Hi,
Yesterday I finished our winter hawkwatching field trips on the Samish
Flats here in western Washington. At the end of the trip, just prior to a
rain squall, we observed a wonderful interaction that deserves to be
described and shared.
As we were leaving the West 90, I caught sight of a second year Bald
Eagle circling under a Short-eared Owl. They were already about 200 feet up.
Looking at the owl, I saw that it was carrying prey in its foot, most likely
a vole. The eagle had also observed this prey and was chasing the owl in an
attempt to pirate it.
Of course, Samish is famous for its high degree of kleptoparasitism
among raptors at this time of year, so we all jumped out to watch what would
happen.
The owl was using a "ringing" strategy (i.e. rising up into the air) to
keep away from the eagle. Even laden with its prey, the Short-ear had
lighter wing-loading than the eagle and was able to keep above the larger
bird. It spent most of the time both above and slightly behind the Bald
Eagle where it could keep its eye on the threat.
We watched this interaction for several minutes wondering which bird
would tire first and retain the prey. I would estimate that they got up to
between 500-700 feet.
As we watched the two birds so very far up, a falcon suddenly shot into
view and made two passes at the eagle, harassing it. It was the immature
brown gyr that many of you have seen at the West 90 this year. It had seen
the laden owl and flown up to compete with a Bald Eagle for the prey.
After the two passes at the eagle, the falcon easily lifted up towards
the laden owl which recognized its peril immediately and dropped the mammal.
The Short-ear knew it could outfly the eagle but it was no match for the
gyr. I don't think I have ever seen any bird rise up so fast as a determined
Gyrfalcon.
We all watched the prey fall and saw both the eagle and the falcon dive
vertically down to catch it. A Bald Eagle diving straight down is a sight to
see but the gyr passed it like it was standing still, grabbed the prey and
rocketed off to the west.
I thought the interaction was over but the gyr almost made a fatal
mistake. As it flew away, you could see it leaning down examining or biting
at the prey in its foot. Falcons often bite their prey in the neck in flight
immediately after capture. As it did so, the eagle noticed the vulnerability
and dove straight towards the preoccupied falcon. The eagle had a slight
height advantage and came in hard and fast.
The gyr saw it coming and did two extremely quick dodges, evading what
could have been its demise. Several falconry gyrs have been killed by Bald
Eagles with a height advantage.
The falcon then set its wings and descended straight to its usual perch
(the tall post) west of the 90 and ate the prey in minutes.
In the past, we have noticed that in late winter, some gyrs on the Samish
tend to switch their prey preferences from birds (primarily ducks) to
rodents pirated from Northern Harriers and now Short-eared Owls. We suspect
that this is a behavioral adaptation generated by piracy from Bald Eagles
that arrive in high numbers on the Skagit Flats system in mid-February.
Any falcon foolish enough to catch a large duck in front of hungry Bald
Eagles will soon learn about piracy. Since falcons can't carry large dead
ducks (widgeon, pintails, etc.)very far, they have no means to escape with
their prey and it will be taken by the larger and stronger eagle.
Since gyrs eat mammals in the arctic, they can adapt to voles during our
winters and they catch them by observing and then and kleptoparasitising
laden harriers.
The equivalent avian prey for wintering peregrines on Samish is Dunlin,
another easily carried prey species.
Anyway, it was a spectacular way to end the season. I am constantly
amazed by the abilities of gyrfalcons.

Bud Anderson
Falcon Research Group
Box 248
Bow, WA. 98232
360.757.1911