese. The ponds at this area are important to us since one of us is mobility-limited and there is usually something interesting here that we can see from the car. First, we saw two Peregrine Falcons circling above and then noticed a Northern Harrier hovering low over the water south of the main pond. After a few minutes, we realized that the harrier was not doing its normal gliding and searching over the marsh grasses but was focused on one area over the water. After a few more minutes, one of the Peregrines stooped down, repeatedly harassed the harrier, and then perched on a swallow house and stared at it. A second harrier arrived, flew over the first harrier—still hovering over water—and chased the Peregrine away. Then the second harrier itself flew away.
Since we were blocked by vegetation from seeing what was attracting the harrier, we drove south to the smaller pool north of parking lot 3 to gain a better perspective. The harrier seemed to be interested in a tight flock of American Black Ducks, which seemed more annoyed than fearful of the harrier, probably because of their large size. We couldn't understand what the harrier was doing as we assumed it wasn't after a Black Duck. Finally, we noticed that a small duck—later determined to be a male Hooded Merganser—was diving repeatedly among the Black Ducks. The harrier kept trying to catch the merganser, making it dive quickly without much chance to breathe between dives. On the merganser's last dive, it surfaced behind the group of Black Ducks. The hovering harrier pounced, lowered one leg, and grabbed the merganser. The harrier flew low with its prey and landed in the marsh too deep in the vegetation for us to see. The whole episode took 15 minutes, as the harrier tried for the merganser many times before successfully catching it.
In the species account, in The Birds of North America (Smith et al. 2011), the only mention of harriers taking waterbirds is in "southeastern coastal marshes devoid of mammals." We do not know the status of small mammals in the refuge's marshes. The species account further states that harriers are known "to subdue large prey by drowning," but this harrier's attack didn't seem like drowning—it was more like exhausting its prey.
In our 40 years of birding we have never seen a harrier take a duck and no one we spoke with on the refuge had ever seen it either.
- Smith, K. G., S. R. Wittenberg, R. B. MacWhirter, and K. L. Bildstein. 2011. Northern Harrier (Circus cyaneus), version 2.0. The Birds of North America (P. G. Rodewald, ed.). Cornell Lab of Ornithology; https://doi.org/10.2173/bna.210