The least tern is a small seabird that breeds in North America and then migrates to coastal areas further south for the winter. Understanding where least terns go in the winter and what habitats they rely on is important for conserving this species. In the opening paragraphs, we’ll provide a quick overview of the least tern’s wintering range and behavior.
Quick Facts
– Least terns winter along the coasts of Central America, northern South America, and the Caribbean.
– Their wintering grounds stretch from Mexico to northern Brazil.
– On the wintering grounds, least terns forage in shallow coastal waters, estuaries, and lagoons.
– They roost on sandy beaches, mudflats, and shorelines.
Wintering Range
The least tern has an extensive wintering range that covers Central America, northern South America, and the Caribbean basin. After breeding in North America during the spring and summer, least terns migrate south in late summer or early fall to their wintering areas.
The southern limit of their winter range is northern Brazil. Least terns can be found wintering along the Atlantic and Pacific coasts of Mexico, throughout Central America, and down the north coast of South America to Brazil. In the Caribbean, they winter on islands such as Cuba, Hispaniola, Puerto Rico, and the Bahamas (Jackson and Jackson 1985).
Some specific key wintering sites include:
– The Yucatán Peninsula of Mexico
– Coastal Belize
– Pacific and Caribbean coasts of Costa Rica and Panama
– Coastal Colombia and Venezuela
– Coastal French Guiana, Suriname, and Guyana
– Islands across the Caribbean Sea
Winter Range Map
This map shows the major wintering range of the least tern, stretching along the Atlantic and Pacific coasts from Mexico to northern South America. Key wintering sites are along the Yucatán Peninsula, Central America, and northern coast of South America. Least terns also winter across many Caribbean islands.
Wintering Habitats
On their wintering grounds, least terns inhabit a variety of coastal and estuarine habitats. Their winter ecology centers around two key activities – foraging and roosting.
Foraging Habitats
For feeding, least terns utilize shallow coastal waters, estuaries, lagoons, and river mouths. High quality foraging sites provide abundant small fish, shrimp, and other prey (Thompson et al. 1997). Key foraging habitats include:
– Shallow marine waters within a kilometer of shore
– Sandbars and shoals at inlets and mouths of bays
– Estuaries and lagoons protected from the open ocean
– Tidal rivers and creeks
In these habitats, least terns can plunge-dive from the air to catch their prey or skim low over the water surface. Access to productive foraging areas with sufficient food is essential to the terns’ survival in the winter.
Roosting Habitats
When not actively foraging, least terns need places to rest and roost. Their preferred roosting habitats are sites along the coast that provide safety from predators and extreme high tides. These include:
– Wide sandy beaches and sandbars
– Mudflats in estuaries and lagoons
– Low dynamic islands and shoals
– Shorelines with sparse vegetation
On beaches, least terns will roost in depressions in the sand to avoid wind. At high tide when beaches are inundated, they may roost on higher elevation sand spits and dunes (Thompson et al. 1997).
Winter Diet
The diet of least terns in their wintering areas consists almost entirely of small fish, shrimp, and other marine invertebrates. By foraging in productive coastal habitats, least terns are able to capture a diversity of prey.
Fish
Small fish make up the majority of the least tern’s diet during the nonbreeding season. Common fish prey include species such as:
– Anchovies
– Silversides
– Killifishes
– Mullets
– Needlefishes
Terns forage on both juvenile and adult fish, typically ranging in length from 2 – 10 centimeters. The abundance and availability of small schooling fish is a key factor influencing the quality of wintering sites.
Shrimp and Marine Invertebrates
While fish are the primary prey, least terns supplement their diet with shrimp and other invertebrates, especially in estuarine habitats. Important invertebrate prey includes:
– Shrimp
– Crabs
– Worms
– Mollusks
Prey diversity allows least terns to utilize a variety of coastal habitats and maintain their energy needs throughout the winter.
Threats and Conservation
Least terns face a number of threats on their wintering grounds that put pressure on populations. Conservation of their winter habitats is essential.
Habitat Loss
Coastal development, human disturbance, and degradation of foraging and roosting sites negatively impact wintering terns. Loss of beach habitat to coastal resorts and cities can displace terns.
Human Disturbance
Human activities on beaches used by wintering terns can prevent birds from roosting and cause unnecessary flight. Off-road vehicles, boats, and recreation in key habitats disturb and stress birds.
Pollution
Pollution from agriculture, sewage, and industry threatens fish prey populations and least tern health. Pesticides and heavy metals accumulate in the marine food web. Oil spills directly kill and contaminate terns.
Conservation Actions
– Protecting a network of coastal reserves for roosting and foraging
– Restricting human access and activities at key sites
– Reducing pollution into coastal waters
– Partnering with communities and agencies through the winter range
Effective conservation will require international cooperation across the least tern’s migratory range. Maintaining winter habitat quality is crucial for the long-term outlook of this species.
Wintering Site | Country | Key Habitats |
---|---|---|
Yucatán Peninsula | Mexico | Estuaries, lagoons, beaches |
Pacific Coast of Costa Rica | Costa Rica | Sandbars, river mouths |
Gulf of Venezuela | Venezuela | Mudflats, mangroves |
Bahamas | Bahamas | Tidal flats, islands |
This table shows some key wintering sites for least terns in different countries across their wintering range, along with the important coastal and estuarine habitats found in each location.
Migration Routes
Least terns take different migratory routes from their breeding to wintering areas depending on the region. Some fly overland while others follow coastlines or cross the Caribbean islands.
Overland Migrants
Many interior nesting terns travel overland across the Gulf of Mexico to wintering grounds. They follow river valleys south and avoid traveling long distances over water.
Coastal Migrants
Terns nesting along the Atlantic Coast likely follow a coastal route southwards through Central America and the Caribbean. This provides ample stopover habitat.
Across the Caribbean
Least terns in Florida may migrate south by island-hopping across the Caribbean, stopping on islands like Cuba and Hispaniola before reaching South America.
Spring Migration
Northward spring migration occurs earlier than southbound fall migration. Least terns arrive on breeding grounds in April-May and begin nesting soon after.
Stopover Sites
On migration, least terns stop to rest and feed at key sites that provide suitable habitat. This allows them to complete their long journeys between breeding and wintering areas.
Coastal Lagoons
Protected lagoons along the coast allow migrating least terns to roost and feed in safety when crossing the Gulf of Mexico. For example, Laguna Madre in Mexico is an important stopover site.
Estuaries
Estuaries along the Atlantic and Gulf coasts provide critical stopover habitat on the migration route with opportunities for the terns to feed and restore energy before continuing their journey.
Caribbean Islands
For terns migrating through the Caribbean, islands like the Bahamas and Cuba represent important midway stopover sites between North America and South America with habitat to support the birds.
Winter Behavior
Least terns exhibit behavioral adaptations on their wintering grounds related to thermoregulation, foraging, and roosting.
Staying Cool
To avoid overheating on tropical beaches, least terns pant, gular flutter, and wet their plumage to aid evaporation. They seek shade and may roost in depressions in the sand.
Foraging
Terns forage using shallow dives, skimming flight, and hover-plunging. They may forage cooperatively in flocks to drive fish together.
Roosting
On beaches, terns roost in scrapes in the sand lined with debris like shells and seaweed. They roost in groups which may aid detection of predators.
Population Connectivity
There is some evidence of connectivity between breeding and wintering populations of least terns:
Atlantic Coast
Terns from New England and the Mid-Atlantic likely migrate down the Atlantic Coast to wintering areas in the Caribbean and South America.
Interior Populations
Banded terns from the U.S. interior have been recovered on Caribbean islands, suggesting they migrate across the Gulf of Mexico.
Florida and Yucatán
A high percentage of terns banded in Florida have been re-sighted on the Yucatán Peninsula, indicating they likely winter in Mexico.
More banding studies and tracking technology is needed to better understand connectivity and migration of populations between breeding and wintering sites across the full range.
Conclusion
In conclusion, least terns are long-distance migratory seabirds that occupy important coastal and estuarine habitats throughout their wintering range in Mexico, Central America, northern South America, and the Caribbean basin. Conservation of key wintering sites with sufficient foraging and roosting habitat will be important for maintaining global populations of these birds into the future. Understanding winter ecology, migratory connectivity, and international habitat networks is essential for their management.