Friday, 24 March 2017

Spring forward

On 26th March we turned our clocks forward an hour and British Summer Time (BST)
began. It's not really summertime yet; hardly even spring, but the idea is there. As the earth's northern axis tilts towards the sun our days get longer and, since we prefer long evenings to early sunrises, the clocks have to be adjusted. We lose an hour from our morning (when most of us are asleep) and add it on to the evening when we can use it more productively. Off to the allotment we go!

In fact, BST was first used in 1916 in an effort to save fuel and energy as well as increase production in a time of war. After the war it was dropped, but reinstated for the same reasons in World War 2. Since then there has been a lot of debate about its usefulness. The strongest argument for keeping it is that it extends daylight when most people are up and a bout and therefore cuts down on accidents.

The change in daylight length has innumerable effects; on the economy, the weather, on plants and animal hormones. And on us too. After months of living in the dark, we get SAD (seasonally adjusted disorder) and we get "cabin fever" from being cooped up like chickens. We feel mildly depressed and our hair and skin look about ten years older than they did in September. We have aches and pains and we have put on weight. In short, February is a miserable month.

A fine day in early March, but not much sign of spring.
At the end of February my wife turned to me from her laptop and said "Look at this. We could move to Shetland and buy a house with eight bedrooms."

We both get this urge to migrate every year. Our current house looks tired and worn, we are fed up with the indoor routine. The garden is a mess. We are bored and feel we are drowning in stuff and a fresh start, a new beginning, looks like the way out. Like our house, the entire neighbourhood looks like it is going to the dogs.

Then we had a spring day. We threw open the doors and windows and bees flew in. There was blossom in the trees and flowers in the garden. Suddenly our rhubarb was knee high and the lawn was ready to cut. The flood of vitamin D felt like a drug, which is what it would be if you got it in a bottle. The tills at the local garden centre rang out like it was Christmas as people queued to buy compost, seeds and tools.

Of course that warm spring weather in early March could only last a day, but it did the trick. We shifted from emigration mode to spring-cleaning mode. If I was a bird, I would have been building a nest.

At Paxton Pits, March brought us our first sand martins. These little brown swallows often arrive when the lakes have ice on them and there is snow coming down, which must be really frustrating for a bird that eats nothing but insects. Why do they come so early? Why not join the house martins and swallows that come at a more sensible time, in April?
Sand martin (RSPB)
I don't know the answer, but here's a guess. Nature is always experimenting and for every rule there is always an exception, or the chance of one. Every year a few birds will migrate on the wrong date, or take the wrong route, perhaps arriving thousands of miles from their normal breeding or wintering area. If they die on the journey, perhaps over an ocean, we say that their genes are "lost at sea". They won't get a chance to breed and start a new population. If pioneers, such as early migrating sand martins, do survive to breed, then more birds will take the same risk. They may not form an entirely new population of birds, just a group of birds in the population that arrives earlier than others. In some years this will pay off and in others it won't. The habit may well have built up in a period when springs were warmer than today.

And what could be the advantage of getting here early? I think competition for nest sites may be the answer. Sand martins form colonies in exposed sand banks. Nowadays there are lots of sites in quarries and gravel pits, but historically nesting sites on river bends and small cliffs must have been temporary and rare. It may have been a good idea to get here early to stake a claim, especially at a time when the sand martin population was much bigger than it is now.

Chiff-chaff  (Phil Smith)
Sand martins usually nest twice in summer (they are double brooded) so an early start might give them a better chance of success with both broods. However, despite their very early arrival date they never seem to lay eggs until May. Despite my guesswork, there are some mysteries still to be solved.

Chiff-chaffs also arrive in March when they feed pretty much like goldcrests, gleaning insects and spiders off the leaves while the sand martins pass to and fro across the lake looking for hatches of midges, which are surprisingly frequent in March. Black headed gulls often sit on the water and catch the flies as they hatch because they are not as nimble in flight as the sand martins.

It is likely that the chiff-chaffs use the stars to navigate but sand martins probably use the sun. As the sun moves north of the equator they get the urge to fly north themselves. The further north they go, the longer the days will be in June, but if they fly too far to the West they may not make landfall until Greenland.

Sailors use a clock called a ship's chronometer (set to Greenwich time) to record the time that the sun rises and sets where they are. The sun rises and hour later for every 15 degrees you travel west. Scientist reckon that birds use a similar system using their biological clock. If that clock is inaccurate they will get their longitude wrong.
Gulls hawking for midges in March.
Effectively then, by turning our clocks forward, we move the time of sunrise on an hour, which is like moving your house 15 degrees further west. In that case, my house is now lost at sea somewhere off Ireland and directly south of Iceland. Help!