Date: 11/4/25 11:33 pm From: James Bailey via groups.io <rivierastarsong...> 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 <jmorlan=
<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.
>
