Science news in brief: From slow sleeping hummingbirds to warring woodpeckers

Fast hummingbirds are slow sleepers

Hummingbirds have the fastest metabolisms among vertebrates, and to fuel their lifestyle, they sometimes drink their own body weight in nectar each day. But the hummingbirds of the Andes in South America take that extreme lifestyle a step further.

Not only must they work even harder to hover at altitude, but during chilly nights, they save energy by going into exceptionally deep torpor, a physiological state similar to hibernation in which their body temperature falls by as much as 50F (10C). Then, as dawn approaches, they start to shiver, rocketing their temperatures back up to 96F.

Now, Andrew McKechnie, a professor of zoology at the University of Pretoria in South Africa, and his colleagues are reporting in Biology Letters that the body temperatures of Andean hummingbirds in torpor and the amount of time they spend in this suspended animation vary among species, with one particular set of species, particularly numerous in the Andes, tending to get colder and go longer than others.

They also report one of the lowest body temperatures ever seen in hummingbirds: just under 38F.

On a trip to the Andes about five years ago, Blair Wolf, a professor of biology at the University of New Mexico and an author of the new paper, and his colleagues captured 26 of the little birds for overnight observation. They measured the hummingbirds’ body temperatures as they roosted for the night and found that almost all of them entered torpor, showing a steep decline in temperature partway through the night.

They also kept track of the birds’ weights, because hummingbirds, like many other birds, lose weight between dusk and dawn, as they burn through the calories they have consumed during the day.

These birds were held in captivity overnight, but McKechnie says he thinks that in a natural setting, there is more to learn about how hummingbirds save energy.

There are stories of hummingbirds in the Andes that will enter a cave during cold spells and not emerge for several days, a pattern that, if confirmed, would suggest that the birds are capable of hibernation, he notes. Similar to torpor, hibernation saves an organism energy, but it goes on longer than a single night.

“The extent to which birds can save energy by going into torpor might well affect how well they do at these high altitudes,” McKechnie said.

— Veronique Greenwood

The hidden history baked into a cooking pot

Sure, astrophysicists have big telescopes, and oceanographers use underwater robots, but some researchers get to cook venison, lots of it, in the name of science.

A team of archaeologists and chemists recently released a report in the journal Scientific Reports describing how they had spent a year cooking a variety of meals in clay pots, and then examining the residues left behind. The researchers found that while some residues traced just the last round of ingredients, others reflected the long-term cooking history of each pot. By documenting the results of these experiments, the team hopes to help other scientists reconstruct ancient culinary practices.

Although preparing and consuming food are integral parts of the human experience, culinary traditions often get lost in the record, said Jillian A Swift, an archaeologist in Honolulu and one of the co-authors.

One way of getting at food practices over time is to look at what’s left behind after a meal. As they are used, cooking vessels naturally build up organic residues such as charred bits, thin coatings known as patinas, and absorbed fats.

Swift and her colleagues designed a culinary experiment using unglazed clay pots from central Colombia. Clay can absorb food residues and therefore provides a record of past meals, said Melanie J Miller, an archaeologist at the University of Otago in New Zealand and another co-author. But that is the case only if the clay is unglazed, she said, adding, “When you have a glaze on a pot, it serves as a barrier.”

Seven members of the research team volunteered to cook. Each archaeologist-cook received a pot and prepared the same meal in it once a week for 50 weeks. Each then switched to a different meal for an additional one to four weeks. The preparations were based on wheat and maize. Venison also made an appearance in three of the meals.

Much can be learned from studying these leftovers, said John P Hart, an archaeologist in Albany, New York, not involved in the research: “It’s a way to get a better understanding of how people lived in the past and what they ate.”

— Katherine Kornei

Extinction is not inevitable. These species were saved

The Przewalski’s horse is the only horse species that has never been domesticated, and it also managed to narrowly escape a brush with extinction.

By 1969, agriculture, hunting and a string of severe winters had caused the species to disappear from its last range in Mongolia. Some horses survived in captivity, but in the 1960s, they were being inbred to the point of no return. The horse was saved, however, by a captive breeding program in zoos and by conservationists who reintroduced it to Mongolia in the 1990s. Today, more than 760 Przewalski’s horses roam Mongolia.

As the horse’s story exemplifies, extinctions are not inevitable. Since 1993, conservation efforts have saved up to 48 mammal and bird species from extinction, a new study published last week in Conservation Letters says. Without such efforts, extinction rates for mammals and birds over the past 27 years would be three to four times as high.

In general, wildlife is disappearing rather than rebounding. From 1970 to 2016, populations of nearly 4,400 species declined by an average of 68 per cent, according to a report also published last week by the World Wildlife Fund. A study published in June found that mass extinctions are accelerating and that 500 species are likely to become extinct over the next 20 years.

“It’s nice to have these positive stories to show that, actually, we can make a difference,” said Rike Bolam, a postdoctoral researcher in biodiversity policy at Newcastle University in England, who led the study on Przewalski’s horses. “There is so much negative press about biodiversity loss, but the knowledge that we can turn things around, even if it’s just for a small number of species, is quite powerful.”

Many species, however, are still critically endangered. At last count, for example, only six vaquita — the world’s smallest porpoise, which are killed as bycatch in illegal fishing in Mexico that is driven by demand in China — still exist.

— Rachel Nuwer

How old is this ancient vision of the stars?

The Nebra sky disk has been hailed as the oldest known representation of the cosmos. Uncovered by looters in 1999 and then recovered in a sting by archaeologists and law enforcement a few years later, the bronze artefact, inlaid with gold decorations of the night sky, has provoked heated debates.

Now, a pair of German archaeologists are calling into question the disk’s age and origin.

The disk had been judged to be about 3,600 years old, dating it to the Bronze Age. The looters who uncovered it said it was buried on a hilltop near the town of Nebra in Germany, next to weapons from the same era.

Rupert Gebhard, director of the Bavarian State Archaeological Collection in Munich, and Rudiger Krause, a professor in Frankfurt, now say that the disk is a product of the Iron Age, making it about 1,000 years younger. They also say the disk was most likely moved by looters to the Nebra site from another location, meaning it may not be associated with the other artefacts or Nebra itself, according to a new study. “We regard the disk as a single find, as a single artefact,” Krause said.

The State Museum of Prehistory in Halle, Germany, which exhibits the Nebra sky disk, called the team’s conclusions “demonstrably incorrect.”

— Becky Ferreira

In this woodpecker kingdom, war is a spectator sport

Every fall acorn woodpeckers stash as many as thousands of acorns in holes drilled into dead tree stumps in preparation for winter. Guarding these “granary trees” against acorn theft is a fierce, familial affair. But all hell breaks loose when there are deaths in a family and newly vacant spots in prime habitat are up for grabs.

The news travels fast. Nearby woodpecker groups rush to the site and fight long, gory battles until one collective wins, according to a new study in Current Biology. These wars also draw woodpecker audiences, who leave their own territories unattended, demonstrating the immense investment and risks the birds are willing to take in pursuit of better breeding opportunities and intelligence gathering.

“I think these power struggles are major events in the birds’ social calendars,” said Sahas Barve, an avian biologist at the Smithsonian National Museum of Natural History and lead author of the study. “They’re definitely trying to get social information out of it.”

Acorn woodpecker societies are complex. Each family consists of up to seven adult males, often brothers, which breed with one to three females, often sisters but unrelated to the males. They live with nest helpers who are typically their offspring from previous years. Together they defend 15-acre territories, on average, encompassing one or more granaries in the oak forests along coastal Oregon down into Mexico.

In California’s Hastings Reserve, Barve and his team follow 50 acorn woodpecker groups. In 2018 and 2019 the researchers observed three power struggles, all involving female vacancies. Each combat site lured up to 50 helper females representing a dozen or more competing coalitions. The birds spread their wings to put on a show of superiority and strength and engaged in incessant bickering; at times the war got bloody.

Barve and his team suspect that spectator birds show up in order to understand other birds around them. “They must immediately see all the big sibling coalitions in the area, gauge their body conditions and the quality of the territory they’re fighting over,” he said.

As the research team continues to understand how and why woodpecker societies make these decisions, Damien Farine, a behavioural ecologist at the Max Planck Institute of Animal Behavior in Germany, said that the study shows the value of tracking individual birds.

“With studies like this one, we’re starting to understand how populations are structured as an outcome of all its individuals’ behaviours,” he said.

— Priyanka Runwal

© The New York Times