hawkowlchicks

Is this a dragon paw?

shredded turtle foot

found by the dog

The Question: Look what my dog dragged into our home! Can you help us identify who/what/where this claw came from?? It was about the size of my palm. My son says it looks like a dragon paw!

Submitted by: Susan, Wisconsin, USA

(click on photos and graphics to expand)

The Short Answer: The only wild animal in Wisconsin that this could possibly come from is a large snapping turtle. Three very similar species of snapping turtles are found only in the Americas, with a Central American version (Chelydra rossignonii) and a South American version (Chelydra acutirostrisI) joining our North American species (Chelydra serpentina). The larger alligator snapping turtle (Macrochelys temminckii), is in the same family, the Chelydridae, but its range doesn’t extend into Wisconsin.

The common snapping turtle is a large turtle, with a maximum length of about 45 cm (18 inches) and weight of about 20 kg (45 pounds) in the wild. Snapping turtles, like most turtles and reptiles, have generally been considered to exhibit “indeterminate growth.” In a species with indeterminate growth, individuals develop at a rate that is usually dependent on the amount of food available, and they typically continue to grow throughout their lifetimes, although at a much slower rate as adults. Most fish, for example, continue to grow as long as they live. Animals with “determinate” growth, on the other hand, include mammals and birds, which, if given enough food, grow at a fairly predictable rate until reaching a certain age, at which point they stop growing at all (except for gaining weight).

baby snapping turtle

baby snapping turtle

The generalization that all reptile species, including turtles, exhibit indeterminate growth is definitely not true, and as we’ve learned more about growth patterns, the picture has become more complicated, even for species that do exhibit indeterminate growth (more on that later). But it is mostly true that most snapping turtles grow throughout their lives. They grow much faster as juveniles, with a growth rate of about 1.5-3 cm per year (1/2-1 inch) for the first decade of life, but only about .2 cm per year (less than a 1/16 of an inch) after the age of about 20. This rate can vary quite a bit, depending on the amount of food and the length of the active season. The growth rate of snapping turtles in Algonquin Provincial Park in Ontario, for example, is about half that of more southern turtles in the first few years of life. And the farther north you go, the longer it takes for turtles to reach reproductive maturity.

If you search online, you can find estimates of the maximum age of snapping turtles that range from 30 years to 150. The 30 year estimate is undoubtedly wrong, and the 150 years may be extreme also. But turtles in general can be very long-lived. A recent study (Congdon et al., 2013) estimated that in some populations it would take 75 years after reaching maturity at the average growth rate of adult snapping turtles to reach the size of the largest turtles in the study. Adding that to the typical age of about 15 years at reproductive maturity gives an age of about 90 years for some of the largest turtles. This is a very rough estimate, but it suggests that some big snapping turtles have lived a long time – especially in the northern parts of the snapping turtle’s range, like Wisconsin, where turtles are likely to grow slowly.

Your “dragon paw” may have come from a turtle that hatched before the Great Depression.

It’s not surprising that snapping turtles live a long time if you look at their adult survival rate. By the time a snapping turtle reaches reproductive maturity, it is big enough and formidable enough to have very few natural predators. In fact, in many parts of North America, the biggest cause of mortality for snapping turtles is people:  boat propeller strikes, cars, and trapping by people for food.

If I had to take a wild guess on this turtle, given that your dog presumably found it in a suburban neighborhood, on land, it was probably hit by a car.  It may have later been torn apart by a coyote, a fox or your dog, but that’s probably not what killed it.  Dr. Justin Congdon, at the Savannah River Ecology Laboratory, has studied snapping turtles for more than 30 years. He gave me a different theory. “When people catch and butcher snappers, they typically cut off the head and feet first because reflex movements of the turtle make both a risk to the person doing the butchering. I suspect that’s what happened here and the dog found one of the discarded feet.”

common snapping turtle

common snapping turtle

More on Growth of Snapping Turtles: The Congdon et al. study looked at tagging and recapture data for nine species of North American turtles and found that all had indeterminate growth, in that about 80% of the individuals in the population continued to grow as adults. Interestingly, however, about one out of five adult turtles didn’t grow at all, even across time periods of a decade or more. So it appears that in these turtles, at least, the determinate/indeterminate dichotomy may not be so clear cut.

There is an evolutionary trade-off for animals with indeterminate growth that pits growth as a juvenile versus growth as an adult. The larger a female turtle, the more eggs she can lay. And generally, the larger a male turtle, the more battles he wins against other males in the competition to mate with females. It’s better to be bigger.

The trade-off occurs because once turtles begin mating, the energy expended by males competing and the energy expended by females to form and lay eggs slows their growth rate to a crawl (pun intended). Turtles that postpone mating so they can grow larger before they begin reproducing are at risk of being eaten or otherwise killed without ever producing any offspring. If they survive to that larger reproductive size, however, they may enjoy a long adulthood of prolific reproduction.

Turtles that begin mating at a smaller size, and then continue to grow slowly after that, may take a very long time to reach the size needed to produce large clutches of eggs or win their battles against other males. They are, however, more likely to have at least some offspring before something drastic happens to them.

Let’s hope your turtle had a long and successful reproductive life. Snapping turtles are still common across their range, but their numbers have decreased sharply in some places, as people overharvest them for consumption in the U.S. and shipment to other countries as well. Because few hatchlings make it all the way to adulthood, it will take a long time for snapping turtle numbers to recover to the levels prior to human harvesting.

Sources:  Special thanks to Dr. Ronald J. Brooks and Dr. Congdon for their help in reviewing this article.

Congdon, J D, Gibbons, J W, Brooks, R J, et al. (2013). Indeterminate growth in long-lived freshwater turtles as a component of individual fitness. Evolutionary ecology, 27(2), 445-459.

Galbraith, D A, Brooks R J, & Obbard M E. (1989). The influence of growth-rate on age and body size at maturity in female snapping turtles (chelydra-serpentina). Copeia, (4), 896-904.

Congdon, J D, Dunham A E, & Sels R. (1994). Demographics of common snapping turtles (chelydra-serpentina) – Implications for conservation and management of long-lived organisms. American zoologist, 34(3), 397-408.

Armstrong, D P, and Brooks, R J. “Estimating Ages of Turtles from Growth Data.” Chelonian conservation and biology 13.1 (2014):9-15.

Bennett, A M, & Litzgus, J D. (2014). Injury rates of freshwater turtles on a recreational waterway in Ontario, Canada. Journal of Herpetology, 48(2), 262-266.

Cite this article as: Pelletier, TC. (October 10, 2014). Is this a dragon paw? Retrieved from http://askanaturalist.com/is-this-a-dragon-paw-2/ on October 31, 2014.

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What is chasing these birds?

Mourning Dove

mourning dove

The Question: It’s VERY hot and humid here in Milwaukee – the cicadas and other insects seem to be the only ones enjoying it. Last night while walking my dog about dusk, I saw two different mourning doves being “chased” by something about 1.5 inches (4 cm) or so. The bird was flying quickly – in one case it had tried to land in a maple tree and then seems to have been sent off as this shape followed it. Could the tormenter be a cicada?

Submitted by: Lezlie, Wisconsin, USA

(click on photos and graphics to expand)

 

cicada killer

cicada killer

The Short Answer: Lezlie, it doesn’t seem very likely to me that it would be a cicada. I would rather expect the bird to be chasing the cicada than the other way around. But in trying to think of a 1.5 inch flying creature that a bird might wish to avoid and that might also be associated with a noisy population of cicadas, I first wondered whether it could it be a cicada killer, of which there are several species in the U.S. These large wasps (as large as 5 cm, 2 in) specialize in preying on cicadas. The female cicada killer stings a cicada to paralyze it and then stuffs the cicada down a hole dug in the ground. The cicada killer lays an egg on the cicada and when the egg hatches, the larva consumers the cicada. Female cicada killers tend to dig their holes in the same area, so in sandy, dry soil, you can sometimes see dozens or hundreds of these holes, especially when cicadas have a big year. During the summer, the males, which cannot sting, form “leks.” A lek is when males congregate to struggle for dominance and females arrive to mate – usually with the winners.

Chuck Holliday, an emeritus professor of biology at Lafayette College in Pennsylvania, has studied cicada killers extensively. He says that when they are on a lek, male cicada killers will chase anything that in any possible way could be a female cicada killer. Pretty much anything that moves.

“They will chase small birds, people and even small stones thrown in front of them. After all, for them, it’s ‘mate in the next 1-2 weeks or die childless.'”

European hornet

European hornet

My first thought was that maybe it was male cicada killers that chased the doves. But Professor Holliday pointed out that cicada killers in Wisconsin (which would be Sphecius speciosus) would be done mating around the middle of August. So since you made your observations in September, that pretty much rules out cicada killers. He suggested that chaser would be more likely to be European hornets (Vespa crabro), another large wasp (up to 2.4 cm for workers, 3.5 for queens). They look a bit like oversized yellow jackets. European hornets build nests in tree holes, and will sting to defend the nest. If a bird were to inadvertently fly near a European hornet nest, it will probably get chased. There have been reports of European hornets killing small birds such as hummingbirds. And Dr. Holliday suggests a hornet might even be hoping to take a bite out of a dove. “Hornets (including yellow jackets) will land on carcasses and even people and bite out a chunk of skin to take back to the grubs in their nests to feed them.”

So it seems more likely that it was a European hornet than a cicada or a cicada killer, and the connection with cicadas may be nothing more than that cicadas and European hornets are both associated with trees. But if you see it again, look to see if it’s a large hornet. If it’s a cicada killer, from a distance it will look mostly black with some red, whereas the European hornet will show yellow, like a large bee or yellow jacket.

Cite this article as: Pelletier, TC. (September 19, 2014). What is chasing these birds? Retrieved from http://askanaturalist.com/what-is-chasing-these-birds/ on October 31, 2014.

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What are these clear jelly blobs on the beach?

The Question: We found clear jelly like blobs washed up along the ocean beach. They look like they could be jellyfish without tentacles. I stepped on one by mistake and it did not hurt. What are these?

Submitted by: Sheri, Rhode Island, USA

(click on photos and graphics to expand)
Aurelia labiata

Aurelia labiata

The Short Answer: Sheri, what you are describing sounds like the remains of jellyfish, probably moon jellies (this includes several species in the genus Aurelia). People report seeing these jelly discs on beaches all over the world. David Albert, professor emeritus at the University of British Columbia, has studied Aurelia labiata, the moon jelly that is common on the west coast of North America (Aurelia aurita is the east coast version). He says that what you are seeing is the “mesoglea” of the jellyfish.

moon jelly anatomy

(1) stomach (2) tentacles (3) oral arm (4) mesoglea (5) gonads (6) endoderm (7) mouth

The mesoglea is a stiffer layer of jelly that provides structure to the moon jelly. So when you find one on the beach, you are essentially finding the skeletal remains of a dead jellyfish.

Live moon jellies don’t generally cause a sting that you would notice, and once they die, the hundreds of tiny tentacles fall away pretty quickly, so as you discovered, you don’t have much to worry about in picking up a moon jelly disk. That is not true of all dead jellyfish, however, so you should be a little cautious.

I wrote previously about moon jellyfish at http://askanaturalist.com/where-did-all-these-jellyfish-come-from/

Aurelia_aurita_-_003

Stranded moon jelly


How do They Get on the Beach?:
A moon jelly doesn’t want to be on the beach, of course. But although they can swim by pulsing their bell to push themselves through the water, they’re not exactly strong swimmers. By angling in one direction or another, they get some directional control, but for the most part, they can swim up and float down. So it seems like it might be pretty easy for a moon jelly to end up on the sand, doomed to disintegrate and be picked up by beach goers. It turns out, however, that moon jellies have behaviors that almost always keep them off the beach.

Dr. Albert has studied the behavior of moon jellies and has found that while they normally keep themselves a meter or two (about six feet) away from the surface of the water, if they bump into or sense the bottom in shallow water, they swim up and stay near the surface for some period of time. Why would they do that?

When waves break in shallow water and then recede, the overall flow of water is shoreward at the bottom and seaward at the surface. That seaward flow at the surface is called an ebb flow. When moon jellies reverse their normal behavior in shallow water to position themselves near the surface, they place themselves in that ebb flow and get carried out into deeper water.

Aurelia_aurita_02

This doesn’t always work, of course. Dr. Albert says, “Moon jellies have behaviours that help them avoid stranding. However, jellies are primitive animals. Their behaviour has to be looked at statistically. The behaviours don’t always occur at the optimum time . For example, in some jellies, swimming toward the surface doesn’t occur until the water has become quite shallow. In that case, the ebb stream may no longer be very strong and it may be very thin. So, a jelly may be less likely to drift out of a shallow area and less likley to avoid stranding. Also, if there is a wind pushing them toward a shore on an ebb tide, they may become stranded.   The ebb tide will serve to help them drift away from the beaches, but the wind initiated currents may be stronger.”

Still, despite these occasions when the normal behavior doesn’t work, Dr. Albert asserts that the vast majority of moon jellies don’t become stranded. He says the ones that end up as mesoglea disks on the sand were probably dead before they washed ashore.

A Little Jellyfish Anatomy: What looks like a simple blob of jelly is actually a fairly complex blob of jelly. Surrounding the mesoglea disk are layers of tissue that contain channels to move tiny particles of food from the edge of the jellyfish bell to the center, where its mouth and stomach are. When you see a live moon jelly, you’ll also notice four prominent horseshoe-shaped objects. These are the moon jelly’s gonads, where it produces eggs or sperm. When you find a dead moon jelly on the beach, you may see a blob that is 25-40 cm (10-16 in.) wide, and includes the four horseshoe shaped gonads. That would represent a fairly intact adult moon jelly. As it becomes more and more degraded by wave action and decay, all that’s left is the tougher center of the mesoglea disk, which might be as little as 7 cm (2.5 in.).

What Does a Jellyfish Think About: Dr. Albert is a behavioral neuroscientist, so his interest in moon jellies isn’t really in how they end up on beaches. He is fascinated by the fact that a moon jelly can exhibit true behaviors, even though it has a nervous system that doesn’t look anything like what we think of as a brain. There is no central mass of nervous tissue in the head of a moon jelly. A moon jelly doesn’t even have a head. It’s “brain” is spread throughout the organism. Yet it changes its swimming behavior and direction in response to complex sensory information that includes temperature, salinity, touch, and light levels. Somehow, without having what we think of as a brain, it coordinates this information from the various parts of its body and “decides” on a response.

These are not simple reflexes, like when your hand jerks back in response to heat. This is more like you lying in the hot sun and deciding, “I’m getting hot, I should go be in the shade.”

No one is suggesting that a moon jelly “thinks” the way we do. But it seems to take in sensory data and then change its behavior over a period of time, which suggests some kind of processing. Jellyfish have been around for about 500 million years. Far longer than us and even longer than dinosaurs. In fact, if longevity is the measure, then jellyfish are one of nature’s big success. Dr. Albert’s hope is that by studying the simple behaviors of an animal that was “thinking” long before we were, we can gain insight into how all animal brains work.

moon jellies

Aurelia aurita

Jelly and Peanut Butter: If you search online for “moon jellies on a beach,” you’ll find other sites that show pictures and if you look at the comments, you’ll see numerous jokes about jellyfish washing ashore in their desperation to find peanut butter. On one of the sites I came across, someone called OceanDreamer went one step further:

“My intuition tells me that thousands of jelly fish came ashore searching for peanut butter fish. They combine for a tasty treat because of the sand-which-is there.”

I should probably turn off the comments on this article to avoid jelly and peanut butter jokes, but I kind of like them.

Sources: Albert, D J. (2014). Field observations of four aurelia labiata jellyfish behaviours: Swimming down in response to low salinity pre-empted swimming up in response to touch, but animal and plant materials were captured equally. Hydrobiologia, 736(1), 61-72.

Albert, D J. (2011). What. Neuroscience & biobehavioral reviews, 35(3), 474-82.

Cite this article as: Pelletier, TC. (September 1, 2014). What are these clear jelly blobs on the beach? Retrieved from http://askanaturalist.com/what-are-these-clear-jelly-blobs-on-the-beach/ on October 31, 2014.

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A hummingbird with an open heart surgery scar?

hummingbirdThe Question: Can you tell me what might have caused the wound on this hummingbird? It looks like it had open heart surgery!

Submitted by: Irene, Ontario, Canada

(click on photos and graphics to expand)

The Short Answer: Irene, that’s a brood patch on a female ruby-throated hummingbird (Archilochus colubris).  Birds that incubate eggs lose their breast feathers when they are nesting.  Otherwise, feathers, which make great insulation, would prevent the eggs and chicks from being warmed as efficiently by the parent. So what you saw on this hummingbird is perfectly normal and nothing to worry about.  This time of year, the parents don’t need the insulation, so losing some breast feathers for a while doesn’t bother them.  They’ll grow back before the weather gets cold in the fall.

hummingbirdGreat photos, by the way!!

More Information: The loss of breast feathers is triggered by hormones released at the time of egg laying. Some birds don’t ever lose breast feathers for incubation. This includes species like the brown-headed cowbird (Molothrus ater), which lays its eggs in the nests other birds, birds like gannets that warm eggs with their feet, and the males of many species, including ruby-throated hummingbirds, in which the female does all the incubation work. Female ruby-throated hummingbirds build the nest of plant material and spider webs and carefully camouflage it, a process that takes a week or more. They lay the eggs, of course, typically two. They sit on the eggs, warming them against the bare skin of the brood patch, for 12-14 days. Once the eggs hatch, it takes 18-20 days for the chicks to begin flying. The female feeds the chicks for another 4-7 days after they leave the nest and then they’re on their own. As with many birds, the chicks actually weigh more than the adults at that point, but their weight drops sharply until they get good at feeding themselves. While female ruby-throated hummingbirds are doing all that chick-rearing work, the males are defending food sources and trying to attract additional females to mate with – and keeping all their breast feathers the whole time. It’s only ever the females that look like they’ve had heart surgery.

Sources: Weidensaul, Scott, T. R. Robinson, R. R. Sargent and M. B. Sargent. (2013). Ruby-throated Hummingbird (Archilochus colubris), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/204

Gill, F. B. (1990). Ornithology. New York: W.H. Freeman.

Cite this article as: Pelletier, TC. (July 17, 2014). A hummingbird with an open heart surgery scar? Retrieved from http://askanaturalist.com/a-hummingbird-with-an-open-heart-surgery-scar/ on October 31, 2014.

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Can caterpillars fly?

The Question: I just saw a caterpillar flying on a silk thread. It was moving along with the air current about a meter (3 feet) off the ground. It was suspended on a long thin thread with no apparent ‘parachute’ on the end. Eventually it descended to the grass level and walked off. I was not aware caterpillars could do this.
Submitted by: Mark, Berkshire County, United Kingdom

(click on photos and graphics to expand)

gypsy moth caterpillar

gypsy moth caterpillar

The Short Answer: Yes, caterpillars can “fly,” although insect scientists actually use the more whimsical term “ballooning” to label the behavior. And if you see a caterpillar flying or ballooning again, I encourage you to take some pictures and video, because although it is a fairly common phenomenon, I was unable to find any good pictures or videos I could share. If you search for “flying caterpillar,” most of what you’ll find is larger caterpillars dangling in mid air. This is not true flying or ballooning, however. Instead, this is a behavior that usually occurs when a caterpillar falls off a branch or drops off a branch deliberately to escape a predator. The caterpillar releases a silk line as it falls, and then climbs back up to return to its branch. I wrote about this previously in an article about dangling caterpillars.

What you’re talking about, however, sounds more like true ballooning. Some species of moth, including the notorious gypsy moth (Lymantria dispar), use ballooning as a way to disperse. Right after the eggs hatch, the tiny caterpillars drop down on a line of silk, sometimes only a few centimeters long, but in some cases a meter long, and then wait for the wind to break the thread. At that point, the caterpillar is carried along till it lands in another plant or on the ground.

Dr. James Bell, a senior research scientist who studies insect behavior at the Rothamsted Research agricultural center in England, says conditions have to be just right for this to work.  “For the neonate caterpillars to be successful, the right meteorological conditions have to be present.  The weather has to be warm, with rising air, and wind speed needs to be less than three meters per second.”

You might think ballooning is not a very effective way to disperse, and in some ways you’d be right. The tiny ballooning caterpillars don’t seem to have any control over where they land. They just let go and hope. And the fact is that quite a few end up on the ground. When that happens, they may quickly dry out and starve.

By chance, some do land on the right trees. Those caterpillars, feeding on their preferred food, tend to grow faster and produce more eggs than those that land on less suitable food plants. In some species, the caterpillars that land on the wrong trees have the ability to launch a second time. So the caterpillars may start out randomly distributed on nearby plants, but since the ones that land on the right food source stay put and the ones that land on the wrong food source sometimes get lucky on the second ballooning, the end result is higher densities on the correct plant, despite having no direct control over where they land.

The other thing that helps is that the caterpillar species that use ballooning to disperse are nearly all generalists about food plants. They usually have a preferred food plant, but can survive and grow to become reproductive adults on many different food plants. Other moth species are often specialized to feed on a single host plant species, or only on the species within one plant genus or family.

Why Doesn’t Mom Pick the Spot: But all of this makes you wonder, why doesn’t mom moth do the dispersing and find the right food source the way most moth moms do? In most moths, adult males and females have wings. They find each other, they mate, and the female flies to the preferred caterpillar food source plant, lays her eggs, and the caterpillars hatch right onto their first meal.

In species that balloon, however, females are wingless. They feed on one plant until they reach adulthood. Flying males locate the females and mate with them. The females then lay eggs on the same plant. When the eggs hatch, some will stay put and others will balloon away to find a new food plant. There are conditions under which it seems that this is a very successful strategy. For example, if you are a moth that lives in a forest where most of the trees are your preferred food, then your odds of landing in a good place when you balloon are pretty good. If that particular habitat is also stable for long periods of time, it means dispersal never has to be very far – or very accurate.

The overwhelming majority of moth species disperse by flying, however, so ballooning is definitely a fringe method for dispersing, but under the right circumstances, it can work. Since females whose offspring disperse by ballooning don’t need to fly, they can use their energy to grow fatter and carry more eggs. Over the long run, females without wings may outcompete females that fly.

Extreme Ballooning – Ballooning has evolved multiple times in several families of moths. Some spider mite species and many species of spiders also independently evolved ballooning as a means of dispersal. Given that ballooning evolved multiple times, it must be a successful trick. The real stars of the ballooning world are spiders. While caterpillars and spider mites typically balloon only a short distance before landing on a plant or the ground, spiders can be lifted high into the air. Caterpillars and spider mites have never been collected in the air out at sea, but spiders can be found ballooning hundreds of kilometers from shore. When he was traveling the oceans on his journeys, Charles Darwin noted that spiders would often rain down onto the famous ship, The Beagle. And when new volcanic islands form in the ocean, often the first animals that show up are spiders that wafted there on a line of silk.

Interesting video on ballooning spiders – http://www.youtube.com/watch?v=kYPABcMzbEg

Cool video that shows a spiderling molting, and then shows ballooning spiderlings – http://www.youtube.com/watch?v=aICZqRY3_d4

Sources:

Bell, J R, Bohan, D A, Shaw, E M, et al. (2005). Ballooning dispersal using silk: World fauna, phylogenies, genetics and models. Bulletin of entomological research, 95(2), 69-114.

Barbosa, P, Krischik, V, & Lance, D. (1989). Life-history traits of forest-inhabiting flightless lepidoptera. The American midland naturalist, 122(2), 262-274.

Cite this article as: Pelletier, TC. (June 16, 2014). Can caterpillars fly? Retrieved from http://askanaturalist.com/can-caterpillars-fly/ on October 31, 2014.
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