"Time and tide waits for no man" or bird either! The need to feed, and breed are the driving forces on birds, but in our insulated, heated homes we are divorced from the natural forces that govern avian behaviour. The relentless passage of time and vagaries of the tide weigh heavily on the birds on the waders on Montrose Basin.
The earth and moon, locked in a spinning embrace, revolve about the sun, and the resulting tides and seasons are the timepieces that regulate the lives of the basin birds. The moon, as it reaches out to keep hold on the earth grabs the oceans and pulls them up into a small mound that we see as a high tide. As the moon swings round us it takes its oceanic prisoner with it and the high tide moves round the world. Behind it the remaining water gives us a low tide. Twice a day water floods in and then flows away over the muddy margins of estuaries all over the world. The second high tide is caused by the spin of the earth trying to throw off the mantle of the oceans and causing a second mound of water on the opposite side of the globe to the moon.
The intertidal zone (the land between the tides) is rich in worms, molluscs, and shrimps - a veritable banquet for hungry wading birds deprived of food as the mound of water invades the estuary. The birds must eat now and live for tomorrow. In our winter climate birds are living on the edge - they are losing heat as fast as they can replenish it with a shrimp and worm cocktail every six hours.
A falling tide is the best time for a wader to feed, as the snails, worms and shrimps are scavenging on or just below the surface on the edible material just bought in on the tide. The knot and dunlin stitch their way across the surface for small insects and snails while curlew and godwit look for surface casts and dig deep to drag out the buried worms. But they must hurry as the next tide will be in soon and cover up the bounty. Feeding is easier on spring tides (so called because the water "springs" up to great heights - nothing to do with the season). Neap tides have a smaller range (high tide is not so high and low tide is not so low) so less mud is exposed and for shorter periods so feeding is much more frantic especially if this coincides with cold weather.
The yearly cycle of the earth’s rotation around the sun brings longer term changes - the seasons. Now the bird’s breeding instinct takes over. In response to longer and warmer days they are restless and make the move to their breeding grounds. Sometimes this is not far from the winter feeding site like curlew which move to inland moors to breed. Some birds put in mind-boggling journeys to breeding sites in the high arctic of Greenland and Canada like knot. This long journey is worthwhile because the arctic region has fewer predators which makes it safer for the eggs and chicks. There is also abundant food in the shape of insect life reaching plague proportions as the ice retreats and temperatures rise.
So about now it is all-change as the winter visitors head north again and our summer visitors arrive to take advantage of a mild climate and ample food. The pink-footed geese return to Greenland and leave the morning and evening skies quiet. The most obvious early arrivals are the swallow and martin but keep an eye out for the more secretive sedge warbler who, after a sojourn in Africa, returns to breed in the reed beds on the margins of the basin.
We can’t stop the flow of time or tide but we can enjoy the rhythms of life that depend on it.