Pairs will defend the immediate area around the nest, and the male is quite aggressive on occasions to intruders. Nests are usually built in some form of hole such as in old trees, buildings, cliffs or chimneys. Birds may nest together, forming mini-colonies. Both male and female birds build the nest together, the foundation of which is made of sticks. The nest cup can be lined with grass, plastic and even wool pulled from sheep or found in the fields.
Copulation usually takes place at the nest site and is repeated over a series of days.
During the laying period, the male is extremely territorial and fights off any potential male intruder looking to take over the nest and fertilise the eggs. Eggs are laid over several days, and the female can sometimes begin incubation immediately. When this happens, the first egg hatches first and by the time the last chick emerges, the first one will be several days old and much stronger. This is a very important strategy should food be difficult to find. It ensures that the oldest chicks will survive.