Date: 5/6/25 10:16 am From: Bruce Mast via groups.io <cathrasher4...> Subject: Status of Black-chinned Sparrows in NorCal. (Was "Re: [EBB-Sightings] Mount Diablo Big Day Hike results")
Forwarding on behalf of Ed Pandolfino, who's not subscribed to EBB.
Bruce
---------- Forwarded message ---------
From: <erpfromca...> <erpfromca...>
Date: Tue, May 6, 2025 at 9:47 AM
Subject: Re: Status of Black-chinned Sparrows in NorCal. (Was "Re:
[EBB-Sightings] Mount Diablo Big Day Hike results")
To: <jmorlan...> <jmorlan...>, East Bay Bird Sightings <
<ebb-sightings...>, Bruce Mast <cathrasher4...>
Cc: Lily Douglas <ldouglas14...>
Bruce,
Ed Pandolfino here.
I don't disagree that there may be annual breeding in those locations (and
Henry Coe park as well), but I think our finding that the timing of the
large numbers of sightings throughout NorCal are also reflected in the
proposed range of *S. a. caurina* weakens any case for a distinct breeding
range for that taxon. This, along with the tiny number of specimens
examined and the complete overlap of those measurements with *cana, *and
the identical song dialect all weaken any (already very weak) case for *caurina
*being a valid subspecies. Much more likely that, if breeding is regular,
it just reflects a historical extension of the breeding range of *S. a.
cana*. In any case, the main point of the paper was that these irrurptions
appear to coincide with SoCal drought.
Thanks for bringing this up and for giving it a lot of thought. Always
great to know that someone is reading this stuff!
Ed
On Tuesday, May 6, 2025 at 08:09:27 AM PDT, Bruce Mast <
<cathrasher4...> wrote:
Interesting if true! I'm cc'ing Ed Pandolfino and Lily Douglas in hopes
they can shed some light on some points that leave me unsettled.
The paper seems to demonstrate that there are irruptions. I find it
plausible to believe that these irruptions account for the vagrant-like
sightings we get in the East Bay, North Bay, Marin, San Mateo Co, etc. I
find it less plausible to believe that ALL NorCal Black-chinned Sparrows
are irruptive. There seem to be pretty stable populations in places like
Loma Prieta / Summit Road (Santa Cruz Mountains in SCL), Tassajara Rd /
Chewy Ridge (MTY), and possibly around the San Benito Mountain Research
Area in San Benito County.
Pandolfino's treatment of the sighting data seems to diminish the
distinction between vagrant birds and core breeding populations. Per the
paper: "We assumed eBird reports or reports from the North American Birds
data from the same location in the same season were from a single
individual unless the reporter specifically noted the number of separate
individuals observed. When multiple individuals were noted by more than one
observer in one location, we used the highest total observed by any single
observer on a single day in that location for the total number of birds.
Because locations of eBird reports are based on where the user chose to
start the checklist, we assumed eBird reports within 5 km of each other in
the same season were of the same individual."
Based on that method, it's hard to see how the analysis could distinguish
between a breeding population in the Santa Cruz mountains versus a lone
bird that shows up at Sibley Regional Park.
There's also a pretty big risk of observer bias with this species. Much of
the best chamise habitat that I'm aware of in NorCal is off limits to
birders, often on private land. In Alameda County, for example, aside from
some remnant chaparral in Strawberry and Claremont Canyons, probably the
best habitat is south of Lake Del Valle on private land. Just last weekend,
I was trying to get into good chamise habitat along Del Puerto Canyon and
it's all either on private land or devoted to the OHV park. Even in public
parks, the chaparral tends to be inaccessible. People generally cut roads
and trails around chaparral rather than through it because it is such a
thicket. My sense is that only a small fraction of the chaparral on Mount
Diablo gets birded regularly. Bear Mountain Trail in Henry Coe SP is
publicly accessible but it's a long hard hike to get to it. In short, I'm
not sure how well we understand the actual breeding status of Black-chinned
Sparrows in NorCal. How many stable breeding populations are completely
undocumented? I suspect the vagrant-like sightings are over-represented.
Then there's the whole issue of synonymizing S. a. caurina and S. a. cana.
I'm still going down the rabbit hole on that one. I'll report back if I
ever find my way back out.
Bruce Mast
Oakland
On Mon, May 5, 2025 at 5:04 PM Joseph Morlan <jmorlan...> wrote:
This is an irruptive species with incursions into Northern California
correlated with drought in Southern California. I recall back in the early
1970's they moved into Tilden Park one year.
More information here...
"Irruptive movements of the Black-chinned Sparrow (Spizella atrogularis) in
response to variations in precipitation: Implications for climate change
resiliency" by Pandolfino, Douglas & Ray. (Western Wildlife 9:24–37, 2022)
On Mon, 5 May 2025 16:30:00 -0700, "Bruce Mast via groups.io"
<cathrasher4...> wrote:
>More generally, it would be gratifying to have breeding Black-chinned
>Sparrows in the East Bay again. I read Grinnell's reports about
>Black-Chinned breeding in places like Claremont Canyon and wonder what it
>would take to bring them back. I suspect a change in fire management
>practices would be required.
--
Joseph Morlan, Pacifica, CA
