Re: [SBB] unusual flock behavior?

["LINDA ADAMS" <[[email protected]]>]

Hello Rosalie and SBBers,

There are probably many who may respond with more expertise in this area, but I see a lot of it here in San Martin at our "Swallow Colony".  Even if they turn out not to be swallows, it is common of many birds this time of year.

Especially with swallows, since there are hundreds here every day, when the nestlings first fledge they make it straight for "grit", with emphasis on "calcium" sources.  Although our swallows do have calcium supplements before and during nesting, the only way the nestlings can meet their dietary requirements is if the adults deliver enough to them while they are still in the nest.  So by the end of a nesting cycle, the adults (especially the female) are depleted and the new fledglings are picking around down on the ground to satisfy any deficiencies.  I would imagine that perhaps the fledging process further stimulates their craving for calcium and other minerals.  So I can't be sure of the rationale for what you observed, but this is what they do here.

If they are not picking up grit, but are laying low to the ground, swallows sometimes do this to warm up.  They especially do this on our black-top.  Young from a first brood and the adults also spend considerable time on the ground picking up material for a second nesting, but this wouldn't seem to be what you saw based on the description and location. 

At any rate, this is normal and many other breeding birds do this less conspicuously because they do not gather in flocks.  I haven't noticed any particular time, although, grit/calcium is usually picked up in the evening, but not particularly at 7 pm.  There naturally could be other reasons for such behavior but this is likely.   

Linda Adams in San Martin   
  ----- Original Message ----- 
  From: R. Strait<mailto:[[email protected]]> 
  To: South-bay Bird List<mailto:[[email protected]]> 
  Sent: Sunday, June 19, 2005 10:53 PM
  Subject: [SBB] unusual flock behavior?


  Hello,

  While walking at Sunnyvale Baylands Park this evening I noticed a lot of
  birds on the now dried mud flat out from the observation platform at the end
  of the Wave Walk.  With binoculars I could tell that the birds were small,
  blackish above and white underneath.  They were too far away for me to
  identify the species.  There were about 150 birds and they stayed on the
  dry, seemingly barren surface for all of the time I watched them.

  The most likely species would probably be Cliff Swallows since these birds
  fly over the park daily.  But, if they were indeed Cliff Swallows, what
  would they have been doing gathering in such large numbers and staying on
  the ground for an extended period?  All this occurred right after 7:00 p.m.
  I thought the birds might have been larger than Swallows, but at such a
  distance I couldn't tell.  I sure could have used a telescope at this point.

  Is gathering on the ground in large numbers something that Swallows do?  I'd
  appreciate any comments.  I may try to take a telescope tomorrow evening and
  hope for a repeat performance.  I'll report back if I learn something more.

  Rosalie Strait

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