A Northwoods Almanac for 9/14 – 27, 2012
by John Bates
Hummingbird Migration
We still had
female and juvenile ruby-throated hummingbirds coming to our feeders as of
Saturday morning, 9/8, but given the strong northwest winds over the weekend, I
suspect most of our local nesting hummers have now hit the migratorial road. Males
precede the females in spring and fall migration, with the juveniles of both
sexes lagging somewhat behind the adult females in the fall. The male’s
earlier departure in the spring gives them time to establish territories so
they can successfully court arriving females at the beginning of the breeding
season, and they follow the same pattern for fall migration in order to
establish their winter territories. If you have hummingbird feeders, you know
how extraordinarily territorial the males can be during the breeding season, an
obsession they apparently continue with throughout the winter.
Ruby-throated
hummers winter throughout Central America, with a few stopping short to winter along
the western Gulf Coast. Many fly across the Gulf of Mexico, but many also follow
the coastal route around the Gulf. Large numbers are often observed flying low
over wave tops to make landfall during spring migration; however, I’m unable to
find any information as to whether they fly this low during fall migration.
On average,
adult ruby-throated hummingbirds have a mass of only 1/10th of an
ounce (3.5 grams.) Despite their almost indiscernible weight, many of these
birds fly nonstop across the Gulf of Mexico during fall and spring migration, a
one-way trip of more than 500 miles. To reach the
Gulf, the hummers migrate by day, but to cross the Gulf, they typically leave at dusk and fly for 18-22 hours to
reach landfall.
To accomplish
this flight, individuals will double their body mass to 6 grams by fattening on
nectar and insects prior to departure. When they
reach landfall, however, they typically weigh only 2.5 grams, having lost more
than their entire normal body weight. While this may sound like a lot to us,
losing only a tenth of an ounce while flying 500 miles non-stop is pretty
amazing fuel efficiency – Prius owners take note!
Given their
near weightlessness, it only makes sense that wind direction and velocity would
strongly influence their migration. One study conducted along the ridges at
Hawk Mountain Sanctuary, Kempton, PA, found that migrants were most numerous
after the passage of strong cold fronts and northwest winds.
The
ruby-throats’ overland fall migration occurs nearly synchronously with the peak
flowering of jewelweed (also known as spotted touch-me-not or Impatiens
biflora), an important nectar source, suggesting that jewelweed may influence
the timing of migration.
For a hummer
that just hatched, there's no memory of past migrations, only an instinctive urge
to put on a lot of weight and fly in a particular direction for a certain
amount of time, then look for a good place to spend the winter. Once it learns
a route, the hummer will likely retrace it every year as long as it lives.
The initial migratorial
urge is triggered by the shortening length of daylight as autumn approaches,
and has nothing to do with temperature or the availability of food; in fact,
hummingbirds migrate south at the time of greatest food abundance. When the
bird has put on enough fat, it migrates.
Although
hummingbirds may fly over water in company of mixed flocks of other bird
species, they do not fly in flocks with other hummers. Individual birds may
spend the winter anywhere in Central America where the habitat is favorable (most ruby-throats only migrate as far as Panama), and most very likely return to the same location each winter, though
banding data is limited.
To go from Wisconsin
down to the Gulf coast would take a hummer about 4 or 5 days, assuming the
hummer did not spend more than one day resting at any one place. It would then
take a day to cross the Gulf, and another couple of days to reach its
destination in Central America. But with big rest stops to wait for good
weather and to build back up fat reserves, it probably takes about two weeks
for “our” hummers to reach their winter homes. One study
found that they usually arrive in Costa Rica by late September to early October.
Some amazing
hummer factoids:
They beat
their wings about 60-80 times per second in normal
flight.
Their
hearts beat about 250 times per minute while at rest, and about 1,220 per
minute while flying. Their hearts are about 2.5% of their total body weight.
They take about
250 breaths per minute while at rest.
To follow the hummers in migration
go to: www.learner.org/jnorth/humm/
Autumn Equinox
Autumn equinox
is right around the corner, occurring this year on 9/22 at 9:49 a.m. CST. The word "equinox" derives from Latin term "æquinoctium"
which, in turn, came from "æquus" (equal), and "nox"
(night). It, of course, refers
to the moment that occurs twice a year when the nighttime is equal to the
daytime.
The seasons of
the year are caused by the 23.5º tilt of the earth's axis. We Northern
Hemisphere inhabitants are slanted furthest away from the sun during winter
solstice, and slanted most toward the sun during summer solstice.
Autumn equinox
is noteworthy because it marks our transition into days that have more darkness
than daylight. Combined with killing frosts, the departure of most of our
birds, and the rattle of brittle leaves in strong autumn winds, it can be a
difficult emotional adjustment. But it’s also the time of many harvests,
brilliant leaf-changing colors, and a crispness in the air that makes you just want
to walk and explore as much of this world as you can. As always, the perception
of outer landscapes depends wholly on one’s
inner landscape. Bringing an energetic, joyful countenance to a morning makes
all the difference.
Hawk Ridge in Duluth
Hawk
migration is now hitting its peak. What makes a good migration day at Hawk Ridge? Birds and the weather are both
unpredictable (note this disclaimer!!), but northwest or west winds are best,
and the more days in a row, the better. North and southwest winds are
okay. South, southeast, and east winds are not good. The day before,
or a couple of days after a strong front, usually produces more birds, and the
flight essentially shuts down in the rain and fog.
So, while on average this weekend
usually produces the biggest flights of the year, Mother Nature always bats
last. Keep an eye on the weather forecast for Duluth, and head for the ridge
when peak conditions appear to maximize your chances for a truly big day. And
by “big,” I mean BIG – the record day at Duluth was on 9/15/2003 when over
102,000 hawks flew over the ridge. They already had a pretty big day this year on
9/9 when 16,135 hawks were counted, so the flight is on!
It’s not just all about hawks either.
On 9/9, they also counted 2291 migrating non-raptors, including among others
603 Canada geese, 35 American white pelicans, 40 sandhill cranes, 752 blue jays,
234 cedar waxwings, 76 warblers (only 3 species identified), 63 red-winged blackbirds,
9 red crossbills, 15 pine siskins, and 277 American goldfinches.
New moon occurs on 9/15. On 9/18, look at dusk for Saturn 5
degrees north of the crescent moon. On 9/19, look for Mars almost on top of the
crescent moon.
Armageddon
As
of 9/10, we’ve yet to experience our first frost, an event so destructive that
author Diane Kappel-Smith writes: “Winter is a
predictable kind of Armageddon, a calamity calmly weathered, an end of a world
that they [wildlife] understand and are preparing for . . .”
The
first frost marks the end of the growing season for hundreds of species of
plants and the end of life for literally millions of insects. While gardeners
and farmers pay attention to it, for wildlife, there may not be a more
important event than this in the entire natural year.
Please share
your outdoor sightings and thoughts: call me at 715-476-2828, drop me an e-mail
at manitowish@centurytel.net, or snail-mail me at 4245N Hwy. 47,
Mercer, WI 54547.
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