Monday, August 30, 2010
9:13 PM | Posted by Sweep Commander | Edit Post
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.
Friday, August 20, 2010
2:14 PM | Posted by Sweep Commander | Edit Post
There hasn't been much news to report lately- nesting season is humming along and slowly winding down. Dead juvenile WEGUs have been showing up here and there but outside of a few scattered reports of peregrine falcon sightings, there hasn't been much to report.
We've all been biding our time, waiting for the late autumn wave of migrating raptors that might return our departed femme falcon to Alcatraz. She spent the winter of 2009/2010 with us and we want her back:
She tore flesh from flesh on the top of tall buildings and we dearly miss her. Sadly, the falcon sighted recently isn't her, but we were happy to finally get a glimpse of it ourselves:
While it appears to be a female, it isn't our female. It's definitely a juvenile, having emerged from the egg as a tiny ball of falcon fluff earlier this summer. I tried in vain to see if we could find a band on her but she was so far away that I couldn't quite manage it.
When falcons fledge, quite naturally they leave their parents' territory and begin to explore the world around them. I'd imagine that every year Alcatraz is visited by a few juveniles recently fledged by the breeding pairs in San Francisco and the bay.
Just had to link to this:
Birdchick yearns to bird with both Jackie Chan and Owen Wilson... and she yearns to engage them in still other extracurricular activities. One activity involves a certain kind of sandwich. Another involves a harness. Oh, Birdchick... when did you get so suggestive? I truly didn't see it coming.
Monday, August 9, 2010
9:12 PM | Posted by Sweep Commander | Edit Post
Warning: This post contains highly detailed images of a dead bird
Not all gulls survive to be the subject of a thoughtful, well composed portrait.
Newly departed birds like the fellow below appear just about every day on Alcatraz. Collectively, adult western gulls treat their young with positive br00tality:
I am grateful that the flies that colonized this guy appeared to be of the common variety. As veterans of the Alcatraz autumn are well aware, the island suffers from a miserable fly season.
The culprit is a strange and exotic insect that specializes in breeding deep within the corpses of cormorants and perhaps other waterbirds.
Once these grubs take to the wing, they terrorize human beings. Other flies actually fear human beings. These guys, by contrast, will evade your swats and slaps positively undeterred in landing on your hair, your neck, your cheek or any other part of your body that might serve to gross you out.
I've had one on my eye. No joke there. God knows what it wanted with my eye.
Rogue Cormorant Apprehended!
This guy was apprehended by our concerned NPS staff. Call it an immature Brandt's cormorant. That's what it is.
The happy fellow was arrested while gleefully marching along the road that stretches from the dock up to the cellhouse. The bird meant no harm to anyone and was apparently healthy but was friendly enough to make itself very suspicious.
Brandt's cormorants are notoriously timid and flush at almost any cause.
This one, however, was so comfortable in the presence of human beings that apprehending it was about as simple as throwing a towel over it and scooping it up.
Finally, acting upon the fact of this friendly bird being both strong and uninjured, and the fact that a gregarious disposition is unusual for a wild animal but is not any kind of cause for arrest, the bird was allowed to reluctantly leave its box and wander free.
Monday, August 2, 2010
9:13 PM | Posted by Sweep Commander | Edit Post
Alcatraz's new western gulls have acquired their flight feathers and their instincts are driving them into the air. Their inexperienced and ungainly flight, as well as the territoriality of other gulls puts them squarely in harm's way.
Take, for example, this WEGU's compromised position:
If you're new to the wing, this is what the excitement of flight can get you. It's a very common sight on Alcatraz.
Allow me to explain. This is what's called the Parade Ground:
Click on the image to get the full effect.
It's an area of flat pavement, dense shrubs and the remains of apartment buildings constructed to house correctional officers and then razed by the federal government in the 1970s after the closing of the prison and the end of the Indian Occupation. The structures were destroyed in order to ensure that a bunch of troublemakers could never again occupy the area and use it to showcase a loud, chaotic and violent mess.
Clearly the government didn't see this western gull colony coming. The gulls breed on the parade ground in huge numbers in a tightly packed configuration. There, they screech, squawk and fight one another in long and bloody engagements.
Then, as nesting season progresses and the eggs hatch, infanticide is suddenly on the menu and the adults happily indulge. When chicks are small enough to swallow, an adult gull will occasionally regurgitate a pellet containing the tiny indigestible remains of one of its own species.
Then, as the young gulls learn to fly, they've suddenly got a novel means to trespass upon the territories of others. And far be it from an adult WEGU, so imposed upon, to forego a shot at violence:
One pair of gulls has been especially prolific thus far in nailing invaders:
The two living juveniles in the above picture reside in this territory and their parents aggressively defend it. The other two birds, open and horizontal, meant no harm. They were learning to fly and they were flying badly. They were unfortunate enough to stumble into this territory which happens to be bordered by the foot tall remains of a small building. As these two accidental trespassers tried to escape, they failed to achieve enough altitude to clear the short wall and they were killed.
Most gulls are luckier, managing to evade the violence of the adults and escape with their lives. Many young gulls on Alcatraz survive to continue their development but retain these badges of honor, sustained in combat with the older brutes they hope to become:
That is not a good haircut. You'd better believe I would get my money back.
One of our awesome bird biologists has spotted and photographed an adult falcon on Alcatraz. It's been a while. Our maturing male falcon appears from time to time and was last seen in late June.
On seeing the picture, I immediately took it to be a female. When I bounced my suspicion off of BourbonHawk, she opined that if turns out to be a female, it's probably too dark to be our friend from last year.
After reviewing the photos, I think she's right. It may be a female peregrine, but it's not our female peregrine.
One park ranger and one Parks Conservancy employee have also reported seeing peregrines recently, but no sightings have been made on birds occupying our peregrines' familiar preferred roosts, which is an additional consideration in favor of this being a bird new to Alcatraz.
If this is a female with designs on hanging around for a while and if our heroic young tiercel is still about, this should make him very happy indeed.
The island's gulls knew this day would come
And they've been practicing their battle moves on anything at all with a raptor silhouette:
Here, they harass a harmless turkey vulture.
The video is short but the chase was much longer. The vulture's reaction to the harassment was easy to read and was something along the lines of: Ugh! What? And why? Do! Not! Want!
On the flip side, I had no idea that vultures were so agile in the air. Can I be excused for taking them to be slow, dumb and lazy?
At any rate, most birds hate the sight of a hooked beak and they will instinctively count it as a threat and mount an attack if they are able.
Their instincts fail to make the distinction between a peregrine falcon which sometimes uses its hooked beak to behead live prey and a turkey vulture which means no harm to most living things, but has a sharply hooked beak in order to open the body cavities of the already dispatched.
- ▼ August (4)