Just to add to the info -- many of the large groups of Swainsons found in the central valley of 50-200 birds are actually “yearling” of “second-year” birds,
hatched in the previous summer, already been to the tropics once, but too young to commence breeding. So they return to the grasslands of the West but are not “tied” to a nesting area. They form various sized nomadic flocks and eat at outbreaks of insects,
particularly orthopterans, or mice/gophers, or at flooded fields.
There are various field marks to tell these birds apart from just-hatched” young of the year. Although they still do not have complete bibs, they are often
really molty, in the wings, but also around the head with a lot of pale underfeathers showing up on heads in some birds. Enough so that a colleague once called them “a field of stunted adult Bald Eagles.”
One recurring site for these teenage gangs has been near the corner of Jack Tone Road and Highway 4, east of Stockton. Usually around July 4.
It would be really valuable to track the dates, sizes, and locations of these yearling Swainsons flocks as they are obviously a critical life stage for this
threatened species. Do some ag fields – alfalfa? – create better feeding than others? What are the impacts of insecticides and rodenticides used in ag fields? Do the yearling flocks depart California in September with the masses of Swainson’s Hawks from
Pacific breeding areas, or do they leave earlier? And do they spend the “non-breeding season” in similar locations and latitudes as adults? Do they stay in flocks throughout the first year? Or do the flock numbers wax and wane?
This whole phenomenon of nomadic Swainie flocks could really use a few years of PhD study and satellite tracking.
Best regards to my fellow Swainsons fans –
Golden Gate National Parks Conservancy
Golden Gate Raptor Observatory
Bldg 1064 Ft Cronkhite
Sausalito CA 94965
GGRO – inspiring the preservation of California’s birds of prey
GGNPC – parks for all forever
GGNRA – National Park Service
Nothing like a newly plowed field or newly flooded to attract them. I have seen them In those places before migration. I have seen a group of about 300 getting ready to head south in late July as I recollect.
It seems too early for them to be getting ready for migration. Young Swainson's Hawks often form fairly large "juvenile gangs" once the parents cut them loose.
I used to have gangs come into my eucalyptus trees near sunset, flying pretty fast and stopping by awkwardly grabbing branches and hanging on "for dear life". In the morning they could take off gracefully. Took a few nights to get the landings right.
Closer to the end of summer at YBWA we often saw Swainson's grabbing dragonflies in midair, pulling off the wings, and then devouring the rest of the prey while
flying, but the grasshoppers were chased on foot.
From: Ray Sides <rsides@...>
To: hummer52@... <hummer52@...>; CV Birds <email@example.com>
Sent: Sat, Jun 27, 2020 1:54 pm
Subject: Re: [centralvalleybirds] Sutter Co. Huge Flock of Swainson Hawks
As I understand it, Swainson Hawks migrate is groups and feed in fields on insects.
Swainson's hawks are largely insectivorous except when nesting. Insect prey commonly taken includes grasshoppers, crickets, and locusts.
From: firstname.lastname@example.org <email@example.com> On Behalf Of Frances Oliver via groups.io
Sent: Saturday, June 27, 2020 1:37 PM
To: CV Birds <firstname.lastname@example.org>
Subject: [centralvalleybirds] Sutter Co. Huge Flock of Swainson Hawks
Posting for Asher Perla:
Lucas Stephenson and I were birding around bobelaine in Sutter when we drove by a field filled with Swainson's Hawks. We counted 102 sitting in a rice field next to the 99. I don't know what they might be doing there, mixed dark and light morphs. Lucas has
a video of them. Does anyone know what they might be doing there? There didn't seem to be prey for them, especially not in those numbers.
They were seen at this coordinates: 38.863, -121.552