An iguana that froze lies near a pool after falling from a tree in Boca Raton, Florida. Credit:Frank Cerabino Iguanas, which can be as long as 1.8 metres, are not native to South Florida. They have proliferated in the subtropical heat, causing headaches for wildlife managers. It took a prolonged cold spell to significantly reduce their population in 2010. (The same cold snap also resulted in the deaths of many invasive Burmese pythons.) Iguanas climb up trees to roost at night, said Ron Magill, communications director for Zoo Miami. "When the temperature goes down, they literally shut down, and they can no longer hold on to the trees," he said. "Which is why you get this phenomenon in South Florida that it's raining iguanas." Green iguanas, like all reptiles, are cold-blooded animals, so when the temperature falls to a certain level iguanas become immobile, said Kristen Sommers of the Florida Fish and Wildlife Conservation Commission. Under 10 degrees, they become sluggish. Under 4 degrees, their blood stops moving as much, Sommers said. Florida's average temperature in winter is around 18-21.

A car sits in frozen floodwaters from Boston Harbour on Long Wharf in Boston. Credit:MICHAEL DWYER The larger the iguana, the greater its chance of survival, Magill added. "Even if they look dead as a doornail - they're grey and stiff - as soon as it starts to heat up and they get hit by the sun rays, it's this rejuvenation," he said. "The ones that survive that cold streak are basically passing on that gene." A Boston firefighter wades through flood waters from Boston Harbour on Thursday. Credit:MICHAEL DWYER He suspects that, within a couple of decades, iguanas will creep north because they will be able to withstand colder climates.

On Thursday, Cerabino poked at the animal with his pool skimmer, hoping to wake it up. In a previous backyard encounter with a paralysed iguana, he said, picking it up with a shovel did the trick. Front loaders dump snow into a melter while clearing the apron around Terminal B at LaGuardia Airport, New York. Credit:JULIE JACOBSON But he didn't move. "But he's probably still alive. My experience is that they take a while to die." So he opted for leaving the iguana where it was, "and dealing with it when I come home." Manatees, or sea cows, huddle up at the Three Sisters Springs in Crystal River, Florida, to stay warm on Thursday. Credit:Luis Santana

"He'll either get enough sun where he'll revive himself and get himself up the tree, or he'll continue to freeze and turn dark brown - almost black - and I'll know he's dead," Cerabino said. And the iguana lived but the winter storm sweeping across parts of the US has prompted animal rescue organisations and local authorities to issue warnings about giving pets shelter, with dogs left out to freeze to death in the cold. Three dead thresher sharks were found stranded, completely frozen, on a beach in Massachusetts, the Atlantic White Shark Conservancy said. One of the strongest winter storms on the East Coast in modern history, it has pummeled cities with snow and sleet, forcing schools and businesses to close, and cutting power to some 80,000 premises. Thousands of flights were cancelled, firefighters scrambled to rescue motorists from flooded streets in Boston and 500 National Guard troops were mobilised in the Northeast, including New York, to assist with emergency response. The storm was powered by a rapid plunge in barometric pressure that some weather forecasters called a 'bombogenesis' or a "bomb cyclone."

The wintry weather has been blamed for at least 14 deaths in the past few days, including road accidents due to the dangerous driving conditions. In South Florida, the cooler temperatures also affect sea turtles, manatees and other creatures that hang out in trees. Loading "Bats sometimes will fall out of the roost of trees when we have a pretty cold snap," Sommers said. New York Times, agencies