Early Bloom

I was just about to talk about the long period of late winter and early spring when nothing much seems to be happening in the plant world, when I came upon a twig on the sidewalk.  Silver maple, I was pretty sure.  Positively packed with swelling buds, as usual.  And did I see flowers peeking out of a few?  Already?!  And in WINTER, for God's sake!  Last year silver maples didn't flower until the beginning of April, more than four weeks later!

Over the next day or two I paid a visit to every silver maple I knew about, and also a good many quaking aspens, which bloom at about the same time as silver maple.  Sure enough, silver maples are popping more than four weeks earlier than last year, and quaking aspens aren't far behind.  The prolonged warm weather we've had lately is probably to blame.  How?

 Silver maple (Acer saccharinum) on Moraine St almost in full bloom on 2/29.

Silver maple on Tuesday, 3/1.  The white filaments sticking out all over are stamens shedding pollen.

 Pussy willow at the high school.

 Some of the quaking aspen (Populus tremuloides) buds above look larger than their neighbors

because they are expanding to flower.  Below are unopened buds.

Quaking aspen at the top of my street is almost in full bloom on Tuesday 3/1.

Why the early blooming?

Trees go dormant in winter on a schedule fixed roughly by the length of uninterrupted darkness.  (By interrupting darkness, streetlights sometimes play havoc with tree life cycles.)  When nights become long enough in the fall, processes are set in motion that cause leaves to turn color and drop, and dormancy to begin.  But dormancy doesn't end according to night length: instead, the tree must experience a certain minimum number of hours of sufficiently cold temperatures.  Just how cold, typically a little above freezing, and for how long, depend on the tree species.  This cold requirement reduces the chance that a tree will become active and grow leaves and flowers during an early thaw, only to be killed by a later cold snap.  But once the tree has clocked the required number of cold hours, any prolonged warm spell can break dormancy and send the tree into action for the new growing season.  

This early flowering was caused mainly by a fluke of the weather.  But over the long term we should expect plants to flower and leaf out earlier in a warming world.  This has consequences that could prove disastrous.  For example, a British bird called the great tit depends on a good supply of winter moth caterpillars to feed their growing chicks.  The winter moths, in turn, eat the leaves of English oak. The birds have always laid their eggs at the right time so that caterpillars are at their peak just as the chicks are at their hungriest. However, warming climate has led to earlier growth for the oaks and caterpillars, while the birds have been left behind.  Laying their eggs too late, the birds fledge fewer and lighter young, putting stress on the great tit population.  It bodes ill that most species studied so far react differently to climate change than the species they depend on.

Food chain being stretched to the breaking point?

Great tit, English oak, and the winter moth and caterpillar. 

(All photos from Wikimedia Commons.)

Bird Season

 Spotted a pair of pair of downy woodpeckers flitting about in the front yard.  This is the male.

My first love, trees, are mostly still pretty sleepy; meanwhile, the birds are busier all the time--mating season has begun.  Birds are perhaps the easiest group of large animals* to watch, or at least the most obvious, and they're virtually everywhere.  And for the next month or two--birds will be at their most visible: trees will not begin leafing-out until almost May.  

Even though I am no kind of birder, I will be observing and learning as much as I can over the coming weeks.  I have used several websites to identify and learn about birds, but the Cornell Lab of Ornithology is the premier site--especially for learning bird songs.  Songs are valuable because we often hear birds that we can't see.  A skillful birder I know can identify many birds with her eyes closed.  

Looking through the Cornell site a day or so ago, I came upon a great way to learn to identify birds by their songs.  If you want to go out better prepared, here is a great place to start. Within something called the Bird Academy, I found Bird Song Hero.  This is a couple of interactive lesson/quizzes that teaches you to "see" birdsong.  And after you've finished it, you get a free download of backyard bird songs that you can study and keep for reference.  (There's also a nifty-looking online lecture course you can take, but it costs money.)

Other sites are easy to find in a search.


*Okay, maybe they're medium-sized animals.  But on the grand scale of things, most animals are the size of insects.  (Come to think of it, most animals ARE insects!)  Of course, we are bigger than the average bird, but you might not realize that we aren't that far from the top of the animal size range.  Blue whales are about 2000 times heavier than a human, a human is about 1000 times heavier than a robin, which is in turn about 3700 times heavier than a lady bug. 

In the winter a young bird's fancy lightly turns to thoughts of love

 Appropriately enough, I first noticed loud, urgent birdsong of several different kinds around Valentine's Day.  (I'm not able to identify more than a few birds by their songs, though I would dearly love to learn.)  I had imagined that spring was mating time for local birds, but some, at least, get a head start much earlier. 

In most birds it is the male who sings to attract a mate, and the female who does the choosing.  For the same reason, the male is often the more brightly-colored.  (Females are more often dull: they don't need to show off.)  The male may sing, "keep out! this is my territory!" to other males, while to the females he sings, "Am I not the most beautiful guy you've seen, and with the most impressive song? and wouldn't you like to raise a large brood of fine, strong chicks with me on this wonderful territory?"

The coloration and singing are textbook examples of sexual selection.  This is a variant of natural selection in which characteristics such as bright plumage are selected for, not by directly improving survival or reproduction, but indirectly--the males most attractive to the females are more likely to succeed in getting a mate and contributing those very genes conferring bright color to the next generation.  It makes evolutionary sense that females, which make the enormous resource investment of gestating the young, will be very choosy about who their partner is.  (This choosiness of female holds true in a great many other animal species as well--likely even in humans.)

 A well-attired White-Breasted Nuthatch on February 19th.  

These birds walk up, down and around the tree trunk looking for food.

On February 19th I spotted a handsome pair of white-breasted nuthatches working their way around the gnarled limbs of an old red maple.  If I'd had any doubt they were lovers instead of mere dining companions, my copy of the Sibley Field Guide to Birds of Eastern North America set me straight: "usually solitary."   

 This Downy Woodpecker is probably the female; the male looks the same

but with a prominent red patch on the back of the head.  These birds brace their tails

against the tree while they hammer their beaks into the bark probing for insects.

Today, February 22nd, the sound of gentle, companionable tapping drew my eyes to a pair of downy woodpeckers searching for food in the bark of some dead oak branches.  Later my wife called my attention a pair of tufted titmice in a big Norway maple tree in the backyard.  

It's worth mentioning that these three particular birds don't differ much from male to female, though the male downy woodpecker does have a bright red patch not shared by his mate.  And in the tufted titmouse, at least, both male and female sing.

I will look and listen more carefully in the coming days.