As you stop to admire the new leaves on a tree this spring, you may notice holes carved in trunks and branches. Who made these cavities, and why?

Smaller pits may be the work of insects, but most of the larger holes were created by woodpeckers, either for feeding or nesting. Here’s a quick guide to some of their handiwork.

Holes for Feeding

Many woodpeckers carve into trees to find food in the form of insects or sap. Here are some of the species you might see.

Pileated Woodpeckers

Master excavators, these huge birds have chisel-shaped beaks and even feathery tufts over their nostrils to protect them from wood shavings. To get at carpenter ants—their preferred food—they dig deep, rectangular-shaped holes often a foot or more in height. Look for piles of wood chips on the ground below, like the shavings on the floor under a carpenter’s workspace.

Hairy, Downy, and Red-bellied Woodpeckers

Smaller birds typically make smaller holes. Those of hairy woodpeckers are usually no more than ½” wide. These birds tear off bark and drill in search of insects such as beetle larvae, making a wavy pattern as they weave back and forth on a trunk. Downy woodpeckers prefer to probe thinner branches and the stems of reeds. Red-bellied woodpeckers also peck into trees, and are more likely than some other species to store seeds in tree crevices.

Yellow-bellied Sapsuckers

These birds make unmistakable horizontal rows of small holes, often in sugary trees such as maple and birch. Sap collects in these wells, and, true to their name, sapsuckers slurp it up with their brush-like tongues. They don’t just drink tree sap, though. Insects that are attracted to the sugary liquid become a protein-rich meal for yellow-bellied sapsuckers.

Holes for Roosting and Nesting

Woodpeckers also dig deeper cavities for roosting (or resting) and nesting. In order to keep out big predators, they carve entrances that are just large enough for them to come and go. The diameter of an entrance can help you figure out which bird is using it.

A few bird species, such as black-capped chickadees and red-breasted nuthatches, also make shelters in trees. However, they only use dead wood that is relatively soft and easy to carve.

An Important Resource

These excavations aren’t just useful to the woodpeckers. Birds such as eastern screech owls, wrens, and bluebirds need pre-existing cavities for their nests, and they often use woodpecker holes. Flying squirrels and mice shelter in them, too.

The sap-filled wells of sapsuckers are an important food source for mammals, insects, and birds. In particular, ruby-throated hummingbirds rely on them in the early spring, before the flowers have bloomed.

Keep an eye out for holes in trees. Next time you spot one, you may have found a bedroom, a cafeteria, or a nursery!