Your questions about plants, animals, and other organisms answered by a naturalist
To celebrate their first birthday, the site arkive.org is holding a vote for the favourite (not favorite — they’re British) animal. I voted Orca, for their beauty, intelligence and power. If the lion is the lord of the jungle, the Orca is the lord of the sea, which covers 75% of the globe.
Go to http://www.arkive.org/vote to vote.
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 Pigeon Question 1: A friend told me she heard that pigeons never poop while flying. Is this true? Kate, Massachusetts, USA
Pigeon Question 2: I often see pigeons in the city that have deformed feet. Are these pigeons just injured or something? Are the pigeons affected negatively by having feet like this? Rick, New York City, USA |
Answer 1: This is one of those items of common knowledge that may have taken a small tidbit of info and exaggerated it. Some people will insist pigeons never poop while flying because feral pigeons (Columba livia) hold their feet against their body while flying. To poop while flying, they would have to poop on their feet, so they don’t. Others insist that pigeons have to back up to poop and they can’t do that while flying. Even people who keep racing pigeons, and therefore have quite a bit of experience with them, will insist that the birds don’t poop while flying.
On the other hand, it’s not hard to find eye-witness reports of pigeons defacing cars as they fly overhead.
Dr. Daniel Haag-Wackernagel at the University of Basel in Switzerland, one of the world’s most knowledgeable experts on feral pigeons, told me that “Normally pigeons discard feces not during flight, mostly when roosting or overnight.” However, Dr. Haag-Wackernagel, who studies how cities can control pigeon populations, also said that “Pigeons can excrete an evil-smelling scare-feces (undigested feces) when attacked by a bird of prey.”
Also, because pigeons can fly for hours at a time without stopping, I suspect they must poop at least sometimes on long flights. The fact that they normally hold their feet in the way doesn’t mean they can’t move them long enough to poop while flying. So, it may very well be that pigeons prefer to poop on the ground, but they do sometimes poop in flight. And if a flock of 50 pigeons flies over your car it only takes a fraction of them to make a mess of your windshield.
Answer 2: Rick’s observation is one that many city-dwellers can confirm. Look closely at the feet of a flock of feral pigeons and sometimes it seems that every other bird is missing toes or sometimes even missing a foot. Others have feet that are swollen and infected. What causes this? When I put this question to Dr. Haag-Wackernagel and to Dr. Lisa Jaquin, of McGill University in Montreal, who also studies feral pigeons (among other things), I got the same answer: fibers. Dr. Haag-Wackernagel explained what happens, “Filaments twist around the feet and toes leading to insufficient blood supply, necrosis and loss of the toe. Sometimes the necrosis shows infections. In cities, a large proportion of the feral pigeons show such mutilation.”
Dr. Jaquin said, “We do pigeon captures regularly in Paris and we often see pigeons with tangled strings or hair in their swollen feet. The fibers can constrain blood circulation and result in necrosis and amputation. Bacterial infections can also cause leg deformity and abscess, but most of the amputations we see in cities have a physical cause (strings or hair caught in the toes).”
I can attest to the ability of fibers to do damage to the feet of birds. I once kept pet zebra finches and when they wanted nesting material, I made the mistake of giving them strips of nylon yarn. A few weeks later, I noticed several had swollen feet and toes. When I got them in hand and looked closely, I realized, to my horror, that tiny fibers of nylon were completely tangled in the scales of their feet and as the poor birds tugged to try and remove the fibers, they just tightened the little tourniquets. It took me quite a long time with tweezers, tiny scissors and a magnifying glass to get all the fibers out, 
but once I did, the bird’s feet healed up back to normal in a couple of days. Needless to say, I never gave the birds that kind of yarn again.
I’m not sure there’s any practical way of reducing the toll that fibers in the environment take on the feet of feral pigeons – aside from the efforts of people like Dr. Haag-Wackernagel to reduce the number of feral pigeons. But if you see a pigeon with damaged feet and can catch it, this website explains how to help remove the fibers. http://www.pigeonrescue.co.uk/feet.htm
As to the question of whether they are negatively affected by missing toes and feet …
Missing a toe or two doesn’t seem to stop them from foraging, flying or mating normally. Missing an entire foot seems more likely to affect a bird’s ability to walk efficiently and certainly to perch well. The fact that there are so many city pigeons missing feet, however, suggests that it isn’t a fatal problem. City life — with very few bird predators — is not as much of a desperate struggle for survival. But I wouldn’t be surprised if missing a foot affects the ability of males to compete for mates and to perform the physical act of standing on a female’s back to copulate.
More Information: All domestic, racing and feral pigeons are descendants of the rock dove, a bird native to a band across North Africa, Southern Europe, the Middle East and India. In its natural habitat, they nest on cliff faces, where presumably they rarely encounter man-made fibers and therefore have all their toes.
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| One of the common challenges for birders in North America is answering the question, “Cooper’s Hawk or Sharp-Shinned?” These are two of the three members of the genus Accipiter in North America, the third being the Northern Goshawk. The Goshawk is larger than a Cooper’s and a Cooper’s is larger than a Sharp-shinned, but in raptors, males are usually considerably smaller than females, and because the size range of a male Goshawk overlaps that of a female Cooper’s hawk and a male Cooper’s hawk overlaps that of a female Sharp-shinned, telling the birds apart on the basis of size can be difficult. I wrote an article on this subject previously (click here), and there are other excellent sites that can help you tell the difference (click here) between Cooper’s and Sharp-shinned, but after collecting a few of these questions, I’m going to answer them together as Episodes 2, 3 & 4. Episode 4 requires some forensics, so stay tuned. I should say that I’m not an expert in identifying these birds, so if you disagree with my identifications, please let me know by using the comment link at the end of the article. Thanks. |
2. Cooper’s or Sharp-Shinned – Jim, Pennsylvania
We know this is a juvenile accipiter because of the vertical streaking on the breast. Adults of all three species have horizontal barring on the breast. The sharp white breast feathers, with very distinct vertical streaks, is most like a Cooper’s Hawk (Accipiter cooperii). A juvenile Sharp-Shinned’s (Accipiter striatus) breast is messier, and though a juvenile Northern Goshawk (Accipiter gentilis) has similarly crisp streaking, it is usually on a lightly buff background. Without knowing how big it is, it’s possible this could be a juvenile Northern Goshawk, but a juvenile Goshawk should also show a darker brown patch behind and below the eye and a more distinct white stripe over the eye. I’m not 100% sure, but I’m going with Cooper’s with a possibility of Goshawk. Definitely not a Sharp-shinned.
3. Cooper’s or Sharp-Shinned – Carl, Nova Scotia, Canada
In this case, I think the answer is neither. The clue here is the tail. The hallmark of the accipiters is a long tail compared to other raptors. Notice that in this bird the tail seems normal bird tail length. Once we decide this bird is not an accipiter, the dark bank near the end of the tail, with a white stripe of about the same width, suggests Broad-winged Hawk (Buteo platyperus). I’m pretty sure this is a juvenile Broad-wing. The Broad-winged Hawk is in the genus Buteo, not Accipiter. Buteos are generally larger and thicker hawks that hunt rodents, compared to the Accipters, which are generally smaller, more agile bird-hunters. The Cooper’s Hawk and Broad-winged Hawks are about the same size, however, and juvenile Broad-winged Hawks do look a lot like adult Cooper’s Hawks. The key field mark is the short tail.
4. Cooper’s or Sharp-Shinned – And Who Killed It? Ali, Nova Scotia, Canada
First of all, nice call on this being an accipiter. I’m pretty sure that’s correct. If you go to this great U.S. Fish and Wildlife feather atlas, http://www.lab.fws.gov/fa/feather.php?Bird=SSHA_tail_ad, it shows you high quality photos of feathers from many of the birds of North America. And although many birds have barred feathers like these, as far as I can tell, only the accipiters have banding that crosses the central quill of the feather and stays the pretty much the same. Compare these feathers from a Broad-winged Hawk and a Sharp-shinned Hawk. Note that in the Broad-wing feathers the shape of the black and white is markedly different on each side of the central quill.
So I think Ali is probably right that it’s either a Sharp-shinned or a Cooper’s. And given that Ali told me the longest feathers are about 17-18 cm (7 inches), that sounds like a Sharp-shinned. Also note the prominent white dot near the base of the Sharp-shin feathers in the Fish and Wildlife feather scans. If you look closely, you’ll see that white dot in a couple of the feathers in Ali’s photo, especially the feather at the very top center. From the scans I’ve seen, this dot is much more well-defined in Sharp-shinned Hawks than Cooper’s, so I’m inclined to say these are the feathers of a female Sharp-shinned Hawk (a male’s Sharp-shin’s feathers would be shorter, more like 12-13 cm 5 inches).
Here are more scans of Cooper’s Hawk http://www.fws.gov/yreka/ES/coopershawkfeathers.html and Sharp-shinned http://www.fws.gov/yreka/ES/sharp-shinnedhawkfeathers.html feathers.
As to the “Who Done It?” the interesting answer is, “Possibly a Cooper’s Hawk!” Predators often compete violently when their hunting ranges overlap, especially if they are after the same prey. Sharp-shinned Hawks and Cooper’s Hawk are both fast and agile flyers that hunt other birds. And Cooper’s Hawks have been known to kill and eat their Sharp-shinned competitors. Also, Cooper’s Hawks often pluck their prey at the spot of the kill before flying off with it.
There are other hawks that might kill a Sharp-shinned, including Red-Tailed Hawks (Buteo jamaicensis), Northern Goshawks, and Peregrine Falcons (Falco peregrines), but it’s more interesting to speculate that this bird was killed by its close accipiter relative, the Cooper’s Hawk. So I think we need to bring any local Cooper’s Hawks in for questioning.
A Warning: Both the U.S. and Canada have laws that make it illegal to possess the feathers of most birds, especially raptors like hawks and eagles, unless you have a special permit. It doesn’t matter whether you killed the bird or just found the feathers on the ground. These laws were passed in response to the decimation of bird populations for the purposes of harvesting feathers in the early 1900s. For more information see http://www.fws.gov/migratorybirds/mbpermits.html. I doubt that Fish and Wildlife has any interest in prosecuting people who pick up a pretty feather on a walk, but you should be aware that technically, it is illegal to keep any feathers from birds covered by the Migratory Bird Act. Exceptions include most non-native species (starlings, house sparrows, pigeons, etc.) and most game birds (many ducks and geese).
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 The Question: I’ve looked through all my insect books, including those that specialize in New England insects, and can’t even identify this species. I’m a rank amateur, but usually can get that far. I saw quite a few of them this summer and didn’t anticipate such a problem! Jeepers, I’m so glad I found this blog!Submitted by: Martha, Massachusetts, USA |
The Short Answer: Martha, thanks for your excitement at finding AskaNaturalist.com. We’re glad to have you as a reader! And what you found is a yellow-collared scape moth (Cisseps fulvicollis), one of a large family (Arctiidae) of moths that as a group are called tiger moths. Cisseps fulvicollis is a common species, found throughout North America. Despite the yellow in its name, the yellow-collared scape moth sports what is clearly a bright orange collar. Like many brightly colored animals, and like most tiger moths, the yellow-collared scape moth tastes bad to predators. The bright colors are an example of “aposematism,” a survival tactic where by advertising your unpalatability, you increase the chance for survival of your relatives. Imagine that a bird tries to eat a yellow-collared scape moth and discovers that it tastes bad. The bird’s discovery may come too late for that moth, but once educated, that bird is less likely to attack any of that moth’s close relatives, who also carry the same bright coloration. In this way, the genes for the bright coloration gain a survival advantage.
To make themselves unpalatable, yellow-collared scape moth caterpillars feed on plants that carry pyrrolizidine alkaloids (PAs). These substances are generally distasteful and mildly poisonous. Plants use them to discourage grazing by mammals and other plant eaters. But yellow-collared scape moths and other tiger moths are generally not affected by PAs. In fact, males release PAs as a sexual attractant when it’s time to mate. By showing how much PAs they carry, the males are proving to females how healthy – and distasteful to predators – they are. This is important because the male transfers some of his PAs to the female when he deposits a sperm package during mating. The poisonous PAs in the sperm pack are then incorporated into the eggs, giving them protection from predation.
For more information on yellow-collared scape moths, go to: http://pnwmoths.biol.wwu.edu/browse/family-erebidae/subfamily-arctiinae/tribe-arctiini/cisseps/cisseps-fulvicollis/
More Information – This is Cool!: Visual aposematism is very common in the natural world. Most people have heard that lady bugs are brightly colored because they taste bad. Poison dart frogs advertise that they are off limits to predators. Even the white and black patterning of a skunk can be considered to be visual aposematism.
But there are other ways to advertise your noxiousness to predators, and tiger moths present a great example. Since most tiger moths are nocturnal, their main predators are bats. Bats, of course, don’t locate their prey at night by sight, so bright coloration to warn of noxiousness is useless. Bats hunt by using echolocation. They send out sound waves, and by sensing the sounds that bounce back from objects in the air, they can “see” what the object is and track its motion. But moths are not helpless in this process. Most moths have some way of hearing the echolocation of bats and taking evasive action. And some noxious tasting moths have evolved another response.
Dr. Aaron Corcoran at Wake Forest University, who studies the sounds moths make in response to bats, describes what happens. “The tiger moths wait until they have been detected by the bat and are being targeted. Then they transmit a warning signal that serves the same function as bright warning colors. Once the bat hears the signal it veers off, wanting no part of a noxious moth.”
It’s been shown that the first time a bat hears the warning sound, it ignores it and captures the moth. It usually then drops the moth, presumably after tasting it and saying, “Yuck!” Once a bat has associated the warning signal from the moths with the disgusting taste, it will avoid that type of moth in the future.
Dr. Corcoran also points out that just as some tasty animals have evolved coloring that imitates that of noxious animals in a phenomenon called Batesian Mimicry, “Some moths that are actually palatable to the bats make sounds that are similar to the sounds the toxic moths make. This often fools bats into avoiding a perfectly tasty moth.” (For more on visual warning signals and Batesian mimicry, go to http://askanaturalist.com/what-is-this-orange-backed-spider/)
This is Even More Cool!: Some moths have taken the life or death game one step further. When they hear an echolocating bat, they wait until the bat is very close and then they begin making a loud “white noise” that confuses the bat and makes it difficult for it to judge where the moth is at the last second. This causes the bat to miss and allows the moth to escape. This is very similar to radar jamming done by military jets trying to avoid detection.
Here are two YouTube videos that show this in action. In the first, the moth’s sound producing organs have been disabled. You’ll hear the bat echolocating and see that it catches the moth. The second video is the same species of bat and moth, but the moth in this case has not been disabled. Just as the bat approaches, you’ll hear a new buzzing noise, which is coming from the moth, and then the bat misses. Very cool.
Without jamming – https://www.youtube.com/watch?v=Qgq12GJV-qA
With jamming – https://www.youtube.com/watch?v=vrZ2hNZsCuE
For more on jamming of bats by moths, go to Dr. Corcoran’s website: http://www.sonarjamming.com/.
Sources:
Landolt, PJ, & Phillips, TW. (1997). Host plant influences on sex pheromone behavior of phytophagous insects. Annual Review of Entomology, 42, 371-391.
Conner, W. E., and A. J. Corcoran 2012. Sound strategies: the 65-million-year-old battle between bats and insects. Annual Review of Entomology. 57: 21-39.
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 The Question: Three days ago I noticed this green jelly-like substance on the top of a moss covered rock in my garden. The recent weather has been very wet and about a week ago we experienced a couple of frosty nights, but the last three days have been dry. Can you tell me what this green jelly slime is, please?Submitted by: Virginia, Scotland |
The Short Answer: I’m pretty sure this is a colony of cyanobacteria in the genus Nostoc, probably Nostoc commune. At the microscopic level, Nostoc forms long strands of individual cells that multiply by dividing. Colonies can grow large enough to form mats like the one in your photo. Nostoc commune typically forms leathery ear-shaped colonies. I suspect that what you have is a deteriorating mat of Nostoc commune. Dr. Walter Dodds, an expert on aquatic ecology at the University of Kansas, believes this is Nostoc commune, but suggests that if you want to be sure, you could take a sample, dry it, and send it to a phycologist at a 
university in the U.K.
Despite the fact that it is phycologists, specialists in algae, who study Nostoc, Nostoc is not actually an algae. Cyanobacteria like Nostoc used to be called blue-green algae, but it’s now known that they are not algae at all, though they perform photosynthesis the way algae and plants do. So although Nostoc looks like some kind of green slime algae, it’s actually some kind of green slime bacteria.
More Information: Dr. Dodds suggested you dry the specimen before mailing it because Nostoc species have an interesting ability to survive drying and then revive once re-wetted. In fact, one laboratory specimen that sat dried in a museum collection for more than a hundred years was revived and grew normally. For all we know, Nostoc can survive hundreds of years dried.
Nostoc has other abilities that help it survive in difficult conditions. It can withstand freezing, for example, and is found in both the Arctic and the Antarctic. Its cells can sometimes be cultured from thin air, suggesting that it is dispersed around the globe on the wind. And it is able to grow in areas of low nitrogen because some of its cells differentiate into “heterocysts” that can fix nitrogen from the air. Earth’s surface atmosphere is nearly 80% nitrogen, and the process of pulling nitrogen out of the air for use by living organisms is called “nitrogen fixation.” The vast majority of animals and plants on earth can’t perform this trick and must rely on fixed nitrogen in their environment. That’s why nitrogen is a key component of fertilizer for plants. Animals get their nitrogen from the plants and animals they consume.
Nostoc, however, is one of the organisms that can fix nitrogen directly, and in some environments, Nostoc is a major source of the fixed nitrogen that eventually sustains all the plants and animals.
So don’t look down on this green slime. It plays a key role in the biological productivity of natural habitats. And it’s probably adding nitrogen to your garden!
Star Jelly: When Nostoc dies and dries and then gets rewetted, it is usually white. Because these white jelly objects seem to show up out of the blue, they are one of the things that have traditionally been called “star jelly” because they were thought to have fallen from the sky. Nostoc is not the only organism that can produce a white jelly, however, and the white jellies called “star jelly” include other substances, including amphibian eggs and slime molds.
Sources:
Dodds, W.K., Gudder, D. A. (1995). The ecology of nostoc. Journal of Phycology. 31, 2-18.
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