Re: [SBB] Black Skimmers

[Al Eisner <[[email protected]]>]

On Fri, 30 Dec 2005, Bill Bousman wrote:

> Folks:
>
> This is a great question.  Is the San Francisco Bay breeding population a
> source or sink population (or is it too early to tell)?  That is, are the
> birds nesting here sustaining the population (a source) or are the small
> increases that we see all from recruitment from the southern populations
> (therefore, the S. F. Bay area would be a sink).  There are two bits of
> evidence that I've seen.  Locally, we have noticed fairly high chick
> mortality.  Skimmers often produce three eggs and often only one chick
> survives to fledgling.  But there have been a number of local observations
> of fledged young dying shortly after they've left their nest island.  As
> many breeding spots are not surveyed regularly, it is difficult to say how
> regular the pattern is.  Secondly, we have seen banded adult parents in
> recent years and these have been from southern California, which suggests
> that southern birds are still moving north and augmenting our breeding stock.

Do the roosting populations in mid-August into fall provide a clue?
For example, Redwood Shores (in San Mateo Co.) has recently become a
roosting area in that period, with a high count of 11 birds seen this
year.  Of those, two were juveniles.  Does this represent successful
local fledging, or could birds have moved in that early from farther
south?  (I had assumed the former.)
							Al Eisner

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