October 2017 Nature Notes

Nature Notes

Continuing with the seasonal theme of change, as I write this we are heading for the autumn equinox when day-length equals night-length the world over.  In the northern hemisphere we progress to shorter days, but south of the equator, it is the nights that get shorter – lucky them!

Meanwhile, the planet is experiencing equinox weather with high winds, heavy rain, floods, landslides and all sorts of turmoil.  Oceanographers have measured the temperature of the oceans getting warmer.  This leads to more evaporation of the seas and loading of water vapour in the atmosphere.  This has the effect of energising the movement of air and results in the wind and rain extremes we have experienced.  This has consequences for wildlife as well as humans.  Migrating birds can get blown off course and end up in strange places.  For example, I went for a walk along the Cuckmere Valley recently and saw an American Baird’s sandpiper on the wrong side of the Atlantic, busily hunting small invertebrates along the waterline of a meander.  There were also many winchats aggregating before venturing forth across the English Channel to France and on to Africa.  I was also blessed to see two peregrine falcons and three ravens annoying each other in the sky.  The ravens eventually flew off into Friston Forest.

The migration away from the northern breeding grounds is usually quite slow, taking up to three months in many cases.  There is no real imperative, as the birds are simply following the tide of insect abundance as it also recedes south.  Most northern insects will die during the autumn, either due to weather or to being eaten by the seasonal abundance of spiders.  Also, most birds will be moulting and producing a new coat of feathers to see them through winter and help them with migration flights.  Incidentally, the spring migration to the breeding grounds is much more rapid, taking as little as three weeks from Africa to England.  If you now look carefully at the gulls, crows and pigeons flying over you in the autumn sky, you should see the gaps in the wing feathers caused by the sequential loss of flight feathers.  Moulting is a well ordered process which varies according to species. Meanwhile, on the ground, many ducks lose the ability to fly properly as they can be too heavy when they lose some of their feathers.  They also often go brown for camouflage, this is called going into eclipse.

Dr. Martyn Stenning