Since our post on American Bittern tracking research in Connecticut was published, we have received more than a few inquiries about how the team captures a species that is known for being elusive, secretive, and generally difficult to observe. The answer will surely surprise some, be somewhat expected by others, and perhaps simply have been overlooked by more experienced bird handlers. The truth is, the method surprised the researchers initially; they thought, "Surely this can’t work!"
This is a guest blog post authored by Sam Merker, research biologist, University of Connecticut, in Storrs, Connecticut.
The primary method can be found in an excellent scientific paper accurately titled “Capturing Adult American Bitterns” (Huschle, et al., 2002). This method was confirmed and further described to us by the authors, but also by Matthew Herring of the Bitterns in Rice Project in Australia. If you haven’t checked out this project, it is a fantastic approach to Australasian bittern conservation in agricultural systems; please consider taking a look and supporting the project if you can.
Anyway, back to captures. In short, we use a mirror trap. This is essentially a large metal cage with a mirror at the back and a trap door at the front. Because bitterns are highly territorial, we can attract them with audio playback. We don’t have a video of this, but their response to playback reminds us of a slow-moving cargo plane. When the males hear the classical “oonk-a-chunk” call, they often respond vocally and then jump into the air, epaulettes blazing, and fly across their marsh with an almost comical slowness. Their wings making very shallow beats as they seek out their competitor. Once they land, the hunt begins. As they stalk through the rushes, they pause to point their heads towards the sky and survey the surrounding areas, always on the lookout for that pesky interloper.
WHERE ARE YOU, PESKY INTERLOPER? A bittern, dead center of the photo, points its bill towards the sky. Note its eyes are still looking at you! Photo Credit: Sam Merker
Sam, posing with the trap, and Bluetooth speaker. Although hard to see, the mirror is visible at the back of the trap. Photo Credit: Laurie Doss
Sometimes they let out their booming call to find their foe, hoping to coax a response. We don’t disappoint and prompt the speaker to play. This can take a while, but most of our captures happen in the first 10-15 minutes and sometimes faster. When the bird finally approaches the trap, speaker booming away inside, the bird circles the trap until it is lined up with the mirror. It will see itself as an intruder and go for the attack. And that’s when it happens! The bird steps on a ‘treadle’ triggering the door behind it and … captured! Now the hard part comes where we wade back into the marsh to extract the confused heron, hoping not to lose an eye in the process (see previous post for necessary attractive eye wear).
An American Bittern circles a trap, looking for the intruder. The bird is below and to the right of the teal speaker; only its head and bill are visible. Once this bird made its way around the trap, it was captured. Photo Credit: Sam Merker
To some, this trap may sound elaborate, but the method is actually a lot like target netting for songbirds. You set your trap out in the marsh. Add playback and a decoy (in this case a mirror). Then you make yourself scarce. In the case of bitterns, the "hiding of yourself" seems to matter very little. The birds are so focused on finding an intruder that in one instance, Sam was simply standing 5 feet away from the trap and the bird walked right in. In fact, we were trying to get a video of the capture, but the bird was just too eager to fend off its foe.
Capturing American Bitterns for tagging is exciting and even a bit of fun, but that’s not why we do it. Species like the American Bittern remain poorly studied despite evidence of recent declines and severe habitat loss. We hope that by trapping and tracking them we can learn where to focus any conservation efforts that might ensure the persistence of this beautiful and elusive bird.
Capture method described in the following publication: Huschle, G., J. E. Toepfer, W. L. Brininger, and D. A. Azure. 2002. Capturing Adult American Bitterns. Waterbirds 25:505-508, 504.