Friday, August 31, 2012

Shorebirds and Raptors at Delta Lake

A flock of mostly Least Sandpipers feed in the shallow water at Delta Lake
 We have few local places where migrant shorebirds can gather, which is understandable since we're located so far inland. Our closest thing to a shorebird “hotspot” is Delta Lake. In years when they draw down this reservoir’s water level, mud flats are exposed and shorebird habitat is created. Of course, just because you have the habitat doesn't mean the birds will come.

Shorebirds come in a variety of sizes, which enables the different species to forage for food in various depths
In recent years, shorebirds have not been flocking to Delta in droves. Low numbers probably reflect smaller overall populations of these species. Factors that affect their numbers include degradation of habitat on their breeding grounds, wintering grounds and at their migratory stopovers. Of course, the vast majority of shorebirds migrate along the coast, so in a way, we are lucky to see any at all in our area.
The Semipalmated Sandpiper is often quite common in mixed shorebird flocks
Though Delta has been known to bring in a few regional rarities over the years --birds like the Marbled Godwit and the Buff breasted Sandpiper, in recent times we consider ourselves fortunate just to locate the more common species like the Lesser Yellowlegs and the Least Sandpiper.
A Merlin perches over the mudflats and waits for a good target bird to come into view
Where shorebirds congregate you also tend to find their predators. Falcons like the Peregrine, Merlin and America Kestrel try their luck chasing down and nabbing unfortunate shorebirds. Sometimes you might infer the presence of a falcon, just by observing the erratic and restless behavior of a shorebird flock. A harassed flock might put down on a given piece of shore only briefly before taking flight again.  While retaining a tight formation, the shorebirds execute rapid changes in direction. These evasive maneuvers are similar to those employed by schools of fish.

Another Merlin watching the flats
My last visit to Delta was rather raptor heavy; I saw a pair of immature Peregrine Falcons zooming over the flats, stirring up the waterfowl and shorebirds. A one point the pair sparred with each other, but in a friendly manner –perhaps they were siblings.
One of 4 Juvenile Bald Eagles that have been seen lately at Delta
About half the size of the Peregrines, a pair of Merlin's were also present that day. Despite their small size, Merlins are fully capable of whipping shorebirds into a frenzy. They also chased after each other in a much less friendly manner than the Peregrines.
A Great Egret hunts for fish that have been stranded in the shallows
As the water gets increasingly shallow, fish often get stranded in isolated pools and this creates a draw for a diverse group of avian predators. Bald Eagles, up to 5 of them were hunting for fish –either to catch for themselves or to take from other fisher birds, like the Osprey.
Double-crested Cormorants show up to fish the Lake
Wading birds also gather in number to take advantage of the easy fishing. Great Blue Herons are the most prevalent, but Great Egrets are also fairly common. Lately, up to 6 egrets have been seen around the lake.

Lesser Yellowlegs
Waterfowl numbers continue to increase as the migration season gets underway. Many Wood Ducks and flocks of teal are already there. Black Duck and Hooded Mergansers can also be picked out among the many Mallards and the throngs of gulls.

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