Following up on recent emails on the Los Angeles County listserve, I
wanted to provide a summary of recent developments with Swainson's
hawk migration in Los Angeles County this year and to discuss plans to
set up a "picket line" to monitor movements by this species.
There was a pronounced burst of Swainson's hawk reports on the LA
County listserve and in eBird on Saturday, March 11, with reports of
dozens to more than 100 birds moving east to west between Claremont
and Monrovia on the southern edge of the San Gabriel Mountains. There
have also been earlier reports and a few since Saturday
Here's a summary of counts of at least 10 Swainson's hawks in LA
County so far in 2023:
N Date Location Observers
45 Jan 06 Bonelli Park K. Condon, K. Dillbeck
30 Feb 26 Hahamongna Park D. Dowell
75 Feb 28 Midwick Dr, Altadena L. Tiller
10 Mar 03 Hastings Ranch, Pasadena J. Rodgers
50 Mar 03 California Botanic Garden K. Dillbeck, P. Thorne, M. Ruiz
141 Mar 08 Gorman Post Road D. Irons, R. Crossley
12 Mar 11 Grand Ave. Park, Monrovia A. Howe, V. Howe
53 Mar 11 Glendora, Sierra Madre Ave M. Peralez
40 Mar 11 Claremont Wilderness Park T. Miko
85 Mar 11 San Dimas Canyon Park S. Kurniawidjaja
250 Mar 11 Monrovia Myrtle & Greystone H. Coates, D. Coates
14 Mar 11 Claremont Colleges M. Peralez
39 Mar 12 Midwick Dr, Altadena L. Tiller
88 Mar 13 Gorman Post Road D. Irons, R. Crossley
Some of these counts lasted more than one hour and are totals of
multiple flocks.
How do these numbers compare with results from previous years? I
checked eBird and tabulated high counts in LA County in the spring
dating back to 2018. Here's a list of reports of at least 50 birds
from 2018-2022:
Count Date Time Location
100 24-Feb-18 17:14 Pitzer College, Claremont
100 3-Mar-18 7:40 Peck Rd. Water Conservation Park
080 5-Mar-21 8:45 Horsethief Canyon Park, San Dimas
100 8-Mar-22 dusk North end of Barranca, Glendora
250 11-Mar-18 9:14 Hahamongna Park, Pasadena
200 11-Mar-18 16:00 Los Feliz/Atwater Village
145 11-Mar-18 16:00 Scholl Canyon, Pasadena
075 11-Mar-18 17:00 Myrtle/Greystone, Monrovia
050 12-Mar-22 8:36 California Botanic Garden, Claremont
400 13-Mar-21 9:30 East Loma Alta Dr., Altadena
100 13-Mar-21 12:12 Bygrove St., Covina
103 13-Mar-22 18:00 Gorman
125 14-Mar-21 7:47 Bernard Field Station, Claremont
051 14-Mar-22 18:07 Palm and Live Oak, Glendora
200 15-Mar-20 6:36 Hahamongna
516 15-Mar-20 10:00 Vina Vieja Park, Pasadena
150 15-Mar-21 12:30 East Loma Alta Dr., Altadena
150 15-Mar-21 15:05 Horsethief Canyon Park, San Dimas
375 15-Mar-21 17:10 Altadena
075 15-Mar-21 17:56 Bowring Dr., Altadena
053 15-Mar-22 8:27 North Glendora
075 17-Mar-20 10:42 Highland Place, Monrovia
070 20-Mar-21 13:01 Claremont Wilderness Park
141 20-Mar-21 13:45 Juniper Hills
367 20-Mar-22 11:00-16:00 Gorman
055 23-Mar-19 9:00 Hansen Dam
070 23-Mar-19 9:12 Altadena
100 27-Mar-18 9:00 Chilao, San Gabriel Mountains
221 29-Mar-22 pm Gorman
050 1-Apr-22 8:35 Haskell St., La Canada-Flintridge
134 5-Apr-22 am Bear Divide
076 6-Apr-22 am Santa Clarita
120 8-Apr-19 9:05 Piute Ponds
Note again that some counts span multiple hours and represent more
than one flock.
To get a better understanding of what the birds are doing as they
traverse Los Angeles County, we are asking for help with organizing a
picket line along the San Gabriel Mountain foothills from Claremont to
Santa Clarita on:
Thursday, March 16.
Observers elsewhere in the county such as the Antelope Valley, the
north slope of the Castaic Highlands (say, along Pine Canyon Road,
Lake Hughes, Lake Elizabeth, the Leona Valley, and the Poppy
Preserve), and anywhere across the county are also welcome. We'd be
glad to hear reports east of Los Angeles County as well.
We plan to communicate sightings of significant numbers of hawks on
the county listeserve, eBird, and more rapidly with each other using
texting and phone calls. If you'd like to help communicate rapidly
about big groups by phone and text, please email me off-list. My email
address is:
<lbenner...>
Thursday also coincides with the first day of migration counting at
Bear Divide, through which decent numbers of hawks passed in the
spring of last year. Richard Crossley and Daniel Irons have also been
counting regularly from Gorman Post Road near Quail Lake, so it may be
possible to cover a significant fraction of the east-west line across
the county.
Although Thursday is a workday for many of us, we hope that there
will still be numerous observers available to scan the skies for at
least part of the day.
We had hoped to establish a north-south picket line into the
mountains this year, but many of the roads in the San Gabriel
Mountains are still closed, and communcations there would be
difficult, so we decided to change plans.
In the bigger picture, the migration underway in February-March is by
hawks that are moving into the Central Valley. Later in April and May,
most birds passing through our area will head into the Great Basin,
eastern Washington, and the Snake River Plain of Idaho.
To get a sense for the annual movements of Swainson's hawk, there's a
time-lapse animation at weekly intervals available on eBird using data
reported from 2007-2021. Check it out at:
Large numbers of Swainson's hawks have been moving through Borrego
Springs southeast of us in the last week so prospects are good for
continued movement by some (or most) of those birds across Los Angeles
County.
