You’ve probably heard of the American robin, and may have seen one tugging at worms in
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 year 2016 marks the centennial of the Convention between the United States and Great Britain (for Canada) for the Protection of Migratory Birds (also called the Migratory Bird Treaty), signed on Aug. 16, 1916. Three other treaties were signed shortly thereafter with Japan, Russia and Mexico. The Migratory Bird Treaty, the three other treaties signed later, and the Migratory Bird Treaty Act form the cornerstones of efforts to conserve birds that migrate across international borders.
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, an educational program for schools and conservation groups, and more!