Trilobites: The Green-Feathered Terror That Slaughtered Bats in Spain


The greater noctule is the largest bat in Europe. It is listed as “vulnerable” on the threatened species list, but for many years these winged mammals found shelter in the hollows of trees at María Luisa Park in Seville, Spain.

Then a few years ago, they started to turn up dead.

The corpses were savaged, with holes torn in their wings, scientists who study the colony discovered. Many of them were nursing pups; one corpse was a pregnant female. Two bats that managed to survive were so injured that they could not climb or fly back up to their nests. What was behind the attacks?

The culprit turned out to be another park inhabitant: beautiful, invasive rose-ringed parakeets who also make their homes in tree hollows.

When scientists first began studying the bats more than 15 years ago, they didn’t pay much attention to the birds. But now, there are thousands of them, and they are pushing the bats out of their holes, killing some, and taking over the trees where noctules once lived.

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Researchers found that parakeets had taken over the hollows where the bats lived, and soon observed the birds attacking the winged mammals.CreditDailos Hernández-Brito

The first attack Mr. Hernández-Brito saw was against a pregnant female bat. He and collaborators then saw more than 30 attacks in the last two years and collected 20 bodies presented in the current study, though there likely have been many more deaths.

Today, the number of trees that noctules live in has dropped by 81 percent since the researchers first began keeping track, with the parakeets taking over the bats’ old homes. Although it is difficult to get exact numbers for the bat population, it appears to have roughly halved since the work began, bringing their numbers down to about 250. The bats are also living in tight quarters, with double the old number occupying a given hole.

The scientists helped the city government come up with an eradication plan to get rid of the parakeets in 2016, but at the last moment, officials canceled the plans. The parakeets are popular, and citizens argued there must be some other way besides killing them — perhaps artificial nest boxes for the bats. However, the bats do not take to such nests well, and the situation is growing urgent.

The parakeet population will surpass 3,000 this year. Dr. Carrete hopes that this paper will help provide evidence that if the noctules are to be saved, eradication is the only option.

More reporting on bats and birds

Trilobites: What Makes Some Hair Curly? Not Quite What Scientists Thought


They were testing two ideas about curliness. The first theory is that as a curling strand is constructed, the cells on one side divide more quickly than those on the other. This would generate a curve in the direction of the side with fewer cells. The other involves the differences between the two types of cells that make up wool fibers: orthocortical cells, which tend to be longer, and paracortical cells, which are shorter. In this theory, a certain proportion of longer cells to shorter cells, arranged on either side of the strand, generates a curl, with the ratio of the two defining the degree of curvature.

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A merino sheep’s hair magnified. On the bottom image, the orthocortical cells, which are usually longer, are colored in red, and the paracortical cells are in green.

Credit
AgResearch

As they examined their strands, they found that there are not fewer cells on the inside of a curve than on the outside, which countered the first theory.

But when they tested the second theory, they found that simply knowing the ratio of long cells to short ones did not allow them to precisely predict a fiber’s curl.

“What we were not expecting was that neither was completely accurate in terms of prediction,” said Dr. Harland.

That is because while orthocortical cells are longer than paracortical cells on average, in reality they each have a wide distribution of lengths. And there is some overlap between them: A long paracortical cell could be longer than a short orthocortical cell. This variation means it isn’t possible to make a direct connection between the number of each cell type and how much curl there is that holds for all strands, Dr. Harland said. You could not say that having 60 percent orthocortical cells and 40 percent paracortical cells will always lead to a 15-degree curve, for instance.

What they did find was that in any given strand, any orthocortical cell will always be longer than any paracortical. That reinforces the idea that the differences between them are linked to the curl.

The team’s findings may not map perfectly to our hair or that found on other mammals. But there is still quite a bit that we can learn by studying sheep’s wool.

“We take hair for granted,” said Dr. Harland, but it is an ancient adaptation, likely to have common developmental roots in the many creatures who sport it.

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