Wisconsin Nature Notes
In February, take a moment to celebrate Groundhog Day and Valentine’s Day nature’s way, track the arrival of spring, and see who is nesting early.
EARLY NESTERS DEFY WINTER
Signs of spring are hard to find in February, but two species of birds – gray jays and great horned owls – are already nesting. For gray jays to nest at this time of the year is particularly surprising given that they nest only as far south as Wisconsin’s most northern counties. Gray jay babies are thus being fed in the nest when the lakes are still frozen, temperatures may drop to minus 20°F, snow lies deep in the forest and there is no obvious food to be found. Most birds time their nesting season to coincide with the period of maximum food abundance, but that is not true for gray jays. The nestlings will actually fledge in early April before 80 percent of migratory birds have returned.
How do they feed their chicks when there is so little food available? Gray jays are “scatter-hoarders,” caching insects, berries, mushrooms and strips of flesh they’ve pulled from carcasses in the fall. They most often coat the food items with their sticky saliva, making a little package that they jam into a crevice, a broken-off stump or under loose bark. They somehow recall where to find all of it months later in the dead of winter.
Gray jays create thousands of food caches every fall, by some estimates up to 8,000 at one time, and retrieve by memory some 80 percent of those morsels. Individual jays may even conceal their stores by jamming a piece of bark or lichen over the food. It’s been said that gray jays have a memory like a Vegas card counter.
Great horned owls also defy winter, beginning their courting in December and nesting usually by February. The female lays one to three eggs, then settles down to incubate the eggs for more than a month; the male meanwhile captures and brings her prey. The females are able to maintain their eggs near 98°F even when outside temperatures are minus 27°F. The eggs are equally hardy. One study showed that the eggs withstood the absence of the female for 20 minutes when the temperature was minus 13°F.
Why do great horned owls nest so much earlier than other birds? Unlike most songbirds, which incubate their eggs for 10 to12 days, with the chicks fledging two weeks later, great horned owls watch over their owlets for months. The owlets are fully feathered and capable of flight after seven weeks, but their parents still feed them well into July. The family stays together into the autumn, but then the young either leave or are driven off by the adults.
Gray jays can be seen in northern Wisconsin forests and will even visit bird feeders. You can find great horned owls all over the state.
AN UNUSUAL DAY FOR GROUNDHOGS
February 2nd marks Groundhog Day, a truly unusual event given that the lowly groundhog is the only animal with an American holiday named after it. More surprising yet, groundhogs are rodents. There’s no special day set aside for any other rodent. No Muskrat Day, Pygmy Shrew Day or Bog Lemming Day.
It’s amusing when Punxsutawney Phil in western Pennsylvania and Jimmy the Groundhog in Sun Prairie, Wisconsin, miraculously emerge from their hibernation on February 2nd, at the precise instinctual time when the TV cameras begin to roll. But these photo ops must bewilder the poor groundhogs, which normally wouldn’t come out of their hibernation in midwinter even if the temperature hit 60 degrees.
Groundhogs do, in fact, synchronize themselves to an internal clock, but not one on the wrist of a newscaster. Instead, the groundhog’s clock is wound in harmonious rhythm with green vegetation, which is only available for a little over a third of the year.
Groundhogs eat prodigious amounts of grasses and herbaceous greens, including garden and farm produce, which places them on the most wanted list throughout their range. But greens don’t store well in moist underground chambers, so the ingenious groundhog evolved the notion that, rather than storing food underground for winter, it made more sense to store the food internally in rolls of fat.
In nature, obesity doesn’t often work well as a survival strategy, because it compromises speed, agility and defensive strength, while making one particularly attractive to predators. But, groundhogs have learned to fatten up very quickly right before they hibernate for the winter, a big belly being the greatest defense against starvation while hibernating in a safe den for six months.
A groundhog chooses to spend half its life slowly starving while in hibernation. Groundhogs typically enter their den in early October, block the passage with soil, and then coil into a ball with their head between their forelegs and their tail wrapped around their head. Their heartbeat falls from 75 beats per minute to 4 per minute, and their temperature plummets from 90°F to 38°F. For six months, groundhogs effectively become a cold-blooded animal, and would appear lifeless if you could observe them in their dens.
Groundhogs enter hibernation weighing on average about 10 pounds, and awaken thin and weak, having lost nearly 40 percent of their weight.
In Wisconsin, the winter will almost certainly last well into March or April, so no matter what newscasters say about seeing the groundhog’s shadow, it’s way too early for groundhogs, and spring, to awaken. Be patient.
OF VALENTINES AND ANIMAL HEARTS
In February, our thoughts turn to love. It is, after all, the month when we celebrate Valentine’s Day, showering our loved ones with chocolates, heart stickers, roses and greeting cards. And, how fine it is that we celebrate a day for love and the heart.
Nature also puts a premium on the heart, but not just in February. In nature, that the heart keeps pumping is what matters: all day, every day.
Some animal’s hearts, like a hummingbird’s, pump with such wild abandon that they approach the realm of impossibility. Hummingbirds drive the Ferrari of all hearts, their hearts racing at a maximum of 1,260 beats per minute, or twenty beats a second.
Hummingbirds have the largest-known, relative heart size of all warm-blooded animals. Yet, if you could place their heart in your palm, you would hold an engine about the size of a dull pencil point. It can be that small because there’s not that much of a craft to fly. The smallest hummingbird, the Cuban bee hummingbird, weighs just 0.056 of an ounce, or less than a ping pong ball.
A hummingbird’s breath must come fast to fuel this race engine—nearly 250 breaths per minute, or four breaths a second. “The price of their ambition,” writes one naturalist, “is a life closer to death; they suffer heart attacks, aneurysms and ruptures more than any other living creature.”
On the opposite end of the speed and size scale, there’s the blue whale, whose heart weighs nearly a ton and is as big as an average living room or a small car. The heart of a blue whale has to be large enough to pump about 15,000 pints of blood, compared to about eight pints in a human. A blue whale’s aorta is large enough for an adult human to crawl through. The valves alone are the size of hubcaps.
Though hard to measure (think about how you would do this!), a blue whale’s heart at rest is thought to beat 4 to 8 times a minute, while its breath may come only once every hour or more in a sustained dive.
Hearts come in lots of different models. Mammals and birds have hearts with four chambers. Reptiles and turtles have hearts with three chambers. Fish hearts have two chambers. Insects and mollusks have hearts with one chamber, while worms have numerous hearts with one chamber.
So, the music of the heart is, as such, a type of chamber music, a rhapsody played continuously, increasing in pace as emotion and exertion rises, slowing as quiet settles in. Whether at 10 to 20 beats per second in the hummingbird, or indiscernible, as in the painted turtle dug into the lake bottom and waiting out the winter in a veritable suspended animation, the heart operates as life’s engine, Ferrari fast or glacially slow. On Valentine’s Day and every day.
TRACKING THE ARRIVAL OF SPRING
Phenology, the study of the timing of natural events, leads people to record the dates of the first returning birds, the first wildflowers to bloom, the first spring peepers to call, the dates for ice-up and ice-out on lakes and so forth. Aldo Leopold, author of A Sand County Almanac, also studied phenology, recording the spring arrival of birds and the blossoming of plants at his famous "shack" in southern Wisconsin from 1936 to 1947.
His daughter, Nina Leopold Bradley, an excellent plant ecologist in her own right, moved back to the Leopold Preserve in 1976, and kept similar records through 1998, providing a record that spanned a total of 61 years. During this time, she tracked 300 different natural events and found that one-third of them are now happening earlier than they once did. She and several other researchers then focused on 55 specific spring events and found one-third of those to also be occurring earlier. In general, the average life cycles of plants and animals advanced 7.64 days, with the shifts more pronounced in spring than in summer.
In looking at birds, Leopold Bradley found that most short distance migrating birds were arriving much earlier. Examples included Canada geese arriving five weeks earlier, American robins arriving three weeks earlier, eastern phoebes returning 20 days earlier and northern cardinals singing four weeks earlier.
The arrival dates of long distance migrants haven’t changed as much, very likely because their departure dates from Central and South America depend more on day length than on temperature.
Plants appeared to be reacting to the warmer spring weather too, allowing them to grow and bloom at times that previously were impossible due to freezing temperatures. Leopold Bradley found that compass plants bloom nearly three weeks earlier than they once did, advancing from July 15 to June 26, while Dutchman’s breeches and trilliums now bloom two weeks earlier.
The Leopolds’ data was collected over a long enough period of time to arguably show that there is an overall trend. Other scientists are finding similar trends around the globe. It appears that climate change may be altering the actual unveiling and appearance of spring.
Why not try keeping a phenology record on the natural events happening in your backyard, like tracking the first sounds of cicadas, the first monarch butterfly at your flowers or the weather conditions when migrant birds first arrive at your feeder?