Ospreys and geese

 

Ospreys tend to return to the same nests year after year. However, often when they return, they find their last-year’s nest already occupied by geese. The osprey sometimes succeeds in driving the geese out, but sometimes the goose just completes its earlier nesting season before the osprey takes over. 

Yesterday, I watched osprey harass geese which had taken up residence on a couple of different nests. There were no good shots of the osprey dive-bombing the geese, but here are pictures of the participants. 

Prior to the osprey’s return, geese took up residence in osprey nests. 

An annoyed osprey flies by.

 

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Herons are back

 

I saw a Great Blue Heron this morning.

This might seem to be an inconsequential observation. One might see herons in every month of the year, so it isn’t as if they are like ospreys: gone in the cold weather; here in the warm. Yet, Kootenay Lake is on the northern edge of the heron’s permanent home in North America and the bird is remarkably fickle when it comes to hanging around us. Indeed, as Cornell Labs notes: “Great Blue Herons generally move away from the northern edge of their breeding range in winter.” This is reflected in the our low frequency of heron observations in the cold months. Indeed, I haven’t seen a single heron this last winter.

This ebird.org graph shows the frequency of observations of the Great Blue Heron locally. It is quite low in the winter but begins to pick up in April.

This morning, a Great Blue Heron flew by, the first I have seen since last fall. They are back.

 

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Bombylius, Not Bombus

 

With the advent of sunny spring, I noticed my first lawn flower of the year, a chionodoxa, a tiny bluish flower with a whitish centre. It is sometimes known as the glory of the snow.

Abruptly, the flower was visited by the first bumblebee of the year. Well, that is what a companion suspected — but it wasn’t a bumblebee, but a bumblebee mimic, a mimicry crafted to avoid being eaten by a bird. Rather than being a bee (Bombus), the visitor was a fly (Bombylius) and a predatory one at that. 

The flower appears early in the spring; the bombylius does likewise. The reason the fly does involves a story about solitary bees, for this is the time that solitary bees temporarily leave their nests unprotected. Unlike the social bees, each solitary bee lays her own eggs and does so in a small tunnel she has provisioned with food such as nectar and pollen. She then seals the entrance.

However, for the short time it takes the solitary bee to do this, the tunnel entrance is open and that is when the Bombylius fly enters and deposits its own eggs inside. When a bombylius larva emerges, it feeds on the provisions meant for the bee larvae. It then changes form and eats the bee larvae, themselves. Bombylius has only a short time in the spring to give its offspring this opportunity.

You do what you have to do.

The tiny chionodoxa graces the spring lawn.

It was promptly visited by the Bombylius major, an early spring bee-mimic fly.

The next day, a Bombylius major visited a dandelion as it sought more nectar. Its long legs and proboscis have probably evolved to protect it from an easy attack by crab spiders.

 

Posted in bugs, wildflowers | 4 Comments

Mountain Bluebird

 

Mountain Bluebirds are arriving. They like open fields where they hunt insects from low perches. Once an insect is spotted, the bird dives on it, returns to a perch, and feasts.

A splash of blue sits in the leafless brush watching the dry grass below.

Between forays, the bluebird preens,  

and fluffs.

A grub, having been spotted, is quickly retrieved, 

and promptly downed.

The cerulean beauty watches between pounces.

 

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Marmot portraits

 

I visited Marmot Village hoping to get pictures of residents doing something interesting. No such luck — the word, torpidity, came to mind. The yellow-bellied marmots would watch the watchers, but they barely budged.

If you ignore the marmot’s size, this big male looks almost leonine.

This scene appears about as it did to the naked eye. Yet, the shallow depth of field of the telephoto lens meant that only one marmot could be in sharp focus at a time. Consequently this picture is a composite of consecutive shots that differed only in focus. 

Peekaboo.

 

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March goulash

 

This is a collection of interesting creatures taken this March that lacked a posting of their own. 

Many are seeing Evening Grosbeaks this year. Why have they become relatively common?

In the spring, we see two species of bluebirds: the Mountain Bluebird and the Western Bluebird. So far, I have only seen the Western, although others have seen the Mountain.

Twenty years ago, we mainly saw Tundra Swans on the Lake during migration. Now, we mainly see Trumpeters. While Trumpeters are lovely to watch, whither the former Tundras?

The Varied Thrush is plentiful at this time of year, but it is skittish and so isn’t easily approached.

Mourning Cloak is both one of the longest-lived butterflies (11 or 12 months) and perhaps the first to appear in the spring. This is one of two seen on March 31st.

An interesting early season arrival is the Green-winged Teal.

 

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Bearded finch

 

Three days ago, I watched an odd looking (female) House Finch: it had a beard. 

These finches like seeds and initially I thought that it had one of those fluffy seeds such as those of a dandelion or a cottonwood. But that could not be right; their availability is still months off.

Today, I watched the bearded finch on a different tree, but at the same place. What was going on?

The clue to its behaviour lay beneath an adjacent home: insulation. In building its nest, the House Finch uses stems, leaves, rootlets, and thin twigs, but chooses finer materials for a lining. Our bird had discovered some home insulation it thought was ideal for a nest lining.

 

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Variegated trees

 

The rainbow season begins with a show of variegated trees on the mountainside.

 

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Dangling legs

 

During an open-air flight, a bird will use dangling legs and open claws as a threatening posture towards another bird.

The first time I became aware of dangling legs with open claws being used in a bird attack was over ten years ago when I watched a drama involving an osprey couple and a juvenile eagle. The osprey husband had left the nest and (as is standard cautionary practice) took his half-eaten fish with him. The eagle, seeking something for free, chased the male osprey across the sky in an attempt to steal the fish. The chase went on for about five minutes when the osprey wife (who is the larger of the two ospreys) intervened. As the eagle prepared to attack her husband from above, she positioned herself above the eagle with claws spread and legs dangling, in what was clearly a threatening posture. She was prepared to attack. The eagle did a barrel roll, saw her, and thought better of the exercise. Two mad ospreys was too much and the eagle’s attack was broken off. The couple took their fish back to the nest. (2010/06/05)

Another time I saw an attack with dangling legs was in 2015 when an eagle succeeded in stealing a fish from an osprey and the osprey (unsuccessfully) threatened the bigger bird. (2016/05/26)

Of course, dangling legs do not necessarily imply aggression. Legs also dangle during take off and landing, as is evident with this Red-tailed Hawk. (2017/03/06)

Legs also dangle when a bird is carrying prey. (2018/08/30)

I thought of all of this on Sunday when I watched a raven Red-tailed Hawk harass another Red-tailed Hawk. It was never clear to me why the raven hawk was doing this, but the it was unambiguously after the other hawk. Alas, searches of the web have failed to turn up any references to the role of dangling legs as a threatening posture in bird attacks. (2021/03/14)

 

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Hoodie travel optimization

 

Much of bird watching involves creature identification, along with tracking seasonal migration.

However, this posting is about neither of these; rather, it treats obscure behaviours of a duck, the Hooded Merganser. The issue is that of the duck optimizing travel so as to minimize the energy required. As do many waterfowl, this duck both swims and flies. So, an example will be chosen from each mode of travel by using two pictures taken about an hour apart. 

Swimming
Creatures that travel over the surface of water (ducks, otters, kayaks, supertankers) and are supported by buoyancy (so, are not planing) leave waves in their wake. It takes energy to create a wake and this is energy the creature must supply. Creating a wake requires work and so is a drag on travel.

The wake has a couple of components: divergent waves and transverse waves. The divergent waves spread laterally; the transverse waves lie at right angles to the direction of travel and are left behind. The transverse waves are the subject of this discussion.

Transverse waves are generated at two locations: the bow (front) and the stern (back) of the duck. As they superimpose in the wake, these two waves can either interfere constructively to produce large waves (producing a maximal drag), or interfere destructively to cancel one another (producing a minimal drag). Which happens depends upon the speed of the duck and so is under the duck’s control. Of course, the Hooded Merganser does not calculate this, but rather senses the effort it takes to move and so travels at a speed that minimizes its wave drag.

While divergent waves remain, the hoodie’s transverse waves have been substantially canceled. 

 

Flying
Flight involves two major forms of drag: parasitic and induced.

Parasitic drag results from energy lost to turbulent eddies shed by objects moving rapidly through the air, such as a runner, automobile, train, bird, or aircraft. Parasitic drag increases as the square of the speed.

Induced drag is equal to the force required to provide lift and results from the change in direction of air flow around a wing which supports the weight of the flying object. Induced drag changes inversely with the square of the speed.

So, one type of drag increases with flight speed, the other decreases with flight speed. At some speed, the sum of the two drags has a minimum value: an optimal flight speed. Birds, including Hooded Mergansers, tend to fly at (or near) this optimal speed because it minimizes the energy required for flying.

However, the Hooded Merganser has an additional consideration: its hood (crest). Parasitic drag is proportional to the forward-facing cross-sectional area of the bird, and that area would include the hood if the bird were to keep it erected, so the bird collapses its hood when flying.

The hoodie collapses its hood (see previous picture) to minimize parasitic drag when flying.

While both of these behaviours — minimizing wave drag when swimming, minimizing parasitic drag when flying — easily pass unnoticed; each is crucial to the duck.

 

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