Birds that build nests with domes could be doomed

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Most bird nests you’ll see this spring will have the familiar open and hollow shape, perfect for securing eggs and possibly hatchlings. About 30 percent of bird species are the starchitects of the avian kingdom, building elaborate domed nests with roofs. While conservationists have long believed domed nests provide greater security from predators and the elements, a new study suggests songbirds that opt ​​for simpler nests may be better off in the long run.

Almost all songbirds can be traced back to Australasia around 45 million years ago, when Australia was attached to Antarctica and covered in lush forests instead of arid deserts. Statistical analyzes of songbird traits and evolution found domed nests were the “ancestral architecture” of songbird dwellings. But domed nests were later abandoned in favor of simpler cups when songbirds began to spread across the rest of the world around 40 million years ago.

Evolutionary biologists, such as Iliana Medina of the University of Melbourne, have wondered why domed nests have been abandoned by so many modern birds, and why only a third of birds build them today. To answer this, she and her colleagues looked at the ecological success of dome builders compared to beaker builders, and then linked that data to their evolutionary history.

For more than 3,100 species of songbirds, Dr. Medina and his colleagues collected as much data as they could find: the birds’ body and range sizes, their latitude and altitude, s ‘they live in cities and, of course, what kind of nests they build. All of this information was needed because many factors influence the success of a species, and Dr. Medina wanted to focus on nest type as precisely as possible.

His analyses, published last month in the journal Ecology Letters, revealed surprising patterns. Songbirds that build domed nests tend to have smaller ranges, with stricter climatic requirements. If the domed nests offer better protection, some conservationists thought, it could allow the birds to spread out and withstand wider conditions. Dr. Medina’s results contradict this thinking.

Based on the results, Dr. Medina proposes that dome builders might be less adaptable than cup builders. Although domed nests offer better protection from the elements, they also tend to be larger – easier for a predator to spot. Larger nests also take longer to build and require more materials, potentially limiting when and where they could be built and making birds less likely to leave imperiled habitat, as a cost error. sunk with feathers.

“Maybe it’s better to have a cheap, disposable nest that you can build a few times a season,” said Jordan Price, an evolutionary biologist at St. Mary’s College in Maryland, who didn’t participated in the study. “You are exposed to the elements, but you can escape predators very quickly.”

Research has also shown that dome builders are less likely to live in cities, possibly due to a lack of suitable nesting sites, a shortage of building materials, or even because cities tend to be warmer. Dome builders also take longer to build nests, an intuitive finding that had not been supported by global analysis until now.

Dr. Medina then went back in time, modeling the natural history of nest-building features and new species over the roughly 45 million-year history of songbirds. She found that dome builders had slightly higher extinction rates than cup builders, a result contrary to notions that domed nests were the safest.

“The cost-benefit analysis of building an open cup nest or a domed nest changed at some point,” Dr Price said. “Some species stuck to their old ways, and some innovated something new, which allowed them to really flourish.” What caused the cost change, however, remains unknown; new parasites or predators could have arrived, or climates could have changed.

Today, dome builders face new man-made challenges including variable climates, habitat loss, and built environments. Birds, like many other animals, know acceleration rate of extinction.

“There are no real management actions we can take regarding a species’ nest,” said James Mouton, postdoctoral researcher at the Smithsonian Migratory Bird Center who was not involved in the study. “It’s not something we can drag them into.” But conservation efforts could help restore and protect important domed nesting habitats, bolstering potentially vulnerable populations.

“There are some pretty old lineages, some birds that split off the songbird tree very early on,” Dr Price said. “We have to be careful with these species.”

He added: “Some of these species that nest in the dome, it would be terrible to lose them.”

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