Falcon feeding

 

A falcon is a small raptor that uses speed to prey upon insects, rodents, and small birds.

We have two falcons present year round (plus three occasional visitors). The smallest of our regular falcons is the Kestrel (80–165 g). Slightly heavier is the Merlin (160–240 g). This last week I watched each of them feast on insects.

A Kestrel chased, caught, and consumed, what I suspect, is a sawfly.

A Merlin chased, caught, and consumed a dragonfly (a darner).

If a dragonfly sees this, annihilation is at hand.

 

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Darner mating

 

One might think that the dragonfly season would be over — not so.

Seen here are (what I believe are) lance-tipped darners mating three days ago. The male (more bluish) is the one above, while the female (yellowish head and thorax) is the one below.

He is holding her by the back of the head, and she has placed the tip of her abdomen at his secondary sexual organs.

A couple of darners coupling.

 

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Waltz of wind, water, & waves

 

As the sun rose yesterday, a neat choreography of a katabatic wind created ephemeral sprites of steam fog, and abruptly ruffled calm waters farther offshore. In fifteen minutes, it was all over.

Katabatic wind
The night had been clear, so the infrared radiation lost by the ground was not offset by compensating radiation from the clouds.  The mountainside cooled, which in turn caused the adjacent air to cool and begin to flow downslope. This drainage wind is called a katabatic wind, but it is usually so gentle as to be almost undetectable. Upon reaching the valley bottom, the air moved out over the Lake. 

Temperature difference
The katabatic air flowing out over the Lake was cooler than the centimetres-thick air already over the water. Certainly, the Lake had also lost energy by infrared emission, but convection in the water had brought warmer water from below to the surface and kept the adjacent air warm. It also kept this thin layer of air moist.

Steam fog
There are two distinct mechanisms that can produce condensation. The best known is vapour cooling. This is responsible for the formation of cumulus clouds and wave clouds. (It is usually explained by saying that cold air cannot hold as much water vapour as warm air, but this glib assertion has been known to be nonsense for over two centuries.) The mechanism for the formation of the steam fog seen here was that of vapour mixing. There was no net temperature change as warm and cool vapour from two sources mixed. (This mechanism also gives rise to the contrails trailing the engines of jet planes.) As the katabatic wind, with its cool vapour, flows over the surface air of the Lake, with its warm vapour, the condensation forms little convective towers of steam fog that drift with the wind.

Surface transformation
As if the katabatic wind and the formation of steam fog were not interesting enough, something else odd took place. Lines of the steam-fog sprites trace the air flow offshore. Initially the wind does not ruffle the water’s surface — then abruptly, a little way out, it does. This pattern is strikingly consistent across the Lake: smooth water abruptly transforms into ruffled water. 

Wave threshold
We are used to seeing the wind drag on a water surface and raise waves. However, waves on water have a minimum speed of 23 cm/s. If the wind is gentler than this (or if a swimming bug moves slower than this), no waves are created. The katabatic wind flowing down the mountainside has been slowed by trees. But, as the air moves out over the water, it accelerates and at the threshold number of 23 cm/s, it begins to abruptly ruffle the water’s surface as it can now create waves.

Termination
This waltz between wind, water, and waves originated with a cooling of the mountainside by the net loss of infrared radiation. It ended quickly when the rising sun began to warm the mountainside. This killed the katabatic wind, and over a period of only a few minutes, the air stopped flowing out over the water, the steam fog vanished, and the Lake became calm.

Thank you for the dance.

A katabatic wind flows over warmer water making steam fog and ruffling the water offshore.

 

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Osprey fattening

 

Ospreys are now eating as many fish as possible in preparation for their long migration.

Ospreys have been present since April. They built nests, mated, laid eggs, brooded chicks, and their chicks fledged. Now, mid-September, all are getting ready to migrate to Central America and points south. Preparation for this long flight requires building fat reserves. 

Consequently, a number of times each day, ospreys bring a fresh fish to a perch and feast.

An adult osprey arrives with a sucker (and a bit of salad).

It lands on a piling.

In an act repeated around the Lake, the osprey feasts. Soon, all will migrate.

 

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HY Bald Eagle

 

For many years, I have been used to Black Bears turning up in my yard early in August. Alas, none have (apparently) done so this year. The berries must be good at higher elevations resulting in a scant need for an early descent into the valleys.

There have been scattered reports of bears visiting the spawning channels, yet my frequent visits to these spots have yet to reveal anything other than one uncooperative and distant cub.

However, during this morning’s sortie, I did have an interesting encounter: a close flyby by a hatch-year (HY, i.e., this year’s) Bald Eagle. 

A hatch-year Bald Eagle flew by so closely that it did not all fit into the camera’s frame.

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Feasting on fish

 

Fish are a staple food for much of the wildlife around the Lake — we are, after all, dealing with a lake — so, I show wildlife feasting on fish.

This posting was prompted by recent pictures, but these images have been supplemented by shots drawn from earlier occasions. The reason for this is that some of the events are so fleeting that few have been recorded, and one can only show what one has.

There are about two dozen species of fish in the Lake. Rather than try to show all, I illustrate only the spectacular spawning Kokanee. Most spawning creeks are well shaded, but for a shot of the Kokanee in their dazzling redness, one must find a spot where they pass through sunlight.

The raven is an inveterate predator upon the spawning Kokanee.

During much of the warm season, ospreys specialize in suckers, but come the time of Kokanee spawning, preferences change. Notice the two wasps taking an interest in the Kokanee.

The Bald Eagle is a versatile eater, so during Kokanee spawning, it takes advantage of them.

The mallard is a flexible feeder that often poaches Kokanee eggs, but here it eats a carcass.

A perennial favourite of wildlife is the sucker. Here a Hooded Merganser downs one.

Most birds must swallow their meal whole, so the size of the prey changes with the size of the predator. This Belted Kingfisher is limited to rather small fish.

A Pied-billed Grebe can handle a modestly larger fish.

A Great Blue Heron can swallow a rather large one.

A gull can pick a fish apart, yet, this fish was swallowed whole as the bird flew.

The fish being consumed by this Common Merganser is unidentified.

A loon swallows a fish far out on the lake.

A lesser known fish is the Slimy Sculpin being consumed by this Horned Grebe.

One might imagine that fish are the preserve of birds. Not so, here a Black Bear eats a Kokanee.

And a River Otter eats a sucker.

I have failed to show a Turkey Vulture eating anything. That they hang around and feast on fish carcasses is clear, but I have yet to catch them in the act. It remains something to look for.

 

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Raft of loons

 

This is the time of year to see rafts of loons on Kootenay Lake.

Often, the loon is a solitary bird, accompanied at most by a mate and chicks. But prior to migration, numerous loons gather in social groups. 

The sequence is roughly as follows: loons winter at the Coast; they fly to the Lake in early May where they fight rivals and meet with mates; they fly to smaller lakes high in the mountains to breed and raise chicks; they gather again on Kootenay Lake; they fly back to the Coast to winter. 

A raft of seven Common Loons meets on Kootenay Lake prior to their migration to the Coast. The five on the right are still in their breeding plumage, while the two on the left have transitioned into non-breeding plumage.

 

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Sandpiper migration

 

This is the season to visit the lakeshore to see sandpipers that have stopped by to feed on their journey south. Already shown have been the Killdeer and the Baird’s Sandpiper. Here are three more.

The Lesser Yellowlegs breeds throughout the Arctic and the northern portion of provinces from British Columbia to Quebec. It winters along the coasts of the US and Mexico. 

The Stilt Sandpiper breeds along the Arctic coast and winters along the Gulf of Mexico. It has a long way yet to go.

Similarly, the Long-billed Dowitcher breeds along the Arctic coast, but winters in Mexico.

A skittish bird, the Long-billed Dowitcher takes to the air when approached.

 

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Perplexing sky

 

Down here on the surface of the earth, we are used to judging distance with the help of contrast: distant objects have a lower contrast than those in the foreground. This insight works for solid objects with sharp boundaries. So, with each successively distant ridge, the trees lose contrast as dark objects become lighter and bright objects become darker.

This is so much a part of our experience that we don’t give it any thought while using it to judge relative distance. It is illustrated with a picture taken through the smoky air of last summer’s fire season (right), but the behaviour is the same, only more gradual, in clear air.

The guideline that contrast decreases with distance can be problematic when dealing with clouds, which range from the opaque to the diaphanous. Consider this morning’s sunrise shot. (The yellowish cast results from the smoke of forest fires farther east, and while the colour adds to the drama, it is not the point of this discussion.)

Rather, look at the contrail on the right side of the picture. We percieve it as being in front of the higher cloud because of its higher contrast. Alas, our perception is wrong. 

Consider the geometry of the scene. The sun is above the horizon and so must be shining down on all clouds. However, the contrail is casting a shadow on that supposed higher cloud. Ergo, despite perceptions, the contrail must be above (more distant than) the high cloud.

A contrail (right-hand side) looks as if it is lower than the high cloud, but it is actually higher.

 

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Horaltic vultures

 

If one wants to watch vultures, a good tactic is to hang out in the vicinity of carrion (sigh).

For most of us, finding carrion before a vulture does is not easy — except possibly during a seasonal die-off, such as what happens with spawning Kokanee. The carcasses of spent fish attract bears and birds for weeks on end.

However, merely spotting vultures does not guarantee that they will be seen in their horaltic pose, and that is what I set out to see. The horaltic pose of vultures (and a very few other large birds) involves perching in the sunlight with spectacularly spread wings. There are questions about this pose, none of which is easy to answer.

• Why do vultures do this?  Speculations are that the pose might facilitate: drying the wings, raising the temperature of the bird after a cold night, baking parasites. At one time or another, the purpose probably involves any of the three reasons.

• Why is the pose given the odd designaton, horaltic? The etymology of the name is obscure, although I suspect that it refers to the Egyptian god, Horus, which is sometimes represented by spread wings.

• Why did I want to see it? Well, it is an unusual pose for any bird and a spectacular one at that. It is certainly worth seeing.

I finally learned when and where to look in the trees above a local spawning creek.

A hint as to forthcoming vulture scavenging is the sighting of a kettle of vultures.

The dorsal surface of the Turkey Vulture looks black from a distance, but is actually a deep brown. Along with that, the adult vulture’s head is red and its hooked bill is ivory.

The underside of the vulture’s flight feathers are light, making the ventral surface two toned. 

A Turkey Vulture strikes a horaltic pose as it rests on the branch of a red cedar. It is early morning, and this pose seems to be struck to warm the bird with the first rays of sunlight following a cool night.

Sometimes the brownish dorsal surface of the wings is exposed, sometimes the two-toned ventral surface is exposed.

Here a juvenile vulture (grey head) warms its dorsal surface, while an adult (red head) exposes its ventral surface in a somewhat different stance. The adult’s pose is reminiscent of that of a heron, which sometimes uses this stance to raise wing temperature so as to allow sunlight to kill its parasites. Indeed, the adult vulture on the right was seen to be picking things out of its feathers.

An adult Turkey Vulture faces the sun and adopts a pose apparently used to cook its parasites. 

 

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