A Varied Thrush scarfs rowan berries.
A male Pine Grosbeak chows down on crab apples.
A robin contemplates plentitude.
A male Pine Grosbeak munches crab apples.
A female Pine Grosbeak twists to reach the berries.
A Townsand’s Solitaire eats a cultivar.
A male Pine Grosbeak twists to reach crab apples.
I have watched a number of feasting animals — birds, bears, coyotes, deer, wasps, spiders — and at no time have the words, picky eater, sprung to mind. That is, with one exception: a dipper.
An uncommon bird of western North America, the American Dipper can sometimes be found hunting in clear, fast-moving mountain streams. Fortunately, I live near a creek where there is often a concentration of dippers (eight seen last Saturday), so I get to watch its behaviour. This easy access to the bird has enabled me to write an article for the BC Field Ornithologists about the way dippers handle surface and anchor ice in cold weather: dippers and ice. I have even watched it tending its chicks.
The dipper is an unusual songbird. It flies underwater to capture aquatic larva and fish eggs from the creek bed. Occasionally it will even capture fry swimming within the stream. About a year ago, I was watching a dipper collect kokanee eggs from the creek bed and was struck by the fact that it would retrieve a group of them, but would then place them on a surface so it could eat them one at a time.
This time, I was struck by the dipper’s behaviour where it would retrieve a clutch of kokanee eggs, but not swallow them upon bringing them to the surface. Rather, it would pause and examine them.
As before, it would first place them on a surface.
It then tried to pick them up one at a time, but unfortunately they were clumped together. So it tried to separate the eggs by twisting and shaking its head. Why it had to eat them individually rather than all at once is unclear. But, having failed to separate them, it then put them down on the rock again.
Oh well, it is time to start all over again. It stuck its head back in the water and this time seems to have grabbed a grub. Food must be plentiful for it to afford to be so picky.
The Common Redpoll is a finch of the Arctic tundra that now and then comes south in the winter to feed. I previously saw them nearly four years ago. I start with a picture from then which enables me to poll both redpoll frequency and evolving image quality.
Of course, I wondered what was the relationship between the words redpoll and poll (as in, take a). Poll is a middle English word meaning head. That accounts for the name of a bird with a red crown. The modern use of the word, poll, comes from the idea of a head count.
A Common Redpoll forages for seeds on January 27, 2012. Obtaining a good picture of such a frenetic bird is always a matter of happenstance, but clearly this image is not as detailed as are yesterday’s, below.
This is one of three female redpolls seen yesterday. The out-of-focus background is lakeshore snow and water. I wonder if this will prove a good winter for seeing redpolls.
Here is a detail of the red poll of a redpoll.
“I’m outa here.”
I have seen few birds around of late. While the geese remain plentiful, ravens seem sparse. Even trees with red berries seem to get few visitors. However, a few did come.
This is a Pine Grosbeak female feasting on rowan berries. I waited for more to turn up; they did not.
A Townsend’s Solitaire was helping itself to some berries from a unknown cultivar.
“I could lead a sleigh.”
If one is walking through a whitened forest on a mountainside, it is easy to tell if the trees are covered with snow or rime. From a distance, though it is often more difficult as details vanish and both merely look white.
Following my last posting about the appearance of the snow to rain transition in the air, it seemed appropriate to treat the transitions on the surface which can be seen with either fresh snow or fresh rime. Later in the season, the whole mountainside will be covered with snow and the transitions I discuss here will not be evident.
The first picture shows snow on the mountainside. Snow is made up of large ice crystals that fall from the cloud. When they fall below the melting level in the atmosphere, the smaller ones melt quickly while the large ones keep falling a bit farther. The result is that the transition between snow and no snow on the mountainside is gradual.
Rime comes about in a different way. A cloud of water drops has been drifting alongside the mountain. Some of the cloud drops bump into tree branches and are collected. Below the melting level, the droplet temperature is above 0 °C and the drops merely wet the tree. Above the melting level, the droplet temperature is below 0 °C and is thus supercooled. When that droplet hits the tree, it promptly freezes to give rime. The visual consequence is a rather sharp transition from no rime below the 0 °C isotherm to rime above that looks different than the gradual transition resulting from falling snow.
At this time of year, weather forecasts often tell of snow in the mountains and rain in the valleys. The forecast sometimes gives an altitude where the transition takes place. Leaving aside the appearance of the transition on the ground (ski above, hike below), what does it look like in the atmosphere? Curiously, the snow-rain boundary in the air can appear to be abrupt.
When falling snow melts to form rain, the visibility of each is quite different. There are two reasons for this:
• When a snow crystal melts to form a raindrop, the surface area that can reflect light decreases. The difference can easily be a factor of two.
• The snow has a larger number density than does the rain below the melting level. This is because the rain has a higher terminal velocity than does snow, so it spreads out over a greater height. The difference can easily be a factor of five. A way to visualize this is to think of highway traffic spreading out when moving to a region with a higher speed limit.
Taken together, there is a factor of about ten in visibility with the rain having only about a tenth the visibility of the snow from which it melted. As the rain is comparatively invisible, it almost looks as if the precipitation fell to some level and just stopped.
The mountainside serves as a backdrop for a shower of snow into rain. The relative invisibility of the rain makes it seem as if there is no precipitation below the snow. Nevertheless, it was raining there.
I have long fancied that I had a grouse in residence, although I do know that more than one individual wanders through my yard. Aside from a hen and her chicks, I have only ever seen a single Ruffed Grouse at a time — that is, until yesterday.
I was watching a Ruffed Grouse display an enormously puffed-up breast,
when another grouse wandered by. Seeing a second was a first.
It struck me as being a tad early in the month, but there they were, seven swans a-swimming.
Of course, as soon as swans are seen on the Lake, the immediate question is: Are they Tundras or Trumpeters? In this case, I lean towards Tundras because of the shape and lack of heft of the bill, the way the neck is held, and the fact that the juvenile has already begun to lose its grey colouration. Yet, none of them show a yellow lore. I am open to suggestions.
After swimming awhile, the swans took to the air. The second picture shows five of them, including the juvenile, flying.
As I watched a muskrat swimming a bit offshore, I wished I had a better grasp of naval architecture (watercraft design) for it looked as if the muskrat were travelling at approximately its hull speed. Its concave body seemed to be draped between two wave crests of its own making.
An object (boat, muskrat) travelling across the surface of water creates a bow wave that necessarily travels at the same speed as the object. However, a bow wave is a wave so its subsequent troughs and crests will extend back alongside the hull. The wavelength depends on the wave speed and thus the boat speed. A slowly moving boat will produce a slowly moving, and thus a short wave. If the boat is long, this leads to many distinct waves along the hull. With greater and greater boat speed, and thus wave speed, there comes a time when the wavelength of the water wave has grown to equal the length of the hull. That speed is called the hull speed and the boat now sits neatly between the wave crests it created, just as did the muskrat I was watching.
For an animal moving across the surface, its hull speed may well constitute a practical speed limit. If it attempts to swim faster, the wavelength increases and the animal must now struggle to continuously travel uphill between the trough and crest of its own bow wave. In a boat, when sufficient power is applied, the bow will first tip up as that hill is climbed, but soon, with even more power, the boat is up and planing. About the only animals that seem to be (temporarily) capable of planing are birds landing on water. Apparently a muskrat swims at a speed just below its hull speed. (Fish, 1993). But what is that speed?
The relationship between wave speed and wavelength in a deep–water wave is,
c = √(g λ/2π), where c is wave velocity, λ is wavelength, and g is gravity.
If we put metric (MKS) numbers in this we get c = 1.25√λ and if λ = 0.3m, the average length, ℓ, of a muskrat body, we get a velocity of 0.7 m/s or about 2.5 kph.
Of course, estimating the actual speed of an object moving in the distance is difficult, so I will play a trick. Again set λ = ℓ, the muskrat’s body length, but now divide through by ℓ so the velocity, V, is expressed as the number of hull lengths travelled per second. We now get,
V = √(g/2πℓ).
Numerically, this is V = 1.25/√ℓ, and with ℓ = 0.3 m, we get that the muskrat travels at about two body lengths each second.
Indeed, that is what the muskrat appeared to be doing; travelling at its hull speed of about two body lengths per second. Incidentally, when travelling underwater, an animal will not encounter this problem with waves and so can travel faster than it can on the surface. Now, if only it didn’t have to return to the surface to breath, it could move really quickly.
The concave body of a muskrat is suspended between the crest of two waves of its own making as it travels at about its hull speed of two body lengths each second.
Ogopogo insights
It is interesting that two observations made this year, a swimming snake and a swimming muskrat, have prompted unexpected insights into our favourite lake monster, the ogopogo. I will show that if an ogopogo existed it would not look as it is always illustrated. Then I will explain why a family of travelling otters does look this way.
A summary of the ogopogo is followed by a discussion of snakes and muskrats.
An ogopogo is a supposed large serpentine monster reported in many of the lakes in British Columbia. Sightings have been made, perhaps every decade, since before European settlement. The ogopogo is now the darling of tourism organizations. So, I begin with a statue of it in Kelowna that appears to be an amalgam of some of the descriptions made on Okanagan Lake. As will be seen from my own pictures of its Kootenay Lake relative, the Kelowna representation is reasonably good, albeit stylized.
Here are some of my own pictures of the ogopogo from Kootenay Lake. First, a distant view where the sinuous loops and even some fins on the serpentine body are apparent.
I match a few of my other ogopogo pictures with historical observations from around Kootenay Lake collected by Tammy Hardwick (I Love Creston, 2011, p. 20).
“The monster…is ten feet long, six inches in diameter at the largest part and has a most hideous head.” Dec. 1900, George Graves and son, of Nelson
“We…were barely out of sight of Kaslo…a black head reared followed by at least one hump above the water some eight feet behind… We sat hypnotized until the ‘Ogopogo’ dived….” July 1937, Naomi Miller
“The visible part about twenty feet long, showed brownish in the sunlight, and the surface looked rough like a tree trunk with moss growing upon it.” April 1953, Two Boswell men
Now, biologists and naturalists have known for many decades that observations of an ogopogo were actually observations of a rapidly travelling family of otters. Indeed, my two observations turned out to be otter families. (All of which has not prevented the ogopogo from being promoted as a tourist attraction.) So, what else can possibly be said on the subject? Indeed, what possible insights could be gained into the ogopogo by watching a snake and a muskrat?
The ogopogo is often described and illustrated as being serpentine, so it is reasonable to ask how a snake moves through the water. It moves sinuous undulations along its body, but not in the way an ogopogo is presumed to do. The undulations in the ogopogo’s body are vertical, but a snake’s bends are horizontal. Only horizontal undulations can effectively press against the water and move the snake forward. If an ogopogo existed, it wouldn’t use the ineffective vertical undulations as a means of swimming. Here is a garter snake swimming by applying horizontal undulations.
But, why is the ogopogo always illustrated as if swimming with the ineffective vertical undulations? Or, more to the point, why do otters swim this way. Here is where the muskrat insights of yesterday come in. The swimming speed of a muskrat is capped by its hull speed — the speed at which the wavelength of its bow wave is equal to the length of its body. At this speed, the muskrat seems trapped between two wave crests. For it to swim faster would increase the wavelength causing the muskrat to endlessly swim up hill from the trough to the crest of the wave and this would take more power than the muskrat can exert. However, this speed limit, the hull speed, being caused by surface waves, is only applicable at the surface. The muskrat can move very much faster when travelling underwater.
The same is true of any swimming animal: it can move faster underwater. When an otter chooses to move slowly, its whole body can be seen. Its speed over the water surface is similarly limited by its hull speed, in the otter’s case a bit over one metre per second.
But, when the otter wishes to travel a great distance quickly, as when swimming up the lake, it avoids the speed limit imposed at the surface by diving. Of course, it must keep returning to the surface where its noise pointing up can be interpreted as the ogopogo’s fins. The otter then dives again presenting us with the ogopogo’s vertical humps.
It is interesting to me that the reason we imagine a serpentine lake monster is that the otters in a family constantly dive so as to avoid the effective speed limit imposed by the waves they create while swimming at the surface. It is also interesting that, as far as I know, no one ever pointed out that an actual serpentine monster would not swim with vertical undulations in the way an ogopogo is always depicted as doing.
Of course, the legend remains good fun and even I made a pilgrimage to Kelowna’s statue of the ogopogo. Yet, I make no apologies to the British Columbia tourism industry when I close with a portrait of the real ogopogo.
