Roseate terns are elegant sea birds found along the northeast coast of North America. They nest in colonies on sandy or rocky beaches and islands. Their preferred nesting habitat makes them vulnerable to disturbance, predation, and sea level rise. Understanding where roseate terns nest is important for conserving this threatened species.
What are roseate terns?
Roseate terns (Sterna dougallii) are medium-sized seabirds in the family Laridae, which includes gulls and terns. Adults have a black cap on their head, a long, wedge-shaped tail, and slender wings. Their belly is white and their back and wings are light gray. Their slender orange bill is distinctive.
Roseates get their name from the rosy-pink tinge on their breast during breeding season. Their Latin species name, dougallii, honors the Scottish clergyman and ornithologist John Dougall.
These birds spend most of their lives far out at sea, ranging widely along the Atlantic coast to feed. They eat small fish and invertebrates like shrimp, catching them by plunge diving. Roseates can dive up to several meters deep into the ocean in pursuit of prey.
Roseate terns are listed as endangered in some northeastern states and as a threatened species under the U.S. Endangered Species Act. Their total population is estimated at less than 100,000 breeding pairs. Threats to their survival include habitat loss, disturbance of nesting colonies, and predation.
Where do roseate terns nest?
Roseate terns nest in colonies numbering from several dozen to several thousand breeding pairs. They prefer islands and remote sandy beaches in warm coastal areas with abundant food sources nearby.
Their historical nesting range extended along the Atlantic coast from Nova Scotia to the Caribbean. Today, about 75% of the total North American population breeds on just a few key islands and beaches in Massachusetts, New York, Connecticut, and Nova Scotia.
Some of the major roseate tern nesting sites include:
- Bird Island, Marion, Massachusetts – 1,800 pairs
- Ram Island, Mattapoisett, Massachusetts – 1,100 pairs
- Falkner Island, Guilford, Connecticut – 800 pairs
- Great Gull Island, Long Island, New York – 1,600 pairs
- Stratton Island, Maine – 930 pairs
- Country Island, Nova Scotia – 5,000 pairs
Roseate terns have very specific requirements for their breeding sites. They select islands or beaches that offer protection from terrestrial predators. These areas must have little or no vegetation and a sufficient area of rocky or sandy substrate for nesting.
Ideal nesting habitat
The ideal roseate tern nesting site has these key features:
- Isolation – Predator-free islands or remote coastal sites
- Substrate – Sandy or gravelly areas with little vegetation
- Security – Low likelihood of overwash or flooding
- Size – Large enough to support a sizable colony
- Proximity – Near marine foraging areas
Access to productive fishing areas is especially important. Roseates won’t nest more than about 60 km from adequate food resources. Competition for safe nesting space close to prime ocean feeding grounds is fierce.
Nesting colony habitat
Within a suitable island or coastal site, roseate terns nest in scrapes or depressions in the open sandy substrate. They prefer elevations above the high tide line to avoid flooding.
Roseates often nest alongside common terns in mixed-species colonies. They tend to aggregate more toward the interior, while common terns nest closer to the water’s edge. The presence of common terns offers some protection from aerial predators like peregrine falcons.
Successful tern breeding sites have minimal vegetation or obstructions that could shelter terrestrial predators like gulls, owls, foxes, raccoons, rats, and other mammalian nest predators.
Favored nesting substrates
The substrate at roseate tern breeding colonies varies. They most commonly nest on these types of surfaces:
- Sand beaches – Wide sandy beaches offer ideal habitat if isolated from predators.
- Gravel bars – Low gravel islands and spits are attractive where suitable.
- Rocky islands – Bedrock islands with crevices provide nest sites.
- Shell fragments – Crushed shell substrate is used where abundant.
Sandy beaches and shell fragments offer the best camouflage for eggs and chicks. Gravel bars and rocky islands also work well in predator-free locales.
Decline in nesting habitat
The availability of suitable nesting habitat has declined dramatically in recent decades. Historical nesting sites have been lost to coastal development, recreational activity, and encroachment of vegetation.
Other factors negatively impacting roseate tern breeding sites include:
- Erosion and overwash of barrier beaches
- Increased flooding due to sea level rise
- Predation pressure from expanding gull populations
Human disturbance of tern colonies, whether intentional or not, also lowers reproductive success. Several historical roseate tern breeding colonies were abandoned after human interference.
Importance of protected nest sites
Because suitable roseate tern nesting habitat is rare, active management and protection of breeding colonies is essential. Primary nesting islands and beaches should be maintained predator-free and closed to humans during nesting season.
Other management strategies include:
- Habitat enhancement such as vegetation control
- Restricting access to breeding sites
- Predator exclosures and trapping programs
- Placement of decoys and audio playback systems
Ongoing monitoring of nesting sites is also critical. This allows researchers to track tern populations, productivity, and threats.
Prospects for future nesting habitat
Climate change and coastal development will make creation of new roseate tern breeding habitat increasingly difficult. Maintaining existing suitable nesting colonies will require long-term planning and commitment.
Some efforts are underway to enhance nesting habitat, including:
- Expansion of existing protected islands used by roseates
- Creation of artificial nesting islands
- Coastal habitat restoration and beach re-nourishment
But these initiatives alone likely won’t offset expected future losses. Sustained conservation efforts for roseate terns will be needed to ensure availability of adequate nesting habitat.
Conclusions
Roseate terns are highly selective in choosing nest sites. They require predator-free islands or beaches near productive ocean feeding areas. These habitats are increasingly rare due to development, erosion, climate change, and other threats.
Conserving remaining high-quality tern breeding colonies is essential for the survival of these endangered seabirds. Management efforts focused on protecting nesting habitat may offer the best hope for their future.