So did a little googling and found this gem of an article from 2007 explaining the why and wherefores. The main reason being that they are a spillover from the Borivali National Park, which also has an approx 80 acres fenced area for Lions and Tigers.
50 People Killed Since 2000, 23 Leopards Caught Roaming The City World's Highest Leopard Density
The leopards stray from Sanjay Gandhi National Park (SGNP), commonly known as Borivali National Park, 103 square kilo meters of jungle (for comparison Kumana National Park is 181 square kilo meters) that lies surrounded by the city's overcrowded areas and desirable northern suburbs. The only large protected area to be located inside a major metropolis, SGNP holds more than 1,000 species of plant, 251 species of bird - more than in the entire UK - and 40 species of mammal. It also boasts the world's highest density of leopards.
The Park's two major lakes, Vihar and Tulsi, provide eight per cent of Mumbai's drinking water, while its forests act as a vital sink, absorbing the city's choking pollution. Some call SNGP the "lungs of Mumbai", and without it, scientists believe the city would drown in its own poison.
The population of the leopard's natural prey-wild pig and chital deer-began to dwindle. Faced with a food shortage, the world's most versatile felid took to hunting on the fringes of the slum villages, preying largely on the stray dogs that roam in packs among the uncollected rubbish.
Hunting so close to human habitation have meant that some leopards have lost their natural fear of people, leading to incidents where children have been snatched from their homes while their parents slept.
Given that the human disturbance in the park had been reduced, why then have the attacks on humans increased so sharply over the past five years?
Most experts agree that one of the root causes for the trend was the closure by the building boom of important corridors that had previously allowed leopards to migrate and disperse to other suitable habitats. Hemmed in by development, young leopards seeking to establish their own territories had little choice but to move into industrial grounds and even gardens on the park's periphery.
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