Friday, November 19, 2010

PostHeaderIcon Returning falcons confound and excite the island's bird detectives



They're back.




Or at least we think they're our falcons from last winter.

Long story short, in late November 2009, I spotted a lightly colored bird standing straight up atop one of Alcatraz's tall cypress trees. It was far away, but its vertical silhouette seemed very out of the ordinary. I pointed it out to Ranger John and asked him to identify it. He nailed it on the first try. It was a peregrine falcon.




The bird, which turned out to be a female, was then joined by a juvenile male. The two remained loosely allied throughout a winter of fun and brutality, feasting on European starlings and unwary seabirds. In their spare time, they provided drama for the usual bird bosses of Alcatraz, our very large and extremely territorial pair of common ravens.

One day in March, our female enjoyed one last meal on the top of the power plant's smokestack, spread her wings like sails into the wind and left us for the summer, presumably to breed with a sexually mature male in a territory somewhere to the north.

The male was last seen at June's closing. Before that, his relationship with Alcatraz seemed more and more tenuous... some experts judged that he was holding Alcatraz as a future breeding territory. The possibility was exciting, especially for those of us who had first participated in discovering and observing him. Alcatraz has never hosted breeding peregrines before. Given the summer population of 1,500 to 2,000 large and aggressive gulls, no one was even sure that breeding peregrines were a possibility. To our dismay, the frequency of peregrine observation was declining, finally approaching zero.

And then...

Last Sunday, October 9th, I saw a male peregrine falcon with mixed blue and brown plumage on the Alcatraz lighthouse, in the exact same spot that I'd seen our male all of last winter, and indeed, at the same time in the early evening. His prime viewing hours are 5-7 pm.


The blue and brown feathers indicate that the peregrine is in transition. He's shedding its brown juvenile quills and donning the prim and chivalrous blue coat of a breeding adult warrior.

The very next day, still stoked from the rediscovery of our male falcon, I made another find: an adult female falcon in the very same cypress tree that our female falcon from last winter preferred. For me, as a birder of The Rock, this was a huge personal lift. BourbonHawk and I have spent countless hours stalking and observing this falcon, neurotically checking her perches even when she had been absent for months. She is the raison d'etre of this bird blog.



But is it the same falcon pair from last winter?

As it turns out, falcons don't wear name tags. Hell, falcons not obsessively stalked by unstable birders don't even have names. Confirmation that the falcon you saw today is the same bird you saw several months ago isn't easy to produce and in the male's case, there may be reason to doubt his identity as our heroic but moody tiercel from the winter of 2009 and 2010.

His age, given away by his plumage, is a perfect fit. His blue and brown feathers firmly indicate that he hatched in the summer breeding season of 2009, just as our falcon did. He sits on the same east facing ledge of the Alcatraz lighthouse at the very same time of day. He looks to be about the same size.

None the less, we can't be sure that he's ours. In June, we saw another male falcon undergoing the same transition from brown to blue. If the two had been the same bird, it sure seems as though the molt would be complete by now. As it stands, we can't rule out the possibility that we've been mistaking two male falcon yearlings for just one.




On the other hand, artifacts of digital photography and bad early evening light in a fog ridden context could also be distorting our sense for his coloration.

One raptor expert told us that the preference of two similar falcons for the same roost might be explained by the attraction that they have for the aggregated guano of other falcons.

None the less, my intuition that this is our same falcon is bolstered by the fact that since May, Alcatraz has had a brown falcon sporting one or two blue feathers. With every observation of a falcon in transitional plumage as the year went on, the blue went up and the brown went down. Call me crazy but I think it's the same bird, even if it's taken several months and our intuition is that the whole blue to brown molt should happen inside of 30 days. (Important to keep in mind: every time I assert a suspicion without concrete evidence, I seem to be wrong. Example: the time I wrote about a thousand words on how the raven pair was deceiving the National Park Service and incubating a nearly unprecedented second clutch of eggs)

The identity of the female seems less mysterious.


Unlike at the lighthouse, her cypress tree doesn't have aggregated guano on it, and she hangs out in each of its boughs and branches without regard for the presence of peregrine droppings. Call it a subjective unscientific judgement, but she seems comfortable and very much at home in this tree.

Watch out, ravens...



The presence of a pair of adult peregrines on Alcatraz should strike fear into the heart of the island's ruling pair of majestic corvids.

The relationships between ravens and raptors are varied, complicated and potentially violent.

There are recorded instances of ravens killing falcons and falcons have certainly put an end to many a proud raven. Falcons, transcending their smaller size, have even killed golden eagles, some of the most fearsome raptors the world has to offer. The warlike behavior of our young male last winter, attacking any bird of any size from large gull to large raven, gives me every assurance that he is an aggressive creature that fears nothing but a lack of suitable targets.


On the other hand, there is also evidence that ravens and raptors can live in cooperation with one another, especially after a period of years in close proximity. The raven and raptor pairs come to accept the presence of the other and there is even some evidence that they share defensive duties and come to understand one another's alarm calls in the case of an unwanted invader.

In peregrine falcons and common ravens, you have two of the smartest and most complicated minds in the avian world. Concrete expectations for how the two pairs might interact are bound to be a source of frustration and disappointment. Still, up to this point, it's been all fistacuffs, and I doubt the ravens are happy to see our falcons return.

Coming soon:

-How the female falcon is a product of the sexual revolution (hint, she has a boy and a house for the summer and another boy and another house for the winter.)

-How long has Alcatraz had seasonally resident falcons? There's reason to believe that it's longer than we think.

Lastly:

There are those that take our aforementioned ravens to be "nasty birds", worthy of little more than target practice for our capable and burly law enforcement rangers.

I would make the case that while they are carrion and trash eating voracious predators, they are also the most committed couple the island has to offer.


The other day, BourbonHawk remarked on just how odd it is that we never see our ravens eating carrion... then we saw this:


Yes, that is the foot of a tiny dead bird, attached to its downy fluff.


They'll even eat the cutest baby gull if it pleases them...


Nasty? Perhaps, but unlike our sexually liberated falcon femme, these two stay together at all times during the year, abiding by each other, feeding, preening and keeping each other company. Falcons should be wary because these ravens will certainly protect each other.

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