Every summer, the calls of thousands of swamp sparrows can be heard across North America's wetlands. These little brown birds know only a few songs, but they know them very well. In fact, their musical set list probably hasn't changed much for centuries.

Like humans, baby swamp sparrows learn to communicate by copying adults. From a young age, they learn to copy, or mimic, songs sung by their elders. “Swamp sparrows very rarely make mistakes when they learn their songs,” says biologist Robert Lachlan. In fact, their mimicry is so accurate that the music changes little between generations.

Just like children, the sparrows don't remember every song they hear. Lachlan says. “They don't just learn songs at random; they pick up commoner songs rather than rarer songs.” In other words, they learn songs they hear most often. It's an example of a strategy that scientists call conformist bias. Until recently, this learning ability was thought to be special only to humans.

Between 2008 and 2009, Lachlan's research team recorded the calls of 615 male swamp sparrows across the northeastern United States. The researchers used computer software to break each song into a collection of notes, or syllables. They then measured the differences between the tunes.

The research revealed that only 2 percent of male sparrows sang a different song from the standard tune. The combination of accurate mimicry and conformist bias allows the birds to create traditions that last for centuries. “With those two ingredients together, you end up with traditions that are really stable,” says Lachlan. “The song-types that you hear in the marshes of North America today may well have been there 1,000 years ago.” Lachlan's study is also among the first to measure the longevity of song traditions within a bird species.

The findings are really exciting, says scientist Andrew Farnsworth. He hopes that future research will evolve from these studies. For example, scientists may be able to identify how other animals are able to preserve their cultural traditions. “Seeing the potential for it in other organisms is super cool,” says Farnsworth.

Four Wild Animal Species Were Endangered

Maybe you can still see them at the zoo. But that doesn’t mean they’re doing alright in the wild.

Tigers

All six tiger species are endangered, with Sumatran tigers and South Chin tigers at a seriously endangered status. The main reasons for their population decline are illegal hunting and destroyed habitats(栖息地), as humans clear forests to gather timber（木材）and build roadways. Only about 3890 tigers presently live in the wild.

Ground squirrels

That’s right, even squirrels are endangered, specifically the San Joaquin ground squirrel. Native to California, USA, these guys have been disappearing since 1979 on account of the construction and human development going through their habitat. Their total population is unknown, but it could be anywhere between 124000 and 413000.

Giraffes

The International Union for the Conservation of Nature recently put giraffes at a vulnerable(脆弱的) status, the level just before endangered. The giraffe population has declined 40 percent in the last 30 years, primarily due to loss of habitat and illegal hunting. Some giraffes are killed just for their tails, which are considered status symbols in Africa.

Asian elephants

The main threat to Asian elephants, one of the most intelligent animals, is their shrinking habitat. As the human population grows, people invade their land to build roads and railway tracks. Elephants in Myanmar are at an especially high risk for being captured and traded or used illegally in the tourist industry. Fewer than 50000 are left on the entire continent.

How to Bring Birds Back to Your Garden

Bird numbers have fallen by 25% over the last few years. Do you want to encourage feathered friends back to your outdoor living space? Here are some useful tips for you.

*Try to position your feeders where birds will have a 360° view of the area. 【小题1】 Because the birds become sitting ducks for predators (食肉动物) such as cats and sparrow hawks. Sometimes, birds get carried away without noticing predators approaching.

*It’s important to keep bird equipment clean and free from dropping. 【小题2】 Also, make sure food isn’t left out for too long. That can lead to potentially serious diseases, such as Avian Pox, which spreads rapidly within the bird population.

* 【小题3】 They only rely on food from your garden when their natural resources are low, but it’s important to always have something on the menu, so they remember where to go when times get tough.

*Try to put out a range of food. Sunflower seeds are a popular choice. Nuts are good too, but make sure they are never salted. 【小题4】

*Choose where you put your nest box carefully. Place it out of the prevailing (盛行的) southwesterly wind and away from direct sunlight to avoid them overheating. 【小题5】 Because it could be destroyed by nervous new parents.