Most everywhere, birds of many descriptions fly among and above us. Most of them began life in nests, which are not so easy to find. But in one place, the Museum of Contemporary Zoology at Harvard University in Cambridge, Massachusetts, you can see more than 25,000 nests. The nests are the raw materials for important research about the human environment.
Nest collecting was immensely popular among scientists and amateurs for seventy or so years, beginning about 1850. Harvard curators assembled the world's largest collection of nests - some complete with eggs and even the branches on which they sat.
Nest-collecting lost popularity, and between 1920 and the 1970s, not a single nest was added to the Harvard collection. It literally gathered dust in drawers. But Douglas Causey, a senior ornithologist at the Harvard museum, and his assistants, have changed that, carefully obtaining specimens in places as far afield as Costa Rica and Siberia.
"The motivation for collecting specimens a century ago or earlier was to have one of each, and most people who enjoy collecting would understand that. But we now are finding that these nests and eggs that were collected many years ago are now providing an insight into what conditions were when they were collected," Mr. Causey said.
"For example, we have researchers at the University of Connecticut who are looking at our bird nests that were collected in the 1880s, not because they are interested in nests. They are paleo-biologists, very interested in seeing what the climate was and how that was reflected in the plant material that the birds used to make the nests," he said. "If you see the nests in our collections as being time capsules of what the environment and the animals were doing in the past, they become, of course, extremely valuable," he said.
Landphair: "And also the eggs themselves were invaluable in proving the damaging effects of [the insecticide] DDT several years ago."
Mr. Causey: "You are right. People were seeing a very serious effect on the breeding of many endangered birds. And natural-history observations showed that something was happening to the eggs themselves. They were becoming very fragile and breaking in the nests. So people went back and looked at eggs of the same species, but they were collected decades before there were any of this kind of organic pollutants in the environment.
"Now people are using eggs as a means of looking at what the atmosphere was like, if you can believe that. There's enough of the atmosphere trapped in the eggs themselves that they can analyze," he said.
For example, nests and eggs gathered in previously pristine environments like Tennessee's Great Smokey Mountains can be examined to see if the haze that often hangs over the valleys is affecting plant and animal life. And, said Douglas Causey, we have no idea how specimens collected today will be used 100 years from now.
Besides, the Harvard ornithologist points out, birds' nests are just plain interesting.
"For an animal that has no hands, it's pretty amazing what birds can do with a beak. I'm thinking of a weaver birds, for example, which can build nests that are so intricately woven that it's extraordinarily difficult to imagine how we could do such a thing. It would be about the same as trying to assemble a nest just using your teeth and your lips," Mr. Causey said.
Hummingbird nests are heavily layered but no bigger than a thimble. And because they're often built with spiderweb silk, moss, and lichen, it takes great strength to pull them apart.
Birds build nests with many other kinds of material as well: twigs, leaves, duck down, animal hair, pieces of string, bits of mud, their own saliva, even other birds' droppings. In New Guinea, for instance, the Megapode bird makes a nest three meters high out of vegetation. That's more than 15 times taller than the bird.
"There's a famous case of a jackdaw nest in India that was composed entirely of gold spectacle frames. The jackdaw nest was located next to an eyeglass shop. And the proprietor learned way too late that his stock had been stolen and used for a nest," he said.
Even after two centuries of study, scientists still don't know why, in some species, males build the nests; in others, females do the work; and in still others, both cooperate to get the job done.
One of Douglas Causey's assistants, Jeremiah Trimble, said some birds take the time and trouble to build nine or 10 "dummy" nests. Then they pick one for roosting. "It's often a young bird that's doing that. He's practicing! In other cases it's for purposes of sort of leading predators off track," Mr. Trimble said.
Dr. Causey said there's another reason as well. "You can have one male 'playing the field' and starting breeding with a number of females and then ending up with only one. So you can imagine what might be the motivation behind that," he said.
While some nests deteriorate, others remain sturdy year after year. Even so, Douglas Causey said, most birds meticulously build new nests all over again as a ritual. "Even birds that come back to the exact same next that persist from year to year - for example, eagles - still, there is a lot of nest-building that goes on. Sometimes these nests get enormous," he said.
In fact, one three-meter-high eagle's nest in Ohio was so heavy, it toppled a gigantic oak.
Douglas Causey at Harvard University cautions anyone who would liken nest-building birds to structural engineers. There's no learning or special creativity involved, he said. It's all instinct. As Dr. Causey puts it, "They're hard-wired" to do what birds do.