Scope

Simple nests breed success, benefits of bull’s-eyes and more

Mark Wexler
Animals
Mar 31, 2023

Simple Nests Breed Success

About a third of the planet’s roughly 11,000 bird species build elaborate domed nests with roofs that would appear to provide better protection for eggs and hatchlings than open nests. But according to a recent study by Australian biologists, just the opposite seems to be the case. In an analysis of physiological and geographical data for more than 3,100 songbird species worldwide, the scientists conclude that birds that build simpler, cup-shaped nests (such as the willie wagtail, above) may be more adaptable to changing habitat and climatic conditions. “Our results support the idea that nest types can be important factors in the ecological success of birds,” writes lead author Iliana Medina in Ecology Letters. An evolutionary biologist at the University of Melbourne, Medina explains that domed nests require more time and materials to build, and their large size can attract predators. The scientists write that species with open nests “have larger ranges with broader thermal niches and are more likely to colonize urban environments.” They also, Medina adds, tend to have lower extinction rates than species that build domed nests.

An image of a Brimstone moth caterpillar on willow in Ireland.

Hiding in Plain Sight

Though scientists have spent more than a century observing and studying the camouflage tactics animals use to deter detection by predators, few of those efforts have compared the effectiveness of different concealment strategies. “There was a big gap in the literature on this topic,” says João Vitor de Alcantara Viana, a behavioral ecologist at the State University of Campinas in Brazil, who led an investigation into which strategies work best. In a review of scientific papers about camouflage published between 1900 and 2022, he and his colleagues uncovered 84 studies that experimentally tested at least one concealment tactic. In general, the ecologists report in the Proceedings of the Royal Society B: Biological Sciences, predators must spend about 60 percent more time finding camouflaged prey than noncamouflaged prey. Their analysis showed that masquerading as specific objects (such as a brimstone moth caterpillar mimicking a twig, above)—as opposed to blending in with a background—provides the best protection against predation. The scientists add that masquerading is more likely to evolve if an animal is similar in size to the object it is imitating.

An image of a Longhorn bee on a sunflower.

Benefits of Bull’s-Eyes

Scientists have long known that sunflower petals produce ultraviolet (UV)-absorbing pigments that create bull’s-eye patterns invisible to humans but not to insects such as bees (longhorn bee, above). Experiments have shown that these UV bull’s-eyes help attract pollinators. Now, in a study of nearly 2,000 wild sunflowers, researchers at the University of British Columbia find that sunflower UV patterns also help the plants survive by regulating water loss. “Unexpectedly, we noticed that sunflowers growing in drier climates had flowers with larger UV bull’s-eyes and found that those flowers are able to retain water more efficiently,” says lead author and plant geneticist Marco Todesco. Writing in eLife, the scientists explain that larger bull’s-eyes contain more UV-absorbing compounds called flavonols that prevent excessive water loss. By contrast, in hot, humid habitats, the researchers saw sunflowers with smaller UV patterns—and presumably fewer flavonols—which would likely promote transpiration and help avoid overheating.

An image of an American bullfrog in water, in Virginia.

Microscope

Freshwater Riches

Covering just 2 percent of Earth’s surface, rivers, lakes, ponds and other freshwater habitats have higher animal species richness relative to area than either land or ocean habitats, report University of Arizona biologists in Ecology Letters.