Re: [SBB] BCSP continues ... and BTPI thoughts

["Alvaro Jaramillo" <[[email protected]]>]

Mike

   Birds don't tend to "process" food for the young, but instead they
generally take the fish/insect/worm back to the young from the foraging
area. This means they need to forage near the nest. However, there are a few
birds that do process the food, and it is clear that this is an adaptation
for foraging distantly from the nest and therefore being able to bring in
"concentrated" food. The classic example are the tubenoses which create a
stomach oil, recently it has become clear that swifts also process food
while foraging and visit the nest seldom but with concentrated food. I
gather that pigeon milk, a secretion from the crop, which is highly
concentrated in fats and nutrients is a similar adaptation that allows
pigeons and doves to forage well away from the nest site. This varies
depending on the species I would guess, and since the Band-tail is much more
of a food specialist than a Mourning or Rock doves (pigeon) would be the one
to do this. I don't have access right now to the Birds of North America, but
it would be the place to check out if this has been worked on. My guess is
that you guys are right and those birds in the lowlands are not breeding
there, but are feeding there and nesting elsewhere. We have lots of
Band-tails here in Half Moon Bay, I am convinced that they come down to feed
here, and nest in the hills. You do hear them singing here rarely, certainly
not as much as when one is up in the areas where they do nest. 

My dos centavos. 

Al

Alvaro Jaramillo
[[email protected]]
Half Moon Bay, CA

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> -----Original Message-----
> From: [[email protected]] [mailto:south-bay-birds-
> [[email protected]]] On Behalf Of Mike Rogers
> Sent: Wednesday, May 31, 2006 5:17 PM
> To: birders
> Subject: [SBB] BCSP continues ... and BTPI thoughts
> 
> All,
> 
> It has been a week since Garth first heard the singing Black-chinned
> Sparrow at Hidden Villa, so I decided to head out there over lunch today
> 5/31/06 to see whether I could upgrade the breeding status from
> "POssible breeder-singing in suitable breeding habitat" to "PRobable
> breeder-singing for at least a week to maintain a territory". Almost as
> soon as I started up the Hostel Trail, I heard the singing BLACK-CHINNED
> SPARROW, although it was best heard from a viewpoint a hundred yards or
> so below the trail junction to Toyon Hill. It was still audible from the
> Hostel Trail past the Toyon Hill trail junction, but sounded like it was
> over the ridge and likely not visible. Scanning the hillside from across
> the canyon failed to locate the bird visually, but my impression was
> that the bird did not move around much. The perceived location of
> singing Black-chinned Sparrows can vary significantly depending on which
> direction the bird turns its head while singing and it seemed to me that
> the variation in song volume was due to this rather than significant
> movement of the bird.
> 
> BAND-TAILED PIGEONS were still streaming overhead (22 total), but with
> most heading to the hills at this time of day (from about 1:00pm to
> 1:45pm) instead of towards the valley floor as Bill noted yesterday.
> Bill raised the interesting question of whether birds that breed in the
> hills could forage widely in lowland areas, perhaps returning
> infrequently to their nests. I have been toying with this idea as well,
> based on birds that are present virtually daily in Sunnyvale, often near
> Knickerbocker and Mary. These birds are apparently attracted to backyard
> feeding stations, mostly in the morning (when seed is put out?),
> sometimes in fairly large numbers (e.g. 15 on 9 May), but disappear
> later in the morning, often leaving to the southwest towards the hills.
> This species caused real headaches for our county breeding bird atlas
> because urban sightings during the breeding season were hard to
> interpret. Were they local breeders? Birds that had already completed
> their breeding? Birds not yet involved in breeding? (Breeding can occur
> early or late in the season for this species.) Or widely foraging
> breeding birds as discussed above? Any insight based on known nests,
> recently fledged young, or other breeding evidence would be most welcome!
> 
> Mike Rogers
> 
> 
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