Awkward in my rubber hip waders, I ran through chest-high plants. I held my hands above my head to avoid being stabbed by the sharp leaf tips of the aptly named “needle rush,” and tried not to trip. Dozens of small brown birds flapped and scuttled ahead of me. Some scurried on the ground like mice; others flew a few feet before disappearing into the vegetation. Nearing the 12 meter-long mist net I had set up earlier that morning, I picked up my pace. Birds hit the net. I grabbed the nearest one and secured its legs safely between my fingers. There, on its right leg, was a small aluminum band with the numbers 2341-39532, and a second small band made of orange plastic. My heart rate quickened and I didn’t bother suppressing the grin on my face. “This is HIM!” I shouted to my colleagues. “THIS is the bird that I have now caught TEN times!”
The source of my excitement was a male seaside sparrow, Ammodramus maritimus. From a distance, he looked dark gray, but in my hand his lores were bright yellow, his throat clean white, and his breast lightly streaked. His bill was long for a sparrow, better-shaped for grabbing amphipods from the mud than for cracking seeds. Seaside sparrows, along with saltmarsh (A. caudacutus) and Nelson’s (A. nelsoni) sparrows, are tidal marsh specialists, and these little brown birds consumed six years of my life. I was a Ph.D. student in Chris Elphick’s lab at the University of Connecticut. During my dissertation research, I unexpectedly caught this particular seaside sparrow not only on ten separate occasions, but on occasions that spanned both years and miles.
I first captured and banded this seaside sparrow on July 26th, 2010, at Barn Island Wildlife and Management Area, in Stonington, CT. He was already an adult, so this initial capture date is just a minimum age estimate. The next summer, my lab-mates and I didn’t catch him at all. If my project had ended in 2011, I would have assumed him to be dead.
On February 6th, 2012—18 months and 750 miles of coastline away—I caught him for a second time. I was at Huntington Beach State Park, in Murrell’s Inlet, South Carolina. I had happened to choose study sites that included this individual’s breeding and wintering homes. Over the next couple of years, I caught this bird multiple times at Barn Island during summer 2012, once again at Huntington Beach in early 2013, twice more at Barn Island in summer 2013, and finally, the 10th catch, at Huntington Beach in early 2014.
A record like this is more than just a series of exciting personal moments. It also provides insights relevant to conservation. In the world of bird banding, catching the same bird in four separate years and on both ends of its migration is nearly unheard of. This type of record requires years of banding in the same locations, and banding in both breeding and non-breeding regions. Many long-term banding programs exist, but covering the entire annual cycle of a species is much rarer.
Just because we can map the breeding and non-breeding ranges of a species does not mean we know where individual birds go. The larger the population of a species is, and the greater amount of habitat there is available, the less likely it is that a researcher will capture the same individual on both ends of its migration. According to the US Bird Banding Laboratory, which has overseen US bird banding since 1920, an average of 1.2 million birds are banded in the US every year, with an additional 87,000 instances of recapturing previously banded birds. This means that, overall, fewer than 10% of the birds that get banded are ever captured again.
I was not expecting to learn any information about where individual birds go during the winter. But, the seaside sparrow that I caught 10 times was not my only long-distance recapture. In South Carolina, I also caught one of my Connecticut saltmarsh sparrows, and saltmarsh sparrows banded by colleagues in New Jersey and New Hampshire. In Connecticut, I did the reverse and caught one saltmarsh sparrow that I had banded in South Carolina and one that a colleague had banded in Georgia. In three incredible days of netting in Northern Florida in 2014, I caught a saltmarsh sparrow that a colleague had banded in southern Maine (and that I had also caught in the same Florida marsh the previous year) and two Nelson’s sparrows that other colleagues had banded a little farther north in Maine.
The odds of capturing the same individuals on both ends of their migration are based on three things: the amount of time researchers spend in the field; the amount of available habitat; and the size of the bird populations. There are currently people banding tidal marsh sparrows in nearly every state along the Atlantic coast, but the cumulative effort is far from comprehensive. We have nowhere near every saltmarsh sparrow banded, and even fewer seaside and Nelson’s sparrows. Across the entirety of this range, tidal marshes are threatened by development, invasive species, a lack of sediment due to upriver dams, and, most critically, by sea level rise from climate change. Even so, there is enough marsh habitat right now that it isn’t saturated with tidal marsh sparrows.
Clearly, our long-distance recaptured sparrows were not products of exhaustive sampling across the entire breeding and non-breeding ranges. With our effort and the amount of marsh habitat, capturing the same individuals where they breed and where they spend the winter should have happened extremely rarely. It didn’t, and each long-distance recapture filled me with a sense of awe and excitement. Holding a bird in my hand is unlike any other experience. There is tactile and visual beauty in soft, iridescent feathers, and there is a humbling reminder of responsibility in palpable heartbeats. The knowledge that the individual I was holding was one that I had held before, so far away, amplifies the experience. But, this unlikely large number of long-distance recaptures suggests that the populations of these birds are small. Smaller than we had thought.