The Best Osprey Migration in The Keys!

October 2, 2014

THERE IS ABSOLUTELY NO DOUBT THAT WE ARE HAVING THE BEST SEASON FOR MIGRATORY OSPREYS IN THE FLORIDA KEYS

Photos by Rafael Galvez and Kerry Ross.

New FKH records broken this season for migratory Ospreys:

Highest seasonal count: 2949 (and 31 days to go)
Highest single day count: 394 (Sept. 25, 2014)
Highest hourly count: 301 (15:00-16:00 hr, Sept. 25, 2014)
Four of the top six all-season highest day counts:
- #1 – 394 (Sept. 25); #3 – 316 (Oct. 1); #5 – 240 (Sept 13); #6 – 229 (Oct. 2)

As of today, we are at a 79% increase for Ospreys over our previous seasonal max (fall of 2002), 163% over our all-season Osprey average, and 93% over 2013’s count for that species!

However, it is important to keep in mind that this year we started counting from the Curry Hammock site 13 days earlier than most seasons. Our typical project start date is September 15, but in order to expand opportunities for the monitoring of migratory kites and songbirds, we started on the second of the month. Only during 1996-97 have standardized counts for migratory raptors taken place before September 15. This year, we counted 771 Ospreys during that period.

If we were to consider only the remaining 2178 Ospreys – counted from September 15 through Oct 2 of this year – this season would still be the highest count for the species in project history, at 32% over the prior seasonal max (2002), 94% higher than average, and 42% over last year’s count.

301 Ospreys in 1 Hour!

On September 25 of this season, we experienced a spectacular flight of 301 “southbound” Ospreys during the final hour of count, starting at roughly 15:00 hr. As can be seen from the chart above, no more than 35 Ospreys had been counted in a single hour prior to 14:00, and a total of 93 had been tallied up to that point. While the winds had ranged from 3 to 12 km/h out of the ENE for most of the day, a sudden squall line pushed by a shift of 15-21 km/h winds out of the east crossed over Little Crawl Key at around 15:50, accompanied by dense and low cloud cover, and hard pelting rain.

View of a squall line developing towards the SE as viewed from Curry Hammock. By Rafael Galvez.

Rain continued for nearly an hour. What followed was a low flying “mat” of back-to-back Ospreys in slow flight over the trajectory of the Keys’ island chain, towards the SSW. At times, dozens of Ospreys could be seen simultaneously. SW and away from our count site, the horizon was dotted with them; at one point I counted about 35 Ospreys in a single binocular view. By the time that hour was over, we had tallied 301, bringing our day’s total for that species to 394, and shattering the previous single-day high count of 340 from 2003!

We have known for some time that many Ospreys don’t follow the island chain as they migrate southward, but rather cross over any point of the Keys from the Florida mainland as they continue directly over the water towards Cuba. It is therefore assumed that we miss many of those Ospreys if we are too far to detect their brief crossing over the islands. You may read more about this phenomenon on our post from September 22, 2013 – Ospreys On The Move.

In the case of the Sept. 25, 2014 event, the sudden shift and increased speed of winds accompanied by the squall line must have pushed birds towards the Middle Keys. These were Ospreys that would have been flying east of us over the water and in direction towards the Caribbean, but were forced westward by weather.

Above are maps from 2012 that illustrate the perceived flights of Ospreys as viewed from the FKH count site at Little Crawl Key, which appear to continue directly over water in general direction towards Cuba.

Ospreys tracked by R. Bierregaard, Jr. (above) at the UNC-Charlotte Biology Dept. with the use of satellite transmitters demonstrated a direct southward flight in some Ospreys as they left the peninsula, flew over Florida Bay, bypassed the Keys and crossed over the Straits towards Cuba. You can read more about the work at http://www.bioweb.uncc.edu/bierregaard/ospreys.htm.

For more information on the Sept. 25 flight and on this season’s Osprey migration visit the following links:
Osprey Surge by Limeybirder
240 Ospreys – FKH post from 9/13/14