Housewife Aurora Cela was getting ready for bed one night this summer when her neighbor shouted "Bear, bear!" and a big black animal scampered through her back garden, around her house and down the street.
More than 30 American black bears have been sighted in and around the city of Monterrey in northern Mexico since April, some in gardens trying to drink from swimming pools and others in schools and on building sites as they seek food and water.
A housing boom in Monterrey, Mexico's richest city 225 km from Texas, risks destroying the officially endangered bears' habitats in the surrounding forested mountains. It is also accelerating Mexico's loss of primary forest that are disappearing at one of the world's fastest rates, environmentalists say.
"When I saw the bear, I felt like he was invading our land, but then I realized that it is us who are invading theirs," said Cela outside her new house, perched on a built-up hilltop, which until a few years ago was home to native oak and pine trees.
Hunting reduced the local black bear population by 80 percent until the mid-1980s, when they became an endangered species in northern Mexico. Laws passed in the 1990s made it a criminal offense to kill a black bear in Mexico, helping populations recover.
A construction worker was arrested in June for capturing a bear that later died of respiratory arrest caused by stress. The government has handed out leaflets across the city warning people not to feed or harm the animals.
Despite such laws and actions, the housing boom in an arid region threatens the bears once again, as Monterrey, one of Latin America's top business cities, benefits from close links to the world's biggest economy and US manufacturers locate to the Mexico border due to lower labor costs.
Despite the US housing and credit crisis, Mexican banks have almost no exposure to the slump and are instead enjoying a credit boom on the back of unprecedented economic stability.
"The appearance of the bears in such large numbers in the city is a sign we are cutting up their biological corridors. Groups cannot reach one another and mate, forcing interbreeding and a genetic breakdown," said Angel Tovalin, an environmental consultant to the federal governmental in northern Mexico.
Known as Ursus americanus and native to North America, there are some 600,000 black bears across Canada, the United States and Mexico, but the large populations of northern Mexico are dwindling to a only a few thousand as deforestation and cities destroy their habitats.
The bears, with black fur and brown muzzles, stand often over 6.5 feet (2 meters) tall, live off plants, fruits and nuts, as well as carrion. But deforestation and droughts in northern Mexico can force many bears to seek food in rubbish dumps on the edge of cities such as Monterrey.
Attacks on humans are extremely rare.
President Felipe Calderon has made ending Mexico's acute housing shortage a central focus of this presidency, vowing to build 1 million homes a year.
Nuevo Leon state and its capital Monterrey make up about 7 percent of that target, or about 70,000 news homes a year.
With excavators gouging out chunks of mountainside and pushing into the national parks that surround Monterrey, activists say corrupt politicians are allowing developers to build in protected areas.
State officials deny any wrongdoing and real estate promoters say they are meeting infrastructure and housing demands in a growing city with the necessary permits.
"We have been demonized as developers but we are working within the law. If building in mountains was such a terrible thing, Switzerland wouldn't exist," said Everardo Garza, head of Nuevo Leon's real estate chamber.