Dry Tortugas May 02—05, 2012
Posted by Michael O'Brien
During the week prior to our visit to the Dry Tortugas, there was a songbird fallout of legendary proportions, mainly in the lower keys, but also in the Miami area. Participants on the South Florida and Keys portion of this tour had the privilege to witness some of this fallout. Although our Dry Tortugas trip saw only the "leftovers" from this major event, there was still plenty for us to see good numbers of migrants, along with the amazing concentration of seabirds that make the Tortugas famous.
Sooty Tern drinking— Photo: Michael O'Brien
Aboard the "Playmate," we sailed from Key West, passing along the edge of the Florida Current, which feeds warm Gulf of Mexico water into the Gulf Stream. Here, we found a number of pelagic birds, highlighted by Audubon's Shearwater, Brown Booby, Bridled Tern, and Pomarine Jaeger, along with our first Magnificent Frigatebirds, Sooty Terns, and Brown Noddies. And a close approach to Hospital Key gave us views of an increasing colony of Masked Boobies.
Upon arrival at the Tortugas, it was impossible not to be captivated by the thriving colony of seabirds that inhabit Bush and Long Keys. Even from a great distance we could see dozens of Magnificent Frigatebirds "kiting" over Long Key, riding the updraft from a steady southerly wind. And when we got a little closer, it was clear that the real show was over Bush Key where some 30,000+ pairs of Sooty Terns and 4,000+ pairs of Brown Noddies make this little island appear to be enshrouded by a swarm of mosquitoes. The "wide-awake" calls from Sooty Terns were constant, day and night. A careful eye on the flow of birds revealed constant "traffic," with steady streams of birds heading off mostly to the southwest and northeast, and other birds coming in from all directions. In order to get an up-close view of this colony, we took dinghy rides along the marked perimeter. Terns were flying all around us, and would regularly skim the water to drink (they drink seawater, and excrete a highly saline fluid from their salt glands). Brown Noddies were often perched on floating structures, allowing extremely close approach, while Sooties perched only on the island. Our dinghy rides did produce a few surprises, such as four Bridled Terns that appeared to be nesting, or at least prospecting, on the gravel strip between Bush and Long Keys. There are no nest records of this species at the Tortugas, and only one previously from the United States, so this would be an exciting record if confirmed.
Antillean Nighthawk— Photo: Michael O'Brien
During our visit to the Tortugas, we spent most of our time exploring Fort Jefferson on Garden Key. This is the most vegetated island, and the only one with fresh water (a modified water fountain), so any migrants around eventually work their way to this precious resource. Although we did not experience fallout conditions, we did see an excellent diversity of migrants. Warblers were numerous, and we were particularly spellbound by absurdly close views of many species as they fed on the ground, literally at our feet. There were always American Redstarts feeding in seaweed on the beach, and our views of Cape May, Magnolia, Blackpoll, Prairie, and Black-throated Green warblers were especially memorable. Palm Warbler was the most numerous species, and the one we saw on all corners of the island. Perhaps our favorite find at Fort Jefferson was a perched Antillean Nighthawk at the campground. Such close, prolonged views allowed us to study every detail that distinguished this species from the very similar Common Nighthawk. Other highlights included a surprisingly good raptor show (five species!), some nice studies of shorebirds, and a surprise White-crowned Pigeon.
During our return trip to Key West, we saw pelagic species similar to those seen on the first crossing, with the additions of a close fly-by Parasitic Jaeger and excellent views of a flock of Roseate Terns (with a couple of Commons for handy comparison) resting on a channel marker just off Key West.
A big thank you goes to Captain Joe, first mate Shane, and our world-class chef, Dianne. They kept us safe, comfortable, and well fed, and added immeasurably to our enjoyment of this trip.