A Northwoods Almanac for 3/2 – 3/15, 2018
Snowy Owl Update
An
estimated 280 snowy owls have been documented in Wisconsin through February 1,
eclipsing the previous high of 253 tallied in 2013-14 and 240+ in 2014-15. The
owls have been reported in 67 of our 72 counties, excluding only Buffalo,
Florence, Forest, Menominee and Walworth. Most of the birds are now, and have
been, on mid-winter territories, so any new birds are unlikely to yet arrive. Most
will be departing by the end of this month while some may linger into April,
with a handful of stragglers staying put into May. Mary and I fondly remember
seeing a snowy owl sitting on an abandoned osprey platform at the Little Turtle
Flowage on May 17, 2005, so occasionally they stay quite a while!
Wisconsin
now hosts five owls tagged for research as part of Project SNOWstorm –
Arlington, Austin, Badger, Bancroft, and most recently, Straubel, named after
the last one caught, a juvenile female, on 2/21 at the Austin Straubel airport
in Green Bay. Straubel is the 22nd owl that has been tagged by
Project SNOWstorm volunteers, and the 70th since its inception.
Why
are there so many snowy owls this winter? No one knows for sure, but the once
held belief that large numbers of snowy owls come here in irruption years
because they are all starving in Canada is erroneous. It is true that many
birds arrive here in poor condition from their journey, but an almost equal
number arrive in good shape. Once here, many of the birds do quite well, though
some die due to collisions with vehicles, electrocution by hitting power lines,
secondary rodenticide poisoning, and from illegal shooting.
The
level of mortality, however, is not unexpected. Like most migratory first-year
birds, juvenile raptors typically have a mortality rate near 70 percent. Juvenile
songbird mortality numbers are typically even higher, demonstrating how
dangerous life is for migratory birds.
Two
theories suggest why we have these periodic mass movements of snowy owls. One thought,
the starvation theory, is that the population of their primary northern prey
source, a small rodent known as a lemming, has crashed, pushing the owls
southward. More recent evidence suggests nearly the opposite, that a temporary
abundance of lemmings allows the owls to successfully raise such large families
that the young owls must disperse further southward to find a wintering
territory. And perhaps both mechanisms play out in some years but just in
different areas of Canada.
It’s
hard to say what causes an irruption year because studying the population
dynamics of lemmings is complex, as is studying snowy owls, since both live in
very remote northern regions.
Sightings – Snowy Owl and Barred Owl
On
2/13, Rosy Richter reported seeing a
snowy owl in Lac du Flambeau. She wrote, “On my drive to work from
Mercer into Woodruff via Hwy. 47, I saw some crows dive-bombing something large
and white just outside the tribal hatchery in Flambeau on Pokegama Lake. I
pulled over, and without field glasses, it appeared to be a big white owl
sitting in the snow in the middle of the bay. This was about 8:30 am.” She
was quite clear that the bird had to be a snowy owl, and I have to agree with
her. A snowy had been seen numerous times earlier this winter around Ike Walton
Lake, which is about three miles away as the crow/owl flies, so I wonder if
this wasn’t the same owl.
The question often comes
up as to why crows mob owls whenever they see one. Well, one good reason is
that great horned owls are known to steal nestlings
at night from crows and ravens who are basically defenseless in the dark. One observer reported inspecting a crow
roost that had been predated by a great horned owl. He found nine dead crows on
the ground in perfect condition except that the top of their heads were gone
and the brains eaten, which is a signature feeding trait of great horned owls.
Generally,
however, other species of owls don’t predate crows and ravens. So, I wonder if
crows simply generalize from hating great horned owls to hating all owls. Crows
certainly appear to have an innate dislike of owls, and they use their flight
advantage in the daylight to drive these potential predators away. I find it
fascinating that numerous studies have shown crows are able to identify predators
that have attempted to harm them and have the ability to share that knowledge
with the rest of the flock. Thus, if owls have taken a pass at, or successfully
killed any crows, the rest of the flock will likely learn about the depridations
and take revenge on any owl seen.
Snowy
owls aren’t known to eat crows, but since crows appear to be profiling all
owls, this particular snowy just happened to be unlucky and the game was on.
Sarah
Krembs in Manitowish Waters spotted a barred owl sitting close to her bird
feeders in the late afteroon on 2/24. Such a sighting usually signals the
barred owl is starving, given that their presence is otherwise rare around home
bird feeders during the day and night.
 |
| barred owl photo by Sarah Krembs |
A barred
owl’s diet varies from region to region, but here are numbers from some
specific studies: In New Jersey, New York, and Connecticut, the breeding-season
diet was 55% mammals, 23% invertebrates, 16% birds, 3% amphibians, and 2% fish
(yes, barred owls have been observed catching fish!). In Nova Scotia, their
diet was 61% mammals, 17% invertebrates, 9% birds, and 12% amphibians,
reptiles, and fish. In Alberta, Canada, their diet was 46% mammals, 25% birds,
24% amphibians, and 4% invertebrates.
Winter diets are, of course, different. The
winter diet in a study in Montana was 97% mammals and 3% birds.
One way or another, mammals, primarily
rodents, consistently make up the largest portion of their diet.
Mary and I have seen barred owls capturing
frogs on roads during a rainy night, but the importance of amphibians in a
barred owl’s diet is unknown since owl pellets consisting of amphibians break
up more rapidly than those made up of the bones of mammals and birds.
Migration Is ON
Birders in southern
Wisconsin are reporting seeing geese by the thousands as well as hundreds of sandhill
cranes, mallards, common goldeneyes, common mergansers and pintails. Red-winged
blackbird flocks have also been spotted as well as the first influx of robins.
Spring migration is taking off!
Mating Mammals
For
humans, March may not feel very warm and inviting for love, but most mammals are either
mating, gestating, or birthing during this period. Animals can't afford to wait
to mate until the weather warms and the flowers are blooming, because their
young wouldn’t be born until June or July, often too late for the growth that
must happen before the young of the year face their first winter. In the
squirrel family, gray squirrels have their first litter in March, while red
squirrels mate in March and give birth in April. Northern flying squirrels mate in April and
give birth in May.
Within
the dog family, red foxes give birth to their kits in late March and early
April, while coyotes produce young in April. Timber wolves mate in February and
March and give birth in May.
In
the weasel family, nearly all members use delayed implantation to govern their
breeding cycle. Mink breed in early March and employ a short delayed
implantation, giving birth in late April and early May. Striped skunks likewise
breed in March, but give birth a little later in May.
Snowshoe
hares are mating, too, and chipmunks emerge seeking a partner to court, the
male singing at the den entrance to entice a female.
Hoarfrost
For
several days last week, hoarfrost coated our world in ice crystals, creating a
laciness on every branch and bud and needle in the woods. It’s a time of
fairyland beauty that folks without winter never see.
 |
| photo by Mary Burns |
Hoarfrost is a relatively common phenomenon
that requires calm winds and a supersaturated column of cold air extending well
above the surface of the ground, like a cold fog. Moisture in the air starts
condensing around nuclei, and once that starts, the moisture in the air “sublimates,”
going directly from a gas to a solid, with ice crystals building up on
everything.
Celestial
Events
With
warm temperatures forecast for this weekend, get out tonight or tomorrow night
for a walk in the light of the moon, which is still 99% full.
On 3/3, the area’s average high temperature
reaches above freezing for the first time since 11/27.
On 3/5,
look low in the west after dusk for Mercury just one degree north of Venus. On
3/7, look in the early morning hours for Jupiter about four degrees south of
the waning gibbous moon.
March 8th
shines with 11 hours and 30 minutes of daylight, and brings us to just 12 days
away from the official spring equinox on 3/20.
On 3/10,
look before dawn for Saturn about two degrees south of the waning crescent
moon.
Thought
for the Week
“It’s a hopeful thing when scientists look to the
land for knowledge, when they try to translate into mathematics the stories
that water can tell. But it is not only science that we need if we are to
understand. Lewis Thomas identified a fourth and highest form of language. That
language is poetry. The data may change our minds, but we need poetry to change
our hearts.” - Robin
Wall Kimmerer
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