hornedpuffin

Who made mysterious rectangular tree holes?

rectangular holes in reddish tree trunkThe Question: I found these holes in a single tree, amidst dense forest. They were freshly made, with no sign of human footprints (there was snow), but no animal tracks either. They look very man-made, but could not have been. They appeared in a 24 hour period. Could you shed any light on them please?

Submitted by: Mark, British Columbia, Canada

(click on photos and graphics to expand)

pileated woodpecker

pileated woodpecker

The Short Answer: These holes are classic foraging holes of the pileated woodpecker (Dryocopus pileatus), the largest woodpecker in North America (assuming Campephilus principalis, the ivory billed woodpecker, is extinct). The ones you found do look remarkably regular, as if made by a saw or a wood chisel. You must have an exceptionally neat woodpecker in your neighborhood. Carol Hartwig, a retired wildlife consultant who has studied pileated woodpeckers, says pileated woodpeckers often make square or rectangular holes. She speculates that the rectangular shape may be energy efficient. She also notes that the grain of western red cedar (Thuja plicata), which is what your tree trunk looks like, is particularly straight.

rectangular holes in western red cedar“The grain of western red cedar is so straight that when the woodpecker hammers with its bill into the trunk, large, straight pieces are excavated. This results in very square corners and a very clean rectangular shape. Their nest cavities are beautifully oval, however, so they are capable of making different shapes depending on the purpose and the type of wood they are excavating.”

Your holes are far too close to the ground to be attempts to build a nest cavity. More likely, the bird was looking for insects, its main source of food. Ants and termites are favorites, and beetle larvae and other tasty insect treats would be on the menu as well. Given the size of the hole, I’m guessing the bird was having good luck.

range map of pileated woodpecker

range of pileated woodpecker

Tree Holes are in Demand: One group of researchers observing the nests of pileated woodpeckers saw wood ducks (Aix sponsa) repeatedly attempt to steal a choice pileated woodpecker cavity. The nest already contained three hatched chicks and the male woodpecker remained on guard a short distance away. When a wood duck hen would attempt to fly to the nest tree, the male woodpecker would intercept her and prevent her from going inside. However, the researchers noted one time when the wood duck hen entered the nest as the woodpeckers were off foraging and another time when the duck was so quick to the tree, the male woodpecker was caught off guard. In both instances, the male woodpecker entered the nest, a fight ensued, and the woodpecker eventually expelled the wood duck hen and retook his family’s nest. For animals that nest in tree cavities but can’t excavate their own, like the wood duck, the relatively large nest cavities of pileated woodpeckers are prime real estate.

Sources: Conner, RN, Shackelford, CE, Saenz, D, et al. (2001). Interactions between nesting pileated woodpeckers and wood ducks. The Wilson bulletin, 113(2), 250-253.

CONNER, RN, JONES, SD, & JONES, GD. (1994). Snag condition and woodpecker foraging ecology in a bottomland hardwood forest. The Wilson bulletin, 106(2), 242-257.

Hartwig, CL, Eastman, DS, & Harestad, AS. (2006). Characteristics of foraging sites and the use of structural elements by the pileated woodpecker (dryocopus pileatus) on southeastern vancouver island, british columbia, canada. Annales zoologici Fennici, 43(2), 186-197.

Cite this article as: Pelletier, TC. (April 16, 2014). Ask a Naturalist.com: Who made mysterious rectangular tree holes? Accessed on April 23, 2014. http://askanaturalist.com/who-made-mysterious-rectangular-tree-holes/

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Why does the snow melt in circles around trees?

trees with melted snowThe Question: Why do my trees have a clear area of snow around them when it warms up a bit. Are they warm? Do they give off or absorb heat? The clear area is anywhere from one to three feet around the base of the tree.

Submitted by: Raymond, Michigan, USA

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outdoor flowerpot with snow melted around itThe Short Answer: I’m answering this question a tad late, in mid-April, so most of the snow in the U.S. is gone, but as deep snow melts, it often melts first around the base of trees, as Raymond mentions. Notice that a snow ring shows in this photo of a flower pot. This is a clue that it’s probably not that the trees are generating heat biologically, although some plants are capable of doing that. What happens with trees is that the tree branches keep some snow from reaching the ground. Suspended in the branches, that snow is subjected to more sun than snow distributed on the ground so it melts and never falls all the way to the ground under the tree. Also, when the sun is shining, the tree absorbs more heat than the surrounding snow. This happens because the tree is darkly colored — especially after the snow has melted so that the dark branches or evergreen needles are exposed. The tree trunk gets warm, and then radiates some of that heat back out, which melts the snow around the base.  The same thing happens with the flower pot and other objects like telephone poles and fence posts.

evergreen tree in a fieldMore Information: This phenomenon occurs under deciduous trees that have dropped their leaves, and even more under evergreens because they catch more snow, and the dark color of their needles helps them absorb more heat, compared to deciduous trees, which are generally lighter colored. In fact, in northern evergreen forests that get large amounts of snow, the “snow wells” around trees can be two meters (6 feet) deep or more. This represents a serious danger to hikers and skiers who sometimes fall into the wells and can’t get back out.

This website gives information on the dangers of snow wells and tips for escape: http://www.deepsnowsafety.org/index.php/

Snow well paradox: Scientists study snow wells because the phenomenon that creates them has a significant effect on how heat and water are absorbed in northern forests. In their studies, they’ve found something surprising. Though the warmth radiating from the tree often melts the snow around the trunk, that same area also experiences the deepest frost. How does that happen? The bare ground at the base of the tree is exposed to the frigid winter air, especially at night or in cloudy weather when the sun is not warming the tree. The surrounding areas, covered by snow that is often quite deep, are insulated from the worst of the cold. Though the snow melts around the tree, paradoxically, that’s also where the frost goes deepest.

Cite this article as: Pelletier, TC. (April 15, 2014). Ask a Naturalist.com: Why does the snow melt in circles around trees? Accessed on April 23, 2014. http://askanaturalist.com/why-does-the-snow-melt-in-circles-around-trees/

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Why won’t my dog watch TV?

RalphieThe Question: My seven year old daughter asked me why our dog will not watch television. I told her that because the TV does not emit smells, he cannot “see” what’s on. Was I correct?

Submitted by: Rich, USA

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The Short Answer: The first thing I have to say is that many dogs will watch television, so maybe you just aren’t turning on Ralphie’s kind of show. A quick search on YouTube will find quite a few dog-watching TV videos. This one has both dogs and cats watching TV. http://www.youtube.com/watch?v=JZVUxuyhIog. You can also find videos of birds, rodents and even fish apparently watching TV.

Of course, it’s hard to know what animals are seeing or how they interpret it. But eye movement tracking studies show that dogs are less interested in a blank video screen than one with a picture; that when shown a complicated scene with a dog in it, they zero in on the dog; that they are more interested in dog faces than human faces on a screen; and that when trained to do so, they will fetch objects shown on a screen. All of that suggests that they can interpret what they are seeing on a video screen as being something like what they see in the real world.

Can Dogs See What They Cannot Smell: Some animals, like Ralphie, don’t ever seem to figure out television, or just can’t be bothered. They’re more interested in the real world around them – or napping – than they are in the flashing box. I don’t think your suggestion that Ralphie doesn’t “see” the TV because the TV doesn’t smell is quite right. The senses of dogs are just as separate as our own and dogs are certainly capable of reacting to things they see visually, but can’t smell or hear. It is definitely true that dogs rely on smell more than we do, and more relevant to the TV issue, it certainly seems that they often find things they smell more interesting than things they see. And if it’s something they can see AND smell, then it really starts to become exciting.

So my guess is that your idea about the lack of smell from TV is not strictly true, in that Ralphie can almost certainly see what’s on your TV. But I’m also willing to bet that you are right in that if TV smelled more like real life, Ralphie would find it much more interesting.

Do Dogs See the Same Thing We Do on TV? Most people know that dogs don’t have the same kind of color vision we do, but dogs don’t see in black and white, as is commonly thought. They have two types of color sensing cells (cones) in their eyes, whereas people have three. As far as we can tell, this means dogs see the world in more muted colors, that are probably like what we see as blue and yellow. They don’t seem to be able to distinguish green from red very well.

Our eyes and the eyes of dogs also have other light-sensing cells called rods. These cells don’t detect color differences, but they are more sensitive to light than color-sensing cone cells. So when the light becomes dim, we get less and less information from the cone cells and we rely more and more on our rod cells. That’s why in dim light, it’s very difficult to distinguish colors.

As primates, our ancestors were probably daytime creatures. With plenty of light, we make use of the extra information that is available in colors. It can tell you, for example, whether a fruit is ripe or not. The sensitive center of our vision is dominated with cones cells so that we can see very sharp color details in daylight. The wolf ancestors of dogs, however, were probably adapted to hunting in low light conditions. Their vision is much more sensitive to low light than ours. The most sensitive central part of their vision is made up of 90% light-sensitive rod cells that don’t distinguish colors very well. In addition, dogs have a tapetum lucidum, a special cell layer behind the retina that reflects light back through the retina, so that the photons that go straight through the retina have a second chance to be detected when they bounce back. Unfortunately, while this increases sensitivity, it blurs the image. (The tapetum lucidum, by the way, is the reason the eyes of dogs and many other animals reflect light in the dark, unlike the eyes of people and other primates, which do not have this feature.)

A dog can see much better than we can in the dark, but we can see more clearly and sharply in good light. Tests of visual acuity in dogs suggest that their vision is the equivalent of about 20/75. This means that something the average person can see clearly at 75 feet (23 meters) would need to be within 20 feet (6 meters) for the average dog to see it clearly. Of course, some dogs see better than others and some breeds are more prone to near-sightedness than others, but the bottom line is that it’s possible that when Ralphie looks at your television, it doesn’t look like High Definition at all.

The other complicating factor is that televisions can flicker. A video screen refreshes many times a second. Once that “refresh rate” is above about 60 times per second, most people can’t detect the flicker and it seems like a steady picture. Tests have shown, however, that until the refresh rate gets to be more like 70 or 80 times per second, dogs can see the flicker. Modern HD TVs refresh at 120 times per second or higher, so they presumably work better for dogs. But older TVs may drive them a little crazy with the flickering.

So, between the lack of smell and the blurry picture and flickering screen, it’s entirely possible that Ralphie sees you watching the TV and wonders, “Why do my people stare at that annoying flashing light?” That certainly seems to be the attitude of my dog, Bella.

Sources: Miller, P E, & Murphy, C J. (1995). Vision in dogs. Journal of the American Veterinary Medical Association, 207(12), 1623-34.

Somppi, S, Tornqvist, H, Hanninen, L, et al. (2012). Dogs do look at images: Eye tracking in canine cognition research. Animal cognition, 15(2), 163-74.

Cite this article as: Pelletier, TC. (April 11, 2014). Ask a Naturalist.com: Why won’t my dog watch TV? Accessed on April 23, 2014. http://askanaturalist.com/why-wont-my-dog-watch-tv/

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Amazing video of pond life, including bryozoans

As the internet’s #1 “jelly-like blob” site, AskaNaturalist.com couldn’t resist linking to this very cool microphotography video of pond life. If you go about 50 seconds in, you’ll see actual bryozoan polyps (the colonial creatures that form the most common jelly-like blobs) doing their filter-feeding thing.  Despite the sometimes over the top audio, the entire video is fascinating, and I highly recommend the segment that begins around 3:30. It shows tiny hydra catching even tinier creatures, daphnia, in their tendrils. Amazing photography that gives an incredible glimpse of a world we rarely see.

To read other AskaNaturalist.com posts about jelly-like blob bryozoans:

What is this Jelly-like Blob Under My Dock?

Jelly-like blob under the dock – part two

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Bryozoans or salamander eggs?

jelly blobThe Question: Yesterday I pulled from my goldfish pond (with a net) a jelly blob that looks like what you describe as bryozoans. However, inside this one were fish about 1/2″ long, at least thirty of them. What is your take on this?

Submitted by: Donna, Mississippi, USA

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The Short Answer: That jelly clump does look a little bit like the freshwater bryozoan blobs we’ve talked about on AskaNaturalist.com. But it doesn’t have the same kind of speckled appearance, and as you say, what’s inside this blob seems fish-like. The other clue that it’s not a bryozoan blob is that this is the wrong time of year (late March). Bryozoans die back during the winter, so this time of year bryozoans would be just starting to come back from the small statoblasts that drop to the bottom of bodies of water in the fall. It isn’t until mid-late summer and early fall that the jelly blob colonies are large enough that people begin to notice them.

spotted salamander

spotted salamander

This, however, is the time of year for amphibian egg mass jelly blobs. Ron Altig, an expert on the eggs of amphibians, at Mississippi State University, immediately identified your blob as an egg mass of the spotted salamander (Ambystoma maculatum), one of the more charismatic of the salamanders, as these photos show. When I asked him what criteria he used to identify the eggs, he said, “The relatively large size and particularly the very firm jelly – as in the picture, it does not collapse and run when taken out of the water. The only species in eastern US that does that is A. maculatum. The only similar eggs are those of the northwestern salamander (Ambystoma gracile), which is only found on the western coast of North America from northern California to southern Alaska.”

jelly blobIf you look closely at your egg mass, you can see that the developing larvae already have external gills and possibly front legs. They’ll soon begin leaving the relative safety of their jelly blob to head out into the world. Spotted salamanders larvae are susceptible to being eaten by fish, which is why they typically lay their eggs only in vernal pools that don’t have fish. I don’t know the likelihood that your goldfish will eat them. 

spotted salamander

spotted salamander

Larva or tadpole – front legs or back legs first? Salamanders and frogs are amphibians, and most have a similar life-cycle that includes laying eggs in water, which hatch into an aquatic (swimming) juvenile stage, and finally an adult stage that lives on land. There are many fascinating and bizarre exceptions to this basic three stage land-and-water life-cycle, but the vast majority of salamanders, frogs and toads fit. There is a very big difference, however, in how salamanders develop, compared to the frogs and toads.

Frog and toad eggs hatch into tadpoles, large-headed fish-like swimming creatures that typically eat by scraping bacteria, algae, and microorganisms off underwater surfaces. Though they may begin with external gills, in most tadpoles, the gills become internal. As the tadpole grows, it develops legs, with the back legs appearing first, and then the front. The tail shrinks and the tadpole undergoes a true metamorphosis, rearranging its body from the streamlined, fishlike shape to the squat shape of a tailless frog or toad.

spotted salamander larva

spotted salamander larva

Salamander eggs, by contrast, hatch into larvae (the term tadpole is not used). A salamander larva looks more like an adult salamander than a tadpole is like the adult toad or frog. In salamander larvae, the front legs appear first, the opposite of tadpoles, and the salamander larvae often has those front legs even before it hatches. Salamander larva are predators, not algae scrapers like most tadpoles. They eat pretty much anything smaller than them. As a salamander larva continues to grow, the rear legs develop, and without needing to undergo a major change, the larva at that point looks very much like a salamander, except for the prominent external gills and fin-like flares of the tail. The gills and fins are absorbed and disappear as the larva completes its maturity into an adult.

If you’re curious about metamorphosis and need a song to stick in your head for a while, check out this guy, Lucas Miller, who calls himself “The Singing Zoologist.” He writes and sings educational songs for kids. This one is on frog metamorphosis: https://www.youtube.com/watch?v=jR0EPHyo128

This very short video shows time-lapse photography of egg to late-stage larva for the western barred salamander (Ambystoma mavortium), a species that is closely related to the spotted salamander: https://www.youtube.com/watch?v=-evWPl_SD4E

This one shows spotted salamander development with mostly old black and white time-lapse, but it’s very good: https://www.youtube.com/watch?v=X_lM7i2TTPs#t=19

This one shows early egg to tadpole development of a frog species: https://www.youtube.com/watch?v=B3d48VfQHbY

This site has very detailed scientific illustrations showing differences in development between salamanders and frogs: http://www.virginiaherpetologicalsociety.com/amphibians/amphibian-development/amphibian-development.htm

Sources: Thanks to Professor Ron Altig for all his help.

Cite this article as: Pelletier, TC. (April 5, 2014). Ask a Naturalist.com: Bryozoans or salamander eggs? Accessed on April 23, 2014. http://askanaturalist.com/bryozoans-or-salamander-eggs/

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