A Northwoods Almanac for April 4 – 17,
2014
Marcescent Leaves – A Defense Against Deer
As winter ebbs and we finally
head toward spring green-up, the dead (“marcescent”) leaves of ironwood and oak
trees, as well as beech trees in eastern Wisconsin, continue to rattle from
their branches in every wind, unlike nearly all other deciduous species that
dropped their leaves in the autumn. I’ve always wondered why these species
would retain their dead leaves throughout the winter. A Danish study from 1992
provides the likely answer – marcescent leaves significantly reduce the
nutritive value of winter browse, a mechanism the trees use to protect
themselves from the immense appetites of browsing deer.
To demonstrate this, the
researchers performed an open-field feeding trial with free-roaming red, sika,
and fallow deer using European beech, hornbeam, and common oak trees, all of
which retain their leaves throughout the winter in Denmark. They removed the
lower dead leaves from one-half of the trees and left the dead leaves alone on
the other half. After 7 days, the branches were counted, weighed, and analyzed in
a host of ways to determine the amount and quality of browse removed. What they
found was both beech and hornbeam were browsed significantly more by weight and
by number of branches when the leaves were removed (the oak branches were
browsed the same regardless of leaf presence). Chemical analyses then showed
that the leaves of hornbeam and beech had a lower fiber and crude protein
content when compared with their woody stems, and the leaves had a higher
lignin content. A previous study had shown that when marcescent leaves
constitute most of the diet, ungulates like deer spend more time processing
food, especially increasing their rumination time because of the lower food quality. Thus, the combination of a
high lignin and low protein content appears to have reduced the overall
digestibility of the available forage for the deer, which was reflected in the
lower browse preference for their leaves.
Given that accessibility to
low-hanging branches and young trees is critical to deer when deep snow covers everything else, browsing woody vegetation often provides
the only source of food. And since deer eat around five pounds of buds and
browse a day in the winter, it’s not surprising that some trees have evolved
some sophisticated defenses to protect themselves. We’re all familiar with
plants with thorns, a typical physical adaptation that renders plant tissues
less desirable. Other trees, like white birch, produce unpalatable or toxic
chemicals to deter browsing. White birch saplings produce papyriferic acid in
concentrations 25 times that of the adult trees to deter snowshoe hare
browsing. So, it appears very likely that leaves of some trees are retained
throughout winter as an energetically inexpensive way of reducing herbivory.
Sightings
3/6 – Marty Kiepke in Hazelhurst worte, “I had a little
5 point buck come in still ‘antlered up’. I don't know if I've ever seen a
buck with antlers in March.” And he noted, “Over the past 3 to 4 years,
we've had turkeys coming in on a semi-regular basis. We have about 30 of
them, one of which is white. But of more interest, we have a number of
squirrels: about 3 or 4 reds, 4 or 5 grays, 2 or 3 blacks, and 1
white. In my 64 years it's only the second white one I've seen.”
3/14 - Hans Delius on Horsehead
Lake just south of Lake Tomhawk wrote, “There is an aeration system that keeps
some water open all winter . . . and I counted a total of 14 eagles
on the ice and there where some more in the trees.”
3/23 – Bob Kovar reported seeing first-of-the-year
(FOY) Canada geese on the small stretch of the Trout River that is open below
Wild Rice Lake in Manitowish Waters. We also saw our FOY pine siskin in
Manitowish, though it promptly disappeared.
3/26 – Three FOY evening grosbeaks arrived at our
feeders in Manitowish, and hung around a few hours, but then moved on.
3/27 – Mary Madson in Preque Isle reported her FOY
red-winged blackbirds, and we had our first ones of the year the same morning
in Manitowish as well.
3/30 – Bob Kovar reported a FOY sandhill crane as
it was flying over Mercer. In Manitowish, we had our FOY robins – eight of them!
– and our FOY grackles and starlings, though these are two species that we
aren’t necessarily excited to see.
Celestial Events – Lunar Eclipse on 4/15!
The
Ojibwe word for April is “ickiganisigegizis,” or “maple sugar-making month.”
Literally, the word means “boiling month.”
On
4/8, Mars will be at its closest approach to Earth and its face will be fully
illuminated by the sun. This will be the best time to view Mars this year.
On
4/14, look shortly after sunset for Mars and the moon rising in the east – Mars
will be directly above the moon.
On
4/15, the full moon will be completely
immersed in the Earth’s shadow causing a total eclipse of the moon. Unfortunately,
the event will occur from 3:07 a.m. until 4:25 a.m., with partial phases being
visible before and after, so you’ll have to stay up late or get up early. This
eclipse will be visible over all of North and South America. Set your alarm!
The full moon of April is known by the Ojibwe as the
Sugarbushing Moon or the Broken Snowshoe Moon.
Bird Territorial and Courtship Displays
Now On Stage
Sharon Lintereur in Lake Tom wrote, “We just
watched what we thought was a mating ritual between two hairy woodpeckers.
I went to grab the binoculars and lo and behold it was two males doing a
definite territory dance. It was a lot of bobbing, weaving and chasing
and a victor was declared. This was quite a show.”
I’m
always fascinated by how in a world so competitive, birds have developed
elaborative and often elegant ways to compete non-violently. On occasion,
competing birds do attack one another, sometimes lethally, but more often than
not, they engage in dances, songbouts, flights, or color displays that send the
needed message of overall vigor to their competitors, with the less virile bird
knowing then to depart or risk a physical confrontation.
Since
hairy woodpeckers are common to just about everyone’s feeders, look for these
particular territorial displays:
-
a “khrr-call” – the male gives a drawn-out call
like a horse whinny
-
drumming – the male hits a resonant surface
faster than you can count
-
perch-taking and chases
Courtship displays include:
-
fluttering flight – the bird beats its wings
rapidly with its head held down
-
bill-waving – the bird waves its bill
repeatedly often while spreading its tail, fluffing its breast and nape
feathers, or flicking its wings
-
still-pose – two birds suddenly stop all
movement and remain absolutely still for one to 20 minutes (perhaps their
version of a stare-down?)
Isle Royale Conundrum: Genetic Rescue?
Mary
and I had the opportunity to meet and talk with Rolf Peterson twice in the last
month. Rolf is now retired, but was involved in and eventually led the
wolf-moose research on Isle Royale for nearly 40 years. The study is now in its 56th year, making
it the longest continuous predator-prey study in the world.
As
Rolf described to us, the wolves on Isle Royale have reached a tipping point. After
years of inbreeding, Isle Royale’s wolf population, which once approached 50,
is down to eight adults and two or three pups, and the National Park Service
must decide what, if anything, should be done about it. Due to inbreeding, the incidence
of malformed vertebrae, a condition known as lumbrosacral transitional
vertebrae (LSTV), has increased such that researchers have not detected a
normal wolf skeleton in the past fifteen years (by contrast, only 1 in 100
wolves suffer from LSTV in healthy populations). Another impact has been poor
reproduction even when there is enough food – the wolves failed to reproduce
for two years of the last three years.
The
small population and its genetic isolation mean the wolves have become highly
inbred since arriving by ice bridge in the late 1940s, about 15 wolf
generations ago. For wolves, the problem is exacerbated because only the alpha
male and female in a pack mate, further limiting the gene pool.
One
interloper did arrive in the winter of 1997 when an ice bridge formed between
Ontario and Isle Royale. A lone male walked the 15 miles of frozen highway until
he reached the island, and went unnoticed initially though his impact was
immediate. Big and territorial, he quickly established dominance and assumed
alpha status in the Middle Pack, one of three packs on the island. The genetic
constitution of wolf#93, dubbed “The Old Gray Guy,” was so superior to that of the
native Isle Royale wolves that in the end, he sired 34 offspring, and has 22
grand offspring (and counting). On Isle Royale, the last wolf unrelated to
male #93 died in 2007, and by 2009, 56% of all the genes in the Isle Royale
wolf population could be traced back to The Old Gray Guy. He initiated a
genomic sweep – of the eight adult wolves left on the island today, not a
single one is unrelated to the Old Gray Guy.
Peterson
is convinced the wolves will die out soon without a genetic intervention. An
ice bridge did form this winter for twelve days, the first since 1997, raising
hopes that a male wolf would cross over. But instead, a collared, 5-year-old
loner female left the island on the first day the ice formed and crossed to the
mainland, only to be shot and killed a day later by someone with a pellet gun.
So,
the ice bridge still works when it finally forms, but when wolves escape the
island rather than colonizing it, that bodes ill.
What
are the consequences of losing the top predator on an island? A trophic cascade
will occur, beginning with massive population growth by moose which, increasing
rapidly with no predator control, will eventually decimate the understory
vegetation. The denuded understory will then in turn create serious
consequences for numerous other species along the food chain.
The
overriding issue here is climate change and the loss of opportunity for the ice
bridge to form and the wolves to cross. According
to buoy data analyzed by the University of Minnesota Duluth’s Large Lakes
Observatory, Lake
Superior’s summer surface temperature increased by 4.5° F from 1979 to 2006,
with a corresponding loss in winter ice cover. On average, the Lake's ice is
decreasing by 0.5 percent each year. Peterson expects that by 2040, Lake
Superior won’t have any significant ice cover in the winter. No ice, no bridge,
no new wolves to prevent inbreeding.
So,
what to do? More on all this in my next few columns.
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.
