Swainson's Hawk Migration Picket Line: Thursday, March 16

Lance Benner

Hi Everyone,

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:


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. 

Thank you, and good luck to us!


Lance Benner

On behalf of Los Angeles Birders

Lance Benner

Altadena, CA


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