Date: 9/27/17 10:39 am
From: Range Bayer <range.bayer...>
Subject: [obol] Cal Gulls Hawking Insects; Small Southerly Directed Dragonfly Flight in Lincoln Co. on 9/27
Hi,

1) At 8:30-9:00 AM this morning (9/27), Betty Bahn counted about 20
"light brown" dragonflies per minute flying "generally south" at her
house in Yachats, out to the Yachat's State Park, north to about 4th
Street. Wind is moderate from the SE.

2) At 9:15-9:45 AM this morning, Chuck Philo observed a a small flight
of about 3-4 "little red" dragonflies flying south . He was along the
Yaquina Bay South Jetty road near the outhouses. Interestingly, there
were many perched on the grass as if poised to take flight, and Chuck
tried to take pictures of them.

About 30-40 ft overhead there were many California Gulls circling and
hawking flying insects. They may have been catching flying ants.
Dragonflies here typically fly up to 20 ft above the substrate, so the
gulls probably were not feeding on dragonflies. In previous years, no
one has definitively observed a gull taking a dragonfly in one of
these mass flights.

3) At 9:45-9:50 AM this morning, I saw no dragonflies during a 5.0
minute watch at 717 SW 6th Street in Newport. This is about one block
from the ocean and is a location where mass flights of dragonflies has
sometimes been noted in the past. There were also no gulls circling
and hawking insects or any indication of any flying insect swarms.

-------------------------
Mass dragonfly flights have been noted in association with winds from
the east in late August-early Oct. in past years.

This morning, weather conditions at the South Jetty are at
http://www.ndbc.noaa.gov/station_page.php?station=nwpo3 and indicate
that average hourly wind speeds were 4-6 knots (5-7 mph) with gusts up
to 11 knots (13 mph) this morning at hourly intervals during 4-9 AM.
The average wind direction then was from eastnortheast, east, or
northeast. Temperature at 9 AM was 68 F.

At the Hatfield Marine Science Center about a mile east of Chuck's
location, the maximum gust this morning have been 14-20 mph from the
east (http://weather.hmsc.oregonstate.edu/weather/weatherproject/hmsc_weather.html).
At 9:50 AM, the wind averages 14 mph and gusts to 19 mph from the east
and the temperature is 72 mph.

Conditions appear to be good here for a large dragonfly flight, until
the wind stops coming from an easterly direction.

------------------------------
Some information about past mass southerly dragonfly flights is at
https://web.archive.org/web/20071222000203/http://www.ent.orst.edu/ore_dfly/migrate.htm

So far, the flight appears to be a small flight with 20 or fewer per
minute, and these flights could easily be missed by casual
observation. However, 2 independent observers reporting it is of
note.

TABLE. Williams' (1958:103-104) book "Insect Migration" gives
density classes for insects flying across a 150 ft line. Along the
Oregon Coast directed flights are often counted over about 75-150 ft
lines, so his 150 ft line is more appropriate than the data he also
gives for a 30 ft line. Further he gives data for 10 min counts, but
when dragonflies are numerous, a 10 min count (and sometimes even a 1
min count) is not practical. As Williams writes: "The observer should
count the number of insects crossing any convenient line at right
angles to the flight that can be measured or accurately estimated.
The length of line, and the length of time suitable for any count,
will depend on the density of the flight and the nature of the
ground."
These Rate/min class boundaries are as he gave them,
and they sometimes overlap between classes and the rate of 24/min does
not fall into any of his classes, although it presumably would fall
into the "Definite" class.
Extr. Thin=Extremely Thin.
----------------------------------------------------------------------------------------------------------------------
Williams (1958:103-104)....................................................
Density Class Rate/min Comment
----------------------------------------------------------------------------------------------------------------------
1 Extr. Thin 1 Probably only
seen by careful watch by an expert.
2 Very Thin 1-5 Should be seen by
any careful watcher.
3 Thin 6-23 Should be
obvious to any competent field naturalist.
4 Definite 25-107 Obvious to any normal person.
5 Thick 108-500 Obvious to the general public.
6 Very Thick 500-2300 Gets into the newspapers.
7 Snowstorm over 2300 Casts shadows on the ground.
----------------------------------------------------------------------------------------------------------------------


Range Bayer, Newport, Oregon.
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