Re: [SBB] Black Skimmers

[Bill Bousman <[[email protected]]>]

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.

It is interesting to note in the case of a distantly related larid invader, 
the California Gull, that Shuford and Ryan have concluded that even after 
25 years of nesting in the South Bay and a population of more than 25,000 
birds, the increase we have seen is largely due to recruitment, that is 
birds moving in from the interior, rather than local production.

Bill

At 08:35 AM 12/29/05, Nancy Teater wrote:
>Having seen a couple of reports of 25+ groups of Black Skimmers, does this 
>mean our area population is growing via local breeding success? Anyone know?
>Happy New Year, and good birding,
>Nancy Teater
>
>
>At 07:50 PM 12/20/2005 -0500, [[email protected]] wrote:
>> From the Adobe Creek Trail today at 10:20-10:30 a.m., I watched 25-28 
>> BLACK SKIMMERS just north of "Skimmer Island" in the Charleston Slough, 
>> across from the pump house and bleachers.  They were not there when I 
>> walked past the same spot at 9:15 a.m.  This is the first time I have 
>> seen them back at this location since June.  As I was about to leave, 
>> Dave Weber came along and counted 28 BLACK SKIMMERS.
>>Good Birding!
>>Dotty Calabrese


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