Loons are fascinating, highly specialized and exceptionally charismatic

Posted: Friday, May 27, 2011

The ice is finally off the lake, and a loon pair is vociferously asserting its claim of seasonal dominance, so I feel compelled to write something about loons. But what to write -- loons are fascinating, highly specialized and exceptionally charismatic creatures, so there is much to be said about them.

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Photo By Roy Toft
Photo By Roy Toft
Common loon.

Since this is a newspaper column, not a book, I'll try to stick to one facet of loon lore with which I feel a special connection: their flight. That seems a fitting topic after spending my last 35 years as a pilot biologist flying amphibious aircraft on population surveys of loons and many other waterbirds.

All things that fly under their own power, both living and man-made, must balance their ultimate occupation or purpose and maintenance requirements with the basic parameters of flight: lift, drag, thrust, stability and controllability. But evolution (or manufacture) to a specialized existence involves tradeoffs, and loons who have become superbly adapted to an aquatic lifestyle are a prime example. Over time their diving and fish-catching adaptations were enhanced at the expense of some of their aeronautical proficiency -- but not equally among all loon species.

Of the five loon species that breed in Alaska (Common, Yellow-billed, Pacific, Arctic and Red-throated), only Common, Pacific and Red-throated are known to nest on the Kenai. Physical characteristics from an aerodynamic point of view are grossly similar among all loon species: bodies streamlined but heavy, wings narrow with little camber (rather flat), and long bones completely marrow-filled and heavy rather than hollow and light like in most other birds. Legs are mounted far aft, which is great for propulsion in water, but puts them out of balance for walking on land. They rarely travel on land, but when they do they push with their feet and slide along on their belly (you can imagine how effective that is for outrunning predators!).

A water takeoff begins with a similar belly-sliding run. Compared with most other birds, loon wing loading (weight per unit surface area) is high, requiring rapid wing beats (200 beats per minute for Common loons) and relatively high speed (70-80 mph for Common loons) to produce enough lift to take off and stay aloft. For comparison, bald eagles weigh about the same as common loons, but their wing loading is only one-third as high.

But what I find most fascinating is the way in which the different loon species, all of which are aggressively territorial and have similar food and nesting site requirements, have evolved differences in flying ability that apparently enable them to breed in close association with minimal physical conflict. Here's the way it appears to work:

On the Kenai, the Common loon is the largest loon, fiercely territorial, and also the poorest flyer of the loon clan. On a no-wind day it requires up to several hundred meters of water "runway" to take off, then a large radius turn to circle while slowly climbing over the treetops to leave a lake. I haven't found a reference for climb rate, but loons that take off from our 23-acre lake usually make 2 or 3 laps around the lake before they can clear the 80-foot trees along the shoreline. This requires a lot of effort, so Common loons seem to leave their nesting lake only rarely during the breeding season. Common loons usually select fairly large lakes, probably because of their takeoff requirements, and because of the practical need for a single lake to meet all their food requirements.

The Pacific loon is less than one-half the size of the Common loon, with relatively larger wings, so it can make use of a smaller lake with relative ease. This not only makes many smaller lakes available to the Pacific loon without risk of running into a big bully Common loon , but the Pacific can afford to at least occasionally make feeding sorties to other surrounding lakes to supplement the prey supply in its nesting lake.

But the Pacific's takeoff also requires a significant water run, so it too is ultimately limited to a certain minimum lake size. This appears to create a safe niche for the even smaller but better performing Red-throated loon to fit into the landscape. The Red-throated is the only loon able to take off from dry land or very small water bodies. Red-throated loons are not common on the Kenai, but all the ones I have seen have been in small shallow bogs. Of course, in such ponds food would be very scarce, but the superior flying ability enables a pair of Red-throated loons to take turns flying to nearby Cook Inlet to catch small fish for their hungry offspring. Red-throated loons are usually found nesting near marine waters, which normally have higher fish populations than fresh water lakes.

These relationships have been studied by various loon researchers, some of whom initially reported that the smaller loon species simply preferred smaller lakes, but on further investigation noticed that in areas without competition from larger species they would select lakes of different sizes randomly according to their availability. I have seen a slightly different situation on the Alaskan arctic slope. There, the large Yellow-billed loon roughly fills the ecological niche of the Common loon, but is restricted in range and is far less abundant than the Pacific loon. The Pacific loon is seen in a majority of lakes of all sizes, with several pairs typically sharing bigger, productive lakes. But, as on the Kenai, there seems to be little room left for the smaller Red-throated loon, which again mainly occupies very small ponds and bogs near the coast.

My plane and I will look in on the loons on the slope in mid-June. Meanwhile, we're hoping that this year the loons on our lake will find the conditions right for raising a family, that we might fall asleep each evening to hauntingly beautiful loon music, and see a youngster or two gliding through the morning mist in their parents' wake.

Bill Larned has spent much of the last 35 years flying aeronautically-challenged amphibious machinery to investigate waterfowl populations in many parts of Alaska, the Lower 48, Canada, Mexico, and eastern Russia. You can find more information about the Kenai National Wildlife Refuge at http://kenai.fws.gov or http://www.facebook.com/kenainationalwildliferefuge.

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