Terns

 


Question:  My friends tell me that many types of terns have been traveling through our area.  How can I distinguish between these birds and gulls? 

 

Least Tern


Answer: Terns are enjoyed by millions of people who flock to Florida's beaches.  These birds lack color, they are black and white, but are beautiful.  Terns are often confused with gulls because they are in the same taxonomic family, Laridae.  As relatives, they share some physical and behavioral characteristics.  Both have webbed feet and usually nest on the ground and near water.  Terns differ from gulls in that they have narrower pointed wings, forked tails, pointed bills, and slimmer bodies.  Their bill is often aimed downward as they fly and hover in search for food.  Of the sixteen species of terns in North America, twelve can be seen in Florida.


Although there are exceptions, each tern species follows a general pattern of migration and occurrence in Florida.  The Caspian (Sterna caspia), Royal (Sterna maxima), Sandwich (Sterna Sandvicencis), and Roseate (Sterna dougallii) are in Florida year-round.  The Sooty (Sterna fuscata), Gull-billed (Sterna nilotica), and Least (Sterna antillarum) terns spend only the nesting season in Florida and migrate south for the winter.  This nesting season is defined as March through August.  Other terns, including the Bridled (Sterna anaethetus), Forster's (Sterna forsteri), Common (Sterna hirundo), and Black (Chlidonias niger) nest north of Florida and winter here.  The Arctic Tern (Sterna paradisaea) nests in the arctic and winters in South America.  We only get the chance to see these terns as they pass through heading north in May and south in September. 


Some species are restricted to certain regions of the state and you should not expect to see them here.  Sandwich Terns have only been known to nest near Jacksonville.  The Caspian Tern nests in the Panhandle and central Florida.  Royal Terns nest along the coast except in extreme south Florida.  Roseate and Sooty terns nest only in the Keys and Dry Tortugas.  Others will nest statewide.


Although fish is the main food item for most terns, their diets can still be very diverse.  Insects are important for several terns while others specialize on other edibles such as fiddler crabs, squid, shrimp, bird eggs, and crustaceans.  Most terns fly over water in search of food near the surface.  They tuck their wings back and dive into the water to catch the prey with their bill.  The Gull-billed, Sooty, and Bridled terns will not dive.  They restrict their feeding to shore or offshore areas in the ocean or gulf.  Other terns will forage almost anywhere including agricultural fields in search of insects.


Terns typically nest in open areas with short vegetation.  Nests are usually shallow depressions in the sand and may have plant materials added.  Because of the limited availability of suitable, undisturbed, natural habitat some terns have resorted to nesting on spoil islands or flat rooftops.  In some areas of Florida, roof nests now outnumber those on the ground.  But terns are well camouflaged when in sandy areas.  Terns lay from one to three eggs depending on the species.  Incubation usually takes three to four weeks and young can walk shortly after birth. These birds can fly after about a month.  If you try to remove a nest from a rooftop, the terns will rebuild and re-nest.  Therefore, it is best to wait until the terns have reared their young.  Typically only one brood is raised each year.


If terns are to persist as part of the natural integrity of Florida's coastal areas, residents need to take an active role in the conservation of these species.  Habitat preservation is probably the most important aspect in this venue.  Several federal and state laws protect terns from human activities.  These laws protect live birds, eggs, nests, and non-live body parts.  Biologists do not know everything about tern biology and behavior so studies and monitoring must continue in order to provide the best conservation efforts possible.

Sandwich Tern

 

Shannon L. Ruby is the Natural Resources/Agriculture Agent with the University of Florida/IFAS and Lee County Extension Service.  To submit questions, call 461-7515 between 9am and 4pm or send questions to 3406 Palm Beach Blvd. Fort Myers, FL 33916-3736 or via e-mail at rubys@leegov.com.