29 October 2010

A well sealed snail shell

I mentioned in this recent post that I was working on a method to measure the volumes of snail shells and that I needed a way to seal their apertures against water. After tape, chewing gum and plasticine failed, my wife came to the rescue and suggested silicone ear plugs. I tried them tonight and got good results. The shell in the picture was sealed with silicone. The main drawback is that the application and removal of silicone is time consuming.

Results are forthcoming.

26 October 2010

An expired northern brown snake in my way

This dead snake was on the path where I was taking my after lunch walk today in College Park, Maryland. I wrapped it up in a paper napkin and carried it to my office right under the noses of security officers on the way in. Luckily, dead snakes don't make metal detectors beep.

The characteristics of the snake's head match the pictures and descriptions in the books for the northern brown snake (Storeria dekayi dekayi). I hope I am not mistaken.

Almost 2 years ago I photographed a live northern brown snake in the same neighborhood. According to Conant's & Collins' Reptiles and Amphibians (Peterson Field Guides, 1998), the habitats of this species include parks, cemeteries and empty lots in cities. This specimen was 23 cm long, which, according to the same book, is the lower limit of the range of the adult size of the northern brown snake.

According to White's & White's Amphibians and Reptiles of Delmarva (2002), the diet of the northern brown snakes includes slugs and snails among other invertebrates. Hence my interest in the species.

The snake is now in ethanol. I will attempt to dissect it one day. Maybe there will be snail remains in its stomach.

25 October 2010

Cepaea nemoralis in Montreal — Part 2

When I was in Montreal in August 2009, I found the European land snail Cepaea nemoralis along a railroad passing thru the city. The little survey I did eventually got published in the journal Check List.

At that time I had some anecdotal evidence that Cepaea nemoralis was also present elsewhere in the city. Since then, my sister and niece, who live in Montreal, have sent pictures of snails from the Westmount district of Montreal. Here is a picture of Cepaea nemoralis my sister found in her garden a few days ago.

I am now convinced that Cepaea nemoralis has established itself in Montreal.

24 October 2010

A new (and wrong) value for pi

For the past several weeks I have been trying to develop a method to measure the volumes of snail shells. The method I am working on involves the immersion of an object with an unknown volume in water and several sets of weight measurements. The method is not yet applicable to snail shells, because I can't quite figure out how to seal their apertures in a practical and reversible way so that water won't leak inside. Nevertheless, I have carried out a test using 6 small balls, including 3 balls from old computer mice, 1 metal ball bearing and a glass marble.

After I measured the volumes and the diameters of the balls, it dawned on me that I could use the data to calculate a value for pi. Here is the plot of measured volumes against measured radii.

This plot is, of course, based on the equation for the volume of a sphere: V=(π4/3)r3. Therefore, pi can be calculated from the slope. The value I got was 3.16, which is 0.6% higher than the true value of 3.14.

There are several sources of error that could have resulted in my erroneous result. For example, if the calipers I used to measure the diameters were off by even 0.1 mm, that could have created an error of about 0.4%. Also, the balls I used are probably not perfect spheres. Another likely source of error is the value I used for the density of water, which depends on the temperature and the purity of the water used.

If and when I figure out how to apply this method to snail shells, these errors will not be important as long as they are equally applicable to every specimen; I am mainly interested in the relative volumes of a sample of shells rather than the absolute values of their volumes.

Tests are continuing.

18 October 2010

A contrary leaf

An interesting find during this evening's walk was this leaf with a peculiar color pattern. Most of the leaf had turned yellow, leaving behind patches of green between the veins.

This is one of those tree leaves that I find difficult to identify. It may be a hickory (Carya sp.). There are about 5 species that may be found in Maryland.

I don't know if this color pattern is characteristic of hickory leaves in the fall. I will look for more examples.

16 October 2010

Calibrating a buret when there is nothing better to do

About 10 days ago I ordered a 50-ml buret from Ward's Natural Science. The catalog said that each buret was "individually calibrated". I couldn't have asked for more.

The buret arrived a few days ago carefully packaged in a tall box. I took out the buret and started examining it. I noticed the calibration temperature etched near the top: 27°C! Where on earth was this thing calibrated? I found the fine print on the cardboard sleeve: "Made in India". Images of un-air conditioned, hot and humid labs flashed before my eyes. Good thing it wasn't a record-breaking day when they worked on this particular buret.

The temperature in my basement is usually around 20-22°C and it never ever goes up to 27°C. The standard calibration temperature for laboratory glassware is 20°C. So I figured I needed to check the calibration of my Indian-made 27° buret.

An old book from my college days, Fundamentals of Analytical Chemistry by Skoog & West, provided the necessary instructions for buret calibration. It is really simple: you deliver with the buret several different volumes of distilled water, weigh each one, convert weights into volumes using the density of water at the lab temperature and finally, plot the calculated (or actual) volumes against the volumes read from the buret and derive the correction factors, if necessary.

Here are my results.

The largest volume I measured from the buret was 43.2 ml, while the calculated "actual" volume of it was 43.71 ml. Measurement errors notwithstanding, the difference of 0.51 ml is probably explainable by the differences in the volumes of water at 27°C during the original calibration and at 21.5°C in my basement. The volume difference at the smallest volume I measured, 9.8 ml, was 0.05 ml, which is almost negligible for my purposes.

14 October 2010

A friendly pigeon in the rain

I was walking to the post office this afternoon when a wet pigeon intercepted my path. It was surprisingly tame and approached within less than a meter of me, especially when I hunkered down under my umbrella to take pictures of it with my iPhone camera.

I also noticed that it had blue bands on both legs.

The post office was right across the street. Has the Postal Service gone back to using carrier pigeons to save money?

12 October 2010

Growth in Euxina circumdata

Tonite's graph shows the growth of foot relative to that of shell in the land snail Euxina circumdata. The blue line is a hypothetical case where growth is isometric, that is, the lengths of the foot and the shell remain equal to each other during growth. The red circles are the actual data for Euxina circumdata.

The largest snail was an adult, while the rest were juveniles. It is clear that in very small snails the foot is almost as long as the shell. But the shell grows much faster than the foot. As a result, in adult snails, the foot is shorter than half of the shell.

What this all means may the be the subject of a future post provided that I can come up with a meaningful explanation.

11 October 2010

Taphonomy of a deer carcass

If you happen to be rummaging around in wooded areas in College Park, Maryland, you may find a deer skull or a leg bone with my name and the date 7 September 2010 written on them. I'd appreciate it if you didn't take either bone, but let me know of their locations.

This all started last August when I noticed a stench permeating the air while walking to work one hot morning. There was a white tailed deer carcass nearby. The next morning I returned with my camera, but the stench had gone. It turned out that someone had covered the carcass with soil. I did take a few pictures for the record anyway.

Later, I figured this would be a good opportunity to carry out a taphonomical study. How long would the carcass take to turn into bones? What would happen to bones afterwards? I started visiting the burial every few weeks to check on it.

About a month later following some heavy rains, I saw that some bones were sticking out of the soil. The decomposition of the flesh had indeed been quick.

Then I started wondering if bone-eating scavengers would come and take the bones away. So, I went there one day last week and wrote my name on the skull and a leg bone both of which were partially exposed. The idea is that if either bone is removed, I may be able to locate and identify them in the nearby woods.

Updates may be posted.

10 October 2010

Squirrel sounds

Eastern gray squirrels (Sciurus carolinensis) could be quite vocal at times, but if you are not familiar with their vocalizations, you may think that you are hearing a bird calling. Until yesterday that's what I used to think. But I finally realized that a peculiar "bird" sound I often hear around here was in fact one of the alarm or warning sounds of squirrels.

Here is the subject squirrel on one of the high branches of the oak tree next to my driveway. Yes, I know it is hard to notice the squirrel and that's why I put an arrow pointing at its tail. This was the best shot I could get of it with my iPhone camera.

And here is a recording of the same squirrel's calls made, again, with the iPhone. You need to turn up your speakers to hear it loudly enough. (Towards the end you will also hear the voice of my son in the background.)

Squirrel calls

The squirrel was uttering a series of short calls followed by a long screech. In Mammalian Species No. 480, John L. Koprowski described the 4 notes used in alarm vocalizations of Eastern gray squirrels as "buzz, kuk, moan and quaa". The calls heard in my recording could perhaps be a series of "kuks" followed by one or more "quaaaaa". Doesn't that sound like a bird?

08 October 2010

Variations on whatshisname's ideas

I often forget the name of the author of the well-known novels Animal Farm and 1984. I have been reading a mildly interesting collection of his essays titled, well, A Collection of Essays and I am still having difficulty remembering his name. Is it Edwards something?

One of the shorter essays in the book, written in 1939, is about the city of Marrakech (Marrakesh) in Morocco. Our author remarks upon the insignificant inhabitants of the city and then summarizes their insignificant lives in one sentence:

They rise out of the earth, they sweat and starve for a few years, and then they sink back into the nameless mounds of the graveyard and nobody notices that they are gone.
This is, of course, the natural way of things, how it is supposed to be. According to the grand scheme of things, we all are meant to turn into nameless mounds of decomposing flesh and bones after we die.

Sweat, starvation and death are all in a day's work for all wild animals and many domesticated ones. It becomes an issue for Homo sapiens, because there is inequality among us; some of us sweat, starve and get buried in anonymous graves, while others relax, fatten up and get mummified in mausoleums. These sorts of comparisons create the impression that it is not fair for some people to live bad lives when there are others living good lives.

There are 2 mutually exclusive states:
1. We will all live more or less equally insignificant lives.
2. We will accept the condition that human lives are and will always be variable: some will be short, miserable and insignificant at one end, while others will be long, desirable and significant at the other end with every possible variant in between.

I don't know about Orwell, but I've been of the opinion for some time that there will always be variation among humans in terms of their levels of intelligence, income and happiness and that therefore, inequality is the norm. That's it, George Orwell! That's his name. But, why do always forget it?

07 October 2010

Isopods—not so cheap

Why would anyone buy isopods? They are freely and abundantly available almost everywhere. The rocks and other flat objects in my yard, for example, shelter large numbers of them. I could possibly collect several hundred isopods in one night.

Yet they are also available for purchase. I was ordering a buret* from my favorite supply company Ward's Natural Science earlier today when I noticed that they were selling a "package of 45" living pillbugs for $25.25 each. That is 56.1 cents per isopod. Rather expensive for so common an animal.

You don't even get a full identification; Wards gives the name of their isopod only as Armadillidium sp.

The only time of the year when isopods disappear mysteriously is when the upper soil temperatures are near or below freezing. So, I suppose if one desperately needed 45 live isopods in the middle of a cold winter—and if one had extra cash lying around—one could buy them. Otherwise, go out and collect your own. The common species one is likely to find in one's backyard are not that difficult to identify anyway.

*What I intend to do with a buret will probably be the subject of a future post.

06 October 2010

Frozen wine

On a warm day back in August, I put this bottle of Turning Leaf Chardonnay in the freezer of my refrigerator to cool it down rapidly. Then I forgot about it and probably ended up drinking something else. When I finally took it out a couple of days later, the wine was frozen. The expanding ice had pushed the cork almost all the way out, rupturing the foil around the mouth of the bottle in the process.

The mixture of water, ethanol and various other chemicals that make up wine freeze at a temperature lower than that of pure water, which is about 0°C. Several internet sources claim that wine doesn't freeze, but turns into slush—a mixture of ice and water. Well, there was solid ice in my wine bottle; slush ain't gonna push no cork out of no wine bottle.

After the wine thawed, we drank it. It was still good.

04 October 2010

How far back can a deer in the rain remember?

My after-lunch walk in a nearby park today interrupted the doings of a couple of white-tailed deer (Odocoileus virginianus) in the light rain. After a moment of hesitation, the slightly larger and braver one, presumably the mother, darted across the path and disappeared behind the trees. By the time I had fished out my iPhone and turned the camera on, the smaller deer was all alone eyeing me nervously from behind a strip of grass.

I started taking pictures while approaching the deer slowly. Meanwhile, it raised its tail and began to stomp the ground with its right hoof. This was a behavior pattern I hadn't noticed in deer before. Was it warning me not to come closer? (Or else, what?) Was it communicating with the other deer, which it could perhaps see or smell behind the trees?

When I was too close for comfort, the deer ran about 20 meters away and stopped. It could have continued to run away along the path or into the wooded area behind it. It didn't do so, because it apparently intended to go after its mother. It either know by sight or smell or some other means that the mother was still there or remembered that she had gone across the path. By this time 2-3 minutes had passed since the mother had disappeared. Can a deer remember a event that took place that long ago?

Finally, it gathered up enough courage and dashed for the other side. I was able to get one final picture.

Now that several hours have past, does the deer still remember its encounter with me?

03 October 2010

Mystery roadkill

This flattened ex-creature was on the road in front of my house this afternoon. The lack of fur or feathers ruled out a mammal or a bird, while the lack of shell fragments ruled out a turtle. It was most likely a frog.

The morphology of the feet, which appear webbed, support the anuran affinity of the deceased.