Tadpoles in the Pond

We have several tadpoles in our classroom's pond.  To see them, you have to be a little bit lucky.  Now that it's warm, the fish are easy to see - they are out in the open water, swimming smoothly and darting skillfully.  But tadpoles are a different story.  They lurk near the bottom in the leaves and muck.  Every once in a while, they clumsily wriggle from one spot to another.  The best time to see them is when you first walk up to the pond - they will wriggle to a hiding spot in response to the shadow you cast over the pond (they respond as if you were a predator!).  If you don't see one right away, wait around and watch - it might be your lucky day.  You could also take matters into your own hands and scoop through the bottom of the pond with a net.  If you do, please keep the tadpole in the water - they are very fragile and can't survive being dry or being squished.

A tadpole in our pond at the outdoor classroom.

Tadpoles are truly strange creatures.  They are the larval (young) form of frogs.  Frogs lay eggs in water, each of which will hatch into a tiny tadpole.  The tadpoles use gills to breathe water - just like fish do.  Tadpoles swim and eat and grow larger and larger, all underwater.  Eventually when conditions are right and they have had enough food, the tadpoles' bodies change form completely.  Their bodies digest and absorb their tail, and they grow tiny forelimbs (arms) and hind legs.  As they change external forms from tadpole to frog, their internal structures change too.  They grow lungs for breathing air!  Adult frogs hop out of the water and live their adult lives mostly on land but near water.  A change in body form like tadpoles have is called a metamorphosis.  If your body changed and suddenly grew wings for flying, that would be a type of metamorphosis.  Other animals that do metamorphosis are insects (maggots become flies, caterpillars to butterflies, etc.).

Tadpoles and frogs are vertebrates.  Vertebrates are any animals that have an internal skeleton with a backbone.  That means mammals, birds, reptiles and fish are also vertebrates.  Can you think of animals that don't have backbones? (Answer below*.)  Any vertebrate that starts its life in the water and undergoes metamorphosis is called an amphibian.  The word amphibian makes sense if you know what the parts of it mean: amphi- means both, and -bian means life form.  Amphibians include frogs, toads, newts and salamanders. 

Why do you think fish are such better swimmers than tadpoles?  Compare the body shape of a tadpole to a fish, then try an experiment.  First, find a pool and a life guard.  Then jump into the swimming pool and swim like normal using your arms and legs to help you.  Then hold your arms and legs into your body and try to swim - it's not so easy without appendages, is it?  Tadpoles do not have fins like fish do, and fins are great for steering while you're swimming.  They have only a tail to help push them along.  That's why tadpoles wriggle around so strangely and fish swim with ease.

How do you think the tadpoles got to our pond?  Frogs had to have laid the eggs that grew into these tadpoles, but how did the frogs get to our pond?  They have to stay near water, and there aren't other ponds nearby.  Frogs could not have gotten to our pond to lay eggs!  One possible answer could be related to the fact that frog eggs are somewhat sticky.  If a bird stood in a different pond and frog eggs stuck to its feet, then the bird came to our pond, it could have brought the eggs that hatched to our tadpoles.  That makes frog eggs disperse just like the kinds of seeds that stick to animal fur - which would be animals imitating plants!

*Invertebrates include insects, spiders, clams, snails, sponges, jellyfish, sea stars, and thousands more types of organisms.

Turdus migratorius, American Robin

The robins are here!  For such a pretty and lovable bird, they have a very unflattering scientific name: Turdus migratorius.  The migratorius part isn't so bad, and robins are indeed migratory birds.  But why the name Turdus?  Scientific names are in Latin, and 'turdus' means 'thrush' in Latin, which is a bad deal for the robin.  A thrush is a type of bird that is usually small and plump and searches for food on the ground.  Bluebirds and wood thrushes are other common Middle Tennessee thrushes.

A male robin.

Robins are grayish with rusty undersides.  The males' heads are darker than their backs, and their underbellies are usually brighter than females'.  Last week a male and female were getting to know each other at our outdoor classroom. 

A female robin.

 In Nashville, this time of year robins are just finishing up their winter migration.  Robins group together near the end of winter into massive flocks (did you notice them a couple weeks ago?), then they migrate to follow food sources and warm weather.  They may not migrate straight north like most other migratory birds do - they just go wherever life is good for robins, which explains why we have some robins here year-round.  At the end of the winter migration, birds form pairs and begin to find a home range to nest in.  They may come back to the same place as last year, but they may not.

A female robin between the two Japanese quinces.

Robins are generalists in both nesting and in feeding.  They build nests in a variety of habitats, from landscaped yards to meadows to forests.  They eat a variety of insects, worms and fruits, depending on what is available to them to eat.  In the spring and summer, they tend to eat more insects, and in the fall and winter they eat more fruit and berries.  This time of year, you are likely to see the cliché of a robin with a worm dangling from its beak.  Robins can usually find their food and shelter requirements around where humans live, so they tend to be very familiar to us.

A female foraging for ground insects or worms and a male sitting on the fence.

If the male and female I saw at our outdoor classroom become a pair, they will have 2-3 broods of baby robins this spring and summer.  The female will soon start building a cup-shaped nest of three layers: twigs first then mud then grass on the inside.  She will probably lay 3 light blue oblong eggs in the nest a couple of days after it is finished.  The female sits on the nest for 12-14 days, getting up every once in a while to turn the eggs or go get food.  The male might bring her some food or might not.  The female's belly has a patch of skin with extra blood vessels that keep the eggs warm as she sits on them.  If the eggs get too cold, they will die.  When the eggs hatch, the female tosses the egg shells out of the nest and broods (sits) for another 3-4 days.  After that, the hatchlings are able to keep themselves warm enough without being sat upon constantly.

Both parents feed the hatchlings after they escape their eggshells.  For the first few days, the menu is regurgitated food the parents already ate.  And if that isn't gross enough, after that the parents bring soft-bodied insects and worms to feed the poor little birds.  The hatchlings beg and peep like mad for their food, so they must like it.  Begging is an important skill for robin hatchlings, because the most aggressive peeper with the longest neck and widest-open beak will get the most food and is most likely to survive to adulthood. 

At two weeks old, the robins usually fledge (leave the nest).  They still don't fly well or know how to find food, so the parents hop around them on the ground alerting them to danger and bringing them insects and berries.  At first, the mom feeds the fledglings, but then when they are starting to become independent, the dad will feed them, and the mom will go and build a new nest for the next brood.  The fledgeling stage is very dangerous for the birds because the young ones can't fly yet.  They might become the food that a mother hawk brings home to her hatchlings, or they might fall prey to a cat.

There are many types of birds at our outdoor classroom right now.  Next time you go, try to count the different types of birds you see.  Last time I was there, I saw 3 kinds.  Pay special attention to the robins, and see if you can figure out what they are doing when you see them (feeding? gathering nest materials? searching for a good nest site? fighting off other birds? or are they watching you?).   

Cirque de Squirrel

It's a good thing you know what squirrels look like, because I don't have a picture of a squirrel for you!  I wanted to write about them this week, but when I went to take pictures, they were gone for the day.  That's OK, though, because there is plenty of squirrel evidence visible in our outdoor classroom.  If you visit and don't see actual squirrels, look for clues instead.

Squirrels are messy eaters.  They unwrap their food, eat what's inside, then drop their food wrappers all over the place.  If you walk around the outdoor classroom and look down at the ground, you can see their food wrappers (complete with squirrel teeth marks) all over the place!  (You may notice that humans are also sometimes messy eaters - I picked up several human food wrappers out there this week.  Somehow human food wrappers are less adorable than squirrel-chewed walnut shells.)

Evidence of squirrels.

Another visible sign of squirrel activity is squirrel nests.  If you look to the top of the magnolia tree in the front yard of the beautiful building next to our classroom, you can see a squirrel nest.  Do you see it in the picture below?

Can you see the squirrel nest in the top of this tree?

Here is the squirrel nest a little closer:

Squirrel nest in the top of a magnolia tree.

Squirrels are probably the easiest topic for me to make interesting, because just about everything squirrels do is either hilarious, cute or annoying.  Here are a few fun things you might notice about them this time of year if you stop to watch them for a while.

1. Acrobatics.  Squirrels climb up and down all sorts of surfaces.  They are the only mammals that can climb down trees face-first, which they do by turning their back feet around as they descend.  Squirrels chase each other on mad dashes through the tree tops, often making great leaps from one tree to another like circus performers on a trapeze.  They also have a great high-wire act - squirrels commonly run across electric and telephone wires as easily as we run on sidewalks. 

2. Nest design.  Squirrels make extremely well-insulated nests in crevices in buildings or trees or constructed in tree branches or on top of bird nests.  They layer their nests with feathers or thistle or dandelion down (those feathery parts of the seeds).  When their nests are made of leaves, they can add layer after layer of leaves to make a hollow ball for sleeping.  The layers of leaves keep the rain out and the heat in.  Since squirrels don't hibernate, they need to keep their body temperature warm all winter, so their nests are important for keeping them warm at night, just like your nest, er, I mean, bed.  Look for squirrels carrying leaves or other materials to build nests next time you see one.  (You can try out a leaf nest for yourself.  If you layer about 50 tightly-packed leaves carefully over a balled-up paper towel then sprinkle water over the top, the paper towel is unlikely to get wet.)

3. Variety of Behaviors.  Squirrels are generalist feeders.  We always think of them as eating only nuts, but they also eat tree bark, berries and seeds.  Generalist feeders tend to have a much wider variety of behaviors than animals that eat only one thing.  Generalists must be curious about new food sources and adapt their food searching to a variety of challenges, which means their brains must be flexible and able to improvise.  Nothing against cows, but compare the variety of behaviors of squirrels to cows, and you can see what I mean.  Try making a list of all the things a squirrel does next time you see one.  I'll start: chase, dig, search in the grass, make a loud alarm call, climb up bricks.....

4. Problem Solving.  If you've ever had a squirrel figure out how to access the seeds in your bird feeder at home, you have seen the evidence of squirrels' ability to solve problems.  Once they locate a food source or nest site, they will try many new strategies to succeed in their plans to eat or build a nest.  Notice how ingenious this squirrel is at getting to what he wants despite human attempts to keep him out of the bird feeder.  Squirrels are an inspiring reminder to try many different strategies to succeed at a task.

5. Memory.  Squirrels have an unusually good memory for where they leave food.  They store food for the winter in a method called scatter-hoarding.  It's the opposite of how humans store food - all in one place in the kitchen pantry.  Squirrels leave little patches of food buried or hidden in hundreds of places, and they remember where they leave the food (they don't find their stashed food by smell - they find it by memory).  Scatter-hoarding is risky because squirrels can't guard all their food at once.  However, if their food is discovered and stolen from one location, they still have hundreds of backup locations that are unlikely to be raided.  Look for squirrels burying their food - the squirrel is almost 100% likely to come back and dig up that food later in the season. 

6. Deception.  I'm not condoning lying, but it sure is amusing to watch squirrels lie!  If a squirrel knows it is being watched by another squirrel, it will not actually hide its food.  Instead, it will pretend to hide the food by digging a hole, pretending to drop in a nut, and covering up the hole.  The watching competitor squirrel will be fooled, then the squirrel will go and hide the food in private so as not to reveal the hiding place.  It is easy to verify if a squirrel has lied.  Next time you see one bury a nut, go check and see if the squirrel has actually done so or if it has fooled you too.

Help! I've Got Hackberry Leaf Galls!

Last week students in our outdoor classroom sent the picture below, wondering what it was.  It's a very logical question, since those...things are growing out of what is obviously a leaf, but no normal leaf has weird miniature mushroom-shapes growing out of it.

Hackberry Leaf Galls (photo: M. Sherman)

The leaf above comes from a hackberry tree, whose bark I think is fantastic, and which we will explore later in the winter.  We have a gigantic hackberry tree in the outdoor classroom, and it's at the end of the row of parking spaces near the road.  Here's our hackberry:

Hackberry tree with most leaves already gone for the winter.

If you search through the fallen leaves around the classroom, you can find lots of hackberry leaves right now.  They have toothed edges (lots of tiny points), and they narrow to a tip.  Also, the wider end of the leaf usually is lopsided with one side larger than the other.  Most of the hackberry leaves have one or more of those big lumps on the lower side of the leaf.  The lumps are called leaf galls, and they are scar tissue the tree has grown in self defense against a parasite.

Three hackberry leaves, two with galls, one without.

So, what exactly is a parasite, you ask?  A parasite is a small organism that lives on a larger organism and often uses the larger organism for food, harming the larger organism in the process.  The larger organism is called the host.  There are lots interesting types of parasites in this world.  Dogs and cats sometimes have fleas for parasites.  Deer often have ticks.  Humans can sometimes have lice.  And plants can have parasites too.  The parasite on our hackberry leaves can only live on hackberries, not humans.  It is a type of insect called a psyllid (SIL'-id).  Psyllids look just like tiny cicadas - smaller than a grain of rice.

I broke open this gall, but it was empty.  The adult has already emerged from it.

Hackberry leaf psyllids lay their eggs on the underside of hackberry leaves in the spring.  The eggs grow into immature psyllids that look like this.  The psyllids damage the leaves, which causes the leaves to grow a lump of scar tissue (a gall).  The psyllids eat hackberry sap and live inside the gall as they grow larger through the summer.  In the fall, the psyllids grow into adults and drill out of the gall.  They fly or crawl to find crevices in bark or buildings to overwinter safely.  When the weather warms up in the spring, they lay eggs and start the cycle again. 

Hackberries grow well in Middle Tennessee, yet they almost always have hackberry leaf galls damaging their leaves.  The trees don't seem overly harmed by the gall psyllids' damage.  This is normal parasite behavior.  Most parasites don't cause extensive harm to their hosts.  They take just a little food from them but not enough to kill them.  If a parasite ate too much of its host and killed it, the parasite would be out of food and would die too.  Parasites use their hosts in a sustainable manner so that their food source will be available in the future.

Busy Fall Ants

Edward O. Wilson is one of my scientist heroes, and he has studied ants for most of the 83 years of his life.  As a child, he loved to go outside and observe ants for hours because they exhibit such a variety of behaviors.  E. O. Wilson eventually became the world's leading myrmecologist (ant expert), as well as an expert on ecology, animal behavior and conservation biology.  Thanks to him, I know some really amazing things about ant behavior, and I always think of him when I observe ants.

A foraging ant.

The ants at our outdoor classroom are busy, busy, busy this time of year.  Frost is coming soon, and the ants are foraging for their last bits of food to help get them through the cold weather coming our way.  If you stop and observe the rocks around the pond, you will start to see some patterns in the ants' behaviors as the ants bustle around in a mad rush to get ready for winter.  Below are some patterns in ant behavior that I observed.

An ant and her shadow.

The ant above was exploring to find food, also known as foraging.  Any ant exploring on its own in a zig-zag or random fashion is most likely foraging for food.  When the ant finds food, it will pick up the food and bring its food back to the ant's nest to share with the other ants in its colony.  If there is more food than it can carry, the ant will do something incredible.  It will leave a scent trail on its return to the nest to signal to its nest mates to go and get the rest of the food!  How amazing that these tiny creatures can communicate such complex information to each other.

Ants following a scent trail.

Ants are social insects that live in colonies.  The ants in a row in the picture above are interacting as a social group by following a common scent trail.  Either they are all going to get food or they are moving their colony.  Ants usually maintain a nest in a space in or near the ground.  The nest stores their food and eggs.  The ants in the picture above are all sisters!  I know this because all worker ants are female and are sisters.  The sisters work together to keep the colony alive and take care of their mom, the queen.  The queen stays in the ants nest and lays eggs.  If you look closely at a line of ants, you might be able to see if they are carrying bits of food or eggs.  If they are carrying ant eggs, they are moving the colony.  There is a colony of ants outside my back door that moves its nest every time it rains: from under the flower pot in dry weather to under a loose brick when it's rainy.  They never seem to get tired of carrying eggs around.

Ants deciding if they are friends or enemies.

If you observe a line of ants, you will probably notice ants are going in both directions, like in the picture above.  That means the ants run into each other.  Every time an ant runs into another ant, it needs to determine if the other ant is a friend or an enemy.  Enemy ants must be run off the territory or killed and eaten, and friendly ants must be allowed to pass.  Ants don't recognize each others' faces; rather, they smell each other with their antennae.  It takes just a flash for the ants to touch antennae, recognize each other, then head on their way. 

Ants are extremely important creatures on Earth.  They live in the soil and on trees and other plants, and they help recycle nutrients in ecosystems.  Ants build soil, eat pest organisms, and provide food for other insects and for birds.  Some plants are pollinated by ants, and some seeds are dispersed by them too.  E. O. Wilson has estimated that ants account for about the same amount of mass on Earth as humans do! I wonder which has had a greater impact on our planet.  I know humans have built cities and houses and reshaped the ecosystems, but ants have built the soil that all other terrestrial ecosystems are built on.

Tube Flowers and Their Pollinators

Butterfly bushes (Buddleja sp.) are very well-named.  The ones in our outdoor classroom are usually surrounded by several butterflies flying from flower to flower and filling their butterfly bellies with nectar.  If you look closer, you'll notice that lots of types insects like butterfly bush nectar, and even hummingbirds have been known to drink from these flowers.  Because of the shape of butterfly bush flowers, not all nectar-feeders are able to use these plants.  All butterfly-bush-feeders must have long, thin mouthparts that fit into the flowers.  Notice the long curved proboscis on the skipper in the photo below.  The proboscis works like a silly straw, curving and extending into the base of each flower for a sip of nectar.

A skipper sipping nectar on a butterfly bush.

Below you can see one individual flower of the butterfly bush.  The green bit is the base of the flower where nectar is produced.  The purple petals form a tube that opens at the top of the flower.  The tube shape does a good job of keeping out insects that steal nectar without pollinating the flower.  Insects that can reach their mouthparts into the flower receive a dusting of pollen as they sip nectar.  When the insects move to the next flower, they drop off the pollen, allowing the flower to produce seeds.  Nectar-sippers and flowers have a trade-off where each organism benefits from the arrangement: flowers are pollinated and the pollinators get food.  This relationship is called a mutualism, and it is a type of symbiosis where two organisms benefit from the interaction.

A single tube-shaped flower of the butterfly bush.

The purple tube-shaped flowers have orange centers to help insects find their way into parts of the flower where the nectar is produced.  Most flowers have nectar guides in their centers.  Usually nectar guides are yellow or orange regions with lines pointing to the center of the flower.  Next time you are at the outdoor classroom, look for nectar guides in butterfly bush flowers and any other flowers you'll see.

Yellow/orange nectar guide inside a butterfly bush flower.

Below you can see two more organisms that are mutualists with butterfly bushes: bees and longhorn beetles.  Both pollinate the flowers and get fed in the process.  There are some insects that 'cheat' the butterfly bushes out of their pollen.  Some types of caterpillars, beetles and ants chew through the base of the flower, drink the nectar, and leave without pollinating the flower.  Look carefully at our butterfly bush flowers for some crime-scene evidence:  if you see holes chewed through the base of their tubes, you know the nectar has been stolen with no pollination payment in return!

Bumblebee and longhorn beetle working the butterfly bush flowers.

Interesting side not:  The bumblebee in the photo above was not actively feeding.  It was just holding on and resting.  This time of year, the temperatures are dropping, and insects that don't overwinter are nearing the end of their lifespan.  It could be that this bee is slowing down because it is old.  Alternately, the bee could be finding its home for the night, since I took this photo in the early evening.  Bumblebees often sleep in large flowers or near small flowers so they have a food source in the morning (wouldn't you love to sleep in a flower?).  A third possibility is that the bee is just slow because the temperature is lower.  Some bees just slow down when the temperature drops, stay in a torpor through the cold winter, and then speed back up again in the summer when it's warm.

Rethinking the Canada Goose

Don't say Canadian - it's Canada.  The Canada goose (Branta canadensis) is a common sight in Lincoln Park, and I got to know their behaviors a little better as I watched them raise their young this spring.  Despite what some people say, they're really quite enjoyable neighbors.

Canada geese pair and young in Lincoln Park.

The geese started hatching in early May this year, and within a day or two, they were out of the nest walking and swimming and finding food.  Adult geese mate for life, with the average goose living around 24 years of age in the wild.  They tend and defend their young, but they do not feed them.  The goslings feed themselves as soon as they are out of the nest. 

Dabbling geese with a duck observing them, probably finding their upended tails completely hilarious.

Geese eat muck from the bottom of ponds, as you can see them doing in the photo above.  The tails-up bobbing for scum is called dabbling, and it never fails to crack me up.  Geese also eat grass, grains, berries and other plants, with the occasional bug thrown in.  Herbivores in general must eat a lot more volume of food to survive, and geese seem to eat constantly.  Such a large volume of food results in respectable quantities of goose poop, which people sometimes find annoying.  Admittedly, there are some beach areas in the US with hundreds of Canada geese where I would not want to walk barefoot or swim, but these are not the norm.  A little bit of goose poop is certainly better than a little bit of dog poop, since carnivore poop usually contains more harmful disease bacteria than herbivore poop.

Many of the geese in Lincoln Park probably flew north to Chicago earlier in the spring from the southern US or Mexico.  More Canada geese are migratory than non-migratory, though some members of the species have begun to live in the same location year-round.  The newer, non-migratory geese are an evolutionary response to the recent changes in their habitat: in the past 100 years, permanent open grassy areas with maintained, predator-free ponds have appeared everywhere.  Indeed, golf courses, airports, office complexes and neighborhoods provide goose heaven, and Canada geese have increased their numbers in response.  Once a fairly rare species, the Canada goose has become common enough to annoy annoyable people, sometimes even being called a pest.

In Lincoln Park, people mostly seem to enjoy the geese.  They watch them, photograph them and feed them, despite signs forbidding the feeding of wildlife.  The goslings provide food for the black-crowned night herons, and the geese eat excess pond vegetation.  Canada goose behaviors are fairly simple and easy to observe, so lots of kids and adults learn about bird biology by observing geese.  Unfortunately, geese seem to be such a common sight that some people have lost their respect for the geese's size and strength.  Parents let their toddlers chase the geese and approach the young, even with the parent geese hissing and ready to bite (yes, they lunge, flap, bite and cause an unnerving ruckus in self-defense).

A wood duck (left) hanging out with Canada gees (right) at the Alfred Caldwell Lily Pond in Lincoln Park.

Where Canada geese are a considered a nuisance, wildlife management personnel have responded with extended hunting seasons, attack dogs, culling of adult birds and donation to food charities, collection of eggs for human consumption (I hear they are delicious) and addling of goose eggs.  Addling is a technical term that means preventing an egg from developing without destroying the egg, by shaking or coating with oil to prevent oxygen from diffusing into the egg.  Goose eggs are addled instead of being simply taken because the geese can lay a second clutch of eggs.  Canada geese, like most animals, are regulated.  Geese are regulated by the Migratory Bird Act, so before someone dabbles in addling, they must apply for a permit.  An easier humane solution to overpopulation of geese would be to modify habitat to make it less inviting.  Geese will not nest in an area without good sight-lines for detecting predators, so smaller patches of lawn interspersed with shrubs or potential predator hiding places will deter them.  If we take a little time to appreciate and get to know Canada geese, they seem much less like nuisances and much more like fascinating clowns of the bird variety.

Black Crowned Night Herons in Lincoln Park

There is a surprising diversity of animal life in Lincoln Park, and that's not even counting the zoo animals.  The latest residents of the park are what appears to be dozens to several hundred nesting black crowned night herons.    The two lumps in this picture are black crowned night herons.  Don't see lumps?  There's one in the center and one left of center near the top.  Try squinting. (Another neat thing about the picture is the lack of overlap in the adjacent tree canopies - competition for light.)

Black Crowned Night Herons Nesting in Lincoln Park

During the day, night herons sleep and nuzzle and generally take it easy.  I'd love to show you a picture of how cute this is, but the area is fenced off, and I don't have a zoom lens.  Trust me - it's cute.  Imagine fat birds cuddling with their heads tucked into each others' feathers.  Here's a better picture from the Lincoln Park Zoo website.  As the birds sleep on their nests or on nearby branches, the wind is waving the branches around like mad.  I wonder what it feels like to have wild rocking be one's version of sitting still.  It must make standing on solid ground feel uncomfortable.

These night herons are nesting in Lincoln Park for the second year in a row.  According to a birdwatcher I met by the night herons who seemed to know everything, this population used to nest in a wetland southeast of Chicago that was destroyed.  Then they moved to an island near Lincoln Park, and last year they moved here - just south of the zoo along the main promenade.  The zoo and the park have erected fencing around the nests for two years now, cutting off the main thoroughfare in the park for several weeks.  Everyone seems to be happy to welcome the birds, and they are back despite the busy park traffic, bagpipe players, dogs, soccer matches and live music concerts.  It will be interesting to see if the new habitat allows their population to survive or diminish.  They have nested earlier due to the extremely mild winter. 

Night herons hunt at night, and they eat all sorts of small meat items - fish, frogs, birds, squirrels.  Given the number of squirrels, geese and ducks in the park, it may be a good thing to have a top predator around to help control populations of these other organisms.

Leopard, Contained

Today I watched a leopard pace in its tiny cage.  Male leopards are used to 30 square miles of home range, and this one was lucky to have 30 square yards.  This subspecies of leopard, the Amur leopard, is critically endangered in the wild, and the zoo is participating in a conservation program that likely helps to maintain biodiversity so the species doesn't go extinct.  Nevertheless, this leopard was pacing.  There was a clear path worn in the grass, and he was bored.

Amur Leopard, Panthera pardus orientalis.

Leopards are often confused with jaguars and cheetahs, but once you look carefully at their spots, you won't confuse them again.  Leopards have hollow spots, called rosettes.  Jaguars' rosettes have little black spots inside each one.  Cheetahs have solid spots.  Leopards are the largest and stockiest of the three, with large males tipping the scales at 200 pounds, though most are smaller.

Notice the empty rosettes that indicate this is a leopard, not a jaguar.

Leopards' biggest difference from other big cats is a behavioral characteristic.  They are generalist carnivores.  They will eat anything from the size of a dung beetle to a 2000 pound male eland, as long as it is in the Animal Kingdom.  They prefer prey in the 44 pound - 175 pound range, which is a bit disconcerting for a species with most of its members in the preferred prey size range.  Leopards could take humans for prey easily - their range overlaps with humans, they are well camouflaged, and they can hide around human settlements.  For some reason, leopards don't choose to take humans - they hunt all other animals preferentially.  A few leopards that were injured or sick have taken humans as prey in the past, and once they started, they kept doing it until they were killed.

As explained in a previous post, generalist predators tend to have more intellectual capacity than predators that don't have to make as many decisions or learn about as many different types of prey.  Leopards hunt alone, which means they are unlikely to evolve complex social interactions, which is likely cold comfort to their prey.  Leopards are definitely stronger than other big cats of similar size, and they have been observed hauling prey up to three times their weight high up into trees to save for a later meal.  This combination of strength and intelligence makes the leopard particularly awe-inducing to me. 

The highlight of our leopard-watching for the day was a dangerous game between the leopard and a squirrel, two smart-cookie generalist consumers.  The squirrel had found a prized piece of hot dog bun near the leopard cage and was trying to decide whether to eat it in place or carry it away to another location, a vegetarian version of the leopard's prey-stashing.  The leopard heard the leaves rustling around the squirrel, crouched, sighted the squirrel and pounced.  The leopard was denied its afternoon snack by only a thin wire fence.  The squirrel continued to appear to frolic in the leaves, rustling them unnecessarily along the edge of the cage for another minute or two before it left to gorge on simple carbs.  The leopard was as agitated as a house cat being teased with crinkly paper.  It struck me that the squirrel had learned the fence would hold and ignored the deadly but contained predator.  The leopard had not completely habituated to the fence and continued to respond to temptations on the other side.  It either hadn't learned the fence was immutable or its brain was so exquisitely tuned to the rustling prey sounds that there was no other possible behavioral response the leopard could offer at the moment.  If you have ever played with  house cat, it certainly seems that they are compelled to pounce on rustling things - perhaps it is the same with big cats.

Leopard focused on a squirrel just two feet away.

Zoos and Conservation

The Lincoln Park Zoo is on my daily walking route now.  It's free and open to the public, and I can power walk right through or linger and marvel, depending on how I'm feeling and what the animals are up to.  It's a small zoo, but the construction of several of the animals' enclosures allow for jarringly intimate observations of the animals.

The gorillas and chimpanzees, in particular, are housed in such well-designed pens that I find myself moved and astonished by them as has not occurred in other zoo experiences.  The floors are elevated so the monkeys eyes are level with mine and the high-quality non-distorting glass allows a 1" distance between my skin and theirs.  I can see subtle changes in facial expression, lines in the soles of their feet, and individual hairs between the fingers of grooming chimps. 

A chimp comforting another after she was refused food by a male.

The resemblance in anatomy, emotion and behavior to humans makes these animals more interesting to watch than any other in the zoo.  Their enclosure is interesting enough that they seem to feel comfortable exhibiting a variety of the complex behaviors I have read about in Jane Goodall's accounts.  They groom each other, ask for food, diffuse conflicts, climb, play and interact with their surroundings.  It is difficult not to assume one understands their motivations and behaviors, since they look so much like us.

I watched this chimp make a nest of burlap sacks, try it out several times, readjust the burlap then roll over and suck her toes.

After awe and utter fascination, the strongest sentiment I have when watching these creatures is how unfair it is that they are put on display in fancy prison cells.  They clearly have lesser environments than they would in the wild.  Their behaviors and free expression are constricted.  They are aware of the constant stream of eyes looking at them.  The big silverback gorillas protest their enclosure by sitting with their backs always to the glass.  The animals are not happy about being enclosed.  I always imagine some more powerful aliens coming to earth and capturing a few of us for their zoos at home.  We would be outraged.

And yet, there is some considerable benefit to animals in zoos from a conservation perspective.  Zoos create opportunities for the development of strong affection of humans for animals, making us care about their continued presence on earth.  We are more likely to push for the conservation of chimpanzee habitat after experiencing reverence for them in a zoo.  In the worst case scenario, zoos have been the last refuge for species that are almost extinct.  The black-footed ferret once existed solely in zoos and has been reintroduced into wild land.  Zoos also provide the means for maintenance of genetic biodiversity, by shipping sperm or arranging for matings, so that a species has a wider variety of genetic combinations, reducing the likelihood of extinction.

If it were up to me to decide to free all the animals in zoos or keep them, I would be strongly conflicted.  Clearly it unethical to keep socially complex animals in tiny, uninteresting enclosures.  As zoos expand and enrich their animals' habitats, the balance shifts more toward the value of zoos, especially since humans will apparently destroy all natural habitats without education and enforcement of the alternative.  Zoos are an imperfect solution, but it seems that at least some zoos are necessary in our current world.  I know I'm going to spend a lot of time in the ape house at our zoo while I'm in Chicago, but my amazement will always be tinged with pity.

Decisions, Decisions

As I was walking on my new daily exercise route in Chicago (up Lake Michigan's shore and down through Lincoln Park and the zoo - tough, I know), I almost stepped on these two mating cicadas.  They made me ponder the behavioral decision-making processes in animals. 

Two-headed cicada!

I'll start with the assumption that behaviors exhibited by animals are generally the result of a long evolutionary history, with a little improvisation and chance thrown in here and there.  This means that behaviors exhibited by animals are ones that caused their ancestors to have more offspring and pass on the traits for exhibiting those behaviors to their offspring (thanks, Charles Darwin).

Clearly the mating behavior I observed in the cicadas is necessary for the production of offspring and passing on genes to the next generation.  However, the fact that the cicadas were mating in the middle of a well-traveled concrete pathway would seem to be counterproductive in the Darwinian struggle for progeny.  Cicadas as a species are probably in the middle of a subtle evolutionary shift wherein those cicadas that mate on tree branches and in grass survive more often than those that mate on concrete.  How genes could be involved in that particular behavior, I don't know.  But I do know that fairly complex behaviors have genetic components.  For example, type of tree branch used for nest site choice in birds can be genetic. 

Obviously the cicadas were incapable of the complex thought process needed to see that mating on a sidewalk would get them both squished and that they should just move 6 inches to the left into the grass.  Animals are not thought to behave rationally.  That means they don't weigh the pluses and minuses of behavioral choices - they just act.  This always brings me to the following questions:  If animals don't actually decide what they are going to do, why do they do anything at all?  And how do they know what they should be doing?

For behaviors to evolve, there has to be a way for animals to 'know' that they are choosing a good behavior versus a bad behavior.  There must be something similar to pleasure and pain to reinforce good and bad choices.  In fact, the hormone that causes pleasure and contentment in humans (oxytocin) has been found in animals.  Animals also have adrenaline rushes, which elicit fear, panic and aggression in humans. 

Unfortunately, there is no way to know what an animal actually feels, so we must come to conclusions by analogy.  If oxytocin is released, the animal must feel something positive - perhaps calming or pleasurable, because that's how it works in people; if adrenaline is released, it must be the equivalent of scared, etc.  An animal that feels pleasure when it swallows food, drinks water, mates and finds safe locations to rest will probably survive.  An animal that feels fear when a larger, unfamiliar animal is near will respond by running away or fighting, both of which can extend life span. 

My favorite example of how this might work involves a study of my least favorite organism: roaches.  In a study to mimic roach behavior, scientists programmed tiny, roach-shaped robots to be still when they are in dark places and near other roaches and to run fast when they were in the light.  With this simple behavioral program, the roaches ended up behaving almost identically to real roaches.  I imagine that in real roaches' ganglia (little clusters of nerves throughout their bodies that act like little brains), they feel roach-y contentment in dark, tight spaces with buddies around, and they feel panic when the lights come on.  Oddly enough, in a test to see if roaches have a stronger preference for darkness or being around their roach pals, they chose the social environment over the safe environment.  Who knew roaches were such followers? More. 

There must be at least a few cicadas out there with a mutation that makes them fear stepping on concrete and therefore move away quickly when they find themselves on it.  The concrete-fear gene should confer an advantage to those cicadas, as they would be less likely to be scraped out of the treads of a tennis shoe one day.  Assuming humans keep building and using concrete sidewalks, some day all the genes for sidewalk-mating will have been eliminated, and only the concrete-fearing cicadas will have survived.  Cicadas as a species will be smarter, all without a single cicada having to think an actual thought.

Of course, humans always make their decisions based on cold rationality, because we have the ability to think and separate our emotions from our thoughts.  We have evolved brains capable of weighing our options and choosing the best path, so we don't need instinctual behaviors.  ...Not so fast!  We have plenty of positively- and negatively- reinforced behaviors: pleasure for eating, playing, making a home and mating, and pain from loss, fighting and overwork.  Humans have repeatedly been shown to act irrationally in less obviously evolutionary ways too.  Some of us take unnecessary risks, get pregnant too young or fall in love with the wrong person.  We have even learned that the average of millions of human decisions is not based on rational principles, as it is impossible to explain or predict the stock markets. 

We must be careful not to fall into the trap of assuming humans are so different from other animals.  There are evolutionary payoffs to many irrational behaviors.  Risk-taking can result in big rewards in status and resources, and perhaps more mates to pass on risk-taking behaviors.  Teen pregnancies tend to pass on genes early and often (not that I'm advocating teen pregnancy).  Romantic decisions are made at least sometimes based on evolved chemical signals (pheromones and antibodies) that might signal compatibility and more healthy offspring.  Human social tendencies can lead to careless financial decisions just as roach social tendencies can draw roaches into unsafe locations. 

So how much of our behavior is instinct and how much is logic?