Migrant Movement: Middle Keys Snapshot
The Florida Keys aren’t just a special place to observe migrating raptors – there are opportunities to observe large numbers of migrating shorebirds, herons, and of course, passerines. Starting in 2011, the counters at Curry Hammock began recording all non-raptor species detected at the site. And in 2012, standardized morning surveys at Long Key State Park also were set into motion.
Since beginning our surveys September 2 of this year, we have been watching migration build and continue to gain momentum. Early September saw high numbers of swallows, Eastern Kingbirds, and Prairie Warblers, but overall diversity just wasn’t there yet. Gradually, diversity began to increase as the month moved along, but it wasn’t until the morning of September 18 where a large pulse of new arrivals made landfall in the middle Keys. Early that morning, dozens of thrushes and hundreds of Bobolinks could be heard overhead at Long Key State Park. As dusk turned to day, passerines aloft began to put down in the tropical hardwood hammock. Numbers of Red-eyed Vireos rallied around fruiting Poisonwood (Metopium toxiferum) while Veery “quivered” nervously in the understory. Warbler numbers appeared to have increased compared to those we had seen over the past few days. Although the composition of species was that typical of that of mid-to-late September, a late Louisiana Waterthrush ran among the prop roots of Red Mangroves (Rhizophora mangle). A couple Prothonotary Warblers, another species which often favors mangrove forest during migration in coastal Florida, blitzed into the mangroves as we left the park for Curry Hammock and the hawkwatch.
It wasn’t until we reached Curry Hammock that we realized just how many passerines had moved into the Middle Keys in the morning. Diversity was high, although the individual numbers weren’t. Just in the vicinity of the hawkwatching platform, we would tally eighty species for the day. Seventeen of them were warbler species, and among them were species we often get in low numbers throughout the season: Blackburnian, Chestnut-sided, Hooded and Prothonotary. Also in the mix were the first Tennessee Warblers of the season and an unseasonable Palm Warbler. Two Dickcissels made a brief appearance in the campground, giving themselves away with their unique call. Buttonwoods (Conocarpus erectus) dripped with orange Baltimore Orioles, Red-eyed Vireos, and a variety of warblers. Also of note was another large nighthawk movement. Although a few thousand shy of a single-day count from earlier in the month (Sept 10, 2014), we would tally a healthy nine-hundred seventy-two for the day.
Curious to see what the day brought as it progressed into late afternoon, a return to Long Key State Park was in order after leaving the hawkwatch. This time around, we would observe a relatively new set of birds. Maybe new birds had made landfall after we left earlier in the morning, or perhaps they were overlooked. Or more likely, it was a bit of both. In the same stretch of trail we had been earlier there were parties of strutting Ovenbirds, and easily-overlooked Empidonax species came in the form of Acadian and silent “Traill’s” Flycatchers. A vocal Hooded obliged us with a hollow and metallic “dink” call from thick undergrowth, and finally an Alder Flycatcher announced it’s identity with insistent “pep” calls. The last highlight of the afternoon came in the form of the day’s nineteenth warbler species, a male Kentucky Warbler that hopped furtively through a heavily-shaded hammock.
Several reasons contribute to the opportunity to observe high diversity of migrating passerines in the Keys. For one, the Middle and Lower Florida Keys appear to get species from two different flyways. With a heavy influence of Atlantic Flyway and Caribbean-bound migrants, the Keys also make up the easternmost boundary of the Gulf of Mexico. This often means Trans-Gulf migrants make landfall in the Keys, especially after western winds over the Gulf. The farther south one goes in the island chain, the more likely one will stumble upon Trans-Gulf migrants. Secondly, there is a bottle-necking effect. Birds travelling down the Florida peninsula have the luxury of spreading over a large swath of landmass. As they move into the Keys, their options diminish, and they funnel down the islands until reaching their jump-off point to Cuba, the Yucatan, or elsewhere. Lastly, the insect-laden hardwood hammocks and mangroves also offer a variety of energy-rich fruiting trees. All of these are important ingredients for a show-stopping fall migration in Florida’s unique coral archipelago.