The Autumn Show

Autumn is finally settling in the St. Louis area; the overnight chill lingers a little longer in the morning, the hours of daylight are decreasing, and the leaves are finally turning colors.

Have you ever wondered what causes the leaves to turn those brilliant shades of red, orange and yellow, and why it seems that the autumn foliage is more colorful some years than others?

Let’s begin with the leaf.

The carotenoids, the pigment responsible for the fall colors, is already present with in the leaf but is concealed by the green color of chlorophyll, the component essential for photosynthesis. The base of each leaf contains a special layer of cells, known as the separation layer, where the exchange of water and food between the leaf and tree takes place.

The leaves are responsible for providing food for the tree and it performs this duty through photosynthesis. In photosynthesis, the leaves use water and carbon dioxide to produce carbohydrates for the tree and oxygen is the by-product of this process. On any given day, the average tree will take in 1-1/2 pounds of carbon dioxide and release about a pound of oxygen into the atmosphere. The leaves also produce more food than is needed and the tree will convert the excess sugar into starch to consume during the winter months.

The shorter hours of daylight and cooler temperatures trigger a reaction that allows the leaves to reveal their autumn colors. During this time, the cells within the separation layer form a cork-like material that cuts the exchange of water and glucose from the leaf. The chlorophyll within the leaf disappears when the water supply is cut off, revealing the hidden oranges, reds or yellows.

The orange leaves are produced from carotene pigments,

yellow leaves are a result of xanthophyll pigments

and anthocyanin create the red and purple leaves.

Interestingly enough, not all trees produce anthocyanin and this pigment is only made during the fall months.

Contrary to popular belief, rainfall is not the only factor responsible for the colors of autumn. Sunlight, cloud cover, temperature and soil acidity also determine the intensity and duration of fall’s colorful show. For example, bright light produces anthocyanin. The brighter the sunlight, the more vivid the red and purple leaves. A warm wet spring followed by a summer that is neither too hot nor too dry that leads into a fall with warm sunny days and cool nights will produce a dazzling leaf display.

Now that you know the work the leaves put into their visual displays, I hope you get a chance to go outside and enjoy Autumn’s show.

The Late Bloomers

For the first time last week, I began to hear the familiar begging calls of young American Goldfinches. I peeked outside and sure enough, there were 3 hatch year Goldfinches on my patio hopping around, pecking at leaves and exploring the covered BBQ pit. One of the goldfinches hopped under the BBQ pit, another one perched on a flower pot, and the last goldfinch started to fly towards the BBQ pit. I think he was trying to reach the top of the pit, but his takeoff was too close, so he settled for the side instead.

A hatch year Goldfinch looks very different from his or her parents. In that same turn, male and female goldfinches also look different from each other. This difference in the feather colors between males and females is known as sexual dimorphism. During the summer, male goldfinches are bright yellow with a black head and wings. The females are a muted yellow, and lack the black head.

The young goldfinches were in various stages of learning to feed themselves. One little goldfinch begged his sibling for food...while on the bird feeder. But there was another young goldfinch that was beginning to master the art of foraging. This little one was plucking seeds off my Purple Coneflowers (Echinacea purepurea) in the backyard.

American Goldfinches nest later than other songbirds. Most birds breed late April through mid June but the goldfinches begin breeding in late June through July. These birds breed when milkweed, thistle and other plants have produced their fibrous seeds. The female builds the nest, usually in a shrub or sapling in a fairly open setting rather than within a forest. The nest is often built high in a shrub, where two or three vertical branches join; usually shaded by leaves of clusters of needles from above, but often open and visible from below. The nest is an open cup of plant fibers and rootlets and the interior is lined with the fluffy material surrounding the seed from thistle and other plants. The nest is so tightly woven that it can hold water. 

Goldfinches are seed eaters, even during the breeding season. While most seed eaters, such as Sparrows, switch to an insect diet during the summer months, the goldfinches continue their seed eating diet and feed their young the seeds from trees, flowers, and shrubs.

 

You can find American Golfinches in parks, weedy fields, pastures, grasslands and in fields containing mature sunflowers. They will also eat from bird feeders that offer sunflower and thistle.

You may think that the bright yellow colors of the American Goldfinch really stand out - and indeed they do in a backyard while perched on a bird feeder. But out in a field of flowers, they are well camouflaged. Can you find the Goldfinch in this picture?

Be on the lookout for our pretty yellow feathered friends. If you are around a small field of, or even a cluster of dried flowers, the Goldfinches are sure to be nearby. 

Glossary

Hatch Year: A bird that has hatched during the spring or summer. A young bird will be considered a hatch year bird until January 1st, when all are then considered adult birds.

Camouflage: The colors and markings of an animal or bird that allow it to blend in with its surroundings so as not to be detected by predators.

An Overview of the Arachnids: Spiders, part one.

What is your reaction when you hear the word “spider”? Do you get a shiver down your spine? Do you feel fear or admiration?  There are often mixed reactions to spiders with movies and the media adding to the misunderstanding of our arachnid friends. The point to this entry is to educate readers on the natural history of spiders. You may still not enjoy being around  spiders after reading this blog entry, but perhaps you will take pause and decide not to kill that 8 legged critter scurrying up the wall. 

Spiders are not insects. They belong in the Arachnida class along with ticks, mites, harvestmen (daddy long legs) and scorpions.  There are about 40,000 known spider species. This is an impressive number, considering there are only 4,000 species in the mammal kingdom.   Missouri boasts 480 species of spiders.

Common Missouri Spider by Nancy Zuschlag. MDC Publication

Arachnids have 8 legs and two body parts, a cephalothorax (a fused head and thorax) and an abdomen.  Spiders have 8 eyes that are grouped in 4 pairs and despite all of those eyes, their sight is poor. To compensate for their poor eyesight, the body of a spider is covered in very sensitive hairs that pick up vibrations in their surroundings and the air.  

Spiders have fang-tipped jaws called chelicerae. They use these fangs to inject venom into their prey and to tear food apart before eating. Pedipalps, the limbs (they closely resemble the spider’s legs, but are smaller) in front of the fangs are used for reproduction, grabbing and killing their prey.  Arachnologists (scientists who study spiders) believe these limbs may also have a function similar to antennae. 

The abdomen contains the heart, lungs, digestive tube and spinnerets. The spinnerets, found at the back of the abdomen, produce silk. Spiders use this silk to create webs to trap prey, use as safety lines during climbing, building homes, mating, and egg sacs for their developing offspring. Incidentally, those newly emerged spiders release silk that catches in the wind and carries them to their new home.

Female Wolf Spider with eggs

 

Spider eggs enclosed in silk.

Believe it or not, those 8 legs of the spider have their functions as well. Arachnids can hear, feel and even smell with those legs. Their feet contain tiny claws that allow them to walk on their webs, and walk up smooth surfaces.

All spiders eat bugs and insects but they are separated into 2 different groups according to the way they catch their prey. Hunters, such as Jumping Spiders and Wolf Spiders, do not spin webs, but actively hunt and seize their prey. Trappers, such as Garden Spiders and Trap Door spiders, made webs and lie in wait for their prey.

Let’s spend some time learning about spider silk. Many arachnid species have been using the same genetic silk recipe for the last 125 million years and for good reason. It has been discovered that spider silk is more flexible than nylon and is five times stronger than steel.

Everyone knows that spider webs are made with silk. But what are the components of that web? Each web begins with a single thread that the spider releases into the wind. This single thread forms the foundation of the web. With any luck, the free end of the thread will catch onto another branch. If the thread catches on to something, the spider cinches the silk up and attaches the thread to the starting point. The spider walks across the thread, releasing a looser thread below the first one. The support structure of the web is formed when this thread is attached to both ends and the spider climbs to its center. This is known as the frame thread. The looser strand sags downward, forming a V-shape. The spider lowers itself from this point, to form a Y-shape. The spider continues to create frame threads between various anchor points. Then it begins to lay out non-sticky radius threads from the center of the web to the frames. After building all the radius threads, the spider lays more nonstick silk to form an auxiliary spiral, extending from the center of the web to the outer edge of the web. The spider then spirals in on the web, laying out sticky thread and using the auxiliary spiral as a reference.

Biology of the Invertebrates, 4th edition. Jan Pechenik.

 Once completed, the spider sits in the middle of the web and patiently waits for an unsuspecting insect to fly into its trap. Once its prey hits the web, the spider will feel the motion through the radius threads and make its way to the vibration source. These spiders have the ability to tell the difference between vibrations from insect prey and other sources (such as a breeze, or a leaf falling into the web). Many species can also distinguish the characteristic vibrations of dangerous insects, such as wasps.

Spider eating bee.

Spider silk is a fairly new area of study for Arachnologists and its use holds much promise for the human world.  In a 2002 issue of the Science journal, the US Army and a Canadian biotechnology company reported that they had manufactured and spun the first man-made fiber with mechanical properties similar to that of natural drag line silk. Creating silk is difficult and time consuming (spiders only contain a small amount of silk and mass rearing spiders is a difficult, if not impossible undertaking) but this discovery opens up many potential applications of silk: Body armor (similar to Kevlar), ropes, athletic attire, and medical device components. The list can go on and on.

All spiders have venom but in most arachnids species the venom is not toxic to humans. These eight-legged creatures prey on small insects and do not have the venom geared towards large animals, such as humans. The mouth parts of a spider are not even capable of piercing human skin. Most spiders do not want to bite, but in the unlikely event that it does happen, it’s usually because a person steps on an arachnid with a bare foot or reaches into an article of clothing that the spider currently inhabits.

A great deal of research has gone into spider bites and several studies have discovered that most “spider bites” are not spider bites, but rather allergies, skin reactions, chemicals, biting fleas or bedbugs, infections, poison ivy or oak, among other possibilities. 

Although spiders may be hated and are low on the cuteness meter, they play an important part in our world. That pesky spider that has set up shop in the corner of your ceiling or the baseboard may be preying upon unseen insects in your home, insects that are more likely to bite humans. Spiders can also be a farmer’s best friend. Arachnologists have estimated up to 11,000 spiders per acre in woodlands to more than 2.5 million individuals in a grassland acre. Since each spider in a field may consume at least one insect per day, their cumulative effect on insect populations is significant.  These hungry spiders prey upon grasshoppers, flies, moths, caterpillars, leafhoppers, some bees and ants, and other spiders. If you still dislike the spiders, think about this; spiders are an important food source for birds and other animals. 

Look for an upcoming entry on some of the spider species found in Missouri.

Glossary:

antennae: a pair of sense organs located near the front of an insect's head. Antennae are usually covered with receptors that can detect odors. Many insects also use their antennae as humidity sensors, to detect sounds and some insects (flies) gauge air speed while they are in flight.

arachnid: A variety of arthropods of the class Arachnida, such as spiders, scorpions, mites, and ticks. Arthropods are characterized by the absence of antennae, four pairs of segmented legs and a body that is divided into two regions, the cephalothorax and the abdomen.

genetic (genetics): The branch of biology dealing with heredity. Heredity is a biological process where a parent passes certain genes, such as eye and hair color, onto their children.

natural history: the study of animals and plants.

offspring: new organism produced by a living thing.

thorax: the middle region of the body of an insect.

venom: a poisonous fluid secreted by certain snakes and scorpions usually transmitted by a bite or sting.

The Sounds of Summer

I was in the park one evening last week when I heard the cicadas sing for the first time this season. I love this time of the year, if only for the cicadas and their song. It's free entertainment in the parks, neighborhoods and your backyard. I will often hang out on the patio during the evening to listen to their metallic buzz that builds up in volume until it gradually softens and dies out, only to repeat the chorus again. I find most insects interesting, and the cicadas are no exception.

Let's start at the beginning of the cicada's life cycle.  After mating, the female will make a long slit in a young twig and deposit her eggs.  These slits will often kill the affected twigs, especially oak and hickory trees. If you look carefully, you can find where the females have been actively laying eggs. There will usually be small clusters of brown leaves (especially on the lower part of a tree) among the healthier, green leaves of a tree.

Cicadas undergo simple metamorphosis. After hatching, the young nymphs fall to the ground, burrowing under the ground to feed on sap from tree roots. Nymphs can live up to 20 years, depending on the species and food availability. Periodical cicadas have life cycles of either 13 or 17 years. When the nymphs mature (from Mid-May through July), they tunnel up from underground and crawl onto the trunks of trees or other surfaces. You can look for their emergence holes around tall trees. These holes are about the size of a pinky and there is no excavated soil around the holes.

The new adults will split from their old exoskeletons and emerge in their new bodies. The adults appear white because their new exoskeletons are soft. It takes several hours for the exoskeleton to harden and the adults to gain their characteristic colors.

After emerging, the adults begin to pump their wings up with blood in preparation to fly to the trees. The males begin singing soon after emergence and both sexes only live 5 to 6 weeks.

A cicada's body is made for singing. The adult male cicada possesses two ribbed membranes called tymbals, (think of drums) one on each side of its first abdominal segment. By contracting the tymbal muscle, the membrane collapses inward, producing a loud click. As the membrane snaps back, it clicks again. These muscles rapidly pull the tymbals in and out of shape and the sound is intensified by the cicada's mostly hollow abdomen. The vibrations travel through the body back to the tympani, which further strengthens their song. The male sings to attract a a female, or to socialize with their fellow cicadas.  Each Cicada species sings during a certain time of the day and in its own habitat. Some species only sing while perched on a certain type of plant. 

As a side note, it has been found that cicadas think the sounds made by power tools and lawn maintenance equipment are made by their fellow species. They get confused and will land on the people using the equipment! If this bothers you, cut your lawn in the early morning or near dusk when the cicadas are less active. 

Cicadas also have ways of protecting themselves from predators. Some cicadas will briefly sing from one perch before moving on to a different location. Many Cicada species have colors that blend in with their surroundings, known as camouflage. Singing at dusk makes it difficult for predators that hunt by sight. Other species have bright colors, such as red, that alert predators they are poisonous when ingested (Monarch Butterflies also display the same warning colors). There is also safety in numbers; a multitude of singing cicadas make it nearly impossible for a predator to single out one insect, and even the volume of the chorus can scare the predator away.

There are over 75 cicada species in North American.Two common cicada species in Missouri are the Dog-Day, or Annual Cicadas (Tibicen spp), and the Periodical Cicadas. Dog-day cicadas are larger than periodical cicadas. They are blackish in color and their wings have a greenish edging. Their life cycle lasts from two to five years, but because of overlapping generations, some adults appear every year (usually July through September).

Periodical Cidada. Picture taken in 2011.

The last Periodical Cicada outbreak was in the Summer of 2011

Other cicadas found in Missouri include:   

    Cicadetta calliope
    Neocicada hieroglyphica
    Tibicen pruinosus 
    Tibicen superbus    
Take pause next time you're outside and listen to the summer song of the Cicadas. What beautiful music these insects create. 

Glossary:

Exoskeleton: Skeletal structure formed on the external surface of insects.

Nymph: Immature stage of an insect with simple metamorphosis

Predator: Animal that moves and hunts smaller animals

Simple Metamorphosis: Pattern of metamorphosis that involves eggs, followed by immature nymphs, and finally adults.
 

Eurasian Tree Sparrows; A St. Louis Specialty

St. Louis is home to an Old World Sparrow that normally resides in Europe, the UK as well as China, and Japan. I'm talking about the Eurasian Tree Sparrow (Passer montanus). On April 25^th 1870, Carl Daenzer and a Mr. Kleinschmidt released 20 Eurasian Tree Sparrows and a variety of other non-native finches in Lafayette Park.  German immigrants largely comprised this part of St. Louis and it was popular during this time period to release European birds in the hopes the introduced birds would control the existing insect population and give the immigrants a little taste of home in their new city. The Eurasian Tree Sparrows were the only birds that survived the release and quickly established a breeding population concentrated near the breweries in south St. Louis. 

It is speculated that the initial success of the Eurasian Tree Sparrow was due to the absence of their aggressive cousin the House Sparrow, which did not arrive in St. Louis until 1878. Once the House Sparrow reached St. Louis, the Eurasian Tree Sparrow population boom slowed but the species extended their range to the Illinois cities of East St. Louis, Alton, Grafton and Belleville, all within about 20 miles of their original point of release.

Today small colonies can be found in the City of St. Louis, Ladue, North St. Louis, Florissant, and east St. Charles County. There are now Eurasian Tree Sparrow colonies in Iowa as well. The first sighting of a pair of Eurasian Tree Sparrows was at West Branch in Cedar County Iowa in March 1987. There were no records for 2 more years, and then 10 birds were found in Des Moines County in December 1989.  A pair of Sparrows nesting was confirmed in Burlington in 1993. The Eurasian Tree Sparrow currently has breeding populations in Lee, Des Moines, Louisa and Muscatine counties

Adult Eurasian Tree Sparrow

A several years ago, I assisted UMSL on a study of Eurasian Tree Sparrows and their cousins the House Sparrows. Their findings suggested that Eurasian Tree Sparrows are homebodies and rarely migrate more than a mile from where they hatched. This could explain why their population has not spread across North America in the same manner as House Sparrows and European Starlings. But there are always the intrepid explorers among the colonies who do wander outside their point of origin and it appears they are following the path of the Mississippi River.

 Eurasian Tree Sparrows are social birds that prefer open fields with shrubby vegetation, especially agricultural areas. These ground feeding birds primarily live on a diet of weed, corn, millet, wheat and sunflower seeds, grass seed and seed shoots but feed their offspring a diet of insects and arachnids during the spring and summer months.

Breeding season begins in April for the Eurasian Tree Sparrow and ends in July (Baicich and Harrison 1997). These birds are cavity nesters, using tree holes, nest boxes or other man-made structures to build their nests.

These birds create an orb-shaped nest with the outer layer composed of coarse grass material and the inner portion lined with down and finer vegetative matter. Eurasian Tree Sparrows can have up to 4 broods per year, though 2-3 broods is the average. Each clutch consists of 1-8 oval eggs (but the average is closer to 4-5 eggs) and incubation lasts 11-14 days. The young fledge around 12-14 days.
 

Eurasian Tree Sparrow chick I banded last summer.

The House Sparrow (Passer domesticus), is an aggressive nest competitor with the Eurasian Tree Sparrow and will displace the latter species from a given habitat. Though both birds are able to adapt to many habitats, the House Sparrow appears to prefer urban areas while the Eurasian Tree Sparrow will occupy more rural, agricultural areas.  However, the Tree Sparrow will move into parks and suburban areas when pushed out of their preferred habitat by their House Sparrow cousins.           

I do know from personal experience that Eurasian Tree Sparrows do visit bird feeders and inhabit backyard nest boxes. Be on the lookout for that little sparrow with the black dot on its cheek.