BIG FLIGHTS of Song Birds over the Keys – Radar Ground-Truth!

Blackburnian Warbler, 1st year female. Photo by Bob Stalnaker.

Big flights of passerines were documented from Curry Hammock State Park during the Oct. 8 count as part of the 2013 hawkwatch. Between 2:15 pm and 2:50 pm, an estimated total of 1320 passerines and other non-raptor “landbirds” were tallied flying overhead during an impressive turn of events in the Middle Keys.

There were birds of several species including warblers, vireos, tanagers, orioles, kingbirds, and buntings, in addition to many indeterminate detected birds observed flying from the NW towards the SE, in general direction towards Cuba at great altitudes. Many of the warblers were only detectable through telescope! After the flights dissipated, and rain dropped for 15 minutes, there were many songbirds all over the ocean-side of Curry Hammock SP.

Chestnut-sided Warbler, 1st-year female. Photo by Bob Stalnaker.

The shift of winds throughout the day played a major role in this event. Up until 1:45 pm this day, we were having a rather slow day at the watch, with frustratingly little movement of birds other than solid numbers of swallows. By that time, our readings at the ground surface from the Curry Hammock site gave us winds out of the S and SE, up to 13 km/h. By 2 pm, winds had shifted, coming out of the WSW. The entirety of the sky suddenly seemed to change. A dense and continuous belt of cumulus clouds that loomed over the Middle Keys along the bay side for much of the day was suddenly broken, reforming along a pronounced SW to NE axis. Bands of rain were visible towards the NE. Falcons, and hundreds of songbirds were suddenly visible at high altitudes. We tallied 114 Peregrine Falcons that hour.

Left: The earlier flight of relatively few raptors is shown in a blue arrow. Birds appeared to “hug” a cumulus formation along the Bay side of the Middle Keys. Right: Soon after the winds shifted (c. 1:45 pm), the raptors began moving closer along the ocean side, and passerines and other migratory land birds were seen flying NW to SE at high altitudes (shown in orange arrows)

THE BACK STORY

I was one hour into my transect count at Long Key SP, when I received a text message from Angel and Mariel Abreu of the Badbirdz blog saying the following:

7:39 am: Hey bud. Not sure if these targets will choose to drop down, but they aren’t flying too high and there is way more north along the west coast. Heads up!

The message included the following attachments:

Left – Reflectivity Mosaic Image: An image showing diurnal migration in full swing along Florida’s west coast and into extreme South FL. Right – Reflectivity Image: Key West radar detects a massive flight of what we presumed to be migrating birds.

I answered their message by saying that I hoped they were right, but that the movements of birds were slow this morning compared to previous experiences.

They replied:

Winds have been shifting… weak SW right now recorded by Marathon Airport and more westerly at Sombrero Key. Good luck.

However, later the Badbirdz duo added:

10:49 am: Winds at Sombrero Key and Marathon Airport are registering SSW at 5-12, but these targets are moving SE at 15-20kts. My gut tells me these are birds. They could be tired and decide to land. 

I did not think I would have much to respond, since often the radar predicts apparently interesting flights, but we have trouble finding birds from the ground. But as we approached 2 pm, the winds really did shift – and suddenly. We first noticed high flying Chimney Swifts at the turn of the hour – a species not often recorded from FKH in high numbers – about 112 of them. Cliff Swallows below moved in packs of 20 to 25. Peregrine Falcons started moving in greater frequency. We suddenly noticed high flying “flocks” of birds well above the path of the Peregrines, all of them moving towards the SSE. When I rushed to put the scope on the first group, I was surprised to find several Eastern Kingbirds on the move. Many warblers could be seen moving through. I picked out the wing pattern of a few American Redstarts, but most were just silhouetted specks against the menacing cloud formations, which had shifted direction with the wind. Sheets of rain could be seen towards the north. I picked out Summer Tanagers moving high through the scope.

Blackburnian Warbler. Photo by Bob Stalnaker.

By the end of that hour, between 2:15 and 2:50 we had tallied the following:
1320 high flying kingbirds, warblers, tanagers, and other passerines
112 Chimney Swifts
293 Magnificent Frigatebirds – all flying towards the SW
114 Peregrine Falcons
and much more.

At 2:38 pm I texted back to the Badbirdz folks: IT JUST HAPPENNED!!!!

Magnolia Warbler taking flight from “Big Bob,” the hawkwatch’s landmark Buttonwood. Photo by Bob Stalnaker.

HOW MANY BIRDS UNDER ONE TREE?

Soon afterward, we were pacing the buttonwoods adjacent to the hawkwatch. “Big Bob” – the large Buttonwood visible from the count site and used as a key landmark, was covered in warblers. Within the 1-acre parcel of habitat surrounding “Big Bob,” we found excellent birding:

Tennessee Warbler 14
Nashville Warbler 2
Blackburnian Warbler 3
Chestnut-sided Warbler 3
Black-throated Green Warbler 3
Ovenbird 4
Yellow-throated Warbler 2
Palm Warbler 20
Northern Parula 4
Magnolia Warbler 1
Common Yellowthroat 4
Prairie Warbler 1
American Redstart 4
Worm-eating Warbler 1
Hooded Warbler 1
Yellow Warbler 1
Red-eyed Vireo 3
White-eyed Vireo 2
Eastern Wood-Pewee 1
Indigo Bunting 12
Blue Grosbeak 1
Rose-breasted Grosbeak 1
Baltimore Oriole 1
Blue-gray Gnatcatcher 3
Northern Cardinal 5

And this was just one tree and its surrounding plot!

The Badbirdz duo added-in more text messages into the afternoon:

2:38 pm. Birds moving 15-26 kts, NW – SW. They have got to be flying 800 ft +.

Left – Velocity Image: Key West radar detects movement of 15-20 kts heading SE towards the radar site, indicating targets have powered flight (birds?). Center – Reflectivity Image: Key West radar detects birds flying over the radar site, indicated by the visible “donut” shape. High density of birds recorded in this image. Right – Velocity Image: Key West radar detects movement of 15-26 kts heading SE. A look at the scale to the right can aid in determining the speeds at which targets are moving.

Nashville Warblers. Left, photo by Kerry Ross with a Leica V-Lux 3. Photo right, by Bob Stalnaker, taken underneath “Big Bob” the landmark Buttonwood.

“Big Bob” – the Buttonwood towards the right, and its surrounding plot. 16 species of warblers, buntings, grosbeaks and oriole were found here after witnessing large flights. Note how the Buttonwood is in flower, possibly helping attract birds.

Later that evening, Angel and I spoke over the phone, excited about how the radar forewarned our experience at the ground level. The Badbirdz duo sent me the following message:

For years, Mariel and I have been watching radar loops of targets we have always presumed to be birds flying along the west coast of FL during October.   After a few years of sending Rafael Galvez of Florida Keys Hawkwatch radar images and calls on the phone, we finally hit pay dirt today!