[ad_1]
Last spring, blackbirds living on an Illinois tree plantation sat on unusual eggs.
Beside the usual bright blue ovoids they had set were objects of unusual shape. Although they were the same color, some were long and thin, stretched into tablets. Others were decidedly sharp – so angular, in fact, that they didn’t look like eggs at all. If the robins were playing Dungeons and Dragons, they might have thought, “Why do I have an eight-sided die in my nest?”
The answer: Evolutionary biologists were evaluating how birds decide what belongs to their nests and what is an invasive piece of trash they should throw away.
Thanks to the results of this study, published Wednesday in the Royal Society Open Science, we now know what the robins thought of the eggs, which were made of plastic and had been 3D printed by the laboratory of Mark Hauber, animal professor. behavior at the University of Illinois, Urbana-Champaign and a member of the Hanse-Wissenschaftskolleg in Delmenhorst, Germany.
He and his colleagues reported that the thinner the false eggs, the more likely the birds were to remove them from the nest. But oddly enough, the robins were more careful about throwing sharp objects like this eight-sided die, which were closer to the width of their own eggs. The results suggest that birds use rules of thumb that are not intuitive to humans when deciding what is litter and what is valuable cargo.
It is not as rare as you might think for blackbirds to find foreign objects in their nests. They are home to cowbirds, a parasitic species that lays eggs in the nests of other birds, where they hatch and compete with robin offspring for food. When faced with a cowherd egg, which is beige and more squat than its blue ovals, parent robins will often repel the parasite’s eggs. This makes the species a good candidate for testing exactly what matters to distinguish its own eggs from other objects, Dr Hauber said.
The researchers 3D printed two sets of decoy eggs. One group became progressively thinner, and the other became more and more angular. They carefully painted them in blackbird egg blue, so the birds could only rely on the shape to tell the difference. Then they deployed these fake eggs in nests scattered around the tree farms. By revisiting the nests, they kept track of the shapes that had been removed by the owner of the nest.
Blackbirds had a good eye for thin eggs. Eggs with a typical width of about 75% were accepted more often than they were rejected. Eggs that were usually less than 50% wide were almost always expelled.
But sharp objects weren’t thrown out that often. In fact, only the sharpest lure, the eight-sided die shape, was pushed almost every time.
“It was very surprising for us,” said Dr Hauber.
Birds seem to respond to important variables in nature. Cowhide eggs, for example, are noticeably wider than theirs, so blackbirds may have developed a crafty sense of when the width is turned off.
“They seem to be quite hesitant to reject the eggs when the variable we changed was unnatural,” Dr. Hauber said, referring to the angular, pointed eggs. “The Robins don’t know what to do with it, because they never evolved to respond to it.”
And rather than throwing one of their own eggs by mistake, they let it lie.
Identifying what screams “egg” at a bird is an intriguing way to find out what the world looks like to other animals, but it may also be useful in future avian brain studies.
“Just like humans have a facial recognition center in the brain, birds have an egg recognition center in the brain,” said Dr. Hauber. He hopes MRI studies can help reveal what happens neurologically when birds see such an important object. These peculiar plastic eggs, increasingly different from those of the robin, can be invaluable tools in laboratory experiments to probe what birds do when they look at their nests.
[ad_2]
Source link