Sunday, June 27, 2010
1:08 AM | Posted by Sweep Commander | Edit Post
There's a small mystery on Alcatraz right now and only our ravens know what's really going on.
The ravens bred in 2010, but only one branchling left the nest alive. The adults watched over their young one closely and killed an adult western gull, apparently for showing a little too much interest in their pride and joy.
Then, suddenly, we went from three observable ravens to two. It seemed that the juvenile was gone. As new ravens will stay with their parents for a period of months, successful fledging and departure seemed unlikely. The speculation was of its possible demise.
As usual, the ravens had us fooled. The juvenile was still very much with us, and hiding right before our eyes. She or he vocalized softly and hoarsely while displaying submissive crouching and begging behavior typical of a juvenile or a subordinate individual in a larger group but unlikely behavior for for a breeding adult.
One mystery was solved. One of our visible ravens was the juvenile. The other was the male, discernible by its size and its trademark "fur pants" dominance display. So where is our breeding female? She's been unobserved for quite some time now.
I have a crazy hypothesis: she may be incubating a second clutch of eggs.
This would be more than unusual. It's almost unprecedented. Ravens are not double brooders, though given enough time, they will attempt another clutch if their first brood of chicks and eggs fails completely. Double brooding by ravens is so uncommon that it's only been documented in one single instance, during breeding season 2001, on the campus of UC Irvine.
My suggestion is just a hunch, but it has the following considerations in its favor:
First, there's time for a second brood. The ravens nested early this year. In the single documented case of double brooding, enough time and plentiful food resources were cited as possible factors enabling the behavior.
As for food, with a home territory like Alcatraz, with so much ecology and so much trash at hand, food wouldn't seem to be a problem.
Second, the natural resources arm of the Golden Gate National Recreation Area has visited the ravens' nest multiple times in 2010 and damage to the nest may have occurred. Just as the number of visible ravens dropped from three to two, they were observed carrying nest building materials to their tree, perhaps repairing damage their nest structures incurred. Bernd Heinrich, noted raven expert and author of the great book Mind of the Raven, observed that the ravens' cue to mate is not a ready female, but rather a finished nest.
Damaging the ravens' nesting structures may have inadvertently put them on a path towards a second clutch.
The third consideration is that while double brooding has never been documented except in the one paper I linked to, the paper's authors complain that not enough observations of this type have been attempted, especially on the divergent California clade, to which our ravens belong.
The surprising genetic differences between ravens of the American southwest and those found in all other contexts will be addressed in an upcoming post laying out what little we know about Alcatraz's raven pair.
The last consideration I'd offer in favor of the double brooding hypothesis is that Bernd Heinrich also says that if a raven minding a home territory loses its mate, he or she will find a replacement quickly, often within a day. That hasn't happened, though another plausible explanation for that might be that it's simply too late for courting and pair bonding this year, though I don't recall Heinrich indicating that this behavior is variable across the seasons.
This, combined with my gut feeling that the outright death of the female seems pretty unlikely, gives me the sense that our ravens are up to something once again.
This double brooding suggestion may be absolutely wrong and I realize that it sounds crazy. My hunches regarding birds are almost universally mistaken but if I'm right in this case, I'd like to be able to say I saw it coming.
The island loves to make a liar out of me. No sooner did I write a post entitled "A Coda on the Falcons of Alcatraz" than did the male peregrine decide to show himself on a consistent, daily basis. For now, the kid is back:
Now all he needs is a female companion to really give Alcatraz's ruling authoritarian corvidocracy a run for its money and I wouldn't miss it for the world.
Also as I disembarked onto the Alcatraz dock on Thursday, I was rendered speechless. I'd heard about ducklings on Alcatraz but neither BourbonHawk nor I had ever seen any. But there she was, a duck mother and her eight chicks, soon to be food for the predators that inhabit the island and the bay.
Sometimes words aren't good enough, so I slapped BourbonHawk on the arm and pointed them out to her, this late in the year and bobbing far too close to the machinery mounted to the rear of the boat we'd just disembarked from. We had a few jokes about these witless ducks being sucked up to their doom, but fortunately that didn't happen.
At any rate, I know they're gonners. My only hope is that they get taken by some novel predator like a seal, a porpoise or a sea lion. I'm getting a bit tired of all of this gull and raven brutality.
Here's your update on Ryan T. Gosling, the honking miracle. He's almost there. At this late date, it's a bit difficult to tell which one of the three he is, but I usually assume that the two proudest looking geese are his parents, and he's just the other one.
Brandt's cormorants! They're back indeed. Here's a picture from last year's disastrous lack of a nesting season:
And a picture from our last very good year, 2008:
And here's a picture from last week:
Progress is clearly being made and there are nests on the ground, but they may be dummy nests. These cormorants have built them multiple times now, only to fail to lay eggs and to retreat from them at any disturbance.
Still, the cormorants are having a resurgent year. They may not yet be successfully nesting on their old colonial grounds, but they're nesting less visibly on cliffs all around the island. I don't envy the wildlife biologists in their task to count them and measure their output in such treacherous places.
Lastly, I authored a post last night on a western gull predating a snowy egret chick. I know this post has been a long one, but check that one out too, especially if you don't mind a gruesome image to go along with it.
Friday, June 25, 2010
5:43 PM | Posted by Sweep Commander | Edit Post
Warning: The following post contains a graphic image of a dead bird
We've been over the challenges faced by breeding geese on Alcatraz many times now, and if you're a new gosling, they are formidable.
Not every infant bird faces survival prospects of less than one percent, but as Darwin noted, there are always too many young for the resources at hand and inevitably attrition and competition do the dirty work of eliminating the excess.
In the world of humanity, the west has infant mortality figured out. In the United States the rate has dropped to just .64%. The highest rates of infant mortality in the United States are found in Washington DC and Mississippi, with 1.41% and 1.074% respectively. The lowest mortality rates are enjoyed by Minnesota and Massachusetts, with .478% and .489%.
Angola has the highest infant mortality rate in the world, where tragically, 18% don't make it to their first birthday.
As with human beings, mortality rates among many young birds on Alcatraz are tied to environmental factors, like the availability of food and fresh water. Our baby birds also have to deal with the presence of the hostile predators which place an additional strain on their prospects.
Let's talk about a curious difficulty faced recently by one of our most successful breeding species, the snowy egrets.
I've seen western gulls hovering low over the thicket where the egrets make their nests and fledge their young:
But I'd never seen one dip down and actually grab a vulnerable chick from an exposed branch. But this last week, that's exactly what happened and this was the unfortunate aftermath:
The victorious western gull was defensive of his prize. Though he obviously destroyed the head of poor chick, he failed to open the body cavity, and his best apparent efforts were gentle tugs on the dispatched egret's wing. As far as anyone can tell, the effort yielded no food.
It reminds me of the time that BourbonHawk, LadyBird and I witnessed a western gull take a tiny gosling in Golden Gate Park. The gull lost interest and several gulls half heartedly fought over the gosling's body, before an immature individual finally and nonchalantly swallowed it.
The egrets have it much better than our black crowned night heron eggs and chicks that our ravens mercilessly predate, but they're still vulnerable to this pointless and opportunistic predation.
Here's a live, healthy snowy egret, on the road to fledging:
The vocalization combined with the display has become known to Maganrord as "The Dinosaur Dance," for obvious reasons. So rad.
And here are their curious shins:
They're almost scaly.
Check back with us soon. We have so much to report, on subjects as diverse as ravens, falcons, and white crowned sparrows!
Sunday, June 20, 2010
10:53 PM | Posted by Sweep Commander | Edit Post
Remember this guy?
His story is short and it bears repeating, so here we go:
On November 22nd 2009, BourbonHawk and I discovered a large adult female peregrine roosting atop one of our cypress trees:
As the days and months went on, sightings were as regular as the rising sun. We determined that she was residing on Alcatraz, either for the winter or longer. More pictures and videos of her and her bloody quarries are available in our back posts.
On February 6th, 2010, we found a second falcon, a male, albeit an immature male, perhaps unable to breed. None the less, the two engaged in fantastic displays of aerial courting, darting, spiraling, sparring with each other. Finally, they perched together, and on Valentine's Day, no less. All who saw them were touched by the romantic spectacle.
On Sunday, March 14th, our female gave us one more majestic and bloody display, filled her crop and spread her wings. She hasn't been seen on Alcatraz since.
The male (or tiercel, as male falcons are called) remained, but since our last report, the frequency of observation of our baby bird-killing-machine has declined steadily. He's become so scarce that I had fully intended to publish a report declaring that the Alcatraz tiercel had departed completely...
...which shows how bad I am at this. During Alcatraz's magic inbetween-hour, separating Alcatraz day tours from our rad night tour program, there are no visitors and there are far fewer staff. The animals behave differently and often, it's the time of day that the bird you're looking for rears its helmeted head.
This is the Alcatraz tiercel as we had last seen him, the brown plumage betraying the youth that may have pushed the female to abandon him:
Today, we saw the following:
The brown is giving way to blue and Alcatraz's baby boy peregrine is growing up!
I pessimistically called this 'a coda' on the presence of falcons on Alcatraz because one sighting every few weeks just doesn't mean very much.
It is our familiar tiercel. He has the same robust helmet, is molting on schedule and he's occupying his habitual roost. But I don't think he lives on Alcatraz anymore.
Whether this is due to pressure from Alcatraz's larger ravens and gulls is unknown, although conflicts with both were common when the tiercel was an everyday sight on Alctraz. Earlier in the year, we posted the following video. The tiercel is the tiny bird diving and pursuing the larger ones before being pursued himself by a western gull. If you don't blink, you can see a few of San Francisco's landmarks in the background:
The shameless romantic birder in me would like to think that this falcon, which had been so significant to us for such a long period of time, had graced our island this evening share with us its progress on its maturing plumage, though my prevailing non anthropomorphic brain knew it was just a brief and aimless layover on the way to somewhere else.
Sure enough, when I checked for him 20 minutes later, he was gone.
Hopefully my hunches are wrong and Alcatraz becomes a yearly site for falcon breeding. But I'm not holding my breath.
Wednesday, June 16, 2010
11:25 PM | Posted by Sweep Commander | Edit Post
Let's start with some cuteness as this baby western gull falls over, then dances and twirls around like a tiny ballerina, enthusiastic for days but lacking of any physical coordination. Please don't write us to tell us you aren't touched. We can't take that very seriously:
If there had been much to report, we'd apologize for the lapse in posting but we've made a decision to avoid bombarding you with posts with titles like 'OMG, the baby gulls are collectively 1% bigger today and here are a hundred pictures and videos documenting the milestone!' Both the readers and writers of this blog have better things to do.
At any rate, here's what we're up to in the coming week: a set of posts, one each on the island's larger breeding birds. Today, it's the avian face of the island, the western gull.
Ahhh, nesting season... that lovely time of year when each utterance I hear of the word "baby" is less likely to conclude a mysoginistic quip than it is to refer to a fuzzy ball of serious cuteness... Oh, the novelty.
Our baby gulls have hatched en masse.
And some of them are very, very sleepy.
Their salt-and-peppery down, however, doesn't protect them from the predatory animals that see ample opportunity in their helplessness. Often, the worst enemy of a western gull chick is an adult gull that is not their parent. These birds kill and eat the young of their own species, usually whole and head first, and they often vomit up a pellet of bones and the remains of downy fibers. Fun.
The raven pair and its current brood will also predate gull chicks and eggs. Recently, Maganrord took a video of our juvenile raven consuming a WEGU chick (the video is available two posts prior).
Yesterday, we observed a dangerous game of cat and mouse between two large gulls, their young and two large ravens. More on that in an upcoming post.
Today, I found what is very likely the dried, regurgitated head of an unfortunate western gull chick. We'll post pictures of that soon. Today's post is about the appreciation of live baby gulls, available for viewing now but for a very limited time:
They just get uglier from here. Stay tuned to Maganrord for full coverage of that process, including a special post on a baby western gull from last summer, affectionately referred to as "runty", for whom BourbonHawk has uncharacteristically expressed an undying love.
Focusing back upon cuteness, here's one little fluffball stretching its little wings and then running too fast and falling over...:
The feeding process: western gull beaks have what nerds call a "red subterminal dot". It's a bit of red pigment near the end of a gull's beak. The chicks instinctively poke at it and somehow, the adult gull regurgitates the contents of its stomach, providing food for its young:
Studies have found that large gull chicks will instinctively peck at any red dot, no matter what bears it.
Although we find gull parenting absolutely abhorrent, due to rampant cannibalism and infanticide, there is one aspect of good parenting at which humans largely fail but at which gulls positively excel: providing nutrition to their young:
One study, performed locally on Alcatraz western gulls, found that the diet of our local WEGUs consists almost entirely of salvaged garbage (surprise!), more than 90% of which is some form of discarded chicken.
But when their eggs hatch, the diet changes. The junk food is absolutely forbidden and fresh fish from the bay is the only acceptable food item. Here is Maganrord's tiny contribution to the body of evidence:
Why don't human beings take the birth of their children as a cue to embrace what is healthy and sustainable? McDonald's advertising may have us all figured out, but you'll never convince a WEGU to feed its baby a French fry, let alone a double cheeseburger or a sausage breakfast burrito from the dollar menu:
Sorry, human parents: In one important way, infanticidal, trash eating gulls are better parents than you are.
To close, here's a video of a baby WEGU that surprised me on the west side of the island:
It hung out, peeped, scratched its face and wandered into the bush. What more do I want from a baby WEGU around hatching time?
As a postscript, I would only add that the anecdotal evidence from employees working on Alcatraz for both the National Park Service and the Golden Gate National Parks Conservancy has been that there are fewer WEGU nests in view and fewer large broods than in years past. Instead of three and four chicks per nest, we've been seeing one, two and only sometimes three.
This year, we've had massive construction projects as well as aggressive management of gulls in areas accessible to island visitors, which may be contributing to these observations.
At the end of the summer, we'll ask our professional biologists what happened this year, and how normal 2010 was for WEGU breeding on Alcatraz.
Tuesday, June 15, 2010
10:22 PM | Posted by Sweep Commander | Edit Post
I know it's been a while, but you have to admit, the news to follow is good:
Our graphics are back up! Thanks a bunch to our shady host! We've got a number of exciting posts coming up:
Coming from Maganrord in the near future:
Hint: There is no hint! Ravens are cryptic! Duh! Read the upcoming post!
At Maganrord, we're geared up to report on babies of every type. It's not just ravens and gulls. It's sparrows, egrets, herons, a certain falcon, a certain goose, and it's a certain theatrical hunger display that we've come to call The Dinosaur Dance! Yay!
And there will be videos, videos, videos!
Thanks to you, our readership for tolerating a slow posting schedule of late. We fully intend to make it up to you in the coming days.
Monday, June 7, 2010
11:10 PM | Posted by Sweep Commander | Edit Post
To rehash, our raven pair bred this year but only one juvenile left the nest alive. After a brush with death, it was on the road to fledging, but then it disappeared.
BourbonHawk pointed out that the juvenile could no longer be easily told from an adult and that it was therefore a possibility that the young raven could be hiding in plain sight.
BH also noticed something strange in the video we took of one of our ravens consuming a gull chick:
This raven has white spots here and there, like a juvenile would. Still, it's consuming a downy prey item, and the scattered fuzzy white debris could be sticking to the raven's feathers, deceiving us.
I began to suspect that the junior raven was dead.
Ravens stay with their parents for six months before departing. Obviously this juvenile didn't hatch in the middle of winter, so it didn't leave voluntarily. It was either dead or still alive and with us on Alcatraz.
While no remains were found, the two ravens we did observe were spending their days gathering nesting materials. If they still had a young one to provide for and protect, they wouldn't have focused on keeping house.
So, we had a mystery to solve:
In retrospect, this one was pretty easy.
On Sunday, BourbonHawk and I had the pleasure of exploring the island for the quiet hour between Alcatraz day tours and our acclaimed night program. We had the island to ourselves. There were no visitors and our comrades were hunkered down in our break room facilities enjoying their dinners or standing on the dock while they smoked and chatted.
We were on a mission to use this time to examine any raven we find for clues in form, plumage or behavior that might expose it as the missing juvenile.
The moment we stepped outside, we saw this guy:
This one had an adult appearance and our breeding pair often hangs out in front of the cell house during our in-between-hour, so we didn't think much of it.
Then, it began to vocalize. The first couple of calls sounded normal enough, but soon it veered badly away from our breeding pair's established lexicon:
We're very conscious of the high variability in raven vocalizations but these hoarsely whispered parodies of familiar vocalizations were unexpected. We immediately suspected that it was the missing juvenile.
It flew towards the gardens on Officer's Row, and I observed it there, apparently calling for mom and dad:
It dug a few holes, carried a stick around, and then, as if to say "here you go!", the adult male swooped in and threw a few chunks of white bread in front of his little one. The juvenile ate a bit, and then cached small bits of bread around the garden:
Our ravens are known to have food caches in some of the island's cypress trees but as far as I know, no one has yet observed ravens burying food in the gardens.
At around 1:10 of the following video, the juvenile falls in the dirt in front of its father and begins what I'm assuming is some type of begging behavior. For anyone interested in raven social behavior, it's an interesting display:
Dining on a gull chick, revisited:
After we had confirmed to our satisfaction that our juvenile raven was still with us, I decided to go back again to the video that BourbonHawk had earlier pegged as possible evidence that this was the case.
Beginning at around 15 seconds in, sticking out of the raven's white wing, is the hollow shaft of a feather and it's white as a bone. Subtly lighter-than-black neck feathers are apparent throughout the video as well, also indicating a juvenile. These are the well known field markings of juvenile ravens.
Good eye, BourbonHawk. Our juvenile raven ate a gull chick.
One mystery behind us, but...
We're still missing a raven.
Where is it?
Is the failure to observe three ravens at once just a matter of bad luck? It's been quite some time now since we've witnessed what should be a very common occurrence.
Sunday, June 6, 2010
11:32 PM | Posted by Sweep Commander | Edit Post
We believe we've discovered the fate of the island's young raven, though our findings have birthed to us a strange new mystery to consider.
I'll compose a post on the subject tomorrow, and since it'll probably take me all night to do it, check back with us on Tuesday to get the latest.
Friday, June 4, 2010
5:51 PM | Posted by BourbonHawk | Edit Post
As noted in the post below, our ravens have been acting strangely. They're always a bit enigmatic, but this year their actions have been particularly hard to decipher. A few points I wanted to bring up:
- - The image above was taken in late July of last year, and shows the first time I saw one of the fledglings actually flying outside of the nest. I observed them in the days prior to this outside of the nest, but still hesitant regarding flying. I actually have pictures of the three juveniles on the first day we were finally able to see them out of the nest, in the very top of their cypress tree, which are dated July 12th. So it seems that with Hrafn/Raven Jr. they were extremely early this year.
- - Sweep Commander observed them pulling the same trick in the gardens of pulling up the bamboo edging that I observed here in January, though obviously this could be completely unrelated behavior.
- - We haven't seen the young raven in about a week now, and as Sweep Commander noted, the ravens appear to be gathering new nesting materials. Is the young one dead? Has he left? The latter seems highly unlikely as all the information I'm aware of says that juvenile ravens stick around for 6 months after fledging.
- - Perhaps he just looks so much like an adult that we can no longer tell? I was looking at this image last night:
and noticed the white patch on his right wing. I then watched the uber-brutal video that Sweep Commander posted below of the raven eating the WeGu chick. It looks like a similar patch of white is found on the right wing of that raven as well. Could Hrafn be hiding right under our noses? Am I totally reaching here? A steady diet of metal and mead will do that to a girl. What do you guys think?
Wednesday, June 2, 2010
7:11 PM | Posted by Sweep Commander | Edit Post
Neither the Maganrord team nor the island's legit biologists can find the juvenile raven anywhere.
We last saw it on Sunday perched in a cypress tree eating an unknown food item. It had made an enemy of a California gull that buzzed it persistently to no effect. The most the gull could elicit from the fledgeling were a few low vocalizations.
The next day, it was gone, either fledged or dead. The bird flew well and it is now believed to have predated a western gull nest, so it appears to be more than capable of fending for itself. Also, though it was a bird in it's first year of life, it was significantly larger than the typical raven I observe on the mainland, just like mom and dad:
For size comparison's sake, the adult raven on the right and the human being on the left were equally distant from the camera as took this picture. Well... not really, but our ravens are still huge.
At any rate, though raven breeding season appears to be over, the pair is not taking a vacation. They have been actively collecting nesting materials in recent days and have been seen transporting them back to their home tree. I caught one collecting moss, presumably for nest lining.
Why would the ravens be working on their nest structures? Breeding season is over. Right?
Well, the nesting structures were examined earlier in the year by our park's biologists and portions of them were tampered with or disassembled in the process. The ravens may simply be rebuilding what was destroyed.
Also, nests must be repaired each year as the hatched chicks defecate inside the nest, but it's very, very early for that process to begin. Nest construction and repair usually occurs in the spring.
A more alarming conclusion might be that these birds are making preparations to lay a second clutch. It's hard to imagine that the moss lining they're collecting could keep from year to year and ravens will sometimes lay a second or even a third smaller clutch if the first one fails, but as far as we know the ravens did successfully fledge a single bird this year and it's awfully late in the season to lay new eggs.
We'll keep watching, however, because our giant and wily ravens are not to be underestimated.
Here's a video we took today of one of them eating a gull chick. As usual, sorry for the camera shake.
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