Living the Good Life

Listen to my episode about Chipmunks on Outdoor Radio on Vermont Public Radio.

Each fall day he appeared with a skinny face and left with ballooned cheeks. Over and over he filled his cheeks and ran away to empty them. Our eastern chipmunk was living the good life. There was an endless supply of sunflower seeds spilling from the bird feeders.

Impossible to count as he gathered them, I wondered how many seeds he carried on each trip. University of Vermont biologist, Bernd Heinrich, pondered the same question. He found that he could insert 60 sunflower seeds into one cheek of a road-killed specimen, about a heaping tablespoon worth.

Chipmunks can hoard up to 8 pounds of seeds for the winter. So how many trips would the chipmunk have to take to fill up his storehouse? I weighed 120 sunflower seeds on a kitchen scale. At 2 ounces a mouthful, it would take him just 64 trips. Continue reading

Salamanders Going Deep

Spotted SalamanderIn the spring Spotted Salamanders crawl to vernal pools, temporary woodland ponds that fill with water but then dry out later in the summer and provide a fishless environment for larval salamanders, where they mate and lay eggs. But for 90% of the year they are somewhere in the forest. Sometimes you can find them by flipping over a large stone or rolling a rotting log, but for the most part, they are impossible to find.

Technology has allowed biologists to easily spy a Spotted Salamander whenever they want. Miniature tags that emit a radio signal are surgically placed into the body cavity of a salamander. After a few days of recovery, the salamander is released where it was captured. All of its movements and locations can then be monitored with a radio receiver and small antenna. Continue reading

Turn Red or You Are Dead

I have often wondered why on one hillside the trees have muted autumn colors, while nearby on another they are radiant red. Recent research might be shedding some light.

There are four basic colors in fall leaves and a different pigment produces each. Xanothophylls is responsible for yellow, carotenoids for orange, tannin for brown and anthocyanids create the red and purple tones.

During the growing season green chlorophyll in tree leaves is broken down by sunlight and constantly replenished. As day length decreases the abscission cells, a special layer at the leaf-stem junction, divide rapidly and slowly block transport of materials. As abscission begins, a chlorophyll production wanes and eventually stops. Continue reading

You Birdbrain

The next time you are rushing around your house looking for your car keys, you might think about the chickadees at your bird feeders. Each fall, black-capped chickadees grow new brain cells that seem to help them remember the locations of things.

Because chickadees are so small, it takes a lot of food during the winter for them to stay warm and alive. A chickadee weighs about the same as two quarters and will easily fit on the palm of your hand. Chickadees have a high surface-area-to-volume ratio, which means that heat loss through radiation during the cold winter can be acute. Combine this with the short daylight hours in which to forage for food, and energy can be a problem.

Chickadees prepare for the onslaught of winter by storing food. Watch them at your feeders in the fall, and you will notice that they eat some of the seed, but they also carry away one seed at a time, trip after trip. They stuff the seeds in the cracks of tree bark or even in little holes and cracks on your house. I have often found a few seeds crammed into little holes when painting my house.

Chickadees store thousands of food items a year. Each cache is usually used only one time. One study found that the birds could find a cache up to 28 days later. How do they find these sites when they need them most? Since songbirds have a very poor sense of smell, they cannot be tracking the seed down like a dog.

Experiments have shown that chickadees use a complex hierarchy of visual and spatial clues to return to each cache. They search in places suggested by large landmarks such as the arrangement of trees or buildings. Then they cue on local items such as a certain tree, and then by things right around the cache site, such as a patch of lichen on tree bark.

In 1994, Dr. David Brodbeck, at the time a student at the University of Toronto and now a professor at Memorial University of Newfoundland, set up an array of four feeders in an aviary. The feeders were all differently colored and in random locations. One of the feeders was baited with a peanut shoved into a little hole. A chickadee was placed in the aviary, and it would quickly find the peanut. It was allowed to eat for 30 seconds, and then it was removed from the aviary to its home cage for five minutes.

“After four minutes of reading the sports section, I would go into the aviary and cover up the holes on each feeder with little Velcro circles”, says Brodbeck. “The bird was let back in and had to find the baited feeder and remove the Velcro and eat.”

“They were pretty darn good at this, getting around 80 percent correct in their first look,” said Brodbeck. The chickadees’ first clue was the spatial location in the aviary; the second clue was the position in the feeder array (second from the left for example); and the third was the color.

“Spatial cues are more stable than, say, color, and chickadees need to remember where their food is in the morning when they get up, or they die. Simple as that,” said Brodbeck. “So they seem to have some sort of specialized memory system.”

With a brain the size of a pea, how do they remember all the cache locations? They grow extra brain cells. The hippocampus region of their brains expands in volume approximately 30 percent each fall with the addition of new nerve cells. This region of the brain is an important area for making new memories, especially spatial memories. Chickadees with lesions of the hippocampus continue to cache food and search for cache sites, but they are unable to find them.

The addition of new cells and the size of the hippocampus fluctuate seasonally in chickadees, with the peak in the fall during the food cache season and the valley during the summer when food caches are not necessary. It is probably energetically costly to maintain those brain cells, so when they don’t need them in the summer, they let the cells die off.

Many of the degenerative brain diseases in humans involve the hippocampus. The hippocampus in Alzheimer’s patients, for example, shrinks. Perhaps ongoing studies that seek a deeper understanding of songbird hippocampus regeneration will someday lead to applications in humans.

It turns out that you aren’t a birdbrain after all for losing your keys once again. You’re actually a squirrel brain. They store a lot of nuts, but apparently don’t have the trick of growing larger brains each year.

A Flower Trap

With its foot stuck in a milkweed flower like a Chinese finger trap, the European Skipper was struggling to free itself. On another flower nearby only a leg remained from a previous struggle. Survey enough milkweed flowers and eventually you’ll find a few dead insects, usually small species, left dangling from a leg or two.

A butterfly leg left behind stuck in the flower with a pollinia attached.

They are not a carnivorous plant; trapping and death are just an accident. Instead, milkweed has solved the problem of pollination in a unique manner. There are five pinkish hoods with horns where the nectar is located. Milkweed produces copious amounts of sweet smelling nectar in the hoods to attract insect pollinators. Between each of the hoods is a dark spot with a long slit leading down from it. With most of the flowers in the umbel hanging downward, these slits are a natural place for insects to grab with their feet while syphoning nectar upside-down.

Unlike most flowers, milkweeds don’t produce tiny grains of pollen to be carried away piece by piece. Instead, the flower produces sticky, orange packets of pollen, called pollinia, which are designed to stick to an insect’s leg. In each of the five slits are two pollinia waiting to be accidentally snagged and carried off.

Butterfly leg is being pulled out with the pollinia attached.

In order for an insect to pick up one of the pollinia from a milkweed flower, its leg has to slip into a tiny slit between the anthers along the side of the flower.  As the insect struggles to pull its leg back out of that tiny opening, it might emerge with a pollinia or two stuck to it. If the insect is too small or too weak, the only way it can escape the flowers grip is to leave its leg behind. Worker bumblebees, much smaller than spring queens, that forage on milkweed often are missing a claw or leg part.

If the flower is lucky, the insect will travel to another milkweed flower in search of nectar and deliver the pollinia. To do this successfully, they must again pass their leg through one of the anther slits in another flower and have the pollinia come into contact with a very small area at the base of the stigma lobe. There’s a cost to the insect for this delivery service. Bumblebees with pollinia attached forage about 25 percent more slowly.

The odds for successful pollination are slim. Seed set in milkweeds is often quite low with only a flower or two in the entire umbel producing seed. But a few flowers are enough to produce clouds of drifting seeds each autumn to sow a new generation in some far off field.

Virginia Ctenucha (Ctenucha virginica) trapped

European Skipper resting on grass blades with milkweed pollinia stuck to several legs.

Can you spot the lost leg among the Common Milkweed flowers?

A Water Lily’s World

Water Lily Beetle (Donacia sp.)

At the height of summer many ponds are covered in lily pads with beautiful white or yellow flowers spread across the water. Moose munch on them. Beaver and muskrat devour them. Deer consider them delicious. But peer a little closer and you’ll find an amazing miniature world inhabiting each floating leaf.

In our region there are several plants with floating leaves that one may call ‘lily pads’. From bullhead pond-lily (Nuphar variegata) with its bright yellow flower petals and deep orange pistil, to the incredibly fragrant white water lily (Nymphaea odorata), or even water-shield (Brasenia schreberi) with its slimy, gelatinous-covered leaves and tiny, dark red flowers that almost escape notice; they all have specialized adaptations to allow them to rise from the deep muddy bottom up through the water column and into the air.

Water lilies are in a quandary. Their roots need oxygen, but the muck beneath the water is anaerobic. To solve this, they pump up to two liters of air from the surface down to the roots each day during the growing season using a special gas conducting tissue running down the length of stem called the aerenchyma. Air enters tiny openings on the leaf, called stomata. While land plants have them on all surfaces of the leaf, they are only found on the upper surface of water lily leaves. When the sun heats the young leaves it creates a pressure gradient that forces air down the aerenchyma. As leaves age they lose this ability to pressurize air. The roots return carbon dioxide to the surface through these older leaves.

There are many species of water lily leaf beetles that ride and feed on the surface of the lily pads. One of the earliest to emerge with the fresh leaves is named by Latin loving scientists as Galerucella nymphaeae. These oblong, dark-brown beetles are just a quarter of an inch long. They lay eggs on the surface of the leaves in June. Soon, the eggs hatch and the shiny black larvae with yellowish bellies begin to feed on the leaves. They cause the leaves to age more rapidly as they chew through them. During the height of their growth, the beetles can cause them to last just a third as long as uninhabited leaves.

Another group of water lily beetles are called Donacia. The quick moving adults have a golden metallic shine and stand tall on long legs on the lily pads. They have a layer of silky hairs on their underside that helps repel water in their soggy world. Depending on the species, some lay eggs by chewing a hole through the lily pad and then dipping their abdomen below the surface to glue rows of eggs onto the leaf. While other species may bend over the edge of the leaf to cement the eggs or climb under the leaf and down the stem to deposit eggs. Tiny grubs hatch from the eggs after about ten days and fall down through the water column eventually finding their way into the roots of the plant. The larvae have two tiny pores, called spiracles, at the end of their abdomen, each guarded by a spine. They use these as picks to open holes into the air chambers inside the plant stem thereby gaining access to a steady air supply for breathing while they feed on the plant. When ready to pupate, they build a silky, waterproof cocoon from special glands in the mouth and fill them with air by once again cutting holes into the stem’s air chambers. After developing quickly into an adult, they remain underwater until the next spring when they bursts out of the cocoon, and holding air bubbles under the wing covers and body hairs, float to the surface to find a new lily pad home.

You might notice tiny serpentine patterns snaking through the leaf surface. These are from the larvae of leaf-mining midges. Active at dusk, these tiny insects resemble mosquitoes, but don’t bite. The larvae tunnel between the leaf layers, which eventually turn brown and rot through the leaf.

Even moths find a home on water lilies. The caterpillars of the water lily borer moth feed on leaves and tunnel into the stalks of the lily pads. The poetically named polymorphic pondweed moth caterpillars feed on the leaves. As they grow larger they cut and tie two pieces of leaf tissue together and hide in it under the lily pad when they are not feeding. But perhaps the most spectacular feat is that of the water lily moth caterpillar. The adults live for just six days, but in that short time a female can lay up to 900 eggs on the surface of the lily pads. The tiny green caterpillars hatch and begin to feed on the leaves. After three weeks they’ve grown from just a few millimeters to over an inch long, turning a deep red color. Amazingly, the caterpillars swim to land using a porpoise motion with the rear third of their body. Once on land, they build a silk-lined chamber in the soil and pupate.

Flip over a lily pad and you’ll find a floating hatchery holding the eggs of mites, snails, whirligig beetles, caddisflies and others. Freshwater sponges, microscopic tube-dwelling rotifers and bryozoans colonize the surface. Snails crawl across the leaves feeding on algae. Spread across the pond each summer are entire floating worlds, each built on a lily pad.

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Note: This article first appeared in print in Rutland Magazine.

The Fresh Smell of Spring Skunk

There is nothing like the fresh smell of a spring morning, unless, during the night, a skunk skulked about your neighborhood. The striped skunk is armed with just a teaspoon of odoriferous oil in its two anal glands, but a little bit goes a long way.

When I was in junior high, I was hit with a burst of spray from a skunk at close range. I can attest that at high concentrations it causes nausea at first. It also acts like tear gas, causing watering eyes and a running nose. Oh, and your mother will most definitely make you take your clothes off outside and throw them out. If you’re lucky, she’ll let you back in after a series of home remedies, which never seem to fully cure the stench.

Skunk oil research has been going on for over a century as scientists have tried to determine what makes the stuff so potent that it can drive a bear away. Way back in 1896, Thomas Aldridge at Johns Hopkins University showed that humans could detect the smell at just 10 parts per billion, the equivalent to detecting just one drop of it diluted into a medium-sized, backyard swimming pool. More recently, William Wood, a chemist from Humboldt State University, pointed out that a number of chemicals have been incorrectly attributed to skunk oil over the years, and his work has now given us a fairly complete understanding of the chemical compounds and how to neutralize them.

The scent-gland secretion is a yellow oil composed primarily of volatile compounds known as thiols, and their derivatives. (A thiol is a compound distinguished by its sulfur-hydrogen bond.) Most of us immediately recognize the smell of ethanethiol (also called ethyl mercaptan), a common thiol that’s added to otherwise odorless propane gas so we can easily smell any leaks. Another thiol creates the “skunky” smell of beer after it has been exposed to ultraviolet light.

The thiol derivatives present in skunk oil are not particularly odoriferous, but they are easily converted to far more potent thiols when they react with water. For weeks after I was sprayed, I would give off the faint smell of skunk at basketball practice. Perhaps the thioacetate derivatives trapped in my hair reacted with the moisture from my sweat. I don’t remember, but I wonder if my defenders backed off a bit affording me more scoring opportunities. The power of thiols.

Many people believe that tomato juice will neutralize the odor of a skunk, but human olfactory fatigue is a better explanation for the apparent disappearance of the odor. I could hardly smell the odor on my body after a few hours, but when a new nose came into range, its owner squealed with disgust. A tired nose will smell the tomatoes rather than the skunk.

You can neutralize the offensive thiols in skunk spray with the sulfonic acids found in most detergents. Oxidizers such as hydrogen peroxide and baking soda are mild enough to be used on pets, although they may create interestingly colored hair for some. For washing down your deck or trash can, try liquid laundry bleach.

The smell is certainly memorable. Even decades later, the thought of that moment when the skunk turned and sprayed almost turns my stomach and brings tears to my eyes again. The skunks are reluctant to use it, though. With only enough for a half dozen sprays at most, and a 10-day period to manufacture more, skunks will only spray if they absolutely have to. In an attempt to avoid spraying, skunks often give warning. First, they show their striped white back to warn you. This is followed by threat behaviors, like stomping with both front feet, sometimes charging forward, and then edging backwards dragging their feet and hissing. If all this fails, watch out.

Each spray gland has a nipple, and skunks can aim and direct the spray using highly coordinated muscles. A skunk can spray up to 25 feet and hit something fairly accurately up to 7 feet away. When there is a target, they can direct a fine stream right at the victim’s face. When being chased, a skunk will instead emit a foul cloud for the predator to run into.

There is one predator that remains undeterred by the odiferous oil, the great-horned owl. The small size of the olfactory lobes in their brains suggests that they have a very poor sense of smell. Some individual owls can downright stink of skunk, a common complaint among wildlife rehabilitation workers. Their nests can even smell of their musky meals. But larger-lobed mammals quickly learn to avoid the white stripe in the night.