Many of the bird nests you will see this spring will have the open, cup-shaped family shape, perfect for securing eggs and finally young. About 30 percent of the bird species are the star architects of the avian kingdom, building elaborate domed roof nests. While environmentalists have long thought that domed nests provided greater security against predators and the climate, a new study suggests that songbirds that opt for simpler nests may be better off in the long run.
Almost all songbirds can be found in Australasia about 45 million years ago, when Australia was attached to Antarctica and covered by lush forests instead of dry deserts. Statistical analyzes of the features and evolution of songbirds found that domed nests were the “ancestral architecture” of songbird houses. But domed nests were abandoned in favor of simpler canopy designs when songbirds began spreading to the rest of the world about 40 million years ago.
Evolutionary biologists, such as Iliana Medina of the University of Melbourne, wondered why domed nests were abandoned by so many modern birds and why only a third of birds build them today. To answer this, she and her colleagues examined the ecological success of dome builders compared to cup builders, and then linked these data to their evolutionary history.
For more than 3,100 species of songbirds, Dr. Medina and her colleagues collected as much data as they could find: the size of the birds’ bodies and range, their latitude and elevation, whether they live in cities, and, of course, what kind of nests they have. . build. All this information was necessary because there are many factors that influence the success of a species, and Dr. Medina wanted to delve into the type of nest as accurately as possible.
His analysis, published last month in the journal Ecology Letters, revealed striking patterns. Singing birds that build domed nests tend to have smaller ranges, with stricter climatic needs. If the domed nests offer better protection, some environmentalists had thought, this could allow bird ranges to expand and withstand wider conditions. Dr. Medina’s findings contradict this thinking.
Based on the findings, Dr. Medina proposes that dome builders might be less adaptable than cup builders. Although domed nests offer better protection against the elements, they are also usually larger, easier to detect for a predator. Larger nests also take longer to build and require more materials, which can limit when and where they could be built and make birds less likely to leave an endangered habitat, such as a sunken cost fallacy. with feathers.
“Maybe it’s really better to have a cheap, disposable nest that can be built several times a season,” said Jordan Price, an evolutionary biologist at St. John’s. Mary’s College of Maryland who did not participate in the study. “You are exposed to the elements, but you can escape from predators very quickly.”
Research has also shown that dome builders are less likely to live in cities, perhaps because of a lack of adequate nesting sites, a lack of building materials, or even because cities tend to be warmer. Dome builders also take longer to build nests, an intuitive finding that until now had not been supported by a global analysis.
Dr. Medina then looked back in time, modeling the natural history of nest-building and new-species traits over the roughly 45 million-year history of songbirds. He found that dome builders had slightly higher extinction rates than cup builders, a result contrary to the idea that dome nests were the safest.
“The cost-benefit analysis of building an open canopy nest or a dome nest changed at some point,” said Dr. Price. “Some species kept their old ways and some innovated something new, which allowed them to really bloom.” What caused the change in cost, however, remains unknown; new parasites or predators could have arrived, or climates could have changed.
Today, dome builders face new challenges posed by humans, such as changing climates, habitat loss, and built environments. Birds, like many other wildlife, are experiencing accelerated extinction rates.
“There’s no real management action we can take on the nest of a species,” said James Mouton, a postdoctoral fellow at the Smithsonian Migratory Bird Center who did not participate in the study. “It’s not something we can train them on.” But conservation efforts could help restore and protect important dome-nesting habitats, strengthening potentially vulnerable populations.
“There are some pretty old lineages, some birds that branched out from the songbird tree very early on,” Dr. Price said. “We need to keep an eye on these species.”
He added: “Some of these species that nest in the dome, it would be terrible to lose them.”