Scientists have found further evidence that dolphins call each other by "name".

Research has revealed that the marine mammals use a unique whistle to identify each other. A team from the University of St-Andrews in Scotland found that when the animals hear their own call played back to them, they respond.

Dr. Vincent Janik, from the university's Sea Mammal Research Unit, said, "Dolphins live in this three-dimensional (三维) environment, offshore without any kind of landmarks and they need to stay together as a group. These animals live in an environment where they need a very efficient system to stay in touch. "

It had been long suspected that dolphins use distinctive whistles in much the same way that humans use names. Previous research found that these calls were used frequently, and dolphins in the same group were able to learn and copy the unusual sounds. But this is the first time that the animals' response to being addressed by their "name" has been studied. To investigate, researchers recorded a group of wild bottlenose dolphins, capturing each animal's signature sound. They then played these calls back using underwater speakers.

“We played signature whistles of animals in the group; we also played other whistles in their repertoire (曲目) and then signature whistles of different populations-animals they had never seen in their lives," explained Dr. Janik.

The researchers found that individuals only responded to their own calls, by sounding their whistles back. The team believes the dolphins are acting like humans: when they hear their names,   they answer.

Dr. Janik said this skill probably came about to help the animals to stick together in a group in their vast underwater habitat. He said, "Most of the time they can't see each other, they can't use smell underwater, which is a very important sense in mamma is tor recognition, and they also don't tend to hang out in one spot, so they don't have nests or burrows that they return to.”

Harbour seals may sound different than expected from their body size. Is this ability related to their vocal (声音的) talents or is it the result of an anatomical (身体结构上的) adaptation? An international team of researchers led by scientists from the Max Planck Institute for Psycholinguistics Nijmegen investigated the vocal tracts of harbour seals, which matched their body size. This means that harbour seals are capable of learning new sounds thanks to their brains rather than their anatomy.

Most animals produce calls that reflect their body size. A larger animal will sound lower-pitched because its vocal tract, the air-filled tube that produces and filters sounds, is longer. But harbour seals do not always sound like they look. They may sound larger —perhaps to impress a rival (对手)—or smaller—perhaps to get attention from their mothers. Are these animals very good at learning sounds (vocal learners), or have their vocal tracts adapted to allow this vocal flexibility?

To answer this question, PhD student Koen De Reus and senior investigator Andrea Ravignani from the MPI worked together with researchers from Sealcentre Pieterburen. The team measured young harbour seals’ vocal tracts and body size. The measurements were taken from 68 young seals (up to twelve months old) who had died. The team also re-analysed previously gathered harbour seal vocalisations to confirm their impressive vocal flexibility.

De Reus and Ravignani found that the length of harbour seals’ vocal tracts matched their body size. There were no anatomical explanations for their vocal skills. Rather, the researchers argue that only vocal learning can explain why harbour seals do not always sound like they look. “Vocal learners will sound different from their body size, but the size of their vocal tracts will match their body size. The combined findings from acoustic (听觉的) and anatomical data may help us to identify more vocal learners,” says de Reus. “Studying different vocal learners may help us to find the biological bases of vocal learning and shed light on the evolution of complex communication systems, such as speech.” “The more we look, the more we see that seals have something to say about human speech capacities.” adds Ravignani.

Migratory (迁移的) birds are specially adapted to find their way over extreme distances. Now, the new research of Kaspar Delhey and other researchers has discovered an unexpected way that migratory birds keep their cool during such backbreaking journeys: lighter-colored feathers (羽毛).

“We found across nearly all species of birds, migratory species tend to be lighter colored than non-migratory species,” said Delhey. “We think that lighter feather coloration is selected in migratory species because it reduces the risk of overheating when exposed to sunshine. Lighter surfaces absorb less heat than darker ones, as anybody wearing dark clothes on a sunny day can demonstrate! This would be particularly important for long-distance migrants that undertake extensive flights during which they cannot stop to rest in the shade.”

Delhey and his coworkers had been studying the effects of climate on bird coloration. Their earlier studies showed that, in general, lighter colored birds are found where temperatures are high and there is little shade. That’s in part because the birds’ lighter feathers help to keep them cooler in the hot sun. Then the researchers came across studies by others showing that some birds fly higher during the day compared to at night.

“Because flying higher is likely costly, these changes require an explanation,” Delhey says. “One possibility was that flying higher, where it is colder, would offset the heat absorbed by the feathers when the sun was shining.”

If so, they realized, another way to reduce the risk of overheating would be to absorb less solar radiation in the first place. It raised a question: have migratory species evolved (进化)   lighter feathers?

To find out, they did much research. Their findings show bird species get increasingly lighter as they migrate more. So, resident birds tend to be darker than short-distance migrants. Short-distance migrants are darker than bird species that travel farther. Delhey said the effect suited different types of birds. The same held true in waterbirds and ground-living birds, too.

The findings are another reminder of the important role of temperature and climate factors more broadly in the evolution of shaping the coloration of animals. They also help better understand the impacts of global warming and underlying adaptive evolutionary responses.