>Hi Tweeters,
>
>Dusted off the 'scope and took in some shorebirds at the Iona Is. Settling
>Ponds last night. Present were:
>
>500-550 Western Sandpipers (WESA)
>Approx only, three ever-shifting flocks thanks to the Killdeers that were
>either panic-stricken all the time or just like watching the little guys get
>up and fly--when is Modern Science going to get off its duff and invent a
>silence pill for Killdeers?)
>All but about 150 in definitive alternate; of the 150 alternate 1 birds,
>about 20 were visually indistinguishable from def. basic, the rest a dog's
>breakfast of alternate WESA plumage features. By bill-length, about 80% were
>definitely female, the rest indistinguishable except for 6 stub-billed birds
>I'm sure were males.
>
Michael, I'm curious but how were you identifying the First Alternate
(young) from the Definitive Alternate (adult) birds?

>During periods of high pressure, I bet a lot overfly the Fraser and Skagit
>Deltas, not stopping until Gray's Harbor, South Jetty of the Columbia, or
>even further south. Trying to figure out how that Rufous-necked Stint
>(RNST), which at this time of the year seem to travel with the first wave of
>nonbreeding WESA, got to S. California so quickly, only 3 days after our own
>WESA, etc. arrived on 6.24.
>
>Rob Butler's work has shown that the average layover time here for a small
>calidris sandpiper is 5 days for it to rest and stoke up, and that some if
>not most travel on the jet streams. My hunch is that the RNST went straight
>there from either southern Alaska or the Stikine Delta, a fairly-recently
>discovered staging area.
>

In my mind, this Rufous-necked Stint arrival bit is a really good
question. What I would like to know is if the pattern of late June/early
July arrival is real or an artifact? Why are there so few (or none?) from
early August, before the juvenile migration of peeps? I have yet to see a
Western Sandpiper here (San Francisco Bay Area), only Leasts, so the
Rufous-necked Stint that got here definitely arrived before the main
movement of Westerns (am I right Joe?). However, I don't think that the
reason is that these birds happen to catch a good wind to ride, particularly
since the jet stream largely goes from the west to the east. Of course,
meandering of the jet stream does occur and it can be shooting air from the
north almost directly to the south, but this would rarely, if ever, happen
accross a large latitudinal difference. So its unlikely that a bird could
ever ride a jet stream from Alaska to California. The jet streams may be
much more helpful to birds like Blackpolls, Grey-cheeked Thrush that have to
go southeast in the fall. I don't imagine that at our latitudes the jet
streams could ever be used to a bird's advantage in the spring. In any case,
this is all speculation. I don't think that we can yet be sure that birds
use the jet streams during migration, but I would be interested in reading
any data that shows this is the case.
So why do Rufous-necked Stints migrate through early? I have two guesses:
1) They are most obvious early in the season. In June and July Rufous-necked
Stints should show a good amount of red on the plumage which makes them more
obvious. Later on they will be more faded and duller and perhaps will have
started moult. Related to this may be that once the Western Sandpipers
really get going, you have very little chance to detect a stint because
their proportion decreases relative to the Westerns.
2) Something in their breeding biology differs from Western Sandpipers. How
about double clutching? I know that Little Stints are double clutchers; this
is when a female lays two full clutches of eggs in a season. The first is
layed for a male to incubate and she will incubate the second clutch, which
is sometimes (often?) fathered by another male. Perhaps Rufous-necked Stints
are double clutchers and Westerns are not? If this is the case, the early
failed breeders in Rufous-necked Stints will be more likely to be males.
Some of these failed males get misoriented and migrate south early in the
season. As well, males tend to be the brighter sex and therefore most
obvious. Failed females may have to spend more time recuperating after
laying two clutches which may allow for them to gather into larger groups,
with failed and non-failed birds, which will be less likely to stray. I am
assuming that it is easier for a single bird to stray than a group because
in a group the correct migratory direction is likely to be followed since
the majority in the group will know where they are going. If that doesn't
make sense then picture the following scenario: one bird is just bad with
directions and is alone, it gets lost, but the same bird in a group will
follow the lead of the group and won't get lost. So it is the early, failed
males that get lost and wind up here.
That was a lot of speculating and arm waving to get at a possible
explanation for the early arrival of Rufous-necked Stints. From the little I
have been able to read on Rufous-necked Stints, their migratory timing
should be similar to that of the Western Sandpiper. If this is the case,
then most of the Rufous-necked Stints along the Pacific Coast of North
America should arrive with the masses of Western Sandpipers, not early as
many records indicate. As well, juveniles should be going through as well,
but the fact that we don't see them is likely the opposite of my point 1).

Any other hypotheses? Maybe if we brainstorm we can come up with something
plausible. BTW, does anyone have info on double clutching in Rufous-necked
Stint? If they don't do it, then its an easy way to kill my wacky hypothesis 2).

Good Shorebirding

Alvaro Jaramillo
Half Moon Bay, CA

alvaro at quake.net