Birds underwater

a variety of avian submersion strategies

Many kinds of bird regularly forage for prey underwater. These birds have a variety of ways of doing so and adaptations to match. Life in the water is very different from life in the air.

The first hurdle to overcome is simply getting there. Some species start from the water surface. A few are able to just sink below the surface by decreasing their buoyancy: small grebes and anhingas do this by compressing the plumage (thus pushing air out) and exhaling. Others tuck their heads and kick with their webbed or lobed feet (e.g., mergansers, goldeneyes, buffleheads, most cormorants, loons, and some grebes) or flip their wings (murres, long-tailed ducks, dippers). Those that surface-dive a lot (e.g., loons) typically have legs set well back on the body, making them awkward on land. 

Another way to get underwater is from above the surface.Dippers often dive into a stream from a rock or low-hanging branches not far from the water surface. Kingfishers may plungefrom several meters above the surface, folding the wings closer to the sides. Brown pelicans can dive from a height of twenty meters, extending the neck and angling the wings back, making a more streamlined shape. The grand champion divers may be seabirds called gannets and boobies; they can start a dive from almost a hundred meters up, turning the body into a sleek dart, with the neck well-extended and the wings held back close to the body. The dives can reach a speed of sixty mph; to protect the bird from the resulting high impact, the skull is reinforced and subcutaneous air sacs on the chest and sides cushion the jolt.(https://vimeo.com/319325491. By Bob Armstrong, in Loreto, Mexico.)

Belted kingfisher diving and rising with fish. Photo by Bob Armstrong

Most of these dives are quite shallow, but some species are adapted for deeper ventures, with heavier, stronger bones than other birds, to resist water pressure and decrease floatation. Gannets are quite deep divers, sometimes going on down to twenty meters. Loons may dive as deep as seventy-five meters and some of the murres and their relatives go down over a hundred meters; the common murre is said to be the deepest diver (sometimes down to 180 meters) in Alaska. Penguins often launch from ice-ledges; small ones make fairly shallow dives, but the emperor penguin can dive down more than five hundred meters!

The second hurdle to underwater foraging is locomotion in a medium that is denser than air. Most aquatic birds have webbed feet, often set far back on the body for good propulsion and steering; grebes have broadly lobed toes instead. But fancy feet are not always sufficient—some of these birds use their wings to swim in pursuit of prey. Gannets and cormorants can wing-it underwater; murres and puffins have narrow, stiff wings adapted to underwater ‘flight’ (without forsaking aerial flight); penguins swim with their flipper-like wings (and cannot fly) and steer with their webbed feet (some of them are very fast swimmers, clocked at over twenty mph).

Murre underwater. Photo by Bob Armstrong

Kingfishers and dippers don’t have webbed feet, so they have their own ways of moving in water. Kingfishers seem to rise buoyantly to the surface after a dive, wing-fluttering as they lift back into the air. Dippers have strong toes for clinging to rocks and walking even in fast currents, and they swim with their wings for short distances in pursuit of prey; they are the only songbird known to do so and do not have the same adaptions of bones and wings as other, more aquatic, birds do.

Plumages of birds that forage underwater are generally dense and well-waterproofed with oils from the preen gland. Penguinplumage has unusually many tiny filaments that hold air bubbles; when the bird swims, the bubbles are released, which decreases the density of water around the body, allowing faster swimming. Birds that decrease buoyancy by compressing the feathers might get a little of this effect, but penguin plumage can hold more bubbles and release them more gradually.

Diving birds hold their breath underwater, storing oxygen in their lungs. But they can also store extra oxygen in their muscles, in a compound called myoglobin–which, like hemoglobin, is a specialized protein with iron-containing compounds that hold oxygen. Species that engage in long dives and underwater pursuits have more myoglobin than those that spend shorter times without access to air. Emperor penguins can stay underwater for twelve minutes or more (for comparison, humans can normally manage to hold breath for less than two minutes).

Mid-April

early flowers and musings about ducks

Skunk cabbages stand as tall yellow sentinels (if deer haven’t nipped them off) in the marshy places. They send out their sweet aroma (not at all ‘skunky’!) and provide a cheery splash of color in the mostly gray-and-green forest. Yellow violets gleam along the forest trails, as the forest floor begins to green-up. The white flowers of miners’ lettuce are showing, along with the delicate little flowers of fern-leaf goldthread. And the purple mountain saxifrage is going strong on rocky outcrops even in the shadier sites.

fern-leaf-goldthread-early-development-through-the-snow-6-good-altered
Fern-leaf goldthread flowers emerging through the snow

Blueberry bushes at low elevations have already dropped many of their little pinkish bells. The deeper pink flowers of salmonberry are borne on canes that are just sending out new leaves. In addition to the early-blooming felt-leaf willow, other kinds of willows are producing their catkins.

In many places, alders have already dropped their male catkins, which have released their pollen for the wind to carry to the waiting female cones. I’ve found lots of catkins lying on the ground under male cottonwood trees too, but for some unknown reason, a substantial number of these have released only some of their pollen. However, the best part (for me) of cottonwood flowering is the light, clear, sweet aroma that fills the air near a stand of these trees. Look on the ground below a tree and find the yellow-brown bud scales and sniff ‘em!

I heard my first fox sparrow of the year in Sheep Creek valley recently, along with the varied thrushes, robins, Pacific wrens, and ruby-crowned kinglets, which have been singing for some time. Just a few days later, there were several singing fox sparrows in the valley. Although hermit thrushes are here, I’ve not yet heard them sing. I have two reports of chickadees cleaning out their nest cavities, and on one creek I have seen a male dipper on guard as his female incubates their clutch of eggs; with such an early start on the first brood, they should be able to rear a second one as well.

Here are some other sightings that were fun:

A pair of ravens harassed an eagle as it sat in the top of a tree, diving at it and yelling. Poor old eagle just hunched its head and took the abuse. Were those cranky ravens defending a nest? It didn’t seem so: after some minutes of continual persecution, both ravens took off and disappeared in the distance.

Out at the end of the Mendenhall Peninsula, under overhanging alders above the beach, I found a number of small piles of chewed-up, very clean barnacle shells. Some consumer had routinely used this place to off-load the shelly ballast after lunching on the prey. Who was the consumer? Maybe a raven or two, or perhaps some otters?

One day we found five pairs of buffleheads on Cashew Lake in the Mendenhall Glacier Rec area. Each pair cruised sedately, male and female side by side, occasionally diving, each pair in a different part of the lake. Suddenly a big kerfuffle broke out—much flapping and splashing and squawking. One male had decided to approach another male’s female, and that was cause for battle. The intruder was chased off, but only temporarily. He was soon back again, and the uproar was repeated, several times. The female who was the object of interest seemed to float quietly at a little distance and let the males duke it out. I think the original status quo was restored, but who could be sure, without banded birds!

Buffleheads are the smallest diving duck in North America. They nest in the Interior, in boreal forest and aspen parklands, near small lakes and ponds, where they feed on aquatic insects. They nest in cavities made by large woodpeckers such as flickers, but readily use nest boxes too. If buffleheads try to use a cavity with an opening that is large, they may be outcompeted and even beaten up by goldeneyes that want the same cavity.

They are reported to pair up mainly in winter but also during northward spring migration. Courtship and sometimes even mating occur en route. Buffleheads often keep the same mate from year to year, according to researchers. The interactions we saw on Cashew Lake suggest that mate fidelity may be challenged at times. There’s more to be learned about all this!