d. Migration calendar at the western flyway

Birds that cross the Mediterranean can be classified as either trans-Saharan, or pre-Saharan migrants. The former are long-distance migrants that cross the Sahara on their way to western Africa, such as Storks, Kites, Honey buzzards, Swallows and Warblers. Pre-Saharan migrants over-winter in the Strait, Morocco or Tunisia and include Hoopoes, Skylark, Chiffchaff and Sandpipers. The migratory patterns of most birds crossing the Mediterranean conform to the general patterns below.

April and September are the most visually rewarding months of migration for bird-watchers. Storks and raptors are not generally visible until after 10am, when thermals start to form.

i. Post-breeding / Autumn migration:

WHAT IS IT?
The migration from Europe to African ‘feeding grounds’ occurs once young are independent and adults have undergone a moult.

WHEN IS IT?
August to December with the main flux from September to November. Within the Autumn migration are two groups.

July-September:
trans-Saharan migrants. ‘Most long-distance migrants leave Central Europe in August and September and don’t arrive at their nesting grounds until November, December or later3’. Some stop-over to fatten up before the Saharan crossing in the 500km belt bordering the Atlantic, which suffers less from the seasonal drought than the barren eastern parts of the peninsula. Overall numbers of trans-Saharan numbers in the Strait are much lower than in the Spring, indicating that many don’t stop-over. Birds generally orient in a south-westerly direction from the Strait, to migrate via the relatively productive coastal belt of the Sahara.

October-December:
pre-Saharan migrants from all over Europe and the western Palaearctic. These birds time their arrival with an increase in food resources in the area, resulting from the autumn rains. Some species establish winter territories on arrival, such as robins, whilst others move to find food, such as blackcaps searching for fruiting trees. Pre-Saharan migrant birds are then usually the first to leave in the spring, e.g. chiffchaffs and song thrushes⁷.

ii. Pre-breeding / Spring migration:

WHAT IS IT?
The migration north from Africa to Europe towards breeding areas, having spent the winter feeding.

WHEN IS IT?
February-early April:

Pre-Saharan migrants return north, some such as the meadow pipit, assumed to have wintered in Morocco, return in conspicuous flocks, while other populations on the Iberian peninsula show a steady decline.

Mid-March-late May:
Trans-Saharan migrants arrive in spectacular numbers. Their fat reserves are low after crossing the Sahara and they feast on the abundance of insects that hatch in March, e.g. yellow wagtails put on 30-40% of their body weight in fat before the desert crossing, and will remain in the Strait longer than on the autumn passage to regain weight⁷.