Hello Bill and All,
The Common Green Darner is one of the larger dragonflies and it is one of the small number that do migrate. Swallow-tailed Kites (STKI) feeding on these in mid-August here in Florida get more energy absorbed per the same energy expended versus the smaller dragonflies, and it is a popular food item of STKI immediately before the STKI migrate.
Here in central FL, there is a dramatic uptick in Common Green Darners migrating in, augmenting existing ones, in mid-August and that coincides with the last large feeding aggregations of STKI before they migrate. We are talking only about a 10 day window here. This is what I have observed and I am hoping there is a statistical based study done in the future to show a positive correlation of these two events. I believe there is a study out there that was done with American Kestrels and dragonflies re migration.
It is possible STKI could move north as you say then come south again as the Common Green Darners continue to move south. After watching STKI feed, they are so skilled in catching even small insects that I personally don't think they need to migrate north in search of prey. They seem to be able to get all the food they want.
Re your, "Dragonflies, and their predators, continue to diminish." ...... Yes, so sad and true. Prey continues to shrink as pesticides grow in use as human population grows, and that will likely have yet another negative effect not only on the prey numbers but on the STKI as well as a huge number of insects and birds that are already in a downward trend.
Bob Stalnaker
Longwood, FL
On Sunday, August 17, 2014 9:58 AM, Bill Whan <[log in to unmask]> wrote:
I gather that only 1% of the world's dragonfly species undertake
migrations, but apparently some large and tasty ones pass heading south
in the US each fall in large numbers, and some birds specialize in
eating them. Some of them are large enough to be too much to handle for
the average bird, but raptors like kites prey on them. Because large
numbers of these dragonflies--and it would be great to hear from
dragonfly-watchers about this--must pass through Ohio this time of year,
it seems that a few of the bird species adept at catching them, like
kites, might move north to intercept them. This still seems to have been
the case in recent years, rare as it is.
Formerly--and we are talking about 150+ years ago--the
swallow-tailed kite had a range into southern Canada, where they no
doubt ate dragonflies that no doubt also had a northerly range.
I read in an 1854 work on hunting in Wisconsin that these kites were "at
one time quite numerous on our prairies, and quite annoying to us in
grouse shooting.” Coues in 1874 had extensive remarks on its presence in
North Dakota at the time. Ohio's Wheaton reported a kite shot near
Pataskala in my area on 8/22/1878. which was first thought to be a bald
eagle from P.T. Barnum's show and discarded, then eventually rescued,
though the specimen has since apparently been lost.
It's probably unwise to celebrate that these charming birds are
returning to our latitude in larger numbers. We just have more observers
who report birds than we used to. Dragonflies, and their predators,
continue to diminish. A few lucky Ohioans may get to see one during the
warm months, but if you want to get a taste of their former abundance,
there are some Florida spots that still routinely provide hundreds of
them at a time at this time of year...what a show!
Bill Whan
Cols
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