Rainfall permitting, flamingos begin breeding each year in late winter or early spring. Depending on the number of pairs and the availability of food, the breeding period lasts until almost the end of the summer. In order to carry out studies on different aspects of flamingo biology, when the chicks reach a certain age, they are captured and marked.

The fact that the chicks gather in nurseries and that they are unable to fly is used as an opportunity to surround them at dawn and introduce them into a pen previously built in the vicinity of the breeding colony. Some 300 volunteers, from all over Spain and even abroad, are in charge of this delicate operation.

Once the capture has been made, the volunteers, organised in groups, proceed to mark and take biometric measurements of the chicks. Each group includes plastic and metal ringers, beak, wing and tarsus measurers, weighers, secretaries who take note of the rings and measurements, carriers who take the chicks to the marking and measuring points, and loosers who place the chicks in certain places and in a certain way so that they can return to the nurseries unharmed.

This whole process of catching and marking requires meticulous organisation and preparation, in which not a single detail must be overlooked, to avoid damage to the chicks and to ensure that the operation is carried out in the shortest possible time and with the greatest of efficiency.

This preparation culminates the afternoon before the ringing with the reception of participants, the handing over of credentials to the volunteers and a meeting in which the Conservation Director explains the whole process and the mission to be carried out by each of the volunteers.