As we near recording the 5000th Swainson's Hawk in Borrego Valley, San
Diego County, this spring, Hal Cohen and I thought we'd take the
opportunity to share a brief summary of the remarkable migration we are
With help from numerous volunteers, we have managed to operate a watch
site on north DiGiorgio Road every day since Feb 22, 2004 from 8 AM to
11 AM. Totals to date are 4974 Swainson's Hawks and 706 Turkey Vultures.
We believe that year's spring total of 2031 SH was comparable because
Hal and I, without much help, only accumulated about half the count
hours as this year. We have also significantly improved our technique in
number of ways but especially by going out each evening to locate and
count incoming birds as they arrive to roost.
The flow of SH and TV's has been fairly consistant. We had 12 days in a
row with 75 or more SH. Our site has not turned up anywhere near the
numbers of TV recorded in the fall at Kern River and other places.
The highlight so far occurred on March 25th when a tornado of 1000-1500
SH dropped out of the sky in the evening. Most migrated out the
following day. Not only does this kind of happening get seasoned birders
excited, Borrego provides one of the only hawkwatch sites in North
America that is a staging area, that is, where birds come to roost, feed
and are seen taking off in the morning.
Many SH have been seen feeding in the air on flying queen ants and
dragonflies, or on the ground on white-lined sphinx moth caterpillars.
One puzzling question is where are all these SH going? Our numbers far
exceed the known California breeding population and routing through
Borrego to other breeding areas seems a bit out of the way (e.g. Nevada,
Idaho, eastern Washington, eastern Oregon and the plains of Canada. They
must go over or around the Transverse Range.
Thanks to Hal Cohen, this year and last year's data are published in
the journal of the Hawk Migration Association of North America (HMANA).
See the <hawkcount.org> website. Our count site, Borrego Valley, will
also be included in the new edition of the soon to be published book
"The Migration of Hawks" by Heinzelman.
The plan is too keep the watch until the end of April-maybe into early
May. Since we are only in our second year, it is hard to predict when
numbers will taper off but, based on last year and historic records,
this could happen in about two weeks. Thanks to the volunteers who have
helped so far. Visitors are always welcome-we have had hundreds this
California State Parks
Colorado Desert District
200 Palm Canyon Drive
Borrego Springs, CA 92004
phone: (760) 767-5748