Sparrows pecking car tyres

Hi, I just noticed some rather odd behaviour of House Sparrows pecking at my car tyres. The cars been on the drive for a couple of days but I guess they must be finding food there, maybe from dried mud or does the car create a micro climate for inverts? There's clearly something desirable there as the Sparrows squabble over position quite a bit.  Anyone else experience this or can shed more light on the phenomenon?