antscarryingleaves

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 September 21, 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 September 21, 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 September 21, 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

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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 September 21, 2014.
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Can I swim with beavers?

The Question: I’ve heard that it might not be healthy to swim in a pond with an active beaver colony in it, as something is in the water from the beaver that can be bad for humans. Do you know if this is so? We have a large beaver pond with an active colony, and deep water at least 30 feet out from the dam, and we’d love to swim in it. Are there any tiny worm-like parasites we should be worried about as well? I couldn’t find any information online about this.

Submitted by: Faye, Minnesota, USA

(click on photos and graphics to expand)

The Short Answer: Before I begin to answer, I should say that I am not a doctor and not a qualified public health official. There are dozens or maybe hundreds of diseases that can be contracted from “surface waters,” meaning lakes, rivers, ponds, etc. Some of them are caused by worms, but giardiasis and cryptosporidiosis, the two most commonly associated with beavers (Castor canadensis in North America, Castor fiber in Eurasia), are caused by protozoan intestinal parasites (Giardia sp. and Cryptosporidium sp. respectively), which are spread through feces. Because beavers poop in the water, they can release the infectious cysts of the organisms. If you swallow the water, you may become infected. Unfortunately, you only have to ingest a small number of cysts to become infected.

BeaverCommon knowledge associates giardiasis and beavers so closely that people often call the disease “beaver fever.” However, it’s not clear that beavers very often contaminate people with Giardia. In fact, it seems that Giardia species tend to specialize. So the Giardia that most commonly infects beaver is different from the one that infects people. However, most Giardia have some ability to infect organisms other than their primary host, and you can find human-type Giardia in beavers. But the evidence suggests that when it is found in swimming waters and in beavers, the most common source of the human-type Giardia is not the beavers but people. Typically, it’s from untreated sewage that gets into the water or from fecal matter washing off people when they are in the water. For that reason, health officials recommend that people with diarrhea stay out of swimming waters.

Even so, swimming in beaver waters is not the most common way to get “beaver fever.” The largest number of cases are among small children in day care centers, who pass it among each other.

So if you want to know if a swimming area is safe, rather than look for a swimming hole with no beaver, you should probably look for one with no people – especially small people. The situation for cryptosporidiosis is similar. And while these diseases tend to be “self-limiting,” they are not fun, often causing severe diarrhea. One common hiker’s saying is that “While beaver fever won’t kill you, you might wish you were dead.”

When I asked Lihua Xiao, who is Chief of the Molecular Epidemiology Laboratory/WBDP of the Division of Foodborne, Waterborne, and Environmental Diseases for the United States Centers for Disease Control, for his opinion about swimming with beavers, he said flatly “I would not swim in a pond where beavers are active.”

I think that is a somewhat extreme view that would restrict you from the joy of swimming in most of the waters of Minnesota, but Dr. Xiao is one of the world’s foremost experts on these diseases and the organisms that cause them, and I am not. So you should weigh our opinions appropriately.

If you do decide to swim in your beaver pond, you should, as much as possible, avoid swallowing the water, and you should never drink untreated surface waters. The recommendation is to boil or use filters that specifically say they will remove Giardia. The cysts of Giardia and Cryptosporidium are somewhat resistant to chlorine, so don’t count on that. Boiling and filtration will also kill or remove most other waterborne diseases and parasites at the same time, including any worm-like parasites.

MuskratFear the muskrat: A study that tested beaver and muskrat (Ondatra zibethicus) in Pennsylvania and New Jersey for Giardia and Cryptosporidium found that out of 10 beaver tested, none were infected with Cryptosporidium and only one was infected with Giardia. The muskrat were a different story. Nearly 90% were carrying one or the other of the parasites and nearly a third were carrying both. So on the basis of this study, it might make even more sense to avoid waters with muskrat than with beavers. Of course, beaver and muskrat are often found together in Minnesota and most other places, so that doesn’t help much.

To Get More Info: The Center for Disease Control’s Giardia page: http://www.cdc.gov/parasites/giardia/gen_info/faqs.html

Lifecycle of Cryptosporidium from CDC: http://www.cdc.gov/parasites/crypto/biology.html

Lifecycle of Giardia from CDC: http://www.cdc.gov/parasites/giardia/biology.html

Very informative page from the Washington State Department of Fish & Wildlife on beaver, how to live with them, and how to discourage them if that’s your goal: http://wdfw.wa.gov/living/beavers.html

Sources:

Monis, P.T. & Thompson, R.C.A. “Cryptosporidium and Giardia-zoonoses: fact or fiction?” Infection, Genetics and Evolution 3 (2003): 233–244.

Bitto, A, & Aldras, A. (2009). Prevalence of giardia and cryptosporidium in muskrats in northeastern Pennsylvania and New Jersey. Journal of environmental health, 71(8), 20-26.

Feng, Y, & Xiao, L. (2011). Zoonotic potential and molecular epidemiology of giardia species and giardiasis. Clinical microbiology reviews, 24(1), 110-40.

Cite this article as: Pelletier, TC. (June 6, 2014). Can I swim with beavers? Retrieved from http://askanaturalist.com/can-i-swim-with-beavers/ on September 21, 2014.

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