This weekend the RSPB's vigil for the capital's house sparrows in Bernie Spain Gardens on the South Bank draws to a close.
The Bernie Spain Gardens house sparrow colony has some 30 birds. At weekends throughout the autumn the RSPB has been running a special viewing point to allow tourists and locals out for a riverside stroll to learn more about these endangered birds.
The RSPB says that a report released last week concluded that house sparrows are in serious decline because of a lack of insects. The falling number of sparrows and shortage of insects suggests London is becoming a sterile place for wildlife.
Once a common sight, sparrows are already absent from many parts of central London.
"We can prevent London from becoming a wildlife free zone," says the RSPB's Tim Webb.
"Imagine a world with no insects and no birds; it would only be a matter of time before there were no people too."
"House sparrows have sent us an end of year warning that we ignore at our peril. The good news is that there's plenty individuals can do to help. Come and chat with our volunteers and staff at our sparrow watch or visit our Homes for Wildlife web pages."
"We can't believe how many people seem to have taken these few remaining birds to their hearts. This is our final weekend at Bernie Spain Gardens. Help us end our sparrow-watch on a high by coming to see us."