Changes in New England’s birds and plants are not being driven by global warming, evolution or ice age cycles, Peter C. Alden told a Yale audience of O.C. Marsh Fellows and friends at the Peabody Museum.
Instead, Alden, author of 15 nature books and leader of birding expeditions around the world, blames forest re-growth, invasive plants, bird feeders, and birds themselves for the waxing and waning of wood thrushes, cow birds, meadow larks, and a host of other avian species.
Alden (pictured at center of the photo, signing and selling books Monday), who has sold 1.5 million books, started his lecture Monday evening with a slide of a young Charles Darwin, whose 200th birthday is Thursday.
“I meet people on planes who think evolution is baloney. I don’t continue talking to them,” he said.
Then he moved on.
Alden is probably among a handful of experts who can lecture about birds, plants, and their ecological relationships for 45 minutes without putting people to sleep. In fact, he’s funny.
Birds of New England are more realistically birds from the Carolinas, Alden said. This is because 20,000 years ago, the glaciers of the last ice age extended about that far south.
As the glaciers slowly receded, flora and fauna moved north. “Now we have man-accelerated climate change, which you believe in if you’re a Democrat,” he said. Climate change is real, and happening, but that’s only a small factor in changes over the past 50 or so years, Alden contends.
During the mid-18th Century most of the forests of New England, New York and Pennsylvania were clear-cut. Grassland birds from the Great Plains took advantage of this new habitat and moved east, Alden said.
The meadowlark is one of these transplanted species, he said. However, forests have re-grown, leaving the bird with nowhere to go. That, Alden said, is why meadowlarks are leaving New England.
The same goes for the brown thrasher, the eastern towhee, and the golden winged warbler.
Paradoxically, curtailment of the re-growth is responsible for driving away wood thrushes, and other birds that depend on forests rather than open fields, he said.
A bird commonly spotted at feeders, the brown-headed cowbird, evolved with the bison, dining on insects drawn to the large animals. Now cowbirds are here, laying eggs in other birds’ nests.
Invasive plants and bird feeders have also drawn in mocking birds, cardinals, and mourning doves, Alden said. Mocking birds, for example, have come to rely on the fruit of the multiform rose, which was introduced to New England in the 1930s to halt erosion and provide “natural fences.”
Birds eat the multiform rose hips, which have the nutritional value of a red Popsicle, and then spread the seeds. The red pigment in Japanese knotweed berries is turning the Baltimore oriole’s yellow chest red, Alden said.
Oriental bittersweet is another invasive plant that provides food for birds, which disseminate indigestible seeds in their droppings.
Bird-Feeder Dangers
Alden is ambivalent about bird feeders. He starved cardinals for a few days in 2004 because of the National League team from St. Louis. Boston won the World Series in four straight games, Alden said, giving himself mock credit.
Otherwise, bird feeders tend to spread diseases, like the one that has cut into the evening grosbeak, he said.
Alden is also not very fond of cats, which he estimates kill 100 million birds (drawn to feeders) every year.
Bird feeders also encourage sparrows, which Alden dislikes. Sparrows, he said, drive away bluebirds. If the bluebird refuses to abandon its nest, a sparrow will kill the bluebird by pecking a hole in its skull, and then toss the body out of the tree.
Alden once called up a city official in Concord, Mass., where he lives, to ask about the best ammunition for doing away with his neighbors’ cats.
The woman started to yell at him, not realizing that he was merely being whimsical, Alden said.