Herons on ice

 

The Great Blue Heron is with us year round. It eats almost anything it can swallow: fish, voles, frogs. But how does it find food in the winter when frogs are hibernating, voles are under snow, and fish are under ice? 

If the truth be told, Kootenay Lake does not freeze over — at most it has a bit of border ice in the coldest weather. However, the smaller, shallower, lakes around it do freeze over, and they present the heron with problems. 

This last weekend I watched a half-dozen or so herons ice fishing. They were monitoring leads in the ice. It was the first time I had noticed this winter activity.

Two out of a number of Great Blue Herons watch for fish at a lead.

 

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Raptors flying

 

On Saturday, I watched three flying raptors.

The closest and most difficult to record, was a falcon: a female kestrel as it left its perch.

While I saw four Red-tailed Hawks, this soaring one was the only one that made for a good image. So, why does it lack its eponymous red tail? It is a juvenile. Next year it will sport a red tail.

The observational gem, however, was this Rough-legged Hawk.

 

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Finch harvesting

 

Finches crave salt. To satisfy this, mixed flocks of hundreds of them will alight on salted winter roads and feast. There is, of course, a problem with this: traffic. Indeed, some truckers refer to them as grill birds, owing to their propensity to be collected by the grills of passing vehicles. 

It turns out that highway traffic is not the only thing that collects finch carcasses. 

This is a view into the midst of perhaps a hundred finches on the highway. Both Pine Siskins, and Cassin’s Finches are seen here as they land, feed, and take off.

The problem, of course, is traffic. The birds try to lift off. While many escape, only to return, not all make it. There is a corpse in the lower left. 

As the finches feed, ravens assemble and watch for roadkill. When it is spotted, they sweep down and carry off the corpses. This raven has a male Cassin’s Finch. 

This one is packing a female Cassin’s Finch. As the raven flew off, it collided with a male Cassin’s Finch trying to escape the mayhem. (I interviewed one of the ravens about this. It prevaricated: “We have a contract with Highways to keep the roads clear of bird carcasses — yum yum.”)

 

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Lake-surface oscillation

 

The varying patterns that can be seen on our lake are endlessly fascinating. Photographers often seek out particularly beautiful ones, as do I, but I also seek the beauty of its physics.

Pop pattern posting: With over 6500 viewings spread over a decade, the posting about Lake-surface patterns during rain is uncomfortably close to being viral for this unpretentious blog.

On occasion, this blog and website have treated various lake-surface patterns: ripples, gravity waves, wind-driven waves, wakes, beach cusps, convergence, divergence, long-shore drift, and patterns from rain. The latest observation was prompted by thoughts about the patterns produced by katabatic winds.

The pattern of interest is this unremarkable-looking patch of calm water amidst a wind ruffled surface. For reference, I note that there is a gentle flow of water from left to right, and a gentle flow of air (wind) from right to left. The calm patch could have resulted from either a locally decreased water or air flow. Either could produce the calm patch because a (relative) wind over the water of less than 23 cm/s cannot produce waves. Why is this?

A wave on the surface of water can be characterized by its wavelength and its speed. For the most familiar form of waves that buffet a boat or shore, gravity is the restoring force. For these waves, speed increases with increasing wavelength. Another (much shorter) form of waves are variously called ripples, capillary waves, or surface-tension waves. For these waves, speed decreases with increasing wavelength. The result is that there is a minimum speed, 23 cm/s, and a minimum wavelength, 1.7 cm, for waves travelling on water. An object travelling through the water, or a wind pushing on it that has a speed of less than 23 cm/s leaves no waves. This light breeze is a ghost — it travels over the water without disturbing it.

So, if the wind is < 23 cm/s, the water is smooth; if the wind is > 23 cm/s, the water is ruffled. But, how does the wind temporarily change from the higher speed to the lower one and then back again so as to produce a limited patch of calm water?

For this, we need to know something about the wind profile, the way the wind changes with height above the surface. A bit above the surface (in this case, maybe only 10 cm above) the wind is stronger. It is slowed at the surface by friction, but that slowing depends upon the roughness of the surface. A general rule is: the rougher the surface, the slower the surface wind; smoother the surface, the faster the surface wind.

The previous image is repeated and labeled. The arrow shows a gentle wind of somewhat more than 23 cm/s coming from the right. The water waves it produces roughen the surface and this slows the wind so that at A the speed has dropped below the wave-cutoff speed. However, that smoother surface allows the surface wind speed to increase so that at B waves are again produced.

What happened with that patch of smooth water can happen again and again to produce an oscillation between rough and smooth water. In the picture of ruffled water, below, there is a train of six smooth patches with a spacing of fifty to a hundred metres. 

Many of the oscillatory forms seen on a lake have been given names. I have been unable to find a name for this pattern, and indeed do not even know if it has been described previously.

Mind you, it is understandable if no one has bothered with it. After all, the pattern is inconsequential for water management, hydroelectric production, fishing, boating, and ecology.

But, it is a delight.

 

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Chips fly

 

What is a resting grub going to do to protect itself when it merely wishes to sleep through the winter inside an old tree? Apparently, nothing. When the Pileated Woodpecker finds you, it’s lights out.

A female Pileated Woodpecker was probing an old cottonwood tree.

The wood chips flew as the woodpecker attacked the trunk.

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Blue wake

 

Just goldeneye ducks.

A jaunt began with a female goldeneye expressing (what looks like) joie de vivre.

It ended with two male Barrow’s Goldeneyes leaving blue wakes across golden waters.

 

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Post-posting ponderings

 

The majority of my postings stand alone. Yet, sometimes following a posting, I continue to ponder it. This is a collection of five further ruminations made this last year.

Speeding hare, Jan. 17, 2018
I was struck by the speed of a snowshoe hare as it easily outpaced two dogs chasing it across a snow-covered field. What I did not appreciate at the time was how superb was this feat. Popular media will assure you that the fastest land mammal is the cheetah. This is true — when the cheetah’s top speed is measured in metres per second. However, biologists compare animals’ speeds in terms of their body lengths travelled per second. The cheetah has an impressive top speed of 23 body lengths per second. The hare trounces it by hitting a top speed of 37 body lengths per second. The hare besting the dogs was a truly impressive sight.

 
Golden Eagle, February 3, 2018
What was a Golden Eagle doing cruising the valley bottom? It normally prefers the uplands and leaves the valley bottoms to the Bald Eagle. My suspicion is that its presence was a result of the unusual large number of snowshoe hares that winter.

 
Cormo_rants, March 7, 2018
The Double-crested Cormorant is an interesting and uncommon bird around the Lake, so when the opportunity arises, I like to watch and photograph its behaviour. It was unexpected to discover that among some folk, the cormorant is demonized for everything from stealing fish, to destroying trees. There is a discussion of this at Why People Kill Cormorants. It seems that some people don’t feel complete until they know just what it is that they should hate. 

 
Horaltic vultures, September 1, 2018
The classic picture of a vulture is one of it perched with its wings spread. It is clear why a bird has spread wings when flying, but why does it sometimes do so when perched? In the posting, I noted that a number of large birds will do this to: dry wings, raise body temperature after a cold night, bake parasites. Indeed, in the picture, below, the vulture on the left is having an early morning warming, while the one on the right is baking its parasites. However subsequent to this posting I realized I have also seen spread-wing perching as: a threatening posture to other birds, a way to shake water drops from the wings, and a way to cover food to avoid the avarice eyes of other birds.

 
Waltz of wind, water, & waves, September 20, 2018
The posting discussed a katabatic wind that flows off the beach and out over the Lake. Initially, the wind velocity at the water’s surface was below the cutoff speed for the production of waves, 23 cm/s, so, although the wind blows, the water just offshore is smooth. Then I  wrote: “But, as the air moves out over the water, it accelerates and at the threshold speed of 23 cm/s, it begins to abruptly ruffle the water’s surface….” This comment was both correct and glib. After all: Why should the wind accelerate a bit offshore? First, the picture, then the discussion.

All winds are stronger a bit higher up but are slowed by friction at the surface. In the case of the gentle katabatic winds here, that higher up might be only 20 or 30 cm above the surface. The wind in the bottom centimetre flowing off the beach has clearly been slowed to below the wave cutoff speed. But as the air flows out over the warmer water, convection causes not only the steam fog, but also a mixing that brings the slightly stronger winds from higher up down to the surface. The surface winds now move faster than the cutoff for waves and so the water becomes disturbed.

This leads to another insight. The wind at the surface is slowed by friction by an amount that depends upon surface roughness. Change the underlying surface and the surface wind changes. (The velocity exchange through the wind profile is facilitated by a mixing from either convection or mechanical turbulence.)

Now consider a wind speed just above the cutoff speed for wave formation, so the water is ruffled. The rough surface now drags on the wind so that its speed then drops below the cutoff, and the water becomes smooth. The smooth water allows the wind speed to increase to above the cutoff and the water becomes ruffled again. And so it goes, back and forth.

I believe I have seen this oscillatory behaviour but have yet to get a compelling picture. Something to watch for.

 

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December goulash

 

This is a compilation of a few images, none of which had its own posting in December. Indeed, December could be characterized as a month of sparse observations.

Early in the month, Trumpeter Swans came through, but were often distant.

Another distant observation was that of two otters fishing through an opening on a mountain lake.

Not seen at all was a snowshoe hare, but its tracks abounded. On the left are the prints of its two hind feet. This seems to suggest that the hare was travelling from left to right, but the reverse is true — it is hopping from right to left. Its two front paws arrived first and made a single hole on the right. Then its two hind paws swing past them and made the holes in front of them. 

This is a pattern I sometimes see at this time of year: rime decorating the trees in a draw. A draw is a steep valley at right angles to the ridge line. It is carved by the water flowing in a creek. A draw also serves as a drainage path for cold air, and when that air contains a supercooled fog, some droplets collide with the trees and freeze there as rime.

I have been watching for irruptive birds all month, but have seen very few of them. These irruptives are a flock of Pine Siskins. This bird uses flap-gliding flight — a strategy that conserves energy. Some siskins are seen flapping; some are seen gliding.

These two siskins are flying off after scrounging for seeds on the ground.

A siskin in a douglas-fir has pried a seed from an adjacent cone and is about to swallow it. 

This is one of four Ruffed Grouse seen together in my yard. All were of the greyish colour morph, although the brownish morph seems more common around here.

 

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Crossbill flicker

 

Experienced birders might suspect that today’s posting is a hoax — it is not. The picture of the crossbill flicker at the bottom is real. 

Crossbills are finches whose bills are adapted to prying seeds from cones.

Flickers, however, are woodpeckers and have parallel mandibles used for carving cavities.

This recently spotted flicker has an unusually long bill that is crossed. While the bird looks healthy, it is unclear how it is able to indulge in a normal flicker’s behaviour with such a bill. I have not previously seen a woodpecker that looks like this, but Gary Davidson tells me that there is an uncommon syndrome known as Avian Keratin Disorder. See also, Deformed Bill Research. First seen twenty years ago among chickadees in Alaska, the disorder has spread to other species and has clearly reached Kootenay Lake.

 

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Trumpeter visit

 

On their annual migration south, Trumpeter Swans are visiting the Lake in threes and fours.

These trumpeters are in the waters beside Kokanee Creek Park.

To my surprise, these swans took flight. The trumpeter is a big bird and must run across the water to pick up the speed necessary to become airborne. This gave me the unusual opportunity to photograph the liftoff. But, why did they take flight? Usually when a swan spots a beach walker, it just lazily moves slightly offshore, so this abrupt departure was unexpected.

Now airborne, one of the Trumpeter Swans flies past.

 

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