A Northwoods Almanac for September 2 – 15, 2011
Mary and I observed a small flock of nighthawks migrating through Manitowish during the early evening of 8/26. While nighthawks migrate both day and night, most flights are observed during the early evening. The great distance they travel between their breeding range in North America and their winter range in central and southern South America makes their flight one of the longest migration routes traveled by any North American bird.
Their fall departure begins as early as July and individuals become quite social, occasionally gathering in flocks of thousands. They fly rapidly with no apparent leader, typically close to the ground, and often with wingbeats in unison.
Nighthawks leave our area early, because they require a constant supply of flying insects which are only available during warm weather. Thus they have no choice but to stay at least one step ahead of the first frost.
Several individuals stopped me last week (8/22-26) to ask if hummingbirds had already begun migrating, because it seemed to them that about half of the hummers at their feeders had left. Several others, however, told me their numbers are still stable, and they are filling their feeders continuously as the hummers tank up for migration.
Both situations make sense. We usually think of “our” hummers leaving by around September 10th, but it’s not a uniform departure. Some male hummingbirds start migrating south as early as mid-July, though their peak of southward migration is late August and early September. Many people notice that adult males migrate earlier than females, because in the last month or so there may be no birds with red throats at feeders. The males precede females in both spring and fall migrations, while the juveniles of both sexes lag somewhat behind adult females in fall.
Hummingbirds may begin to accumulate fat in early July, and their body weight can double in as few as 7 to 10 days. If a larger bird gained that much weight, they would not be able to get off the ground. It’s during this time you may notice a hummingbird swarm around your feeders.
But by mid-September, essentially all of the ruby-throats seen at local feeders are migrants from further north coming through our area. The number of birds migrating south may be twice that of the northward trip, since it includes all immature birds that hatched during the summer.
The juvenile hummers fly alone and have to find their own way south. But the following year, each hummingbird will follow the same path or fly zone they did when they first made the trip. The best analogy I have heard is that hummingbirds are like commuters on a freeway, all going the same way on the same road, but doing so alone to get to their own individual homes.
While migrating, hummingbirds generally will fly during the day and sleep at night. Adult ruby-throats have a mass of only 3.5 grams on average (about one-tenth of an ounce), but despite their tiny size, many of these birds fly nonstop across the Gulf of Mexico during fall and spring migration, a round-trip of nearly 1,000 miles. Despite all the research done on hummers, their migratory routes remain poorly documented, and some proportion of the population appears to follow a coastal route south during the fall.
Ruby-throats have been documented arriving in Costa Rica by late September to early October. Remarkably, their overland migration occurs at nearly the same time as the peak flowering of jewelweed (Impatiens biflora), suggesting to researchers that the timing of jewelweed flowers may influence the timing of hummingbird migration.
The North Lakeland Discovery Center hosted an exceptional talk given by Dr. Stanley Gehrt on his 10-year research on coyotes living in Chicago. I highly recommend you visit his website at www.urbancoyoteresearch.com to peruse his findings. His study has been call “the most ambitious work of its kind in the country,” and I believe it. Dr. Gehrt estimates that there are 2,000 coyotes living in Chicagoland among 9 million people, and the vast majority of people have no idea that they’re there.
One of his major findings from his 250+ radio-collared coyotes, and one that should interest many people, is that coyotes prey on Canada goose nests and appear to be a major controlling factor on their urban population. He showed video footage of a coyote scaring off a nesting pair of geese, then eating some of the eggs, and carrying off the others. However, most of the coyotes in the study were found to be feeding on rodents and rabbit.
Loons typically start socializing in the late summer/early fall, often gathering together on large lakes in surprisingly big numbers prior to migration. Terry Mann from Cassian sent me a photo of what he estimated to be about 100 loons on 8/20 on Pequot Lakes, Minnesota.
In our area, Fence Lake, Lake Tomahawk, and Trout Lake are best known as potential gathering sites for large flocks of pre-migratorial loons. The adults migrate independent of their chicks and of each other. Fall migration generally begins in September, peaks in early-to-mid-October, and by late November most migrants have arrived in their wintering areas.
Mourning Cloak Butterflies
We’ve had numerous mourning cloak butterflies puddling and basking in our driveway recently, and Mary got a few pictures that display their remarkable beauty. All butterflies prepare for the winter by either laying eggs before they die, overwintering as larvae (caterpillars), overwintering as pupae, partially migrating, or in the case only of the monarch, migrating completely out of their summer range. The mourning cloak is one of the few butterflies that chooses yet another strategy, overwintering as an adult, and in the process winning the butterfly longevity contest by living up to eleven months. The mourning cloaks hibernate under loose bark, in logs and in woodpiles, waking in early spring to emerge as the first butterfly of spring.
Mary and I recently led a group of paddlers from the River Alliance of Wisconsin on a section of the Manitowish River. Twenty canoes and kayaks comprised our little navy, and we were blessed with a picture-perfect late summer day in the Northwoods. Perhaps our most interesting sightings of the day were sturgeon jumping on four different occasions on Benson Lake. Why these very large fish fling themselves from the water is unclear – perhaps they’re seeking to dislodge leaches or some other parasitic organism. George Becker in his classic book “Fishes of Wisconsin” notes: “Lake sturgeon have the habit of leaping entirely out of the water until they appear to be standing on their tails. Sometimes just the head and upper third of the body slides up and out of the water at a forward angle and falls back, creating a sliding splash. This leaping action may serve to get rid of parasitic lampreys attached to the sturgeon. Twenty-seven lampreys were removed from one 62-inch sturgeon in Lake Winnebago. The lampreys probably do little damage, but they must be a nuisance.”
We don’t have lampreys in the Manitowish, thank God, so perhaps they are leaping simply because they can. Regardless of their purpose, they create a lot of excitement when one five-feet long jumps from the water!
The full moon occurs on 9/12. Called variously “The Harvest Moon,” “The Acorns Moon,” and “The Leaves Changing Moon,” it marks the last full moon of the summer – we’re moving fast toward the autumnal equinox on 9/23.