It's not only the abundance of food that attracts wild animals to cities.
They're usually several degrees warmer than the surrounding countryside.
And here in Rome, in December, one animal is taking full advantage of this extra heat.
And it's leaving it's mark.
In a single winter's day, ten tonnes of its droppings rain down on the city.
Starlings. In the evening, they come back to the warmth of the city after feeding in the neighbouring countryside.
They must return to their roosting trees.
But the first to do so are at the highest risk of being caught by birds of prey.
So, they wait for others to arrive. There's safety in numbers.
As daylight fades, the sky fills with a staggering one million starlings.
And then follows one of nature's great spectaculars.
How, or indeed why, they perform these marvellous aerobatics, we still do not fully understand.
Eventually, en masse, they brave the descent and fill the branches of their favourite trees.