Last week I wrote about a dead cedar waxwing that was killed in a collision with our window. As I wrote, the rest of the flock chattered and whistled their high-pitched calls in the chokecherry trees (Prunus virginiana) above me. This week the trees are silent and bare. Did our windows kill them all? No, thank goodness, it’s natural for cedar waxwings to be an exciting presence one day, and gone the next. These large, gregarious flocks are facultative migrants – they move around as their food supply requires. One day you may have several dozen descend on your bushes, the next day they may be gone. These songbirds dine heavily on many kinds of berries, and also the tiny cones of Eastern redcedar trees, hence their name.
As a kid in Iowa, I remember late winter days when colorful flocks of waxwings gathered in the highbush cranberry hedge (Viburnum trilobum) outside our kitchen window. The tart berries with a high acid content last well through the winter, and provide a much-needed food source when less-hardy berries have dried out or spoiled. How fun it was to watch them pass berries bird-to-bird down a row if the cluster of fruit could only be reached by one at a time! The birds’ lemony-yellow feathers, rakish black mask, and bright red wax spots captured my mom’s heart, too, and helped guide our Christmas shopping for her.
Since cedar waxwings prefer edge habitat like fields and riverbanks, they have adapted well to human-altered landscapes like my yard and the Museum’s Outdoor Classroom. Their population is stable or even increasing despite the heightened dangers of windows and cats in suburban settings. Brown-headed cowbirds share some habitat preferences with waxwings, and are also doing well in fragmented, edgy habitats. The problem is that cowbirds are nest parasites who lay their eggs in the nests of other species, and force other birds to raise their young. The cowbird chicks grow fast, and usually smother or push the host nestlings out of the nest. Cedar waxwings have a simple solution: they eat so few insects that brown-headed cowbirds in waxwing nests die from a lack of protein. [Although waxwings can go through stretches of strict vegetarianism, they are also excellent flycatchers. While paddling various rivers, I’ve admired their aerial acrobatics as they feasted on summer’s abundance of insects.]
Eating berries has other benefits and consequences, too. Overripe fruit may ferment, causing waxwings to become intoxicated, or even die when they eat too many. Perhaps the birds who crashed into our windows last week were a bit tipsy. A more benign outcome is the waxwing’s tail tip, which is usually yellow, may become orange if it eats the berries of Morrow’s honeysuckle, an introduced species, while the feathers are growing. The pigment rhodoxanthin (a red carotenoid pigment) is responsible for the color change.
As the birds fluttered between clusters of chokecherries last week, I caught glimpses of their bright red waxwings. Used to attract mates, the red is actually flattened extensions of feather shafts colored with a carotenoid pigments – similar to the pigments in carrots and autumn maple leaves. The waxwings obtain the color by modifying pigments acquired from their diet of red and orange berries, and the color increases with age. These birds maximize their nesting success by mating with other birds of similar age and experience levels – information gathered at least partially by comparing the number of red wax tips. Yet another reason why color is not just pretty!
Where is that gregarious flock now? Are they eating YOUR chokecherries? Have they started in on the mountain ash berries and crabapples already? Watch for these year-round residents to visit a yard (and hopefully not a window) near you!
Friday, October 21, 2011
The feathers are glossy brown and streaked with white. The tip of the tail looks like it was dipped in paint made from golden aspen leaves. A jet-black mask outlined by white extends from eyes forward to the nostrils. The warm body is limp and still. This beautiful young cedar waxwing died in my hands just now.
As I pulled up to the back of the Museum on my bike, exhilarated from the delicious air and golden morning sunlight, a loud thunk sounded from the window above my head. At my feet dropped this lovely creature. I observed it for a second to see if it would rouse on its own. It lay still, beak open, so I stooped to pick it up. As I held it the beak opened and closed one last time. The lower eyelid slid up to cover one shiny black eye, and the body slowly cooled.
While saddened by this death, I am thankful for an opportunity to examine such a beautiful bird up close. I often admire the adult cedar waxwings in our Collections Room, and show visitors their lovely yellow tail-tips, rakish black mask, silky lemon breast, and brilliant-red wax droplets on the wing feathers, but this one in my hand is different. Many birds change their plumage for the breeding season and then again for winter. Goldfinches are one of the most common and distinctive examples of this. Cedar waxwings, on the other hand, look the same all year round, and even males and females look virtually identical. Only immature cedar waxwings during their very first summer and fall look any different.
One of the purposes of museum collections is to represent and preserve the diversity of nature. Larger museums may have dozens of specimens of the same species representing various ages, sexes, seasons, and habitats. These can be used for research and study. While our tiny Museum doesn’t have the space to collect quite so extensively, we use our wide variety of specimens to help visitors with identification, and to illustrate concepts.
So, although we already have two adult cedar waxwings preserved in our collection, this immature bird will be labeled with the date and location of its death, and stored in our salvage freezer. This winter, Katie Connolly, the Museum Naturalist in charge of Collections, will mount it or preserve it as a study skin. Watch our Calendar of Events for taxidermy observation days.
While we have the capacity (and the state and federal permits) to salvage dead animals for educational purposes, we still feel saddened and shamed that our windows cause so many deaths. Millions of birds each year die in collisions with windows. Some are just stunned, and if you hold them for a minute they may soon fly away. Others, like my cedar waxwing, suffer brain trauma or break their neck. The main issue is that windows reflect the trees, and birds try to fly right through them.
There are several things you can try to keep birds from hitting your windows. Window clings and silhouettes are somewhat effective, although you may need to attach them to the outside of the glass. Dangling things in front of windows can also help. We have pretty feather-shaped windsocks on our lower windows, but the not upper ones. Shiny ribbon, mirrors, glass beads, old compact disks, and other pretty trinkets can be hung in front of windows. Fine mesh netting can be stretched outside windows. This both reduces reflection and softens the impact. Today I will spend time hanging more ribbons on our windows.
If a bird dies in a collision with your window and it is fresh and in good shape, you can call and ask us if we need it for our collection. Then stick it in a plastic baggie in your freezer until you can bring it to the Museum. As long as you contact us, you will be covered under our permits until we make the transfer. While the death of something wild and beautiful is always sad, knowing that it can be used to teach hundreds of people about nature and conservation makes it just a little less tragic.
Thursday, October 20, 2011
Biking along Highway M on my way to work, I am dazzled by the gorgeous rainbow of color. It started with the red maples in the swamps. They turned scarlet several weeks ago, brightening up the landscape like nothing else can do. The interrupted ferns and bracken ferns in the ditches turned yellow, and then a rapid cascade of other plants changed into their fall wardrobes. Now the forest is mostly orange and gold – from the thick litter of leaves on the ground, all the way up to the crowns of the trees. In gloomier falls I often quip that this is the season when the sun shines from the ground up. Recently we’ve been completely surrounded by sunshine, with not a cloud in the sky.
While the colors this fall have been stunning, I like to think about how useful the colors are, too. Green plants, for example, get their color from chlorophyll, the powerhouse of photosynthesis. Chlorophyll captures the energy of the sun, uses it to make sugar out of water and carbon dioxide, and supports the entire food chain. Including us. We have all known this since grade school science class, but it never ceases to amaze me.
The yellows and oranges finally revealed during the past couple weeks were always there. They were just masked by the greater amount of chlorophyll. When the plant stops producing new chlorophyll, the old is broken down into a colorless chemical, and the other colors shine through. Yellow and orange aren’t just useless underdogs -- they have important jobs to do, too.
Yellow colored xanthophylls are found in most plants, and they help keep the machinery of photosynthesis from being damaged by absorbing too much light. Animals get xanthophylls from their food, and we can see them in the color of egg yolks, butter, fat, skin, and even the macula lutea – a yellow spot in our retina where the pigment helps protect our eye by absorbing UV light.
Orange carotenoids (as in carrots) also absorb extra UV light. In addition, they are antioxidants that capture renegade oxygen molecules. They are important to human health in the form of vitamin A.
Red anthocyanins aren’t revealed in the same way that yellow and orange are. They are created from the breakdown of sugars once phosphate has been sucked from the leaf down into the twigs. Sunlight is necessary to create anthocyanins (and more anthocyanins are needed in sunny weather), which is why sunnier autumns have more brilliant colors. We see the red color again in the new leaves of spring. During both seasons, the pigment protects against damaging light at low temperatures.
Anthocyanins protect humans, too, and have been shown to help stave off cancer, inflammation, diabetes and bacterial infections. One study even showed that anthocyanins cause cancer cells to die faster! We don’t eat red maple leaves for our health, of course, but we do eat blackberries, blueberries, cranberries, and many other fruits with plenty of red in their skin and juice.
Speaking of red skin, kayaking on Lake Namakagon for three hours in the sun reminded me about the importance of melanin. This brown pigment not only protects us, bacteria, and fungus from UV light (it creates our summer suntan), it is also important in the immune systems of invertebrates.
While I think the biochemistry of color is fascinating, there are many other ways that colors provide protection. As a gray-brown deer materializes from the shadows at dawn, camouflage comes to mind. The short-tailed weasel (aka ermine) skins in our Collections Room also show this quite well: the summer fur is light brown, and the winter fur is bright white. In contrast, a bright-orange monarch butterfly fluttering by my paddle vividly warns birds that it would be a bitter mouthful, simply through its colors.
The pale, smooth trunk of a paper birch also has protective coloration – this time from heat. In winter, trees freeze very carefully to make sure their cells are not damaged by ice. Darker trees may thaw and then freeze again too quickly, while birches stay cool and safe.
Paddling close to a loon, I am struck by the vibrancy of its glowing red eye. Even that has a specific purpose. Since we perceive color based on the wavelengths of light that are reflected off a surface, the loon’s eye is reflecting red light and absorbing all others. Under the water, red is the first light to be filtered out, allowing the loon to still gather as much light as possible with its eyes.
My brown eyes are taking in as much as possible. Despite my love of science and explanations, I think one of the most wonderful uses of color is the rejuvenation of our hearts and souls in the presence of natural beauty.
Saturday, October 1, 2011
By: Lacy Sellent, Writing Fellow at the Cable Natural History Museum
A classic sign of the end of summer and the beginning of fall is apples ripening on the trees in our yards, along back roads, and in orchards. Throughout the state, thousands of apples are ready to pick, and some are already in a bowl on my table! Fallen and rotting apples can sure make a mess (that deer and wasps love!), but if you want non-wormy apples for eating, then you might want to keep the area around your favorite trees clean. Leaving fallen apples beneath a tree may cause an insect infestation. One of the biggest pests to apple trees is the apple maggot (Rhagoletis pomonella).
The annual life cycle of the apple maggot begins in July, usually after a good rain. This is when the adults emerge from their winter pupal form and make their way up out of the ground. Although named for its larval stage, adult apple maggots are actually flies. Each five millimeter long fly has black and white colored wings and a distinctive white dot on its back. With a little imagination, black markings on the wings resemble the letter “F.” The apple maggot adult’s coloration resembles the forelegs and pedipalps (grabbing and sensing mouthparts) of one type of jumping spider. This method of defense, where a harmless species mimics one that is better protected, is called Batesian mimicry. Viceroy and monarch butterflies are a classic example of this.
After being above ground for close to a week, female flies will begin the search for a place to lay their eggs. Although adults can fly up to a mile, they don’t usually travel far from the trees that they were burrowed under. Apple maggot flies originally deposited their eggs in thornapples (hawthorn), but have gained notoriety by also laying their eggs in domestic apples. It is not a very healthy experience for the apple. Wherever the apple maggot fly lays her eggs, that area of the apple will stop growing. This causes the apple to look all lumpy. Then, newly-hatched maggots munch and burrow their way out. Wherever the small white maggots tunnel, the apple begins to rot. Brownish trails appear throughout the apple’s flesh. It is this tenacious tunneling that earned apple maggots the nickname “railroad worm.”
After the maggot-infested apple falls to the ground, it is time for the next stage. Maggots exit the apple and enter the soil. Once safely burrowed several inches below the surface, the maggots form a brown, quarter-inch long, oblong case called a puparium. This pupal form allows them to go into a type of hibernation over the winter. They don’t eat until the next spring, when they emerge from the ground as apple maggot flies—bringing the cycle full circle.
The apple maggot is native to North America, but its original range was confined to the eastern United States. It fed mostly on the fruit of hawthorn trees, sometimes know as “thornapples,” which look like tiny apples. About 150 years ago, some of the hawthorn-eating flies began to eat domestic apples planted by settlers and our old friend, Johnny Appleseed. What fascinates scientists (and me!) is that the apple maggots eating domestic apples are adapting to their new host plant, and not reproducing with the apple maggots still feeding on hawthorns. They are suspected to be in the early stages of diverging into two separate species. This process, known as speciation, is usually thought to happen because of a physical barrier – like a mountain range or an ocean – dividing a population. There is no physical barrier in this case, so it is an example of “sympatric speciation.” This is a unique opportunity for scientists to study the genes of these critters as they are in the process of changing!
Unfortunately for us and our many orchards, apples provide more protection from predators for the apple maggots than hawthorns do. Two species of wasps parasitize the maggots by depositing their own eggs inside the maggot, giving the wasp larvae a protein-rich meal when they hatch. In hawthorn fruits, apple maggots feed close to the surface, partly because several species of caterpillars prefer to eat the core, and partly because the smaller fruit just doesn’t have as much area away from the skin. In domestic apples, the maggots can feed farther in, out of range of the wasp’s ovipositor. This means that there are fewer natural predators for the apple-eating population of Rhagoletis pomonella. Removing dimpled apples from your orchard before the maggots exit into the soil can help reduce their population.
As the old joke goes, the only thing worse than finding a worm in your apple is finding half a worm. Next time you see a small white apple maggot tunneling through your fruit, I hope you’ll take a moment to appreciate the interesting life history of this tiny pest!
For over 44 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 in Cable at 13470 County Highway M. The new exhibit, The Joy of Birds: Feathers in Focus opened in May, 2011. Find us on the web at www.cablemuseum.org to learn more about our exhibits and programs. Also discover us on Facebook, or at our blogspot, http://cablemuseumnaturalconnections.blogspot.com/.