mjm@oliven.olivetti.com (Michael Mammoser) (08/24/89)
Last weekend I participated in the shorebird census that is conducted by the Point Reyes Bird Observatory. I was assigned a section near the east end of the Dumbarton Bridge at the south end of San Francisco Bay. Basically, the exercise was supposed to be a couple of hours of counting the multitudes of Least and Western Sandpipers, Willets, and Marbled Godwits with a few of the more interesting birds interspersed: a Spotted Sandpiper, a Snowy Plover, and a few Baird's Sandpipers. Then there was the falcon. I had slogged through a small pickleweed marsh and was standing at the edge of San Francisco Bay scoping the tidal flats. The tide was out and the water's edge was over 100 yards away - and most of the shorebirds with it. I was panning along the water line counting peeps by hundreds; 100, 200, 300 ... Then suddenly all the birds were up in the air. After my initial frustration at losing my count, I realized that something must have put the birds up. Scanning the air, I spotted a large dark bird above the wheeling flocks of shorebirds. Looking at it through my binoculars, I recognized it as a Peregrine Falcon; the dark blackish helmet and upperparts and the short dark streaks running across the width of the body on the underparts identified it as an adult. As a large flock of peeps flew in a circle (a foolish maneuver, I thought), the peregrine stooped from about 40-50 ft. above them. It pulled up short and quickly regained altitude to stoop again. I was impressed by the powerful flight of the falcon; its shallow, seemingly lazy, wingbeats belying its ability to attain great speed in flapping flight. I was soon to be even more impressed; for, after a number of shallow stoops, it scattered a few individual peeps out of the flock. One took off across the mud flat about ten feet above the surface with the falcon in hot pursuit. In the space of about thirty yards the falcon overtook the peep, reached out one of its big yellow feet, and snatched the bird right out of mid air. It then turned and flew towards me, looking for a convenient perch. As it approached I could see the light buff coloring of its breast, marking it as a member of the subspecies "anatum". It flew so low overhead that I could even identify the Least Sandpiper that it clutched in its talons. Although I have seen Peregrine Falcons before, this was the first time that I had watched one make a kill. Before this, the closest I had come was at Elkhorn Slough along the coast of Monterey Bay. There, I watched a juvenile stoop repeatedly on a flock of phalaropes before it gave up and flew off. Other people there said that it was just playing and that it was typical for peregrines to do so. After watching this incident at S.F. Bay, I believe that the "playing" theory is just anthropocentric. I don't think that a falcon will make a strike into a flock, out of fear of injury in a collision. It stoops on a flock in order to scatter individuals, which it then chases independently. If individuals don't scatter out of the flock, the bird gives up and looks for other opportunities. Rather than "playing", I believe that these are failed hunting attempts. At any rate, this observation lent a little dramatic spice to an otherwise predictable morning of counting. Mike