This past week we experienced a spectacular natural phenomenon known as a "fallout". Fallouts occur when birds migrating across the Gulf of Mexico run into a weather system with unfavorable (usually northerly) winds and/or precipitation. When the birds fly into bad weather, they seek refuge as soon as possible and quite literally "fall out" of the sky once they make landfall. Fallouts occur when there are favorable migration conditions for birds to leave the Yucatan and a front comes through just as the birds are beginning to arrive on the coast.
All the pieces of the puzzle fell into place last Wednesday afternoon. A weather system had moved through earlier in the day preventing us from banding. As the wind began to die down, we decided to go out to the banding site and see if any new birds had arrived. When we got to the site, we immediately noticed a difference in bird activity. All around us we heard chips and buzzes and saw birds flitting around in the shrubs. The birds where literally whizzing by our heads. There were birds everywhere, and as we sat and watched, more and more birds began to show up. There were swallows, and martins as well as chimney swifts eating small insects just above the shrub level. Scarlet and Summer Tanagers, Rose-breasted Grosbeaks, and several species of vireo flew from tree to tree looking for caterpillars and other nourishment. Seemingly every shrub we walked by held a gray catbird or a thrush. Flocks of Orchard and Baltimore Orioles sat atop every other tree. And then there were the warblers—we immediately found Worm-eating, Prothonotary, Yellow, Blackburnian, Bay-breasted and Golden-winged warblers feeding on our site! But by far the most common warbler was the subtle and diminutive Tennessee Warbler. As we left, we were a little overwhelmed and excited to see what would happen when we opened our nets in the morning.
When we showed up at our site the next morning, there were even more birds present. We played it safe and only opened 4 nets (out of 17). By the end of the first net run, about 15 minutes after opening, we had captured a total of 66 birds! In order to safely process the birds and release them in a timely manner, we had to shut our nets! Tim and Trischa began processing birds and Gunnar doubled back and began clearing the nets of any birds and closing them. By the time he was done closing the nets, it had been 30 minutes and he had released 30+ birds that had already refilled the nets. Luckily for us, the volunteers who ran the site last year called and asked if we could use any help. We said, "Absolutely!" An hour later, Bea and Jim Harrison arrived and went to work extracting birds and assisting with banding. Time flew by and we barely had a moment to eat. We kept reminding each other to drink water and stay hydrated. We're pretty sure we were running on adrenaline for most of the day! In the end, we captured 315 individuals while running only two mist nets! We ended up catching most of the species we had seen the previous night, highlighted by two Golden-winged Warblers, a Bay-breasted Warbler, a Cerulean Warbler, a Blackpoll Warbler, a Swainson's Warbler, a Canada Warbler and an adult male Scissor-tailed Flycatcher! It was an amazing experience. We all went home and enjoyed a brief celebration before collapsing into sleep. Without the help of Bea and Jim, we would have never been able to post such a huge number! So, we have to thank them again…Thank you, Bea and Jim!
For the next couple days, birds lingered around the site and we continued to capture them in large numbers. We hit the 200-bird mark (twice) and averaged ~140 birds per day the rest of the time. After a 300-bird day, 150 felt slow! But with fewer birds, we were able to spend more time checking out the less common species that turned up in our nets. One of the highlights was a Chuck-will's-widow! Chuck-will's-widows are a member of a nightjar family and very much like the Lesser Nighthawk we caught earlier this season…except they are humongous! They have a wingspan of ~26 inches and a mouth that looks like it's made to swallow small mammals; like other nightjars, however, it feeds almost exclusively on large moths and other insects. In the hand the bird made growling noises and barked, opening its huge maw, it was a little intimidating!
I have been surprised and pleased with the number of Golden-winged Warblers that have found their way into mist nets this season. I studied Golden-wings in Minnesota and Manitoba during the past two summers. Since Minnesota is home to roughly 65% of the global Golden-winged Warbler population, there is a good chance that the Golden-wings I caught here in Texas are on their way to Minnesota. But where did they come from? Did they spend the winter in the mountains of Costa Rica? Nicaragua? Or Northern Colombia? I will begin a master's program this fall that will focus on answering these questions by revealing the migratory routes and wintering grounds of this declining species. The long-term goal of the project will be to develop life-cycle management strategies to benefit golden-wings and other songbirds throughout the entire year instead of only managing for the birds when they are on their summer breeding grounds in North America.
Possibly the biggest surprise of the season (so far) showed up on another "slow" 155-bird day. Tim came back from checking the nets with a box full of birds, among them, a rare Mexican visitor. A Yellow-green Vireo! At first glance the bird looked much like a red-eyed vireo, but the bigger bill, lack of a dark eye-line, and overall lime-green coloration left no room for a mistaken identity.
During all of the excitement this week, we've processed so many birds that our supplies have quickly dried up and we've had to receive two emergency shipments of bands and envelopes (for toenail and feather collecting)! The days are long and hot and we're all exhausted when we come home but every morning brings new birds and a new, unique glimpse of migration, which is enough incentive to help us get out of bed! We're looking forward to the last 10 days of our season and trying to increase our tick sample and break the 3,000-bird mark! It is shaping up to be an exciting finish.
Written by Gunnar Kramer, Bird Educator, Smithsonian Migratory Bird Center
Number of Captures: 2573
Number of Species Captured: 81
Number of Species Seen: 244
Number of Birds with Ticks: 47