Natural History
The
common tern (Sterna hirundo) is a small colonial waterbird. There are
four breeding species of terns in Michigan (Caspian, black, common, and
Forster's terns). The common is smaller in size than the Caspian tern. Black
terns nest along sandy shores, but as their name suggests, they are black and
tend to be smaller than the common tern.
Common terns are white with a black cap, and pale gray back and
wings. Their bill is red orange with a black tip. The tail is deeply forked and
dark along the outer edges. Immature common terns and adults in their winter
plumage have only a partial black cap. It can be distinguished from its close
relative the gull by a smaller body size and longer wings. The common tern's
call is a rolling ter-arr and rapid kip-kip-kip.
Common terns are frequently seen hovering in the air over a
school of fish. With a sudden plunge downward into the water, they seize fish
with their bills. Sometimes they will dive entirely below the surface of the
water. Terns eat small fish such as shiners, chubs, and other minnows. They will
also eat crustaceans and occasionally, insects such as dragonfly nymphs.
Their winter migration takes these birds to the Atlantic coastal
areas in Florida, the Caribbean, and South America. They return to their nesting
sites in early spring.
Arriving on their breeding grounds in May, common terns nest in
colonies of 10 to 1,000 breeding pairs. They prefer sandy, well drained areas
away from mammalian predators and human disturbances. Currently, common terns
are using natural and human made islands in the Great Lakes with a few nesting
on inland lakes. Common terns construct their nests by creating a depression in
the sand with their feet, smoothing and shaping it by sifting in it and turning
their bodies. Egg laying and incubation lasts until late June or early July.
Both adults take turns sitting on the nest. The adults defend the eggs and young
fiercely, diving at intruders, and even striking them with their bills.
Michigan History
Once numbering over 6,000 breeding pairs in Michigan, common terns were found
on every Great Lakes shore. Data from 1992 suggest that the population has
decreased to an estimated 1,400 breeding pairs. Several factors have contributed
to this decline including loss of habitat, competition with gulls, predation,
and effects of contaminants. As a result of these factors, the common tern was
officially listed in Michigan as a "threatened species in 1978 and has recently
undergone a status assessment by the US Fish and Wildlife Service in the Great
Lakes for possible listing as Federally endangered.
The Michigan Department of Natural Resources (MDNR), through citizen
donations to the N. Nongame Fish and Wildlife Fund, has supported monitoring
efforts throughout the state.
Lime Island Colony
Lime
Island is located in the St. Mary's River along the eastern shore of the Upper
Peninsula of Michigan. This site was once used as a refueling facility for
barges. The MDNR took ownership of the island in 1982 and is developing camping
and cabin rental facilities.
During 1997, the island supported the largest common tern colony in the Great
Lakes (649 breeding pairs). Common terns were using the old coal dock and a rock
pile in the harbor as their nesting sites. At that time, Lime Island was one of
the most valuable colonies in Michigan. Researchers from Michigan State
University were working with the MDNR to understand how the colony was thriving
in this unusual location for common terns. Data collected there will also enable
managers to make the best decisions on how to protect the colony while
maintaining the recreational use of the coal dock and island.
Unfortunately, in 1999, the colony abandoned the island to find nesting
habitat elsewhere. Dense vegetation cover on the coal dock made the terns more
susceptible to entanglement and predation, in turn reducing the nesting and
hatching success of the colony. In addition, a torrential rain early in the
spring had flooded the area where the 20 remaining nests were located.
However, early reports for 2003 indicate that common terns may once again be
nesting at Lime Island. Why the change? It is not known, but in
general these terns do not seem to be very faithful to any particular nesting
area and move around to to find a place where the conditions are "right."
What can you do?
The continuing decline of the common terns in the Great Lakes should be of
concern to all who enjoy Michigan's natural resources. Hopefully, with careful
management and increased public awareness, the common tern will soon thrive
again. Here are some hints on how you can help Lime Island's tern colony or any
other colony you may encounter.
- Avoid the fenced nesting areas from May 1 to August 30.
- Enjoy the birds from a distance.
- Keep any pets on a 6' leash and away from the nesting sites.
- Dispose of litter properly, particularly food items which attract tern
predators like gulls, raccoons, and skunks.
- Do not disturb the birds by throwing items such as rocks, sticks, or
firecrackers into the nesting area.
- Photographers are asked to keep their distance.
- A viewing area is provided at Lime Island along the camping boardwalk.
This area provides an excellent area for viewing and photography.
Non-DNR Links
Identification Tips & More (USGS Patuxent Wildlife Research Center)
Common Tern (Wisconsin Dept. of Natural Resources)
Sterna hirundo (University of Michigan, Museum of Zoology)
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