Monday, June 7, 2010

PostHeaderIcon Juvenile raven found but strange question remains...



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.

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