Sydney - Kangaroos are eating up grassland in Canberra, Australia's capital, threatening the survival of lizards, says a university study released on Friday.There are more than 300 kangaroos per square kilometre in grasslands around Canberra, leaving lizards and snakes without enough shelter to survive, Australian National University researcher Brett Howland said."When there are too many kangaroos, they overgraze grasslands until they are like a lawn, which leaves lizards with no shelter," Howland said in a statement from the university.Lizards depend on grass cover for both food and shelter, he said."They are an important part of food webs. They are food for birds and small mammals, and provide pest control by eating insects."Just because kangaroos are native, doesn't mean they don't do damage.""Many reptiles are under threat. Species such as the striped legless lizard are on the vulnerable list. They face possible extinction in the near future."However, there are millions of eastern grey kangaroos in Australia, making them one of the most populous large mammals in the world."Howland said kangaroos should be culled to fewer than 100 kangaroos per square kilometre. Around 1 500 kangaroos were killed in 2014, fewer than planned due to protests and legal challenges from kangaroo supporters.Scientists are testing a kangaroo contraceptive, but it is expensive at up to $2 000 per kangaroo. Shooting them costs about $300 each.