Woodpeckers, Trees & Houses

July-August 2009

IF YOU HAVE WOODPECKERS, you know you have woodpeckers. They are holding on to trees and the house, hopping up vertical surfaces, hammering loudly and throwing woodchips everywhere. Everybody recognizes woodpeckers, of which there are more than 200 species worldwide. With strong toes for clinging, upright postures, stiff tails to brace themselves, thick necks and chisel-like bills, woodpeckers are custom built to take advantage of the myriad of microhabitats that trees offer.

The Basics
When woodpeckers become a nuisance by attacking trees and houses, it is helpful to look at biology to understand why the birds are acting as they do. Woodpeckers: An Identification Guide to the Woodpeckers of the World by Winkler, Christie and Nurney is the basic compendium for understanding these species. Any field guide to the birds of North America, however, will be useful for identification. The species accounts in the Birds of North America are the single best source to get an overview of an individual breeding species. If you don’t want to invest in the book, these accounts are available online on a fee basis (http://bna.birds.cornell.edu/bna).

Woodpeckers are like every other organism – they seek to reproduce and survive – and most of their behaviours can be related to these basic instincts. Start analyzing what the birds are doing and why, and maybe you’ll have an idea of how to outwit them.

Noise Makers, Not Singers
If you are going to reproduce, you need to communicate with a mate. Woodpeckers make noise, some lots of noise. They call, they hammer on deadwood and even metal, and make noise as they excavate holes. During territory establishment and maintenance, birds communicate to let others know that they have a territory staked out, and to attract mates. Woodpeckers make a wide variety of noises but do not sing.

Calls do not contain as much information as a song, so woodpeckers have learned to communicate by making other noises. Many woodpeckers hammer on dead, dry limbs to communicate. They seem to drum on specific branches because they produce the best sound. Ornithologists studying bird sounds call this the drumability of the material.

Drinking & Eating
To survive, woodpeckers must feed. Ontario species use four primary feeding methods: sapsuckers literally drink sap; flickers forage on the ground for ants; and the majority of woodpeckers forage for insects in trees by searching under bark and excavating holes. Many also glean for berries and buds.

Sapsuckers are a group of four species known for literally drinking the sap of trees. The yellow-bellied sapsucker is a common Ontario nesting bird that migrates to areas from Texas south to Panama and the entire West Indies. While they eat large quantities of insects, berries and buds, nearly half of their breeding season diet is composed of sap.

Birds have trap lines where they move between trees with feeding wells, feeding, maintaining the holes and making new ones. Birds not only drink the sap but also eat the insects that are attracted to the sugars of the sap. The holes are drilled in vertical and horizontal rows and may even form a grid. In severe cases, trees may be girdled by sapsuckers.

Many woodpeckers will “scale” the bark of trees to find the insect larvae hiding underneath. This is very common on elms infested with elm beetles, fire killed trees, and other trees infested with cambial feeding larvae. This is common behaviour by both the downy and hairy woodpeckers which are found throughout southern Ontario. These same species may also excavate holes to find larvae feeding in decayed xylem wood.

The pileated woodpecker is in a class by itself in North America. This large bird feeds almost exclusively by excavating holes and scaling bark. Its preferred food source is carpenter ants (Camponotus sp.) but excavating may uncover termites, wood-boring larvae and even the plump larvae of beetles. They will excavate rotted, decayed and seemingly healthy trees in search of food. The excavations are often ragged as opposed to the regular round holes they excavate for roosting and nesting cavities.

Nesting & Sleeping
All woodpeckers use excavated holes for nesting and roosting at night. These holes are easily identified by having round entrances and are often excavated into decayed wood. The larger the bird, the larger diameter the tree needs to be to support the bird. The requirement for large diameter trees with decay has brought a number of species to extinction or near. The famous ivory-billed woodpecker was literally brought to extinction as its preferred large old trees were decimated by logging, both in the US and Cuba. In the pine forests of the southeastern US, the red-cockaded woodpecker has had similar difficulties as the pines on which it is dependent have been harvested and undesirable hardwood bush has been invaded.

Don Your Detective’s Cap
When you have problems with woodpeckers, it is useful to identify the species and the type of damage being done. Pull out your favourite field guide and identify the species. In Ontario, the species choice is relatively limited. Next, identify the damage done and whether it relates to communication, feeding or nesting. From here you might be able to do a little more investigation (like what might the pileated be drilling feeding holes in my house for) or remedy the problem.

If drumming is a problem, any holes made will be small and birds will return to the same spot over and over. The simple way to ease the problem is by removing the limb. If the bird is drumming on a house or a piece of metal, then remove the birds ability to hang on. Don’t use grease or a substance that may damage the bird, instead apply sheets of steel or aluminium. Hanging netting or streamers will make it hard for the bird to manoeuvre and may cause it to move on. When birds are drumming on a built structure, it is because they like the noise and as such the entire structure may be a target. In this case, deterrents such as fake owls may also be useful.

If you find holes, determine if they are feeding holes or roosting nesting holes. The quick differential is that feeding holes are excavations that expose wood and are easily viewed into. Cavities for nesting will have a well formed round entrance, you will need a light and a mirror to look into one of these holes.

When woodpeckers create feeding and nesting holes in trees they are excavating decayed wood. As such, a tree risk assessment may be necessary. As the trees are being used for wildlife, it is important to consider what impact the removal of all or part of the tree will have on wildlife populations. Woodpecker holes are used by many species in addition to the individual that originally excavated the cavity.

When holes are made in built structures, examine the working to determine if they are for feeding or nesting. Holes used for nesting or roosting can be closed with expanding foam and sheathing material (after the cavity is empty of its occupants). If the holes are made for feeding, it likely means that the structure has become home to insects that the birds are seeking. In this case, exterminators may be needed to remove the insects and home renovations done to repair damage and seal up entrances that the insects are using. Scaring off the birds is not enough, get to the source of the problem which is the insects underneath the exterior sheathing material.

Sapsucker feeding is a difficult subject to address as the birds attack healthy trees. One train of thought is to allow the birds to use the one tree in hopes that they do not use another. This does not always work as multiple individuals may pass through during migration and from year to year. Wrapping the affected tree in burlap or similar materials may protect the tree. There are also suggestions that highly scented products such as mothballs hung near the feeding areas may discourage the birds.

Woodpeckers are a common associate of trees throughout all of the forested areas of the world other than in many islands and Australia. As such, arborists can be expected to run into questions about woodpecker damage to trees and its alleviation. Understanding the basics of the biology of the species is the beginning of understanding the individual and the ultimate preservation of trees and wildlife.

Ontario Species of Bredding Woodpeckers

Red-headed Woodpecker
Red-bellied Woodpecker
Yellow-bellied Sapsucker
Downy Woodpecker (pictured here)
Hairy Woodpecker
Three-toed Woodpecker
Black-backed Woodpecker
Northern Flicker
Pileated Woodpecker

Bang, Bang, Bang: How Do They Do It?

Woodpeckers have evolved to use their bills as chisels to remove bark and wood in search for insects. Concurrently, woodpeckers have also evolved a system to not only prevent headaches but brain damage as well.

Woodpeckers can peck thousands of times a day with enough force to break wood. They may move their heads at speeds of 6-7 m/s yet decelerate instantly without damage. A human head impacting a tree at this speed would sustain considerable damage. A combination of technique and structure has allowed woodpeckers to exploit insects sheltered from many other predators

Woodpeckers peck straight into the tree, thereby reducing torsion and associated damage. Just before the strike, the heavy neck muscles contract and are able to transmit some of the force into the body. A cushion like bone also absorbs some force (and is being studied by helmet manufacturers). To prevent eyes from being damaged, woodpeckers have a heavy third eyelid which is closed during strikes and not only prevents damage from shrapnel but also holds the eyeball fast in place. The final major adaptation of woodpeckers is that their brains float in very little cranial fluid. By not floating, the brain does not receive shock waves and does not concuss as human brains do with severe impacts.

By smart evolutionary engineering and technique, woodpeckers are able to do what few others can – literally bash their heads and come out the winner.

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