The birds are back! Coming off a highly successful 2025 nesting season, state-threatened least terns (Sternula antillarum) have returned to the Sanibel Causeway islands. This is the fourth year in a row that least terns have nested on the Sanibel Causeway following a 30-year absence! Black skimmers (Rynchops niger), which nested on the Causeway in 2025, have returned to nest as well.

Least terns are colonial nesters, meaning they nest in large groups as a strategy to protect eggs and deter predators. These migratory seabirds arrive in Southwest Florida in April and depart in August, they require large, open areas to nest.

Related Story: Least Terns Have Highest Success on Causeway Since 1990s

A History of Causeway Nesting

Both least terns and black skimmers regularly attempted nesting on the Causeway islands after the Causeway was built in 1963. Unfortunately, vehicle traffic and summer storms left most nests unsuccessful.

“There are several newspaper articles detailing the struggles that least terns and black skimmers on the Causeway historically faced from nest washovers and car strikes,” said SCCF Shorebird Biologist Audrey Albrecht.

“Despite the best efforts of our local conservation organizations to protect them and lure them to other nesting sites away from the Causeway, the birds continued to fall victim to traffic and the weather. They turned to other nearby beaches and rooftops but struggled to find suitable nesting habitat.”

Things began to turn around in 2023, when least terns nested on the Causeway for the first time in at least 30 years, and that trend has continued, with 2025 being a banner year for the birds. 

This year, the terns began nesting just before Memorial Day. There are currently 40 tern nests and around 80 adult least terns on the Causeway. Black skimmers have joined the terns again this year with approximately 60 adults in the Causeway colony. 

A Tern of Events

If you’ve visited the Causeway tern colony in previous years, you may notice fewer birds this time. That’s because the terns have not one, not two, but three separate colonies this year! 

SCCF has been diligently working to cover all three colony sites and ensure the birds have adequate protection during nesting, especially as chicks are beginning to hatch. 

Nest colony locations on the west end of Sanibel have been fluctuating due to coyote depredation. Initially, 40 nests were laid at a West Gulf colony; only 7 remain. A Clam Bayou colony initially had 13 nests, of which 9 were depredated. The number of nests at Clam Bayou then rebounded to 21, but due to further depredation, the count is now down to about 10.

Due to this increased depredation of the West Gulf nesting locations, least tern numbers on the Causeway are expected to increase.

Since the terns started renesting on the Causeway, SCCF has worked closely with the Florida Department of Transportation, Florida Fish & Wildlife Conservation Commission (FWC), and Lee County to protect the colony and nests.

“Without our partners, the support of our volunteers, and the public’s interest in protecting these tiny birds, least terns would not have experienced this continued nesting success,” Albrecht said.

Stewards Needed!

SCCF is continuing its volunteer shorebird steward program, where staff and volunteers are stationed near the colony during peak weekend beach times. The stewards provide education and outreach to the public, offering information about the birds and giving them a chance to view the birds up close with a spotting scope.

If you’re interested in becoming a steward, join us for our stewardship training on June 6 at 9:30 a.m. at SCCF’s HQ building or via Zoom. Following the presentation, volunteers are invited to join us for an optional field trip to the nesting colony to see the birds and our stewarding set-up.

Learn more and sign up!