Editor 's note : In our Behind the Scenes series , CNN correspondents share their experiences in covering news and analyze the stories behind the events . Here , Anderson Cooper goes to the Congo where he covered the killings of endangered mountain gorillas . Ten mountain gorillas reportedly have been killed in the Democratic Republic of Congo in the last year . NEW YORK ( CNN ) -- You hear them before you actually see them . Some branches snap just ahead of you . The adult male silverback grunts somewhere off to the side of you . He even pounds his chest . You approach slowly . Mountain gorillas have been used to seeing scientists for decades , but these are wild animals , and you have to be respectful . When you see them , it is shocking . I 've been visiting mountain gorillas since I was 17 -- I 've probably been about six or seven times -- but each visit is extraordinary . They are among our closest animal relatives , and when you stare into their eyes , you see the spark of intelligence . You know these are individuals , with personalities , thoughts and feelings . Each gorilla group or family is headed by an adult male silverback . They are massive creatures , weighing up to 500 pounds , and are fiercely protective of their brood . Around them baby mountain gorillas tumble and play . They beat their chests just like their father , though the display is far less impressive . If you look closely , you may notice some of the mountain gorillas have lost a hand or a foot . Poachers ' snares are a problem , even in a well-protected park in Rwanda I visited . There are about 700 mountain gorillas left in the world , according to Flora and Fauna International , an organization that acts to conserve threatened species and ecosystems , and they live in a lush forest that straddles Rwanda , Uganda , and the Democratic Republic of Congo . Watch a close-up view of a mountain gorilla » . In Rwanda and Uganda , where they 're well-protected , the mountain gorilla populations are thriving . They are major tourist attractions that bring millions of dollars each year to both countries . The real problem right now is in the Democratic Republic of Congo . For the last 10 years , there has been fighting in that country , and in the last year , according to the U.N. Educational , Scientific and Cultural Organization ( UNESCO ) 10 mountain gorillas have been killed , shot to death . We went to the Congo to find out why those mountain gorillas were murdered . And the answer is we just do n't know . Because of the fighting , the mountain gorillas are completely cut off . The rangers who protect them have had to flee the park , and no one 's been able to check up on the gorillas . What we do know , and what is so sad , is that these gentle giants trust us . You see it when you sit with them , when they allow you to come so close . They 've been taught that man wo n't hurt them . This year , in the Congo , the gorillas have been lied to . E-mail to a friend .
Conservation organization says Ten mountain gorillas are left in the world . 700 mountain gorillas have been killed in the Congo in the last 10 years , CNN agency says . Mountain gorillas weigh 700 .