Hi Tweets

Monitoring the Iona Island Sewage Treatment Plant settling ponds in
Richmond BC over many summers, it became clear that after the last of
the northbound shorebirds (usually Western Sandpiper) cleared the
ponds about Week 3 - Week 4 May, there was a hiatus of about three
weeks where a handful of Westerns---I'm guessing First Summer
birds---would loiter on the ponds and foreshore.

In June, the first southbound migrant shorebird was usually the Lesser
Yellowlegs (First Summer birds?) just before or just after the Summer
Solstice, with a (then) average arrival date of June 21, followed by
(in sequence) Definitive Alternate-plumaged (adult) Western Sandpiper
and ad Semipalmated Sandpiper.

July is the month of juvenile arrivals, the young birds of that
summer; depending on species, they usually arrive about two-three
weeks after southbound adult arrival---the usual sequence for July
was: ad Least Sandpiper, ad Greater Yellowlegs, ad Red-necked
Phalarope, ad Baird's Sandpiper, ad Short-billed Dowitcher, ad
Pectoral Sandpiper, ad Semipalmated Plover, juvenile Semipalmated
Sandpiper, juv Lesser Yellowlegs, Juv Western Sandpiper, juv Wilson's
Phalarope, ad Whimbrel, ad Sanderling, ad Long-billed Curlew, ad Ruddy
Turnstone, ad Red Knot, juv Least Sandpiper, juv Short-billed
Dowitcher.

August had the same pattern of adult birds in Definitive Alternate
plumage arriving a few weeks before the appearance of their
juvenal-plumaged young; the sequence was usually: juv Baird's
Sandpiper, ad Wandering tattle, juv Stilt Sandpiper, juv Red-necked
Phalarope, Black Turnstone, juv Pectoral Sandpiper, juv Sanderling, ad
Pacific Golden-Plover, American Golden-Plover, juv Ruddy Turnstone,
Surfbird, juv Pacific Golden-Plover, juv American Golden-Plover, ad
Dunlin, juv Buff-breasted Sandpiper, juv Wandering Tattler.

September and October see a real tailing-off in southbound arrivals:
ad Willet, juv Ruff, juv Sharp-tailed Sandpiper, juv Bar-tailed
Godwit.

One question, among many others, is the juveniles' tracing their
parents migratory routes without their parents showing them the way.
The usual explanation is that they're hard-wired to go those routes,
no matter what. But I've always wondered if---as a back-up
strategy---there's some genetic cueing which tells the young bird,
"when you see a bird of that other species, follow it!"

In any given year, there may be early arrivals of some, late arrivals
of others, so this note is intended only as a very general sequence of
southbound shorebirds at the particular mid-latitude coastal locations
of Iona Island, Reifel and Boundary Bay. Further, global warming is
modifying many species' migrational dynamics. Also, I've omitted
unpredictable (at these locations, anyway) rarities such as Red-necked
and Little Stints, though there are discrete migrational windows in
which they may appear.

Hope this is helpful.

Michael Price
Vancouver BC Canada
loblollyboy at gmail.com

Every answer deepens the mystery.
- E.O. Wilson