Monday, August 30, 2010

PostHeaderIcon Scattered birds of prey sightings and the changing of the season...

The doldrums...

There hasn't been much news to report, but that's typical of this time of year.

The trials of nesting season are largely behind us. The gnashing of bloody bills in combat to the death, the infanticide against your neighbor's young, the desperate pursuit of a morsel of food that might help to sustain your brood of one to three needy young furries, the solemn necessity of bloodying a newly airworthy young gull that accidentally flies into your breeding territory... it's all largely over and it's given way to this:

Quietude. I wonder if the gulls have the capacity or the inclination to sigh in relief. Perhaps they know that a respite like this lasts only until next spring. Then, we'll live the horror again.

Personally, I wonder if these birds find themselves relieved that they can again indulge in a diet of discarded chicken and other trash.

Who could know?

Birds of prey spotted on Alcatraz

When a red tailed hawk has occasion to visit us on Alcatraz, the gulls, occasionally with a bit of help from the ravens, give the invader the boot. One recent example:

And this is what it does to the gull colony:

They go crazy. While I've heard rumors that red tailed hawks have had their way with a juvenile gull here or there, my experience in the six or so hawk invasions I've seen over the last two and a half years is that the hawks are harassed and pestered by several hundred gulls until they simply leave with nothing.

Why the ravens choose to get involved seems mysterious at first, but they engage with the invaders to ensure that birds of prey don't take advantage of the ample food resources that avail themselves on the ravens' island. Our two ravens preside over a large seabird colony equipped with thousands of large gulls ready to repel any visitor sporting broad wings and a sharply hooked bill.

These ravens are quite serious about protecting what's theirs. Our apex predators will do all they can to ensure that any winged animal adapted for killing finds its way off the island.

BourbonHawk and I recently witnessed an example of this first hand:

An unidentified juvenile hawk perched on a fence outside the entrance to the Alcatraz cellhouse. One of the National Park Service's fabulous bird interns helped us to conclude that it was probably a red shouldered hawk.

Just as soon as the young raptor arrived, one of our large ravens landed next to it and began to examine it up and down, quizzically, as if to ask, "youngster, just what are you doing here?"

Well, after just a few seconds of physical or social discomfort, the young hawk flew off to the north side of the island, causing a terrified cacophony among the gulls there. C'mon gulls! It's just an immature red tail; grow a pair!

Lastly, on the raptor note, falcons have sadly not been seen since our last post.

The year of the California gull comes to a close:

Earlier in the year, we could reliably expect to make constant visual and auditory contact with these holy-to-Mormons gulls on every outing. Now, we don't see them much at all.

Breeding California gulls have recently increased their numbers on Alcatraz and they did so markedly in the summer of 2010, perhaps because the South Bay salt flats that brought them so much reproductive success in the last thirty years are undergoing conversion to tidal salt marshes. Some of the displaced birds may have bred on Alcatraz.

An interesting tidbit from Alcatraz's pro biologist: the California gull eggs are laid and hatched a week prior to those of the larger and more numerous western gulls. It's hard to say but this may offer the Californias a tiny bit of protection against their larger cousins.

Both western gulls and California gulls also breed on the Farallone islands just 27 miles outside the Golden Gate. There, the California gull eggs and young are universally predated by western gulls, giving the impression of impermanence to the California gulls' first recorded nesting habitat on the open ocean.

The news isn't all bad for our CAGUs... in 1982, they sported 200 breeding birds in the San Francisco Bay Area. The recent salt marsh restoration not withstanding, they reached 46,800 birds in 2008. Holy birds, indeed.

On Friday... a special seabird has returned to us. You might say that it has 're-terned!' Haha, puns are awesome.


Anonymous said...

great photos of the juvie red-tail!

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