Hi Tweets,

Regarding California Gull (CAGU) age-sorting in southbound migration, Ray
Korpi writes:

>There certainly is a significant migration of California Gulls going on
>here along the COlumbia, but what's very interesting is that I've seen
>no first-year juveniles on the ground here. Every new juvy I've
>seen has been floating over the Clark campus or wherever I might be
>birding in the area, going oceanward. The fields here at Clark, when
>they have Californias right now, have pretty exclusively adult birds--there is
>occasionally a second-year bird.

>This leads to an interesting question about the behavior of California
>Gulls (given, of course, that I might be missing some birds somewhere)
>is this: are the juveniles led to the beach for the winter pretty
>exclusively? There are bunches of freshly plumaged and very attractive
>juvy Californias on the coast. The high migration seen may be birds
>that are going very fast to the coast rather than working down the river
>or areas. An interesting thread . . .

Ray, the answer may be in Harry N's entry in the thread.

Harry Nehls then writes:

>There is a very heavy adult California Gull migration down the Columbia
>River beginning about mid June. These may be birds from the Columbia Basin.

Wow, that's a full month ahead of our adults' arrival back out to the SW BC
coast. Ours arrive mid-July with main numbers in August. And they don't seem
to use the Fraser River, not around New Westminster BC anyhow. I watched the
river closely last summer through July & Aug and was stunned at how little
southbound migratory action there was: a few small calidris flocks, once a
small flock of yellowlegs, a single merganser, not even an Osprey.

>As the movement is primarily northwesterly birds from more distant Great
>Basin colonies move at higher elevations and fly directly over the
>mountains. We see tnem regularly flying over the mountains all along the
>Cascades.
>
>An interesting sidelight. California Gulls molt during the movement and
>many arrive on the coast in very poor condition, often with considerable
>mortality. Many of these adults drop down along the migration route and are
>regularly found on mountain lakes and interior valley wetlands.

Folks, sorry for using lots of bandwith to quote both posts but there's
information in each that may shed light on this question of 'adults on the
field, juvs on the coast'.
Ray, probably the eatin's better in the grass than on the beach. If the
adult CAGU are so severely stressed by the double whammy of long-distance
migration *plus* molt as to suffer significant mortality, it might make
sense that they'd appropriate the best feeding areas. Hm, but if that's so,
and assuming parents and juvs leave at roughly the same time, then the juvs
*should* beat them out to the coast because their plumage is complete and as
fresh as it's going to be, and they'll be able to make better time. The
adults in poor plumage would need to make more pitstops to gas up.

Maybe at one time, adults and juvs migrated together but over time the
adults, being more opportunistic through experience, learned to stop on
fields and campi whereas the juvs, propelled by instinct alone, went
straight to the coast (why wouldn't they imitate the adults' behavior,
then?) Interesting! As another sidelight, that means family bonding vanishes
very quickly in CAGU (and perhaps the other migratory gulls). Compare to
non-migratory Glaucous-winged Gulls here in Vancouver BC where the
First-year bird hangs around bugging the parents for food for
months--sometimes almost the entire year-- after fledging.

Cheers

Michael Price The Sleep of Reason Gives Birth to Monsters
Vancouver BC Canada -Goya
mprice at mindlink.net