Band Resighting Sheds New Light on Delaware Bay Oystercatcher Population

When CWF began monitoring American oystercatchers nesting on the Delaware Bay this past spring, we also set out to place field-readable bands on as many oystercatcher adults and chicks as logistically possible. Band resights allow biologists to collect a wealth of information about site fidelity, habitat use, dispersal, and migration, especially when data is collected over many years. Since the Delaware Bay population of oystercatchers was previously unmonitored, we have a lot to learn about their life histories and how they may differ from other oystercatchers in the state, if at all. Where are these birds staging and wintering? Do breeding adults return to the same mates and nesting locations each year? Where do fledged chicks disperse, and will they return to their natal grounds on the Delaware Bay to breed upon reaching sexual maturity? Banding efforts, combined with resight data reported by biologists, dedicated volunteers, and the general public will help answer these questions (and more) as we increase the number of marked individuals on the Bayshore.

Thanks to our partners at The Wetlands Institute (the lead banders on the project), we were able to equip seven more adults and four unfledged chicks with field-readable bands during our first season of monitoring. One banded chick did not survive to fledge, which brought our total banded tally to nine adults (24% of the nesting population) and three fledged chicks (75% of the total fledged chicks). Seven pairs (37% of total) had at least one banded adult, with two pairs sporting bands on both mates. By the end of the season, we were proud of our initial banding efforts and excited to collect new movement data as the birds began to disperse from their breeding grounds on the Bayshore.

We didn’t have to wait long for the first resight reports to roll in! So far, we’ve received staging and/or wintering sightings for 100% of our banded chicks and 56% of the adults. Early observations indicate many Delaware Bay birds join the large pre-migration staging roosts just across the Cape May peninsula at Stone Harbor Point and North Wildwood. Five of our oystercatchers – three adults and two juveniles – were seen staging in that area prior to fall migration. We were also encouraged to receive some recent reports from wintering grounds in southern states. Two adults and one juvenile have been recorded in Florida, while another fledged chick has been seen in North Carolina. Notably, “Alfredog” (the previously mentioned Atlantic Coast disperser) regularly winters at Cedar Key, a critical wintering ground on the northwest coast of Florida that hosts around 40% of the Northeast oystercatcher breeding population each year.    

The migration data we can gain through band resighting is especially interesting for oystercatchers since their migratory behavior can vary significantly. A large portion (approximately half) of the birds that breed from North Carolina to New Jersey don’t migrate at all. The birds that do migrate follow highly individual migratory routes, which suggests that oystercatchers do not learn routes and wintering ground locations from their parents. One banded family group from the Delaware Bay already fits that pattern. The female from the group, “Evermoore,” probably overwinters in southern New Jersey (last sighted at Stone Harbor Point in mid-November 2023), while her mate, “Moby” (Orange C44), was recently seen on wintering grounds in Old Tampa Bay, FL. Interestingly, their fledgling from this season, “Schooner” (Orange C40), has been wintering at Masonboro Sound, NC, following a brief staging period at Stone Harbor Point, NJ. 

Band resights are already beginning to shed light on our Delaware Bay oystercatcher population, and we are confident that we will continue to learn more over the years as we band more birds. That said, banding the birds is only one piece of the puzzle. Similar to sending out a message in a bottle, you have no idea where your bottle (or oystercatcher) is going to end up. As a result, success is completely dependent on someone being at the right place at the right time to find it. That’s why volunteers and biologists who conduct resight surveys at staging and wintering sites are so important!  The American Oystercatcher Working Group makes it easy for citizen scientists to report sightings of banded birds to a shared database, so keep your eyes peeled and make sure to report any banded oystercatchers you come across. You never know what discoveries your observations could reveal! Learn more about American oystercatcher banding here.