Guest Post: American Bitterns in Connecticut

This is a guest blog post authored by Sam Merker, research biologist, University of Connecticut, in Storrs, Connecticut.

In affiliation with Min Huang of Connecticut Department of Energy & Environmental Protection (CT DEEP) and Chris Elphick of the University of Connecticut, in March of 2022, we began fieldwork to tag Connecticut's American Bitterns (AMBI). As a bird listed on the state’s endangered species list, there exists an important need to develop management strategies of suitable habitat. Although abundant habitat exists in the state for AMBI to use, and in spite of being regularly detected in some locations in Connecticut, documented AMBI breeding events are uncommon; in the last decade, there were only two recorded nests.

Documenting such breeding events is made particularly difficult by the dearth of information on the species’ biology, ecology, and natural history. Gathering information about AMBI's nesting biology, habitat distribution, and migratory behavior is both time-consuming and challenging. However, attaining annual cycle data has become easier thanks to novel technology like CTT's ES-420 transmitters.

This image shows how a Bittern's eyes face downward, an adaptation that allows them to hunt without moving their head very much.

In late March 2022, we captured our first American Bittern and successfully attached one of the ES-420 transmitters. Then we waited for the first connection. Although Connecticut is a small state surrounded by large cities, it also contains plenty of rural areas with wetland habitat--just what AMBI prefer. The general lack of cellular infrastructure in rural areas meant that the transmitter, which began collecting points from its deployment, didn’t check in right away. However, a few weeks later the transmitter finally picked up a connection, and we were rewarded with an upload of our first data points.


Right wing of an American Bittern showing feathers from at least two molt periods. Also seen here is an ES-420 shortly after being fitted to the bird. Photo Credit: Laurie Doss.



Nicole Krauss holds an American Bittern following tagging. Note its covered head and her protected eyeballs.

Handling American Bitterns is a challenge, and it takes at least two people (even better if it’s three!) to handle them safely––for us and for them! Handlers need to wear safety glasses because the birds tend to strike at the eyes when threatened. We also cover their heads with a sock to keep them calm during handling. 

Slow-motion footage of a newly tagged AMBI.

In 2022, we successfully captured 5 American Bitterns in Connecticut. We have observed that not all of them remained for the breeding season. Two went to Massachusetts, and one traveled to New Hampshire. Four of the 5 have migrated and are overwintering in Florida and New Jersey. Two bitterns have been confirmed dead, and with the help of the Clay County Audubon Society, Southeast Volusia Audubon Society, and volunteers like Drs. Brian Crawford and Amy Briggs of Florida, we recovered both tags, which still work! Unfortunately we were unable to determine what caused either bird's death, but they appeared to be natural predation events.

This ES-420 (see magenta circle in the photo) continued to work as expected, which helped Sam's team to ultimately recover the unit––even after the bird had died.

One Bittern has remained in Connecticut, though we expect it to migrate soon. We are learning a great deal about their movements and as long as the transmitters stay charged, we will document complete annual cycles for 3 American Bitterns in the spring. The success of the project has garnered support from CT DEEP, and we will attempt to put more transmitters out this spring.

Southbound migration by an AMBI that spent the breeding season in New Hampshire.  After making a series of stops along the east coast the bird is now wintering along the north shore of Lake Okeechobee.

Finally, the AMBI wintering in New Jersey appears to have settled right in CTT's backyard! The bird has been occupying ponds in Cape May Point State Park, and although no photographs have been submitted, we believe the bird has appeared on some eBird checklists. If you find yourself birding the point and are fortunate enough to see a bittern, be sure to get a good look at its back and let us know if you can spot the ES-420 uploading data.

***Funding for this study was provided by the Waterbird Society and the Connecticut Ornithological Association.  

***A story on this project was recently published in the July/August 2022 issue of Connecticut Wildlife Magazine. Sam also presented on the project to the Western Connecticut Bird Club and the Litchfield Hills Audubon Society in early January 2023.