Wednesday, June 20, 2018

Loons - Damariscotta Lake, Maine

The common loon is a northern hemisphere’s failed attempt at approximating a penguin. Fish eater – yes. Diver – yes. White belly and black back – yes. Dense bones (the better to dive) – yes. Ungainly travel on land – yes. Only one or two eggs a year – yes. Otherwise coming up short. (Or tall, depending on which penguin species is up for comparison.) Loons dive for 30-60 seconds versus 5-20 minutes for penguins. Loon use their webbed feet for propulsion, whereas penguins – faster swimmers – use their wings. Penguins dive deeper. But loons can fly.

There are actually five species of loons: common, yellow-billed, black-throated, red-throated and Pacific. The species we see in the northeastern United States is the common loon. Breeding territory is across Canada and Alaska, with the southern edge of the range extending into the US around the Great Lakes and northern New England. The common loon worldwide population is estimated at about 600,000 birds, with perhaps 30,000 nesting in the contiguous 48 states.  

Common loon (Gavia immer), Damariscotta Lake, Maine. Photo taken from
kayak at 5:45 AM. More light would have shown the red eye. Before diving,
muscles under the skin contract, forcing out air trapped by the feathers, 
causing the bird to be less buoyant. Click on photos to enlarge.
Loons migrate. In late summer, adult birds will molt (shed) their spring/summer plumage for a drab gray/brown back and neck, then head south and seaward in the fall, looking for waters that will remain ice free in winter. In late winter there will be another molt, to the black and white pattern that we find so striking, followed by migration north. Any sightings in eastern Massachusetts are of migrating birds.  

Loons often return to the same body of water they left in the fall, especially if they succeeded in raising chicks there in past years – males first, to claim the territory, then the females. Loons practice serial monogamy. If both birds of last year’s pairs show up at the same body of water they will stay together, but if one of the pair does not, a replacement loon will move in.

Loon with chick perched on back. (Internet download).
Loon reproduction fits into the K-end of r/K selection theory, a means of describing two reproductive strategies. K-selection describes a low reproduction rate combined with parental investment in caring for infants, a high infant survival rate and a long lifespan. The other end of the spectrum, r-selection, describes high reproduction rate, low survival percentages and a short lifespan. Both modes have evolutionary advantages and disadvantages. A loon pair will produce one or two eggs each year, with roughly 50% surviving to fledging (flying). In contrast, Atlantic cod produce more than one million eggs each year and provide no parental care. Scientific support for r/K theory has declined since first proposed back in the 1970s. It has been incorporated into “life history theory.” For nascent naturalists, both theories are well defined at Wikipedia.

Loons are best known for their vocalizations, which can be heard for distances of a mile and more. The nature writer John McPhee reflected, “If he were human, it would be the laugh of the deeply insane.” The major calls are yodel (males only), wail/howl and tremolo. The reasons loons so loudly announce their presence, both day and evening, is that to raise a family, each nesting pair needs exclusive use of 50 to 100 acres of pond or lake to catch the 1000+ pounds of fish and other foods needed for breeding and chick raising. Territory is so important that males go beyond the types of threat displays seen in other species, to actual combat. In roughly one-fourth of the struggles the losing male dies either by being drowned or from puncture wounds. If the intruder loon is a female, she and the resident female will fight, but not to death. Loons have also been known to kill goldeneye duck ducklings, possibly to reduce competition for food needed to feed their own chicks. 

In Walden; or, Life in the Woods, Thoreau wrote that one October day, rowing on the pond, he heard and spied a loon, a migrator stopping off for a fishy snack before continuing southward. Thoreau tried to approach the loon for the better part of an hour, but failed to guess where it would emerge from its feeding dives. He wrote: “This [howl call] was his looning — perhaps the wildest sound that is ever heard here, making the woods ring far and wide.” And also, “At length, having come up fifty rods off, he uttered one of those prolonged howls, as if calling on the god of loons to aid him, and immediately there came a wind from the east and rippled the surface, and filled the whole air with misty rain, and I was impressed as if it were the prayer of the loon answered, and his god was angry with me; and so I left him disappearing far away on the tumultuous surface.”

Not in the newspaper column:
  • Loons do not start to breed until 3-5 years old, possibly because need to be completely adult to compete for breeding territory.
  • When males fight to death, it is almost the defending male that dies; an intruder that is losing a battle will retreat to try somewhere else.
  • Although taking off is a strenuous process requiring hundreds of feet of space to build up speed, one in the air loons are vigorous fliers that reach speeds of 75 mph.
  • Newly hatched chicks can swim within hours, but will needs about ten weeks of parental feeding and care before being able to fly, and exist on their own.
  • Young chicks will often perch on a parent's back, for safety from predators such as pike or snapping turtles. Grebes are another family of bird species with the same behavior. 
  • When feeding, loons move slowly across the water, sticking their heads under the surface to look for fish. Loons are daytime, hunt-by-sight feeders, and so need to be on bodies of clear water. Small fish will be swallowed before rising back to the surface, so not seeing a loon surface with a fish does not mean that it failed.
  • To dive, loons tighten muscles under the skin. This forces out air trapped by the feathers, allowing them to swim under water with neutral or negative buoyancy. Once back to the surface they fluff their wings and body feathers to retrap air. 
  • Loons eat 10-15% of their body weight every day! Mostly fish, but also frogs, crayfish, dragonfly nymphs, salamanders, leeches...
  • Loons, like many other bird species, swallow pebbles that will stay in the gizzard, to aid in physically grinding swallowed fish into small pieces. A cause of illness and death is swallowing lead fishermans' sinkers, and being acutely lead poisoned.   

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