Friday, May 28, 2010

PostHeaderIcon Rehash: Alcatraz is an awful place for geese to breed


Sure, we've written extensively about this already but BourbonHawk's walk through Golden Gate Park this afternoon underscored the difference between a suitable breeding environment for geese and an annual disaster like Alcatraz.

If Mike "The Situation" Sorrentino taught us anything (and he did) it's that when it comes to success in reproductive activities, it's a numbers game.


So let's review some numbers.

Pairs of geese that nest on Alcatraz at present: 10 (estimate)
Goslings typically hatched to each pair: 8
Rough total of goslings produced, based on the estimate of 10 breeding pairs: 80
Total number of goslings known and recorded to have ever fledged on Alcatraz: 0 (there is a rumor that one once fledged, but our biologist denied the existence of a record thereof)

Yes, zero. We do have one brave little gosling threatening to fledge this year and as wonderful as 'Ryan T. Gosling' aka 'Robinson Crusoe' aka 'The OMG Gosling' may be, Mike "The Situation" Sorrentino would hit us with a cocky reminder that many years of zero goslings fledged followed by one season in which they went one for eighty, is an absolute disaster, bro.

One tiny ray of light

We have an unknown number of mallards that nest on the island as well. The ducklings fail unfailingly, year on year. While a Canada goose may fledge every few years, the ducklings never do.

This afternoon, BourbonHawk took a stroll around Stow Lake in Golden Gate Park and she saw this:


It's a creche of four breeding adults and seven hopefuls. These young geese are on the five yard line to fledging rather than being gull or raven food and it has everything to do with where they are.

LadyBird, BourbonHawk and I probably encountered this same creche five weeks prior and I blogged about it here.

The long and the short of it was that we saw four adults and eight goslings going about their business when an opportunistic western gull, lured to the creche by children throwing bread, snatched up a defenseless fuzzball, leaving only seven.

As tragic a moment as that was, five weeks later there are still seven goslings likely to fledge.

In contrast, Alcatraz is a place where breeding geese apparently do not form cooperative creches, and the numbers of young geese go from this:


to this:


and in very short order, the last goslings are predated.

On Alcatraz, there isn't much fresh water, perhaps contributing to territorial behavior and a lack of cooperation among them as they fight over what little there is.

Between that and the efforts of our thousands of large gulls and our two enormous ravens, nary a gosling goes uneaten.

Numbers:

2010 Alcatraz Canada geese: 1 for 80. (1.25% success)

Some random Stow Lake creche: 7 for 16 (43.75% success)

C'mon, Alcatraz geese... One gosling fledged is nice but the bottom line is that we want to see fewer of you breeding on the island in 2011.

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