Sandbath
House sparrows often take a "bath" in soil or fine-grained sand. It is believed that this is to remove parasites that live amongst their feathers. Parasites eat the feathers and suck the bird's blood.
Clean and scratch
Birds constantly preen their feathers in order to remove parasites (see the sparrows in the rear). This is important, as the parasites are common and far from harmless. They cause almost as many deaths among young birds as do preying animals.
