A Northwoods Almanac for April 1 – 14, 2022

 A Northwoods Almanac for April 1 – 14, 2022  

 

First-of-the-Years

            One of the many pleasures of spring arriving is the concurrent arrival of the first-of-the-year (FOY) migrant birds. We hit 52° on 3/16, and along with that warmth came our FOY red-winged blackbirds, followed the next day, 3/17, by our FOY common grackle. Our FOY robins and Canada geese appeared on 3/20. A chipmunk poked up out of the snow on 3/21, and our FOY dark-eyed junco arrived on 3/23. 

            Nancy Burns in Manitowish Waters reported her FOY hooded mergansers on the Manitowish River on 3/22.

            All of them were likely rueful of their haste when a heavy blanket of wet snow descended upon us on 3/23 and 3/24, but such are the risks of those who want to secure the best territories. 

            As for birds that are continuing at our feeders, we remain inundated with common redpolls, as does just about anyone we know that feeds birds. Many people are reporting one hundred or more at their feeders! When a far northern Canadian bird like the common redpoll descends upon us in these numbers during the winter, birders call it an “irruption” year. You could also describe it as an “eruption” year, because like a volcano, they just keep on coming.    

 

Eagle Migration

            On 3/17/22, bird counters at Hawk Ridge in Duluth tallied 1,206 bald eagles, a new daily migration count record This broke their previous record from 3/21/19 with 1,076 Bald Eagles counted in one day. The lead counter reported it as a remarkable flight with huge kettles of birds coursing through all day. 

            Bald eagles are early breeders. Ron Eckstein, retired DNR wildlife manager and the eagle expert for our area, always told me that on average eagles are incubating eggs by April 1, the eggs hatch around May 1, and young have fledged by August 1. BTW, bald eagles now nest in all 72 counties of Wisconsin – quite the success story!

            The Hawk Ridge spring count starts March 1 and continues daily (weather pending) through May 31. The timing of species arrival is the reverse of what it is in the fall with the first arrivals in spring being the larger raptors like eagles and rough-legged hawks. Red-tailed hawks arrive soon after, and then broad-winged and sharp-shinned hawks begin showing up in April.

             

Golden Eagle Survey

            The counters at Hawk Ridge also tallied 41 golden eagles on 3/17. In a previous column I had mentioned that the Wintering Golden Eagle Count survey takes place in mid-January in the western part of the state. The final tally for this year’s survey was 99 golden eagles found by 195 surveyors, a bit below the average number for the survey. The number of bald eagles, however, was the second highest in the 18-year history of the survey, and the numbers for red-tailed hawks at 866 and rough-legged hawks at 199 were the highest in the survey's history.

 

Widespread Lead Poisoning in Eagles

            A first-of-its-kind, eight-year study led by scientists from the U.S. Geological Survey, Conservation Science Global, Inc., and the U.S. Fish and Wildlife Service, evaluated lead exposure in bald and golden eagles from 2010 to 2018, and found widespread and frequent lead poisoning impacting both species’ populations. Using samples from 1,210 eagles over 38 U.S. states including Alaska, the researchers found almost 50 percent of the birds sampled showed evidence of repeated exposure to lead. 

            Short-term exposure was more frequent in winter months, largely because both eagle species scavenge more during the winter months when live prey is harder to find. Lead poisoning typically occurs when an eagle eats lead ammunition fragments lodged inside an animal carcass or in gut piles left behind by hunters. The frequency of chronic lead poisoning found in both species increased with age because lead bioaccumulates in bone as eagles are repeatedly exposed to the heavy metal throughout their lives.

 

Landmark Study on How Migrating Birds Use Magnetic Fields as a Map

            Migrating birds use many navigational cues in precisely returning to their home grounds, among them sight, the location of the sun, landscape formations, and even the stars. Most remarkably, however, they are endowed with a biological compass that helps them follow Earth’s magnetic field.

            But how? 

            This is so complicated that the researchers say “This is about as close to magic as possible.” Scientists already know there are three components of our planet’s magnetic field that play a role in helping birds navigate during their migrations: 

·      Intensity, which is the magnetic field’s strength 

·      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)

·      Inclination, which is the angle between the Earth’s magnetic field and its surface. 

            However, here’s what a new study recently published in the journal Science found. The researchers discovered that a specific aspect of our magnetic field, the magnetic inclination, is what informs a bird most during migration. It serves as the magnetic address, or stop sign, for for birds as to when and where to come down to breed.

            But how do birds sense magnetic inclination? 

            “The answer is almost unbelievable,” says the lead researcher. “It’s not unreasonable to suggest birds can see the Earth’s magnetic field.” 

            As best as is understood currently, it works this way: 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. The chemical reaction in the eyes sends a signal to the brain to interpret it, and the sensor is located in the visual system of the birds’ brains. 

            The researchers figured this out by considering how the planet’s magnetic field isn’t fixed – it moves. In fact, since 1831, the magnetic north pole has shifted more than 600 miles. So, they reasoned, if birds use the planet’s magnetic field to return to their breeding sites, then it stands to reason a shifting field should mean that breeding sites shift, too.

            The researchers studied 80 years of breeding data for Eurasian reed warblers and discovered that while the birds usually arrive at the same site year after year, sometimes they’re slightly off. And when they are, it’s typically in the same direction that the inclination angle has moved, which strongly suggests that the Eurasian warbler are tracking magnetic inclination to navigate.

             Since the magnetic field moves, it’s not the most precise map, but it’s detectable around the world and guides migratory birds most of the way, often within feet of where they were raised or where they now breed. Once they’re in the vicinity, they likely use the sight of a familiar lake or tree to find the right spot. 

            There’s more to it than just inclination, however. Previous research suggests that birds can pinpoint their location at any point within a magnetic map of the world, what’s called “true navigation,” even if they’re displaced thousands of miles, whereas inclination only signals when birds should stop.

            One way or another, I concur with the researcher’s summary statement – it’s as close to magic as anything we know.

 

Celestial Events

            The new moon occurs on April 1. Look before dawn on 4/4 for Saturn and Mars, separated by just half a degree (the width of a full moon), with Venus just to their east.

            We are blessed with 13 hours of sunlight as of 4/5.

            For planet watching in April, look before dawn for Venus, Mars, and Saturn all rising low in the east southeast. Jupiter will also be rising, but more to the East.

            For planet-watching after dusk, only Mercury makes an appearance. Look in the northwest, but not until mid-April.

 

Artic Sea Ice

            During the 2020-2021 winter, the Arctic likely had its thinnest sea ice on record, with old ice in the Arctic Ocean plummeting to a tiny fraction of what it once was.

 

Thought for the Week – On the Metaphor of Wintering

            “When you start tuning in to winter, you realize that we live through a thousand winters in our lives –  some big, some small … Some winters creep up on us so slowly that they have infiltrated every part of our lives before we truly feel them.

            “We are in the habit of imagining our lives to be linear, a long march from birth to death in which we mass our powers, only to surrender them again, all the while slowly losing our youthful beauty. This is a brutal untruth. Life meanders like a path through the woods. We have seasons when we flourish and seasons when the leaves fall from us, revealing our bare bones. Given time, they grow again.” – Katherine May (Wintering: The Power of Rest and Retreat in Difficult Times)                

 

Please share your outdoor sightings and thoughts: e-mail me at manitowish@centurytel.net, call 715-476-2828, snail-mail at 4245N State Highway 47, Mercer, WI, or see my blog at www.manitowishriver.blogspot.com.