Crossbill irruption (forward MBBirds)

Ethan Monk

Not necessarily in the East Bay, but a good read and a reminder to record
any crossbills that might be cooperative enough to be recorded! Our current
irruption seems to be mostly type 2 but I wouldn't be surprised if type 3s
(or something rarer?) were mixed in.


---------- Forwarded message ---------
From: Alex Rinkert <arinkert12@...>
Date: Wed, Nov 13, 2019 at 8:06 PM
Subject: [MBBIRDS] crossbill irruption
To: mbbirds <mbbirds@...>

The beginning of a RED CROSSBILL irruption seems to be underway. I’d like
to offer some initial observations on this irruption based on what has been
observed in Santa Cruz County recently.

While still early, this irruption seems to be on par with some of the
largest irruptions in the last decade. Reports are coming from both lowland
and montane areas where there is moderate to high birding coverage.
Crossbills have been found in areas with stands of Ponderosa or Monterey
pines, however there are a handful of reports from elsewhere, including at
places lacking conifer-dominant habitats (e.g., coastal Wilder Ranch,
Capitola Village). Crossbills in areas lacking sizeable stands of conifers
may blink out at some point in early winter.

Of the ten call types of Red Crossbill in North America, two are documented
to have occurred in Santa Cruz County—types 2 and 3. In recent irruptions
when numerous sound recordings were obtained, type 2s were locally present
on both the coast and mountains in areas with Ponderosa and Monterey pines.
Type 3s were widespread in the mountains and tended to be most abundant
where Doug-fir was the dominant tree species. In previous irruptions type
3s were also present at some areas on the immediate coast were there are
stands of Monterey cypress (e.g., Pajaro Dunes and vicinity). Both types
have been found elsewhere on the coast where conifers are sparse,
especially early in an irruption. Flocks containing multiple call types
have been found at a few locations.

So far the only crossbill type reported to eBird in this irruption has been
type 2. Notably, large flocks are missing at Quail Hollow Ranch and
Ponderosa Lodge at Mount Hermon where some of the largest stands of
Ponderosas are in the county. These areas served as strongholds in recent
irruptions for this call type. The large stand of Ponderosas at Bonny Doon
Ecological Reserve has had a flock, however they have thinned out there
recently. As far as I know there are no observations of them feeding on
Ponderosa cones in this irruption, and some observations at Bonny Doon
suggest they are actually feeding on the rare Santa Cruz cypress. Did our
Ponderosas not have a good cone crop this year?

Following up on a crossbill report from Empire Grade a few days ago, I came
across a large flock of type 2s voraciously feeding on Doug-fir cones in
mixed evergreen forest with patches of knobcone-manzanita. While such an
observation may not be unusual for this call type which feeds on a
diversity of conifer cones, in the recent irruptions I do not think type 2s
were ever noted feeding on Doug-firs. Instead, they were only seen feeding
on the much larger Ponderosa cones (preferred across their range), willow
catkins, and presumably Monterey pine. Recently the flock of type 2s at
Sunset State Beach were seen feeding on Monterey pine cones.

Most excitingly in this recent type 2 flock on Empire Grade were two type 4
crossbills, which I believe are the first documented in the county. A sound
recording can be listened to here: Type 4s are known from this
region, however there are few records. Groth reports in his 1993 monograph
that this call type was part of the 1984-85 irruption in the San Francisco
Bay. More recently in 2013 one was recorded in the Diablo Range in Santa
Clara County.

I highly encourage birders to attempt recording the calls of crossbills
they encounter. With practice the different call types are recognizable in
the field however they sound similar enough to cause confusion, and with
the possibility of multiple types in a single flock, sound recordings are
important for correctly identifying them. A few years ago eBird published
an overview of call types that is worth reading:
Birders would also do well to note what tree species they are seen foraging
on to help further elucidate their ecology in this region.

Happy crossbill hunting,

Alex Rinkert

Santa Cruz