Most heronries are in trees, with the majority of nests at least 25m above the ground. However, reed-bed heronries are not unusual, and they will also nest on cliffs, bushes, sometimes even on buildings of bridges.
Heronries can reach a prodigious size: one at Great Snowden's Wood, near Brede in Sussex, contained around 400 nests in 1866.
The biggest heronry in Britain is currently at Northward Hill in Kent, an RSPB reserve. Numbers here have peaked at over 200 nests, but the current total is around 150.
It's not unusual for a single tree to hold as many as 10 nests.
It's quite normal for herons, disturbed at their nest, to regurgitate their last half-digested meal, an unpleasant experience for anyone unfortunate enough to be underneath the nest.
An increasing number of British heronries now also have little egrets nesting alongside the herons.
Herons are among the earliest nesters. It's not unusual for some birds to lay their first eggs in early February, though the normal start is early March, peaking at the end of the month.
The number of herons breeding in Britain and on the Continent has been growing steadily for many years.
They suffer badly in cold winters when ponds and streams are frozen for prolonged periods. The recent run of mild weathers has helped boost the population.