San Francisco Environment Department

Why Woodpeckers Don’t Get Headaches*

It always amazes me when I see the first spring migrants – in January! I saw my first Allen's Hummingbird on January 29th this year, performing its awesome courtship display at Fort Mason. Named after Charles Allen, a bird collector who lived in the Bay Area, these diminutive birds can drop from the sky at 61 miles per hour, and when they pull out of their dive, they experience more than nine times the force of gravity.

Hummingbirds are the lightest birds in the sky, and they command a lot of superlatives – they beat their wings 60 times a second, their heart beats 1,250 times per minute, they visit 1,000 flowers a day, they can hear better than we can, see better (including ultraviolet light), can fly sideways or even upside down, and their hollow bones weigh less than their feathers.

The Maya believed that the hummingbird's brilliant colors were a parting gift from the Sun God. They have been given names in different cultures that reflect their brilliance – in the Dominican Republic they are called "buzzing flower," the Portuguese call them "flower kisser," and ancient Mexicans called them "rays of the sun."

Unlike other birds that get their colors from pigments, the emerald, ruby and amethyst colors of a hummingbird actually come from air. Hummingbird feathers contain tiny structures called platelets that are filled with microscopic air bubbles. These air bubbles diffract light into colors, depending on the amount of air and the shape and thickness of the platelets. This is all controllable by the bird, and males can flash their colors at will. That's why this male Anna's Hummingbird can seem dull one minute, and iridescent the next.

While Anna's Hummingbirds are commonly found in San Francisco all year, the Allen's is present only during their summer, which lasts from late January to late June. A third species of hummingbird, the Rufous Hummingbird, flies through San Francisco in spring and late summer on its way to and from its breeding grounds in the northwest and Canada.

Hummingbirds have such amazingly long forked tongues that when they are retracted, they extend back to the rear of the throat and curl around to lie on top of the skull. Interestingly, many woodpeckers have the same anatomical characteristic, with a tongue that forks in the throat, goes below the base of the jaws and then goes over the top of the skull, ending just behind the eyeball. This Downy Woodpecker's tongue, for example, is three times as long as its bill.

Woodpeckers have other amazing adaptations as well. They have a third eyelid, to protect their eyes when they are hammering away at a tree. And why don't they get headaches? Well, the third eyelid helps (it acts like a seat belt) and they've developed a large brain case, which prevents them from getting a concussion when they eat. They've also developed one of nature's best shock absorbers – a muscle and bone structure at the base of their bill to cushion the impact of their feeding habits. Their tail also can act as a kickstand to prop them up, and they have two toes in the front and two in the back to give them a better grip (most birds have three in the front and one in the back).

While the Downy Woodpecker is the most common woodpecker found in San Francisco, twelve species of woodpecker have been seen in the City. The most unusual woodpecker that I've seen was this hybrid woodpecker that I found at Lake Merced in January. At first glance, it reminded me of a Red-Breasted Sapsucker, a common summer resident in the humid forests of the Pacific Northwest, which is usually present in very small numbers in the winter in San Francisco. But Red-Breasted Sapsuckers pretty much always have a completely red head.

Turns out this bird is a cross between a Red-Breasted Sapsucker and a Red-Naped Sapsucker, a common Rocky Mountain bird. A number of bird species can hybridize with other species (ducks in particular are known for this), which makes bird identification even more challenging.

Sapsuckers drill rows of "sap wells" in the bark of trees, and then come back to drink the sap oozing from the tree. Surprisingly, this doesn't seem to hurt the tree, and there are a number of places in San Francisco (including in the San Francisco Botanical Garden in Golden Gate Park) where you can see trees with thousands of holes drilled by our wintering sapsuckers. This unusual habit can also provide food for other species – Rufous Hummingbirds are known to nest near sap wells and feed at the supply of food provided courtesy of the Sapsucker.

My favorite woodpecker, however, is the Acorn Woodpecker, commonly known as the Clown Bird. Because we don't have a lot of oak trees, this colorful bird is rarely spotted in San Francisco (there were only four reported last year).

Acorn woodpeckers collect and store acorns – lots of them – in trees. The trees they select for their storage are known as granaries. There are records of granary trees that have 50,000 holes drilled in them by woodpecker families (and each hole contained an acorn). This predominantly western bird lives in extended families – with up to seven males and three females making up a family. Young woodpeckers stay with their families for several years and help their parents raise more young before they leave the family grouping.

These gregarious birds are very versatile – I've seen them drill holes in palm trees to store acorns. They don't restrict themselves to trees either – they've been known to drill holes in fence posts, utility poles, buildings, and even automobile radiators. They have also been known to put acorns in places where they cannot retrieve them – there's a report of woodpeckers putting 485 pounds of acorns into a wooden water tank in Arizona, and then not being able to retrieve them. Acorns are not their only food – the Acorn Woodpecker also eats insects, sap and fruit but acorns are their food insurance policy, particularly for winter. Another claim to fame for the Acorn Woodpecker is that Walter Lantz is believed to have patterned the call of his cartoon character Woody Woodpecker on the call of the Acorn Woodpecker, while patterning Woody's appearance on that of the Pileated Woodpecker.

The Pileated Woodpecker, by the way, is the largest of the woodpeckers found in North America (except perhaps for the Ivory-billed Woodpecker, generally believed to be extinct – although a few reported, but unconfirmed, sightings several years ago led some to believe that there may be a handful of Ivory Billed Woodpeckers left in Arkansas). This majestic bird has only been reported three times in San Francisco (in Lafayette Park and on Bayview Hill). It needs big trees to provide it with carpenter ants and other insect food sources.

We also have another woodpecker, the Nuttall's Woodpecker, found only in California and Baja California. Named after naturalist Thomas Nuttall, this small woodpecker is often spotted in San Francisco, although the habitat it prefers, oak woodlands, doesn't really exist in the City. Even though its preferred habitat isn't found here, the Nuttall's Woodpecker feeds mainly on insects, which are easily found in San Francisco.

*Why Don't Woodpeckers Get Headaches And Other Bird Questions You Know You Want to Ask by Mike O'Connor (Beacon Press, 2007) is a well-written, fun collection of facts about birds.

All pictures were taken by David Assmann, Deputy Director of the San Francisco Department of the Environment. Do not reproduce pictures without permission.


Bird List

Allen's Hummingbird
Rufous Hummingbird
Downy Woodpecker
Red-Breasted Sapsucker
Red-Naped Sapsucker
Acorn Woodpecker
Pileated Woodpecker
Ivory Billed Woodpeckers
Nuttall's Woodpecker

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