Hi Tweets,

Cycled to the end of the Iona South Jetty this afternoon and learned an
interesting thing about Parasitic Jaegers Stercorarius parasiticus today:
some can look *very* much like Pomarine Jaeger S. pomarinus in size, jizz
and behavior to the extent that the central tail-feather shape is the only
good way to separate them if they stay too far out to provide any other
plumage cues.

There were no small gulls or terns of any description offshore today, just
tons of California Gulls Larus californicus. It wasn't many minutes before
the first jaeger, a light-morph bird, showed up and on wingbeat, shape and
size---too far out to see the central-tail lollipops (or spoons; the central
rectrices resemble both)---I immediately thought 'gotta be a Pom'. I watched
it go to afterburner and literally crash into a California Gull and pound it
down to the water. For me this helped confirm the ID, as not only do Poms
seem to follow the California Gulls and key on them, attacking them in
exactly the manner just witnessed, but also Parasitics will chase a tern or
small gull all over the ocean without exerting anything more than
psychological pressure: this contact was a pure cold-cock mugging. After
feeding on whatever upchuck the gull gave it, it came close enough to see
the central rectrices: spikes, not spoons. Oho, this is an interesting ID
problem: a whacking big jaeger tackling big gulls with all the grace and
elegance of the average NHL hockey-player and it turns out to be a
Parasitic. Jeepers, what next?

Next was a honkin' big dark-morph bird: it splashed not one but two
California Gulls out along the tide rip, lumbered inshore and-- Parasitic.

That's how the next two hours went: in every chase, jaegers physically
thumped the gulls, whether in mid-air tangles and/or with the jaegers
forcing down the gulls to the water and attacking them there, then moved
inshore to show themselves as Parasitics. There were at least four and
possibly as many as six individuals.

After watching all these bruisers at their butchershop work for a couple of
hours, I saw a skinny little jaeger close in and instantly recognised it as
a 'regular' Parasitic. Don't go out there, pal, I thought; you'll be needing
to punch way above your weight.

So here's what I think is happening: Parasitics come in two sizes: male and
female (g), with the bigger females being much more robust and Pom-like in
all ways but the central rectrices and a few plumage details. They have the
size and power to slap the bigger gulls around and since the larger gulls
are used to competing with each other and with even larger gulls for food,
it takes an actual slug-out for a jaeger to take what they've got. The
scare-'em-till-they-puke technique---which works on the smaller gulls and
terns---won't work with California Gulls. So maybe there's a division of
labor much like that between tiercel and haggard in falcons, each sex works
a different prey-size zone, the female taking on the bigger gulls and the
smaller males handling the small gulls and terns. It also makes me wonder if
there isn't some sex-sorting in the northbound migration, but that's only a
guess.

So what I learned is, don't take for granted that a big thumper of a jaeger
that's got the heavy, lumbering flight when it's not bashing some hapless
California Gull into a hole in the ocean is a Pomarine Jaeger. Gotta see the
those central-tail lollipops to be sure.

Oh, yeah: also at the jetty-tip, unusually numerous for here this late in
the northbound migration were 40-50 Pacific Loons Gavia pacifica and ~20
Red-throated Loons G. stellata, many in Def Alternate plumage, and a group
of 4 Brandt's Cormorant Phalacrocorax penicillatus, just NW of the tip. The
colony of Double-crested Cormorants P. auritus on the offshore beacon is in
full swing.

On the NW settling pond was 1 Western Sandpiper Calidris mauri in partial
Alternate, 4 pairs of Spotted Sandpipers Actitis macularia and all six
swallow species were over the ponds with a single Bank Swallow Riparia
riparia joining the regular mob.

Michael Price
Vancouver BC Canada
mprice at mindlink.net