“Keep out or I'll chase you out! This is my property!” You hear this every spring. It is a long musical sound —a bird song! Birds use their songs to communicate different messages to one another. People who study bird sounds are learning their meanings.

    Usually it is the male that sings. Early in spring he sings to say that he has picked out a piece of property. He sings to attract a female of his same kind. Together they will raise a family in his territory (领地). He sings to tell all other birds of his kind to keep out.

    Each kind of bird has its own type of song. Cardinals sing something that sounds a little like “What cheer, cheer, cheer.” Towhees sing, “Drink your tea.”

    Most of the time, birds pay attention only to the songs of birds of their own kind. Cardinals answer cardinals, and song sparrows answer song sparrows. A cardinal knows that a song sparrow will not try to steal its mate. So you can see one reason why a cardinal may chase away another cardinal but will not bother a song sparrow.

    Most different kinds of birds eat different things. To find enough to eat, a bird needs a big piece of land to search in. Many kinds of birds have some ways of dividing up the land into territories. Song sparrows, cardinals ovenbirds, and white-throated sparrows are some of the birds that have territorial systems.

    Especially in early spring, birds work out the boundaries between their territories by singing “keep out” threats and by chasing and fighting each other. The birds continue singing to tell females that they have set up territories. Neighboring birds seem to agree that there are make believe fences between their pieces of property. Then they do not have to waste energy chasing each other instead of taking care of their young.

    Scientists guessed that some birds could recognize their neighbors by small differences in their songs. Two scientists who studied white-throated sparrows found that these birds can even tell the difference between songs of individual birds of their own kind. White-throated sparrows have songs that seem to say “I'm your neighbor” or “I'm a stranger” or “I'm your neighbor to the west.” Other kinds of birds could tell neighbors from strangers by their songs, too.

    Soft winds blew throughout the Windy City today. We welcomed the winds, as it was another hot day in Chicago. The wind blew, bringing us some coolness—and making the weather not that hot. But it was a beautiful summer day with a blue sky.

Chicago is a great city for eating, and we have enjoyed tasting the different foods. Last night, we tried one of the city's most famous foods: deep-dish pizza. Chicago claims credit for the rich and cheesy thick-crust pizza, covered with a sweet tomato sauce. We topped it with olives and green peppers.

       We were touring the city, mainly looking for delicious local foods. Today, we enjoyed a Polish specialty at lunch: Pierogis, an Eastern European dumpling-like dish, filled with foods like potatoes, cheese, mushrooms, cabbage and meat. Polish immigrants started settling in Chicago in the 1850s, and the city has one of the largest Polish communities in the U.S.

    We took a break from exploring the city to talk with some of you! Ashley and Caty logged onto the Internet for an on-the -road version of TALK2US. We spoke to an English teacher in Tokyo, Japan, and a graduate student in India.

Meanwhile, Adam searched for some locations around the city to shoot some video. He chose a spectacular spot: Navy Pier, Chicago's most-visited attraction. The winds from Lake Michigan keep visitors cool, and the view of the Chicago skyline never fails to impress. In fact, the view made all of us head over heels!

    Our time in Chicago has come to an end. Tomorrow, the true journey begins, as we pass through Illinois and into Missouri via Route 66. Springfield, the home of Abe Lincoln, and St. Louis, the “gateway to the West,” wait for us.

    Songs that make our hearts happy can make them stronger too, US researchers reported on Tuesday.

    They found that when people listened to their favorite music, their blood vessels (血管) dilated in much the same way as when they are laughing, or taking blood medications.

    “We have a pretty impressive effect,” said Dr Michael Miller, director of preventive cardiology (心脏病学) at the University of Maryland Medical Center in Baltimore.

    “Blood vessel diameter improved,” he said.“The vessel opened up pretty significantly. You can see the vessels opening up with other activities such as exercise.” A similar effect is seen with drugs such as statins.

    When blood vessels open up more, blood flows more smoothly and is less likely to form the clots (凝块) that cause heart attacks and strokes. “We are not saying to stop your statins or not to exercise but rather to add this to an overall program of heart health,” said Miller, who presented his findings to a meeting of the American Heart Association in New Orleans.

    Miller's team tested 10 healthy, non-smoking men and women, who were told to bring their favorite music.They spent half an hour listening to the recordings and half an hour listening to music they said made them feel anxious while the researchers did ultrasound tests designed to show blood vessel function.

    Compared to their normal baseline measurements, blood vessel diameter increased 26 percent on average when the volunteers heard their joyful music.Listening to music they disliked — in most cases in this group — blood vessels narrowed by six percent, Miller said.

    Miller said he came up with the idea after discovering that laughter caused blood to literally flow more smoothly. “I asked myself what other things make us feel really good, besides calories from dark chocolate of course.Music came to mind. It makes me feel really good,” he said.

    Most of the volunteers chose country music but Miller said the style is not so important rather than what pleases each individual.

    Andrew Jackson has been sitting pretty on the $20 bill for 87 years. Is it time to bring some new blood to the banknote?

    The non-profit organization called Women on 20s is campaigning to put a woman's face on American money. Barbara Ortiz Howard, the company's founder, would like to see a woman on the $20 bill by 2020.That year marks the 100-year anniversary of the 19th Amendment to the United States Constitution, which gave women the right to vote.

    Howard got the idea when she realized that her daughter had no everyday reminders of famous women in history. She asked her friend Susan Ades Stone, a journalist, to join her cause. “Part of the aim is to educate as many people as possible about as many women as possible,” Ades says. “We want to see how many people we can reach.”

    American money values the successes of former presidents and founding fathers. Currently, there are only two women on money: Susan B. Anthony is the face of the rare dollar coin, and Sacagawea can be seen on the gold dollar coin. There are no women on paper bills.

    With help from writers and historians, Howard and Stone came up with a voting list featuring 15 important women. Ades says there is a standard for choosing candidates. They look at the women's contributions to our world, and at what challenges they faced.

    More than 72,000 people have voted so far in the poll. Ades says the competition has narrowed to a “very close race”, but won't say who's in the lead. After two rounds of voting, Women on 20s will send their campaign to the White House for consideration. The final decision is up to the Treasury Secretary, Jack Lew. Lew is unlikely to make a change without the president's approval. But last year, when a little girl asked the president why there aren't any women on US currency, he said that adding a woman is a “pretty good idea”.

    I had reached the age of twenty-eight. Still, I doubted the letter from my past would make it to me, all these years later. It was a simple creative writing assignment from when I was eighteen. The teacher collected our letters to our future selves in self-addressed envelopes with stamps and promised to mail them ten years later. Yet so much time had passed. Would he even remember?

    Thinking back on the letter, I vaguely recalled giving my future self some advice. When you're eighteen years old, twenty-eight seems like a grown-up age but I wasn't feeling as grown up as I believed my younger self had expected me to be.

    When the letter finally reached me, I opened it eagerly. It began," How much do you bet this letter will never get to you "It continued to greet me casually as if we were having an IM (instant messaging) chat. My eighteen-year-old self was so stressed! As a senior in high school, facing the SATS and college applications, I was apparently not quite happy and hoped I wouldn't worry so much in the future, and that I wouldn't forget to be present and enjoy my life!

    Contrary to my belief, my eighteen-year-old self did not have any demands of me, or expectations I might have failed to meet. Instead, she wrote," I'll stand by whatever you do. Even if you are not who I'm imagining now, I'll support you, because maybe who I' m imagining is someone else, and you are-well you're not someone else, you're me."

    I was blown away, and tears welled up in my eyes at this self-acceptance through time. I had put a lot of pressure on myself to be the best version of myself that I could be. However, I came to realize what I would have accomplished in ten years' time would pale in comparison to how I'd feel and who I'd be.

    What would it be like to live on Mars? Volunteers are spending eight months in an area that looks much like the surface of Mars. They are isolated(孤立)high on top of Mauna Loa, a volcanic mountain on the Big Island of Hawaii, living on a simulated(模仿的) or make-believe, Mars Base.

    The project called HI-SEAS is in the charge of Kim Binsted. She says this wild environment is as close to Mars as you can find on Earth. Because it is so high, the land is not warm or rich with plants, like the rest of Hawaii.

    "You will see there is really no visible plant life or animal life. And you have got this wonderful volcanic material."

    Mauna Loa, 2,500 meters above sea level, is geologically very similar to Olympus Mons on Mars and almost as tall as the Martian mountain. When measured from its base, deep in the ocean, Mauna Loa is the second largest mountain in our solar system, after the one on Mars.

    The six member HI-SEAS crew is mostly self-sufficient. Food and supplies are brought to them. But the individuals bringing those supplies cannot communicate with volunteers inside the habitat, or base.

    Kim Binsted says this experiment looks at how the astronauts get along with each other. "We study how well they work together, how we can keep them happy and supported, and not wanting to kill each other over these long durations (期间)."

    Crew members communicate with the outside world through e-mail and blogs. They also produce video on the YouTube website, like this one from mission commander Martha Lenio. "I am really enjoying this opportunity to live here and pretend that I'm on Mars and get to learn all sorts of new skills." One of them said. "Whoever gets there first, the trip will not be easy", says Kim Binsted, "It is going to be challenging."