One of the most graceful of birds in the marismas is the Black-winged Stilt. These birds started to return to their nesting sites in March and were soon mating and preparing to breed (post of 16th March). Part of the reason for the early arrival is the proximity of the wintering areas to the breeding grounds. Many stilts remain in the area of the Strait of Gibraltar, wintering along the Atlantic coast of Morocco. Others move down the West African coast. So they are able to return quickly to exploit the spring burst of aquatic insect activity.