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Posts Tagged ‘Cooper’s Hawk’

You are walking down a trail in a city park right here in the city of Berkeley. As it winds its way between huge boulders and beneath overhanging bushes, your attention is drawn up into a nearby tree by the sound of scratching. There, a squirrel is scrabbling up the trunk of a tree. As it ascends you notice a thick mat of sticks higher in the tree, way up near the tree’s crown. Is it the squirrel’s nest? The squirrel climbs higher, and then moves beneath the lower edge of the stick platform and then up around the side. As the squirrel begins to get on top of the mass of sticks, it is met with the oncoming rush of the beak and talons of a female Cooper’s Hawk. The mass of sticks is not squirrel’s home, it is the Hawk’s. The squirrel is in full retreat now, and the Cooper’s Hawk in full pursuit. The squirrel begins racing in the direction in which it can go the fastest, strait down the tree trunk. The Cooper’s Hawk immediately drops after it, skimming strait down along the bark of the tree. As the hawk gains, the squirrel jumps, letting go of the tree completely and free-falling into the bushes below. It is only then that the hawk gives up the chase and returns to her nest.

What you just witnessed was the defense of one of about a dozen Cooper’s Hawk nests in Berkeley and Albany. Cooper’s Hawks in Berkeley? That’s right. These roughly crow-sized predatory birds get along quite well with humans and the cities humans live in. They eat birds and small mammals which they often capture by ambushing their prey in dense vegetation and then chasing it down in a burst of speed. They are superbly adapted to this style of hunting with short rounded wings which give the speed while not getting hung up on foliage and a long tail which acts and a rudder allowing them to turn and twist through thick undergrowth and not lose their prey.

The ability to live well with humans is unusual for a predator. Most birds of prey are too sensitive to disturbance to live in such close contact with humans or need larger areas of open spaces in which to hunt than are available within such a human-dominated landscape as downtown Berkeley, but Cooper’s Hawks find a way. They are so tolerant in fact, that in Berkeley and Albany, more Cooper’s Hawk nests can be found per square mile than in any other recorded area in North America. They nest in mature trees in almost any kind of habitat from quiet city parks to busy city intersections. And Berkeley in not alone in being an urban area that has nesting Cooper’s Hawks. In California, most urban areas have populations. Outside of the state, populations that have been studied in some detail include urban areas of Arizona, Illinois, and Vancouver, Canada.

Beginning about 15 years ago, a group of dedicated volunteers have been keeping tabs each year on the levels of Cooper’s Hawk activity in Berkeley. The group, the Cooper’s Hawk Intensive Nest Survey (CHINS), has divided the 10.4 square miles of Berkeley into smaller units. Each volunteer takes responsibility for one of these units, and searches it to locate and track the presents of Cooper’s Hawks. Searching begins in late January when the hawks first arrive in the area back from their wintering grounds, and continue all through the breeding season until the adults and a new generation of young Cooper’s Hawks depart to return south in August. In between, many observations are made and recorded such as when the hawks arrive, when nest building begins and ends, how many young hatch and when, how many young fledge and when, what they are eating and how much, and finally when the adults and young disperse.

Some the information that CHINS has found is that while Cooper’s Hawks nest in greater density in Berkeley than elsewhere.Also, they are eating a lower number of species then in more rural areas, and of these fewer species a large portion (~33%) are Rock Pigeon, European Starling, and other species that are not native to California. On this limited diet, the hawks are able to breed just fine with most nests fledging 3-4 young each year.

The CHINS project is a branch of the Golden Gate Raptor Observatory, and both are examples of scientific studies made possible by volunteers from the community working to monitor and record raptor populations. Cooper’s Hawks, and birds of prey as a whole, can function as indicators of ecosystem health and stability. This makes them especially important and useful to study, and the fact that individuals from the community are able and willing act as citizen scientists and devote their time and energies to such an endeavor show both that such work can be done and that there is interest and support that such work be done.

To find out more about the CHINS Contact Allen Fish at (415) 331-0730 and find out how you can help protect your raptorial neighbors.

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Over the past couple of weeks spring has been becoming ever more evident in central California.  For one, large flocks of American Robins have been showing up.  These are likely groups of Turdus migratorius propinquus, large and pale subspecies, that are migrating from their wintering grounds in central Mexico, through central California on their way to their breeding grounds which could be anywhere from northern California to British Columbia or Montana.  I saw another sign that spring is in the air Tuesday as I was walking across campus.  Near one of the large lecture halls, I heard and saw a male Cooper’s Hawk kekking from the top of a large tree.  This was the first Cooper’s Hawk breeding behavior that I have seen this year, and two day later I saw and heard him again in almost the same spot.  Hopefully he will attract a female and set up a nesting territory here.  It would be a lot of fun to watch.  Another breeding behavior that I have just seen starting is that the male House Finches have stated mate-guarding the females.  I watched one particular male as he followed a female around as she foraged, and repeatedly chased off other males that approached too close to the female.  A final sign from the birds that the seasons are changing was a male Nuttall’s Woodpecker checking out cavities as potential nesting sites.  He was moving through a couple of dead trees in West Sacramento, and stopping at any hole he could find.  he would take a few moments at each to look at the external hole, and then stick his head in to take a look at the interior.  He rejected all the contenders save for one, which he poked his head into, and apparently liked.  He climbed all the way in, and over the next 10 minutes or so that I stayed to watch, he did not come out.  Apparently that was a good spot!  To add to these avian signs of spring is one of my favorite plant signs.  The fruit trees that fill the orchards and line many of the streets in the West Sacramento and Davis areas are all in bloom!  I do love the beauty of trees covered in small white or pink blossoms.

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