Monday, March 29, 2010

Bird Flight & Height

By Susan Benson,
CNHM Director of Education

While recently talking with some girlfriends, we got on the topic of our experiences speeding along area roads in our cars. Some interesting stories were told. The next morning I was watching a flock of robins migrating through my yard, and started wondering about their speed. How fast do they fly? How high do they fly? Certainly the science of flight speeds in the bird world must be imprecise given that birds deal with head or tail winds, or barometric pressure. Does bird age affect their flight? How can we tell if a bird is flying at its top speed, or is just cruising along? What estimates exist on flight speed and altitudes was a question I wanted to answer.

A robin has been measured at 30 mph, while an arctic loon can fly at 56 mph, the common loon at 90, and the killdeer and wood duck at 55 mph. A canvasback duck can reach 72 mph, and a tiny hummingbird has been “clocked” at 27 mph, but at 50 mph with a tail wind. This top speed, by the way, rivals a Canada goose – apparently size is not an indicator of speed!

Bird air speed has been estimated from cars and planes. Doppler radar, the device similar to that which police use to catch speeders, has been used to measure ground speed of birds. Alternatively, using wind speed measurements with an anemometer, scientists have estimated bird airspeeds. These measurements were also calculated with power requirements. For example, there is a top speed with which a bird can fly, and the speed with which it usually does fly. Birds appear to minimize their energy use, or metabolic rate, and maximize the distance they can travel during the time in which they expend their energy. A bald eagle that is searching for prey may minimize their energy expenditure by soaring while using a thermal, or bubble of warm air. A bird might also choose its maximum speed when in flight from a predator. These studies found that a gull can fly 15 to 28 miles per hour (mph) without raising its metabolic rate more than 15 percent. Some bird species that have a courtship flight reach their maximum speeds during these flights. Small woodland birds fly faster in open areas, while birds in flocks fly faster than when flying alone. During a chase, a duck can reach up to sixty mph, while a peregrine falcon can reach 200 mph. That is fast!

How high do birds fly? Birds have been spotted on the top of Mount Everest, at more than 29,000 feet, and in the Himalayas at 25,000 feet. Even the smallest warbler has been seen flying at an altitude of 9,000 feet, a real feat since breathing at high altitudes, mixed with cold air can make flight challenging. On the flip side, the emperor penguin has been recorded swimming at an ocean depth of 875 feet.

Most birds fly below 500 feet except during migration. Long-distance migrants have been observed flying at 5,000-20,000 feet. Whooper swans were observed by a pilot at 29,000 feet. This is amazing considering the air at 20,000 feet has less than half the oxygen at lower levels. Vultures will rise to over 10,000 feet, presumably to scan larger areas for food, and to observe where other vultures are feeding. Radar observations have shown that nocturnal migrants fly higher as well. Scientists believe that this might make for better tail winds, and cooler air decreases water loss due to evaporation and allows migrants to regulate their body temperature with greater ease. Landmarks might be easier to locate from up high. The birds also do not have to do battle with fog, clouds, or other physical barriers. On the other hand, some water birds and land birds have been observed migrating low over the water, rarely rising above 200 feet. What amazing diversity birds can show!

We often hear stories of birds flying “a mile a minute,” and although we know that most birds do not reach that accelerated speed for long, we can certainly appreciate their abilities. As I sometimes fly around “a mile a minute” in my own personal life, nature and birds can be a reminder to slow life down for a moment, or two, or two thousand, giving us time to enjoy the beauty around us.

For over 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility and new exhibit, Our Shared Planet, in Cable at 13470 County Highway M. Also find us on the web at to learn more about our exhibits and programs. Post your own stories on the Nature Watch blog at

Monday, March 22, 2010

Bird Tasty Treats

By Susan Benson,
CNHM Director of Education

Just as birds have evolved to fill most habitats on Earth, and have also evolved an amazing diversity of bills, so too is it interesting to study what birds eat. To say that a bird “eats like a bird” is misleading, as birds have very high metabolisms, and so need more food than many other animals. For a human to maintain a metabolism as high as a hummingbird, it would have to eat one and a half times its own weight daily. Imagine how many quarter pounders that would take! Take a few moments to learn about the fascinating diversity of bird foods and feeding habits.
• Grebes continuously eat their own feathers, and can feed feathers to their chicks. This is thought to be a way to protect their stomachs from the sharp bones of the fish prey that makes up the bulk of their diet.
• Peregrine falcons have a strange notch along the lower edge of their upper mandible (beak.) When they catch their prey, if their fast attack does not kill their prey, they can quickly slice the spinal cord of their prey with this notched beak, killing the prey instantly.
• The anhinga uses its bill as a spear, diving through the water to stalk for bluegills and other small fish. Once their meal is speared, they toss their beak into the air, throwing the fish into the air where they can grab and swallow it – head first. Great blue herons, however, do not spear their fish prey, and would have a more difficult time removing the prey from their beak if this did occur.
• Green-backed herons have been observed taking bread crumbs from a picnic area, dropping them into shallow water, and then diving in to feed on the minnows that are coming to feed on the crumbs.
• To determine if owls use their sight or hearing, scientists experimented with barn owls. In a completely darkened room, the owls still killed the mice. To isolate whether they used hearing or infrared vision (to detect body heat,) scientists released mice with balls of paper tied to a length of string. Through this experiment, designed so the paper would make more noise than the mice, they discovered that the owls attacked the paper, proving that owls hunt by sound.
• Most birds are known to eat fine gravel, which has no nutritional value, but assists in the birds gizzard, grinding seeds on which a bird feeds. Turkeys can have up to two ounces of grit in their gizzards, and moas, an extinct bird, swallowed up to five pounds. Penguins, however, do not eat seeds, and apparently use rocks as a ballast for swimming.
• Turkey vultures, a bird that eats the less desirable food, carrion, have interesting adaptations to assist them with feeding. First, they have a surprising sense of smell and sight to find their dead food. When they have been successful, they have no feathers on their head to keep their body cleaner and more “sanitary.” They will wipe their head on the ground, or preen themselves to stay clean.
• Some birds are generalists, and eat a wide variety of foods. Others are specialists, and depend on more specific food sources. An ivory-billed woodpecker feeds exclusively on wood-boring beetle larvae. The acorn woodpecker on mostly acorns or other nuts that gets stored in communal caches. The storm-petrel eats floating oil from dead marine mammals. Ospreys eat fish, while black–necked stilts eat brine flies. The Wilson’s phalarope spins rapidly in the water and feeds on insects as they are swirled to the surface. An American woodcock eats earthworms. A northern flicker eats ants. A groove-billed ani eats parasitic insects on cattle. Finally, the red and white-winged crossbills eat conifer seeds they pry free with their crossed beaks.

Such a smorgasbord of tasty treats does the bird world eat. I will never look at a buffet in the same way, and appreciate my “generalist” lifestyle of eating. Now that spring seems to have sprung, enjoy watching birds outdoors, as you never know what you might see them eating!

For over 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility and new exhibit, Our Shared Planet, in Cable at 13470 County Highway M. Also find us on the web at to learn more about our exhibits and programs. Post your own stories on the Nature Watch blog at

Monday, March 15, 2010

Hairy & Downy Woodpeckers

By Susan Benson,
Director of Education

“What are the red and white woodpeckers at my feeder? Are they the same bird or just an adult and young bird?” These are questions I have been asked by several people recently. I have also enjoyed both of these species at my own suet feeders. They are two species, the downy and hairy woodpecker. These birds have many similarities. They are common throughout most of North America. They both visit our suet feeders. They are the only common woodpeckers that display a vertical white stripe on their back. The males of both species have a red patch on the back of their head. However, there are also many differences between them, some obvious, and some more subtle.

Two features that make the downy woodpecker easier to identify are the size and bill. The downy woodpecker is much smaller, approximately six to seven inches long. Their bill is shorter, smaller than the width of the head, and about one-third as long as the hairy woodpecker. The white outer tail feathers are barred in black, giving the bird a spotted effect. They also have a squeaky call and slower drum in comparison to hairy woodpeckers. There are other characteristics and behaviors to look for when comparing downy and hairy woodpeckers. The hairy woodpecker forages along trunks and main branches of large trees, with an erect posture, while downy woodpeckers use smaller branches.

What makes these two woodpeckers different? The downy woodpecker joins flocks of chickadees and nuthatches. Flocking with mixed bird species is an advantage as these birds spend less time watching for predators, and have better luck finding food. During the winter, males and females split up to look for food, and males seem to prefer small branches and weed stems, while females feed on larger branches and trunks. Both sexes of “downys” find foods that larger woodpeckers cannot, so downys can be found feeding on insects they find on plant stems and goldenrod galls, round ball on the stems, in which fly larvae are living inside. Downy woodpeckers also eat beetle larvae, ants, or caterpillars in wood or tree bark. They also eat berries, acorns and grains, and are common suet and sunflower seed eaters. They have been observed drinking from hummingbird feeders. They sometimes even hop across the ground for food.

Downy woodpeckers excavate nesting holes, taking up to three weeks to make, with an entrance that is round, but only up to 1.5 inches across. The best place to look for an entrance is in a small, dead tree stub that is around seven inches in diameter, on the underside of the snag. Sometimes their excavations can be found inside of the walls of buildings. They prefer open deciduous woodlands, and their dead nest trees are sometimes filled with fungus that makes excavation easier. They drum against wood as a way to find their mate or to set up territory, and downys will drum more in the early morning.

Hairy Woodpeckers are more common in mature woodlands, and will be found in coniferous deciduous, or even mixed forests with medium to large trees. More than seventy-five percent of their diet is made up of insects, as they prefer wood-boring beetle larvae, bark beetles, ants, and moth pupae. They eat many other types of insects as well. They will drink sap that is leaking from trees. They are often seen cleaning up a site after a pileated woodpecker has finished. Around twenty percent of their diet is made up of fruit and seeds, and they also visit suet and sunflower feeders. They do not feed on weed stalks or plants like the downies, but sometimes forage at the base of trees.

The entrance to a hairy woodpecker nest is a cavity with an opening two inches tall and 1.5 inches wide that takes up to two weeks to create. “Hairys” are a little different as they excavate their nests in the dead stub of a living tree, or in a dead tree, also with their entrance on the underside. The cavity is often in a branch or stub that isn’t perfectly vertical, with the entrance hole on the underside, which perhaps keeps flying squirrels or other woodpeckers from taking over their nest. These birds also drum against trees, more quickly than downy woodpeckers, and their drum is about ten times per minute.

I find that writing these Nature Watch articles makes me look at the beauty in nature I often see in a different way. So, for those who are looking to identify these woodpeckers, or other birds at their feeder, here is a simple tip. First take a look at the overall size of the bird. Size is a reliable field mark, but is difficult to judge when looking outdoors. Some people will measure their feeder, or mark different lengths on their feeders to help them judge the size of birds visiting their feeders. Happy birding!

Monday, March 8, 2010

Gray & Fox Squirrels

By Susan Benson,
CNHM Director of Education

I must be crazy. While others are trying to squirrel-proof their feeders, this past Sunday I decided to feed them. I wanted to do some “scientific” observation of squirrels eating, so I put out some piles of sunflower seeds near the sliding glass doors on the patio. One that I’ve dubbed “chicken pants” would not come near, but along came another “braveheart” that wasn’t at all afraid. I watched it eat for a while, sharp claws and teeth at work, and then along came “chicken pants” who although was afraid of me, was not afraid of “braveheart.” I had never heard squirrels growl, but that was the only way I could describe their territorial attempts to claim the food piles. These two squirrels did not quite look alike, so I decided to research a little deeper.

In this part of Wisconsin we have two types of tree squirrels, the gray and the fox squirrel. The fox squirrel is bigger, and its fur is brown to gray, with a bushy tail that ends with tawny-tipped hairs. The gray squirrel is just a bit smaller, with gray color and a bushy tail tipped with white. As I read about these two squirrel species, I realized that “braveheart” was a fox squirrel, and “chicken pants” was a gray squirrel. We do indeed learn something every day.

Gray and fox squirrels have very sharp claws for climbing trees, and vibrissae, thick hairs or whiskers that are used as touch receptors to sense in their environment and help find their way in dark tree cavities. The conspicuous bushy tail of both squirrels assists them with communication, balance, covering as a blanket, and umbrella. Both squirrel species are both scatter-hoarders, hiding food in many small caches for later retrieval. Some cache sites are for shorter-term use that they eat within hours or days, or sometimes will re-bury at another site. It is believed that both squirrels make thousands of caches each season. Fox and gray squirrels both have very accurate spatial memory, using distant and nearby landmarks to retrieve their caches. Their sense of smell is then used as they approach more closely to the cache. In spite of these advantages, they often leave behind food supplies that germinate and become new trees.

Fox squirrels depend primarily on tree seeds for food, especially acorns and hazelnuts, and will also consume buds, fruits, cultivated grain, and insects. Gray squirrels have a more diverse diet, eating acorns and other tree nuts, fruits, fungi, insects, inner tree bark, sap, and underground sections of plants. They will also eat small rodents, including other squirrels, and will raid bird nests for eggs and young.

Gray squirrels are one of the few mammal species that can descend a tree face-first, turning their feet so the claws of their hind paws are pointing backward, gripping the bark. Fox Squirrels are non-territorial, and spend more time on the ground than the gray squirrel. They are still, however, agile climbers. They can span fifteen feet in horizontal leaps, and fall twenty feet to a soft landing on a limb below.
Both species of squirrels construct nests called “dreys,” made of dry leaf and twig platforms high in the trees. Gray squirrels will use old woodpecker holes as dens to raise young, but only build dreys when cavities are not available. Fox squirrels also have winter dens that are usually hollow cavities in trees, in which communal denning can occur, and the home itself can be used by a succession of squirrels for thirty or more years.

Gray and fox squirrels have a large vocabulary. Gray squirrels use sounds and posturing, including a squeak similar to a mouse, a low pitched sound, a raspy, repeated “mehr” sound, and a chatter. Fox squirrels cluck, chuck, and warn the world of nearby threats with screams. They make high-pitched sounds when mating. When threatening another fox squirrel, they stand upright with their tail up high, flicking it.

Gray squirrels prefer mixed hardwood forests with mature, nut producing trees. Grays will usually stay very close to home, with a territory as small as 1,000 feet. Fox squirrels prefer agricultural areas mixed with forested woodlots, with a home range of 10-40 acres.

As I am writing this story, my fiancĂ© has complained to me that these squirrels just chewed up a gas can. Are they chewing at something like this simply to keep their teeth sharpened? Is there anything they won’t chew? For whatever reason this squirrel chewed, we all know the rodents in our world bring us the occasional frustration, and for the most part, entertainment and joy.

For over 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility and new exhibit, Our Shared Planet, in Cable at 13470 County Highway M. Also find us on the web at to learn more about our exhibits and programs. Post your own stories on the Nature Watch blog at

Monday, March 1, 2010

Bird Bills

By Susan Benson,
CNHM Director of Education

Just think about a crossbill, spoonbill, bluebill, ivory-billed woodpecker, great hornbill, channel-billed toucan, yellow-billed stork, saddle-billed stork, or shoebill stork – all birds that are named because of their bills. Others are named for their mandibles, which is what the top and bottom parts of a bird’s bill are called, such as the black or chestnut-mandibled toucan. Then ponder the use of your own mouth, and compare it to that of birds, which use their bill for eating, killing prey, probing for food, grooming, manipulating objects, courtship, and feeding their young. Bird bills show amazing diversity, both in physical anatomy and their use. Check out the following bill facts:

• Bill anatomy – the jaws of a bird’s bills are made of a hollow or porous bone designed light for flight. The outside of the bill is covered with keratin, the same material in our fingernails. Bird bills have two holes called nares that connect to their respiratory system. When birds open their mouths, the lower jaw does most of the movement. Their bills continue to grow throughout their lives in order to replace the wearing that occurs at the tips.
• What are some of the common bill types? First, there is the probe, such as hummingbirds, that have long straw-like bills to sip nectar from flowers. Next are the chisel-like beaks, such as woodpeckers, that chisel for food or cavities. Some birds, such as herons or mergansers have spears, bills with serrated edges and a hooked point for grabbing fish. Birds of prey have hooked bills for tearing apart their live prey into pieces small enough to swallow. Blackbirds, meadowlarks, and warblers have tweezer-like bills for probing for insects. Flycatchers and goatsuckers have wide bills surrounded by a net of bristles that funnel flying insects into their mouth while in flight. Nutcrackers such as grosbeaks, sparrows, and finches have thick, conical beaks, for cracking open the hard outer shells of seeds. A kitchen strainer is similar to the edges of a duck's bill which is fringed to strain plants, seeds, and small invertebrates from mud and water. Finally are the burrowing birds, such as stilts, woodcocks, or avocets, which have thin, probing bills to jab in the mud.
• It is worth peeking at the local American woodcock bill, which has a flexible tip specially adapted for probing into moist soil in search of earthworms. It is believed that this bird steps heavily, causing worms to move more in the soil. Their beak then probes and feels the worms in the moist soil.
• Crossbills also have an odd, crossed bill that assists them with getting into tightly closed cones. Their jaw muscles are strong, so the bird places its bill tip slightly open under a cone seed, and then bites down. The crossed tips then push the cone scale up, exposing the seed underneath.
• Looking around the world, there are interesting bird bills as well. The sword-billed hummingbird has a bill is longer than its body. A skimmer’s lower mandible is larger than the top mandible, allowing them to place this part of their bill into the water, flip fish into the air, and catch them. The shoebill has a bill that looks like a shoe, and these birds use their bill in muddy waters, preying on fish, frogs, young crocodiles, invertebrates and small mammals.
The United State Fish and Wildlife Service reports that birdwatching brings in $36 billion annually to our economy, and its no secret why. Having a bird life list is not enough for many of us. Imagine being able to watch a skimmer skim for fish, or to observe with binoculars a crossbill pull seeds out of a cone. These kinds of experiences are priceless.

For over 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility and new exhibit, Our Shared Planet, in Cable at 13470 County Highway M. Also find us on the web at to learn more about our exhibits and programs. Post your own stories on the Nature Watch blog at