A Northwoods Almanac for 9/25 - 10/8/2026
The Magic of Migration and Navigation
Over five billion birds, comprising some 500 North American species, migrate annually across the Northern Hemisphere. The Cornell Lab of Ornithology estimates an average of 4 billion birds pass from Canada across the northern border of the U.S. in autumn, with 2.6 billion birds returning to Canada in the spring.
Across our southern U.S. border, an average of 4.7 billion birds leave the U.S. for Mexico and points south each fall, with 3.5 billion birds coming back across the border in the spring.
In Wisconsin, 133 of our 240 nesting species migrate to Central and/or South America. Many of these neotropical migrants started their journeys in August with many still currently on the wing.
But why migrate at all? After all, it’s incredibly dangerous and arduous. Most songbirds migrate at night, landing in the morning to feed and refuel for the next evening’s flight. The dangers are endless, including weather extremes, food not being available in the quantity and quality needed, predators, power lines, the lights on city buildings, windows, cats, et al.
And there are topographical barriers to migration like Lake Superior, mountain ranges, deserts, Gulf of Mexico, etc.
The general consensus is that 80% of the juvenile neotropical birds migrating this autumn won’t make it back this spring.
Still, it’s the best option in a limited menu of options, which comes down to a cost-benefit equation. Birds have learned to exploit resources that are seasonally abundant, and to avoid places during seasons when resources are scarce, or conditions are harsh or over-crowded.
In temperate/Arctic regions, food is abundant during the short summer, so billions of birds migrate north to take advantage of our troves of insects. More food means increased reproductive success, which outweighs the risks of migration.
In autumn, of course, the reverse occurs. Our insect population crashes with the first frost, and if you are an insect-eating bird, you need to stay ahead of the frosts.
The mystery remains, however, of how these birds so precisely navigate. Birds utilize the sun, the moon, the stars, landscape cues, and even olfactory cues to guide them, all of which can act in consort to orient them in the right direction.
But the true precision tool they utilize appears to be their ability to “see” magnetic fields. There are three components of our planet’s magnetic field that play a role in helping birds navigate during their migrations:
1- Intensity, which is the magnetic field’s strength.
2- Declination, or the angle between the Earth’s magnetic North (which varies with the magnetic field, and is what compass needles point to) and true North (a fixed point).
3. Inclination, which is the angle between the Earth’s magnetic field and its surface.
However, the Earth’s magnetic field shifts slightly every year. If the magnetic field guides the birds, then they should end up in a slightly different location every migration season, and yet, they return to the same places with baffling precision.
Well, here is where it gets truly amazing. Experimental evidence suggests a bird’s compass “relies on subtle, fundamentally quantum effects in short-lived molecular fragments, known as radical pairs, formed photochemically in its eyes.”
Got that?
Me neither.
In somewhat simpler terms, in birds’ eyes, a light-dependent reaction yields a chemical that’s proportional to the environment’s active magnetic fields. As the birds move their heads through the field, the chemical reaction fluctuates. This chemical reaction in the eyes sends a signal to the brain to interpret, providing precise directions.
Researchers have also discovered a small spot on the beak of pigeons and some other birds that contains magnetite. Magnetite is a magnetized rock, which may act as a tiny GPS unit by giving birds information about their position relative to Earth’s poles. Magnetite detects variations in magnetic field intensity, helping birds map roughly how far north or south they have traveled and signaling an invisible "stop" sign when they reach their destination.
It’s one thing, of course, to know exactly what direction to go, but another thing to know exactly when to stop.
See this article for more detail: https://www.scientificamerican.com/article/how-migrating-birds-use-quantum-effects-to-navigate/)
Joe Wynn, one of the principal researchers who has studied how bird’s eyes can interpret magnetic fields (Science, Jan. 2022), wrote that this ability “is about as close to magic as is possible.”
I thinks so, too. Tom Clancy famously wrote, “The difference between fiction and reality? Fiction has to make sense.”
That pretty well sums up the whole story of migration - it almost exceeds what we believe is possible from “reality.”
Sightings - Duluth’s Hawk Ridge Count
19,768 broad-winged hawks on 9/17 (record is over 101,000!)
1,282 sharp-shinned hawks on 9/16
13,427 blue jays on 9/16
20,738 green darner dragonflies on 9/17
First Frost
A siren went off all around the Northwoods on the morning of 9/14 when we experienced our first hard frost. What we humans may interpret as an inconvenience - we had to cover the garden, poor us - animals and plants interpret as an impending catastrophe if they don’t react and adapt. Wrote Diane Kappel-Smith, “[The coming] winter is a predictable kind of Armageddon, a calamity calmly weathered, an end of a world that they [wildlife] understand and are preparing for.”
Indeed.
I’ve written about this before, but it bears repeating. The options for wildlife are MAD - Migrate, Adapt, or Die.
So, migration is in full tilt, and adaptations are now triggered and beginning to be implemented, some in haste, some more calmly.
Most of the plant world heard the siren, too, and is shutting down. The first frost is a cliff edge for nearly all plant species, a time when cells can freeze and burst if they haven’t adapted. The photosynthetic engine stops producing chlorophyll and begins to salvage nutrients, withdrawing nitrogen and phosphorus from the leaves and pumping them into the branches and roots.
Hormonal changes cause cells at the base of leaf stems to cut off the flow of water and nutrients to the leaves, forming what’s called the abscission layer. Once the tourniquet is completed, the dead leaves drop off.
And as the chlorophyll fades, pigments that have been hidden in the leaves like carotenoids (yellow/orange) and anthocyanins (red) are revealed, allowing the curtain to come up and reveal the fall riot of colors.
Is There Any Value to Autumn Colors Beyond Beauty?
There may be more to trees and shrubs revealing colors than simply a chemical quirk. Research suggests a number of plausible roles that having colorful leaves may play for a species.
Two theories have been advanced. One suggests bright autumn leaves carry a message to insects via their vivid colors to leave them alone. The intensity of the pigments can act as a warning signal to insects that a plant is really healthy and able to fend off any use by an insect for over-wintering. Many insect species choose trees in the fall to lay their eggs, and when they hatch in the spring, they often feed on the tree with potentially killing effects. But healthy trees typically ward off insect attack better than unhealthy ones, so just as male birds intimate their reproductive vigor to females and maintain their territories through the display of their brilliant breeding plumage, trees might be advertising to insects the same sort of story. I’m bright, I’m strong, I’m potentially lethal – go away.
 |
| photo by Jeff Richter |
The second hypothesis, the “sunscreen theory,” argues that by the time the leaves change in a Wisconsin autumn, the foliage-feeding insects are already gone, so bright leaves have no insects to warn away. The theory suggests that fall colors, particularly the reds of the anthocyanins, act as a sunscreen to protect the leaves from harmful rays of sunlight in the reduction and eventual absence of chlorophyll.
But, some trees like birches produce no anthocyanins, instead only making yellow carotenoids. Carotenoids help chlorophyll absorb sunlight in the summer, but they don’t shield the leaves in the fall, so birches must have another process by which they protect their leaves.
The truth is that there is no truth that fits all species. And that’s fine by me. I’m just grateful for the beauty of fall, whatever the ecological value may be.
Celestial Events
The full moon - the Harvest/Acorn/Leaves Changing Color Moon - occurs on 9/26.
For planet watching in October, look after dusk for Venus very low in the WSW (lost by mid-month), and Saturn rising in the E.
Before dawn, look for Mars high in the SE and Jupiter high in the E.
We’re down to 11 hours and 29 minutes of sunlight as of 10/4.
Look on 10/5 for Mars below the waning crescent moon. On 10/6, Jupiter will trade places with Mars and be just below the waning crescent moon.
Thought for the Week
“Make a home. Help to make a community.
Be loyal to what you have made.
Put the interest of the community first.
Love your neighbors - not the neighbors you pick out, but the ones you have.
Love this miraculous world that we did not make, that is a gift to us.
As far as you are able make your lives dependent upon your local place, neighborhood, and household - which thrive by care and generosity - and independent of the industrial economy, which thrives by damage.
Find work, if you can, that does no damage.
Enjoy your work. Work well.”
-Wendell Berry, from an essay published in 1989, “The Futility of Global Thinking”
No comments:
Post a Comment