Many different animals live in tree hollows or tree holes, which can be created by fungi, animal excavations or lightning.

Rot holes

Rot holes are one of the most common types of tree hollows.

A rot hole begins to form when the bark of a tree becomes damaged - possibly by human or animal activity, heavy winds or lightning.

Once the bark of a tree is damaged, fungi attack the underlying layer of sapwood, and eventually the inner heartwood. Beetles burrow into the wood, helping the fungi to spread.

The action of the fungi and the beetles causes the damaged area to grow until a hole eventually forms. This hole is known as a rot hole.

If a rot hole is exposed to rain, it can become filled with water. This water can accumulate, particularly if rotting leaves line the tree hole, or it can drain through the rotting wood.

Some rot holes are in positions where they are sheltered from rain, and so remain even when it rains heavilty. Others become filled with rainwater. The water may drain away through the rotting wood or it may accumulate in the hollow, especially when the tree hole is lined with rotting leaves.


A pan is another very common form of tree hollow.

Pans are shallow depressions in the surface of a tree that are lined with undamaged bark.

They develop when trees are crowded together, causing trunks and branches to become distorted.

Pans are usually shallow, and while they can hold water, the water evaporates quickly.

Wet Tree Hollows

A tree hollow that is filled with water forms an aquatic habitat for many different kinds of animals.

These include protozoa, small crustaceans, rotifers, springtails, mosquitoes and fly larvae.

Rotting wood and leaves provide the animals that live in these holes with many nutrients.

Tree holes in the tropics dry out periodically. Therefore, the animals that live in them must either have very short lifespans or be able to live through dry spells.

Dry Tree Hollows

Various birds, mammals, insects and spiders live in dry tree hollows.

Some dry tree holes are made by woodpeckers. Other birds will sometimes take over woodpecker holes after the woodpeckers have left.

Many small mammals will use dry tree hollows to shelter themselves from predators, or from snow and rain. Squirrels and bats may nest in holes in high branches.
A dry hollow can become enlarged by the action of fungi, filled with water, and transformed into a wet tree hole.