You’ve
probably heard of the American robin, and may have seen one tugging at
worms in your yard. These birds – harbingers of spring, joyful
songsters, jolly, round bundles of grey and rust – are a common sight in
Michigan.
In fact, the robin is so identifiable and well-loved that it
was named the Michigan state bird in 1931. There was a time, however, when robins
were not as common as they are today.
In the post-World War II years,
DDT and other pesticides were widely used. Farmers sprayed DDT on their
fields to reduce crop pests, cities applied it to elm trees to kill the
beetles that spread Dutch elm disease, and homeowners used it to
control household insects.
Luckily, scientists began to
recognize that widespread use of pesticides, including DDT, was causing
problems for birds like the American robin. An ornithologist from
Michigan State University named George Wallace and his graduate students
collected birds from MSU and surrounding suburbs from the mid-1950s
into the 1960s. Most of these birds were robins. While some birds were
found dead, others were discovered on the ground suffering from seizures
or tremors before dying. Tests on the birds’ carcasses revealed
elevated levels of DDT.
The studies by Wallace and his
students revealed that DDT did not kill only insects. Because DDT does
not quickly degrade, the poison remained on the leaves of sprayed
plants. When the sprayed leaves dropped in the fall, they became compost
in the soil, bringing the DDT with them. DDT also came in contact with
the soil when rain washed it off the leaves or when it fell directly
onto the soil during spraying.
Earthworms ingested the
affected soil and compost, and then robins and other birds ate the
earthworms. The DDT concentrated in the birds’ fat cells and was not
excreted like some other toxic substances. A little DDT in an earthworm
became a lot of DDT in a robin eating dozens of worms a day.
The U.S. Environmental
Protection Agency banned DDT use in 1972. Since then, robin populations
have bounced back, and these cheerful birds are common in backyards once
more.
The federal Migratory Bird
Treaty Act, offering protections for migratory birds and their nests and
eggs, also helped bolster robin populations. Birds, their nests and
their eggs must be left alone, and unless you have a permit, taking a
baby bird or eggs from the wild is breaking the law.
The 2016 Migratory Bird Treaty
Centennial celebration will include monthly featured bird stories to our
DNR Wildlife Viewing email subscribers, celebration events including a
weekend of bird-based programming at state parks and visitor centers
June 24-26, an educational program for schools and conservation groups,
and more!
To learn more about the Migratory Bird Treaty Centennial, visit www.fws.gov/birds/MBTreaty100.
