Wednesday, March 31, 2010

Rain Chasers

Waterbirds are now gathering in the marshes of the Guadalquivir to breed. They come from diverse sources as these images show

there are year-round residents like the Little Grebe (above) and the Coot (below)

then there are migrants that have come from tropical regions of West Africa, like the Purple Heron (below)

Night Herons (above) also move in from the south, from tropical West Africa, only a small number remaining here in winter

Some Spoonbills winter in Senegal but they may be belong to the breeding population in Mauretania. But Iberian birds may join them some years. The key to success in these wetlands is the ability to change behaviour from one year to the next. And the bad season here is not the winter but the dry summer, from July to September. It is then that the wetlands are vacated, many birds moving south into Morocco and many more crossing the Sahara Desert. They arrive in countries bordering the Sahara (Mali, Niger) at the start of the wet season. With the onset of the dry season in the tropics, they return north to hit the fresh bout of rains that usually reach Iberia in October.

Some years the autumn rains arrive late, or they hardly make a presence. During drought years many of these migrants hardly make their presence felt. Some arrive but soon depart if feeding conditions are insufficient for successful breeding. But when the rains come they make the most of it, producing offspring before the summer drought arrives in July.

Burst of waterbird activity with the arrival of the rains

The White Stork, until recently, behaved very much like the migrants I have described. Many still do. The Iberian birds migrate south in July and early August, crossing the Strait of Gibraltar in huge numbers. They cross the Sahara and arrive in Mali, Nigeria, Upper Volta and Ghana at the start of the wet season. Then they start to return across the Strait of Gibraltar in October and continue to pass into January by which time the southern birds are on the nesting sites. West European storks pass later in the spring. 

But in the past two decades many White Storks have changed their behaviour. They have become resident and manage to cope with the summer drought by living off open refuse tips where they find sufficient food.  You can always tell them from the others as their plumage is usually badly stained. The White Storks in these photographs are now with eggs. They are birds breeding in the marismas and appear not to be regular visitors to such tips as their plumage is immaculate. They are among the early arrivals from Africa and are now well established in the breeding grounds.

Black Storks (this one photographed on the 12th February) are scarcer than White Storks, although numbers have increased significantly in recent years. They don't frequent rubbish tips and most are migratory although a few winter in the marismas. They don't breed here but pass through and stop to feed. Curiously, Black Storks are more widely distributed than Whites, breeding across Eurasia into the Far East. The White Stork, on the other hand, is practically confined as a breeding bird to the Western Palaearctic.