Saturday, May 8, 2010

PostHeaderIcon is the last Alcatraz gosling too big to fail?



Alcatraz is down to one final gosling. With this fledgling having achieved a formidable size and with the fresh water provided by today's rain, the bird's odds of ultimate survival aren't bad at all.


Though it's hard to know just how many pairs of Canada geese we have breeding on Alcatraz, my estimate is that around ten pairs, give or take a few, produce offspring. These geese lay around 8 eggs, meaning that perhaps 80 goslings hatch on Alcatraz each year. The number will be lower if fewer eggs are laid or if some are predated or fail.

One surviving gosling seems like an astonishingly low number given the large numbers of baby geese this year, but one survivor is actually an astonishingly high number given that once hatched, every Alcatraz gosling is equal parts of cute and vulnerable to gull and raven predation.

Their prospects for survival are understood to be zero, though there is a rumor around the island that years ago, one heroic Alcatraz gosling fledged. In the usual case, the goslings are so consistently predated that a park service intern from an Alcatraz summer past once referred to these fluffy cuties as "crunchy gosling snacks". One park ranger refers them to them as "an island delicacy". Another island staff member calls them "popcorn".

The factors limiting their reproductive success on Alcatraz are self evident. Fresh water for drinking is limited, perhaps driving families of geese to be territorial over scarce resources, driving aggression towards each other and diverting their attention from the danger posed by predators. Meanwhile, opportunistic and wily gulls and ravens predate young geese with interest. Their parents are aloof and hapless defenders, often wandering too far from their defenseless young to defend them from predators that know the dance all too well.

Recently, LadyBird, BourbonHawk and I were hiking Stowe Lake in Golden Gate Park when we became witnesses to tragic circumstances. A group of young children, ranging in ages of around four to seven years old, were trying to throw white bread for a family of four adult geese and eight goslings that were happily grazing on their natural diet of grass.

The geese were barely interested, hesitantly munching on a few crumbs. The loose bread, however, attracted gulls and while they came for the bread, they stayed for a gosling. The parent geese hissed at the children for getting too close but their hisses and threat postures are so unthreatening that the children were not even aware that they were being challenged. While the adult geese were preoccupied with the children, a gull snatched a gosling and after the gulls fought over the dispatched chick, they disinterestedly allowed it to float in the lake before one gull finally swam over and swallowed it whole.

Two onlookers loudly and naively exclaimed that these murderous gulls have no sense for their own immoral behavior. When you watch gulls for a while, you get it. They eat trash and kill the weak, young and defenseless. They make their living by being above nothing and they do very well.

For any adult geese reading this post, I have some words of advice.

First of all, weaving your head from left to right and hissing quietly at a perceived threat is not a defensive strategy. More honking, charging and erratic, unpredictable movements would better alarm potential predators. Also, kill or maim a gull every now and again. When a gull is six inches away from you and your young and your lame threat posture won't phase it, bite the bird's neck!

Also, don't reproduce on sandstone islands with thousands of gulls and no fresh water.

The geese on Alcatraz have very limited fresh water resources so they are very territorial about what's at hand. By contrast, the geese at Stowe Lake aren't faced with these limitations, so they can pursue more advantageous strategies including the formation of a crèche, a cooperative grouping of multiple pairs in which defensive responsibilities are shared by four or more adult geese instead of the usual two.

We'll keep you updated on our miracle gosling.

Odds, ends:

Today, I noticed that at least five California gulls have staked out an enclave near the old prison incinerator, on top of the old, now defunct brandt's cormorant colony (more on that soon).

This is rad because the ubiquitous gulls on the island are western gulls and California gulls are invisible by comparison. I had been working on Alcatraz for more than a year before I finally spotted one of these.

Next thing.

Although the cormorants have left this nesting site for areas around the island far less friendly to observation, it's nice that a few of the island's locally rare birds may be setting up shop on this stage. I guess the old saying is true, God never closes a door without opening up a window nature never starves a thousand cormorants without giving you five uncommon gulls to observe in return.

Our snowy egrets have chicks! There are no pictures because these birds nest in thickets and having your camera focus on an object with 50 twigs in front of it is difficult work.

Lastly, I've been seeing these around the island. Does anyone know what I can do with them? Shoot me an email.


4 comments:

Anonymous said...

How to report banded birds:
http://www.pwrc.usgs.gov/BBL/homepage/call800.cfm

Ian Miyashiro said...

I've called the BBL a couple of times with live banded birds I've spotted. They'll be able to report where the bird was banded. Good stuff.

P.S. Here's hoping that CAGU makes it.

Chris said...

I do not understand this at all. When I was a kid, there was a Canada Goose that used to try to divebomb my ass when I tried to cross over the creek on my bike on the way to karate class. Scared the shit out of me. Aren't they bigger than a gull?

Also, isn't laying your eggs on an island with no freshwater the world's worst reproductive strategy? I know birds can be pretty stupid but if you invest all this energy into pooping out eggs every year and all of them die, wouldn't they figure it out eventually?

Anonymous said...

Hmmm. Maybe in a a thousand billion years Alcatraz will be the new Galapagos Islands. --Sue in MA

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