Thursday, September 22, 2011

Historic raptor flight

Last Friday, September 16, I was able to be at the Boothe Park Hawk Watch site for 9 hours to witness history with a few friends. I was joined primarily by Bill Banks, Charlie Barnard, and Frank Mantlik, all birding experts who helped us bring the day's total to 8,234 raptors! Yes, eight thousand, two hundred, and thirty-four. If we had more observers, the total would have been even higher. This site is not regularly staffed by volunteers, and no one is paid to count - for the most part, it is a pleasant diversion for a few local friends. In the middle of the day, I sent out a help email to the CT birding listserv because it was only Bill Banks and me, and our necks were getting sore as hawks overwhelmed us.

It was very quiet through just after 11AM before we broke our hourly record of raptors with 892 Broad-winged Hawks between 12-1PM. This was broken with 1,278 from 1-2, and broken again with 2,887 (!) from 2-3. It looked like we would crack 3,000 from 3-4, but around 3:45, the raptors dropped off dramatically.  I believe it was because the winds eased up, allowing them to take their more normal inland course instead of being pushed to our semi-coastal site. It did not have to do with the thermals collapsing (thermals are columns of rising air that raptors ride in migration) since we still saw some extremely high raptors in the hour, including a large kettle at the limit of binocular vision. We ended that hour with 2,468 and then "just" 175 from 4-5 as they pushed further inland before stopping for the day. We had nearly 200 non-Broads as you can see below with the other birds.

Raptor migrants:
Osprey - 30
Bald Eagle - 11
Northern Harrier - 5
Sharp-shinned Hawk - 122
Cooper's Hawk - 12
Broad-winged Hawk - 8,041
American Kestrel - 12
Un. Buteo - 1
TOTAL - 8,234
Plus local Red-tailed, Red-shouldered, and Turkey Vulture.

Southbound migrants included:
Canada Goose 14
Green Heron  1
Chimney Swift  392* all-time high count more than doubling 09-09-2011's recent record of 183
Ruby-throated Hummingbird  6
Tree Swallow  1
Barn Swallow  2
Cedar Waxwing  34

Migrants in the park included:
Empidonax sp.  1
House Wren  1
Blue-gray Gnatcatcher  2
Gray Catbird  1
Common Yellowthroat  1
Palm Warbler  1
warbler sp.  3
Rose-breasted Grosbeak  1

If we had another hour of powerful winds from the northwest, I do think we may have bested 10,000 raptors. Regardless, how did we get that total?! Let me explain...

It is basic hawk watching knowledge that raptors move behind fall cold fronts because winds behind these fronts are often from the west, northwest, or north. Cold fronts essentially come from low pressure systems which have a center with cyclonic motion, or counter-clockwise. You can visualize these winds spinning down from the north and west once it moves past us to our east. High pressure ushers in this cold air mass, and these highs have anti-cyclonic motion, or clockwise, with winds coming from the north and west when it is to our west. These are the perfect times for hawks to move as typically high pressure means no precipitation, sunny skies, and the perfect winds.

In this case, a strong cold front cleared us Thursday afternoon as predicted. This in itself was awesome as Twan saw hundreds of dragonflies drop in to Stratford Point suddenly along with a few birds like the first of fall for Connecticut American Pipit and an Eastern Kingbird. They were likely riding the front or putting down just in front of it, as there was precipitation along and after it.

For Friday, a strong high pressure moved in over the Great Lakes region on the perfect date, as northeast raptor expert Neil Currie has said historically that September 16 and 17 are the best dates for a Broad-winged Hawk flight. It came at a good time of day, moving in overnight and setting up in the critical location for daytime hours. This came after weeks of backing hawks up with repeated tropical cyclones passing over or by Connecticut keeping a southerly flow open. It was the perfect confluence of events.

With all of this in mind, I pestered people with the mega hawk Friday event we had coming for about a week, though I had been afraid we would have everything except the clouds. However, Boothe Park ended up perfectly positioned to receive some high clouds from an upper level disturbance to our west. I do not think these clouds made it far enough east for even the Lighthouse Point hawk watch during the critical hours on Friday. If not for that upper level disturbance, I would surmise we would have seen 25% of those hawks or less. Better to be lucky than good, huh?

Neil is putting together some records of flights such as this one at coastal sites and will be providing me with more information on just how historical this was. Once he does, I will share it with everyone here.

Scott Kruitbosch
Conservation Technician

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