Europe's Warm Winter Surviving a False Spring

Frogs have started mating, wild hamsters can't sleep, and the mild climate intimates spring. How dangerous is Europe's warm winter for animals and plants? A look at the miracle of biological clocks.

By Rafaela von Bredow


People with allergies were stunned this winter by the earliest pollen alert anyone could remember -- alder and hazel had aready started to bloom. Roses blossomed, titmice chirped; it was shortly before Christmas, and spring was starting in central Europe, before winter had even arrived.

Fall was barely worth mentioning. Temperatures at the end of November, normally known for nasty wet cold, had broken all known records for warmth. The unseasonable temperatures gave a second lease on life to many forms of flora and fauna. Insects like mosquitos, moths and ticks that would normally be dead by now have survived. Brown bears in Norway and Sweden were still wandering the woods in January -- instead of hibernating -- and Japanese cherry blossoms added patches of pink to rain-gray cities. On Wednesday last week, people in Munich sunbathed in parks and public squares. Temperatures in Germany rose as high as 16°C (61°F) -- it was warmer in some parts of the country than on the Mediterranean island of Mallorca.

Europe is basking in a phony spring, which for all anyone knows might still give way to winter. What if the baby birds hatch too early? What if the frost comes after all and kills the offspring of hamsters that woke up too early from hibernation? What if flowers freeze?

The short answer is: No problem. Nature can cope. Biology anticipates mild winters, and animals and plants in European latitudes adjust to changing seasons with incredible flexibility. Flower bulbs can sprout twice if necessary, and the animals can bear to miss part of their hibernation since they can still find plenty of seeds and worms in the ice-free soil. If hamsters do mate prematurely, from a biological point of view the first litter might as well die. "They can easily produce a second and third litter," says hibernation expert Franziska Wollnik from the University of Stuttgart.

Cranes and other birds can adapt too: Plentiful food is what keeps them from migrating south. "That's how it is with migrating birds that take rest stops," John Dittami from the University of Vienna explains. "As soon as winter really hits, they will be gone."

The incredible, universal, internal clock

Animals and plants have developed a fascinating system to navigate seasonal change -- a universal "internal clock," which sets the rhythm for each individual life. The study of this phenomenon is called chronobiology. Molecular and behavioral biologists, zoologists, botanists, psychologists and neurologists all try to understand the complex function of the natural pacemaker seemingly built into every cell. Chronobiologists have managed to describe in detail the complex dance of DNA-snippets, protein molecules and light sensitivity that tells, say, a crocus when to blossom.

Internal clocks cause leaves to lift and lower in daily cycles; they also make migrating birds restless at the same time every year. The rhythms are passed on from generation to generation. Even plants kept in the dark move their leaves according to a pre-set cycle.

The inner clock runs on certain genes and the proteins they produce. They oscillate in a predetermined rhythm. At one point in the cycle a maximum number of proteins collects in the cells; at another point, also precisely timed, there is a minimal concentration of proteins.

The daily and annual clocks are somewhat imprecise, though. Humans follow a roughly 25-hour daily rhythm, for example, but environmental stimuli like light and food adjust our inner clocks to a conventional day. Plants are sensitive to temperature as well as nutrition and light, and this constant calibration with the environment lets creatures know whether it's currently fall or spring.

A key signal for both animals and plants is the length of days and nights. The duration of daylight can stimulate molecular signals which align with the body's genetic rhythm, letting the body know if the days are getting shorter or longer.

The European hamster, for example, will notice a difference when days shorten from 16 hours in late June to 15.5 hours in late July, according to Dr. Wollnik. The message, even in mid-summer, is: "Winter's coming." In the hamster's hypothalamus -- in its brain -- the genetic clock interacts with light stimuli to set a rhythm. The longer nights become, the more the brain's pineal gland produces melatonin. This substance communicates with the inner clock, and the hamster starts preparing, instinctively, for winter.

The exact molecular process is still unknown, but complex metabolisms will ready the hamster's body for hibernation. Reproduction, for example, becomes impossible. In females, the vagina closes; in males, the testicles withdraw into the body. The animals hoard food, cower in their dens, and finally start to hibernate.

Fates worse than spring

Even if mild temperatures shorten hibernation or a deep frost prolongs it, though, the hamster's internal clock will still prepare him at the appropriate time for spring fever. "It's a kind of safety mechanism," Wollnik says. Natural rhythms keep the animal from sleeping through spring, and also guide its fertility cycle. The same rhythms prevent crows and cranes from mating prematurely and exposing their eggs, potentially, to cold.

Migrating birds wintering near the equator rely heavily on their internal clocks because equatorial daylight changes so little. A built-in calendar is essential to get the birds started on their return journey.

Plants are also strictly timed. In temperate latitudes many so-called "long day" plants blossom only when the duration of sunlight exceeds a certain number of hours. There are also "short day" plants, which don't bloom until the nights last long enough.

"The measurement of the length of days is the best thing plants and animals have," says John Dittami. "The temperature, the available food, all of that gives them a certain degree of flexibility in their actions, but the cornerstone is set by an internal calendar."

So the cosy temperatures this winter have -- for the most part -- just changed the blooming time in plants that can afford the leeway. Hazel and alder are wind pollinators, which means they don’t have to wait for the real spring to draw bees out of their hives and spread their pollen. The Japanese cherry, which did in fact bloom dangerously early, is a foreigner from the Far East -- evolution hasn't prepared it for the drama of central European weather.

Dittami trusts that nature will ride out this year's tepid mid-winter spring. He says humans present tougher challenges on a daily basis for animals as well as plants. "Street lights, for example -- and all that other light we send out into the world," he says. "That throws off all of their measurements."

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