Date: 4/26/24 8:25 am From: Mark Holmgren via groups.io <maholmgren33...> Subject: Re: [sbcobirding] Vaux's Swift
Very interesting. Thanks, Larry, for posting.
Communal roosting during migration is an interesting feature of this
species' biology. In our area the birds seem to migrate along the coast
and they choose roost sites close to the coast. The authors of the *Birds
of the World* species account for Vaux' Swift use eBird checklists to build
their understanding of this phenomenon. So I hope this observation gets
into eBird.
Other questions are:
- for how many nights does this roost serve? and
- where exactly did the birds settle for the night?
Below are some excerpts from Birds of the World.
Mark Holmgren
San Marcos Pass
~~. ~~. ~~.
Spring Migration
In spring, individuals generally arrive in Oregon from late April and to
late May (Table 1
<https://birdsoftheworld.org/bow/appendix/ACT1055672/APP1005585>; 67
<https://birdsoftheworld.org/bow/species/vauswi/cur/references#REF30573>, 63
<https://birdsoftheworld.org/bow/species/vauswi/cur/references#REF30566>, 5
<https://birdsoftheworld.org/bow/species/vauswi/cur/references#REF58794>).
One monitored roost site in Monroe, Washington, has shown an increase in
roost use during mid June, following the main migration event which may be
attributed to nonbreeding individuals leaving overwintering grounds after
others (LS, unpublished data). In California (41
<https://birdsoftheworld.org/bow/species/vauswi/cur/references#REF7103>),
generally appear first week of April, with major passage flights seen
mid-April to late May. Analysis of individuals migrating north appear to
follow a coastal route as they enter southern California and are commonly
reported in from Los Angeles to Point Conception (LS, unpublished data).
From here the migration route is not well understood, though various
anecdotes suggest swifts enter the Sierra Nevada range via the Kern River
Valley. Swifts may use the Sierra Nevada range to avoid strong northwestern
winds (LS, unpublished data). Groups ranging from 5,000–10,000 have been
observed roosting in old growth trees in the southern Sierra Nevada range,
and participants in the Kern River Valley Spring Nature Festival report
large numbers of swifts flying north (W. Fritz and B. Barns, personal
communications).
Migratory Behavior
Diurnal migrant. Generally fly high, often at the limit of sight, but may
be much lower (i.e., 1–2 m above ground) in cooler weather or in headwinds
(CTC). Along the California coast in spring, largest flights seen along
coast when low clouds and fog force swifts to migrate at treetop level (41
<https://birdsoftheworld.org/bow/species/vauswi/cur/references#REF7103>).
Often migrate in large flocks, roost in hollow trees and chimneys at night.
An unusual roost in a barn where 3,000 swifts roosted in a hayloft for
several nights (68
<https://birdsoftheworld.org/bow/species/vauswi/cur/references#REF54692>);
also on exposed trunk of tree, about 2 m above the ground (69
<https://birdsoftheworld.org/bow/species/vauswi/cur/references#REF37596>).
Numerous other reports of swifts roosting on exposed tree trunks in large
numbers (K. Garrett, R. Nelson, P. Nelson, W. Fritz, personal
communications). Time spent at each roost site during migration requires
more study, and there is significant variation in the number of swifts
using the same roost each night. Radio-transmitters attached to migrating
swifts in September 2014 indicated a mean daily distance of 95 km covered
in 5 d (T. Lorenz, unpublished data). Additionally, premigratory mass gains
are not as large as in other migrant species (21
<https://birdsoftheworld.org/bow/species/vauswi/cur/references#REF41478>).
This may indicate that swifts alternate travel day with feeding days during
migration. During the fall migration, Vaux's Swifts appear to spend an
average of 2–3 nights at large known roost locations before moving on (LS,
unpublished data).
On Thu, Apr 25, 2024 at 8:16 PM Larry Ballard via groups.io <larryincarp=
<aol.com...> wrote:
> I just got a report and a video of about 800 Vaux's Swifts swirling over
> the County Bowl just before Wille Nelson came on.
>
> Larry Ballard
> Carpinteria CA
>
>
>
