Date: 11/5/25 9:26 am From: Jim Holmes via groups.io <jfholmes...> Subject: Re: [CALBIRDS] Cassia Crossbill reports San Mateo Co
I was recently in Scotland voice recording Crossbills.
I put several of my recordings into BirdNET (an AI bird sound identification app, similar to Merlin).
Multiple of my recordings in Scotland came back as Cassia Crossbill (albeit with low probability).
Pretty sure the AI is not yet capable of definitively identifying the crossbill “species.”
Thanks,
Jim Holmes
Sacramento
From: <CALBIRDS...> <CALBIRDS...> On Behalf Of James Bailey via groups.io
Sent: Tuesday, November 4, 2025 11:33 PM
To: <jmorlan...>
Cc: <rishab.ghosh...>; <tgmiko...>; calbirds <calbirds...>
Subject: Re: [CALBIRDS] Cassia Crossbill reports San Mateo Co
Hi,
In my experience it is difficult to compare European and American crossbills, even within the same species. In Europe the calls of red (and also parrot and “Scottish” crossbill) are indeed variable. The hypothesis is this is because the populations there are a contiguous amalgamation over a huge geographic area, with fluid ecological needs, and so without so established “types”.
This is different to the case in the US. Our crossbills here are much more specialized to specific geographic areas and corresponding ecology. As a result individuals from these “types” are far more consistent. “Intermediate” calls are apparently rare and more often caused by recording error (or in my experiences birds being too far away, and the spectrogram being incomplete…). But that question is better answered by Tim. I don’t believe any past recordings from Skylawn in 2023’s irruption were conclusively intermediate. Last spoken, I don’t think a Cassia-call could be produced as a false positive because it the call structure is not “between” two types.
P.S. wouldn’t be surprised if it turns out Cassia crossbill isn’t sedentary if conditions are dire. Apparently in 2023 their habitat was severely damaged and burned by fires.
JB
On Tue, 4 Nov 2025 at 10:53 PM, Joe Morlan via groups.io<http://groups.io/> <jmorlan...><mailto:<gmail.com...>> wrote:
I'm taking the liberty of posting from an advanced draft copy of the 50th
CBRC report about these records:
"CASSIA CROSSBILL Loxia sinesciurus (0, 0). IDENTIFICATION NOT ESTABLISHED:
Large numbers of Red Crossbills (L. curvirostra) were encountered at
Skylawn Memorial Park in Half Moon Bay, San Mateo County during a
widespread irruption of this species in fall 2023. Among a flock of up to
60 crossbills giving flight calls of several different types included one
or more birds that were thought to be consistent with Cassia Crossbill 26
Oct-16 Dec, 2023 (2023-108); this species was considered endemic to the
Albion Mountains and South Hills of southern Idaho, but has recently been
found in Colorado (Gent 2022). Outside experts agreed that field recordings
most closely matched those of Cassia Crossbills recorded in the South Hills
of Idaho. However, after two rounds of voting, the majority of the
committee felt that there was too much uncertainty in the variation within
Red Crossbill call types, and that the recordings did not precisely match
those of classic Cassia Crossbill. Some members were also concerned about
the likelihood of long-distance vagrancy in an ostensibly sedentary,
range-restricted species."
FWIW, the voting was 5-4 in favor, the first round, but 2-7 against on the
second round. A recent paper found rapid evolutionary change in Red
Crossbill vocalizations in Europe. It is reasonable that some of our birds
evolved calls that are similar to, but not exactly like Cassia Crossbills.
In a recent visit to Skylawn, I recorded previously unknown call types that
are intermediate between Type 12 and Type 7.
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