Posts Tagged ‘Doug’

A Closer Look at Cones: Norway Spruce

by Doug Morin

 

Thwack……thwack……

What was that, I wonder?  Never mind, I have to focus.

thwackclunkbang………

Bang? Was that a bang?

thwackbang……thwackthwack

I couldn’t help myself.  I opened the window and look down to the garage and driveway.  Nothing moved.  The neighbors weren’t even home.  Back to work.

thwackthwackthwack

I raced over to the window, catching a flash of rust-colored fur bolting along a spruce branch to the inner tree.  I looked down; the driveway was covered with spruce cones.  I stayed put, waiting to catch the culprit red-handed.  A minute later, the squirrel ran boldly out one of the long spruce limbs, 40 feet above the ground.  It ran to the end of the branch, hung down off it’s back feet, grabbed a cone with its front feet, chewed the cone’s base for a few second, then let it fall.  thwackclunkbang……… The cone tumbled to the ground, hitting the neighbor’s roof, the side of our house, then my housemate’s car.

Norway spruce. Note the swooping branches and drooping branchlets. Source: http://bioweb.uwlax.edu/bio203/s2009/madisen_neil/

Over the course of the last week, the squirrel dropped about 200 cones into our yard and driveway, by my estimate.  The cones were coming off a Norway spruce (Picea abies) tree in our backyard.

Native to Europe, Norway spruce is one of the main trees in the forests of Germany, Switzerland, Austria, and Russia.  In the U.S., it is commonly grown as an ornamental and in plantations, but rarely establishes on its own.   It is widespread throughout the cities and suburbs of the Northeast, so keep an eye out and you will start seeing it everywhere.

Norway spruce may be the tree most easily identified from a distance.  Once you get the search-image, you will be able to recognize it while driving 60 miles an hour on the highway.  An evergreen, Norway spruce has short, dark needles.   The trees usually grow 50-80 feet tall and two feet in diameter, and often have branches almost all the way to the ground.  And, most importantly –here’s your 60mph field mark— branches off the main stem arc upward (“swooping”) while branchlets growing from the main branches are long and hang down (“drooping”).  Swoop and droop – it’s that easy.

Now, back to the cones.  When you imagine a cone, I bet you think of a dry, brown one, light as a feather.  But, cones are not always so. The dry brown ones most of us imagine have passed maturity and already released their seeds.  In contrast, the cones pelting our house were still developing – leathery, green (or pink early in the season!), and dense.  Plenty dense to dent a car, as we discovered.

But these cones are only one of the two kinds of cones conifers produce.  The big cones we tend to think of (and the kind now all over my driveway) are female cones.  They are usually between 1 inch and 6 inches long depending on the species and produce seeds under their scales.  Squirrels eat the seeds, explaining why our squirrel was amassing a collection of female cones.  Lesser known are male cones.

Separate structures from female cones, male cones tend to be small (1/2 inch or less in length) and not as long lasting (they often disappear in days or weeks).  They produce pollen for a short time in the spring then, having fertilized female seeds, their job is done, and

they die back.  Interestingly, the difference between male and female cones explains why the squirrel was dropping cones from high enough to bombard our roof.

Male cones on left, Female cones on right. Sources: http://projectbudburst.blogspot.com/2010/05/look-at-conifer-phenology.html, Wikimedia Commons

Most trees concentrate male cones on their lower branches and female cones on their higher branches.  This serves an evolutionary role: it prevents self-fertilization. With male cones down low and female cones up high, pollen from male cones must get blown by the wind to get high enough to reach a female cone. This wind will usually carry the pollen to another tree.  If, however, the cones were intermixed or the males were on top, the pollen would fall directly into its own female cones.

So, if the tree wants to mate with another tree, rather than itself, it puts its female cones up high… giving them plenty of time to accelerate as they fall before pelting roofs, cars, and the occasional unsuspecting bystander.

 

 

 

 

Why do birds fly south for winter?

by Doug Morin

I opened my backdoor and stepped into the yard to a flash of red and buzz of wings – a hummingbird.  Maybe the last of his kind I will see this year, he perched on a small branch, tilted his head to either side, then flew off down the road.

Here in Vermont, hummingbirds disappear in late September and reappear in late April.  We know the story well: birds fly south for winter.  Of course they do.  But, have you ever wondered why?

First, let’s turn the clock back a few thousand years.  It turns out, most migratory birds in North America trace back to ancestors that lived in the tropics.  Over time, these birds expanded their ranges until a small proportion eventually made it to North America.  Even today, most birds arrive in late spring and leave in early fall – spending less than half their year in North America.  The real question then isn’t, why do birds fly south for winter? but, why do birds fly north for the summer?

This is a particularly important question because migration carries a deep cost.  It’s easy to discount the effort required to fly to and from the tropics, given the convenience of modern air travel (though I’d still like more leg room), but the journey for a bird takes huge amounts of time and energy as well as exposing the bird to unfamiliar environments and predators.  The hummingbird in my yard, for instance, weighed only as much as small handful of paperclips, yet over the next weeks, it will first fly to the southern coast of the U.S., then across the Gulf of Mexico to the Yucatan Peninsula in a single, non-stop flight lasting nearly 24 hours, and finally overland to southern Central America.

The time, energy, and risk involved in migration have severe impacts: migratory birds are twice as likely to die in any given year, compared to tropical non-migratory birds.  So, why in the world do they do it?

The answer is that the benefits outweigh even these high costs.  Since relatively few birds come to North America, migrants have easy access to abundant insects, plants, and nesting grounds.  With plentiful food and territory, migratory birds produce many more offspring each summer than their non-migratory counterparts.  As winter arrives, however, insects and plants disappear, and the diminished food supplies (rather than dropping temperatures per se) drive migrants south.

Overall, migratory birds do not live as long as non-migratory tropical birds, but produce more offspring each year – resulting in nearly the same number of over their lives.  Since the number of offspring determines how many birds will be in the next generation, these two strategies are roughly equivalent in evolutionary success.

So, the birds that grace our summers with color and song do so for windfall payoffs, but at immense cost.  As you see the last of our migratory birds leaving over the next few weeks, wish them well on their way.

Also, look out for a more in-depth post by Emily Brodsky on Raptor Migration in the next few days!

 

Note: For excellent maps of where birds spend their summers and winters, see the Cornell Lab of Ornithology’s website All About Birds.