By Peter Bowes
BBC News, Los Angeles
They are cute, fearless and majestic. Emperor penguins from Antarctica, with their extraordinary mating rituals, have become the surprise superheroes of the summer US box office.
The film tracks the annual breeding habits of the Emperor penguin
The March of the Penguins, by French film-maker Luc Jacquet, is the second most successful documentary in US box office history after Fahrenheit 9/11.
A four-man film crew spent 14 months shooting the annual journey of Emperor penguins as they migrate single file to their traditional breeding ground in Antarctica.
The result is a stunning wildlife documentary that is captivating cinema audiences around the US.
"The more you think about it the more freakish the success of this movie really is," said Joe Leydon, a film critic for Hollywood trade paper Variety.
"For most Americans, when they hear the word documentary, it's like Superman hearing the world kryptonite - they involuntarily wince."
With the exception of features about pets doing stupid things, mainstream US television rarely screens animal programmes. Going to the cinema to watch wildlife is almost unheard of.
"For entire families to sit down and watch any kind of documentary together is unusual - to sit down and watch a wildlife documentary is more unusual," said Mr Leydon.
"I thought it was marvellous," said Wendy Turner, Curator of Birds at SeaWorld in San Diego. The California animal park is one of only two places in the world where Emperor penguins are kept in captivity.
A crew spent 14 months filming penguins in Antarctica
"I am in awe of the people who made this film and all the time they spent in the Antarctic to tell this story.
"Because Emperor penguins breed in deepest darkest Antarctic winter there hasn't been anything like this ever done - nothing that has ever documented the entire process. It was very exciting to see this."
The film's success is testimony to the positive word of mouth reputation it has generated over a number of weeks.
It is probably also down to some shrewd tweaking of the original film for the US market.
In the French version actors' voices speak for the penguins. The film, which features the same footage, focuses on one breeding pair and its offspring and attributes human emotions to the birds' behaviour.
The result, according Mr Leydon, was "a bit disconcerting... hearing real penguins, not CGI (Computer Generated Imagery) penguins or cartoon penguins, murmuring sweet nothings to each other."
He said the dialogue between the animals was "mushy and sometime comical."
For English-speaking audiences, the distributors felt that the style would not work and the dialogue was replaced by a more traditional commentary by Morgan Freeman.
"He literally could read the phone book and you'd want to listen to him," said Mr Leydon.
"This more distanced approach actually makes the story more compelling because this is not a sweet cuddly movie about sweet cuddly animals."
While carefully edited to avoid showing too much gruesome detail, the film does not shy away from the harsh realities of nature.
There are scenes where the penguins fall victim to predators or succumb to the excruciatingly hostile Antarctic environment.
"You don't see them actually mating - and I don't know if you really want to see hot penguin whoopee up on the big screen. There are enough hints though of how hard life is," adds Mr Leydon.
"I really wonder how many parents are going to be in for a rude shock when you have scenes where penguins die, offspring don't make it or penguins going beneath the ice trying to get food are gobbled up."
March of the Penguins has become an unconventional US hit
But it is the brutal honesty of the film that has won it so many plaudits. One scene shows a penguin being chased underwater by a leopard seal, one of the region's most deadly predators.
"Those of us that know about leopard seals know how incredibly aggressive and ferocious they are - and those close-ups of the jaws of the seal as it came up after the Emperor penguin were scary," said Ms Turner.
"This can only help people's appreciation of Emperor penguins - to learn this much detail about their life."