La distance d'envol, un indicateur de dérangements : L'exemple de quelques espèces d'oiseaux en milieu estuarien

During the summer estuaries are used by numerous species of birds taking advantage of the abundant food supplies, and by large numbers of tourists whom create some disturbance and modify the possibility of resource exploitation by the birds. The objective of this study, done in the Somme Bay on 8 species, is to measure the take off distance of birds following the intrusion of human in there feeding grounds and to discuss the possible use this parameter as an indicator of disturbance pressure. This variable is affected by several factors but it seems the disturbed birds leave their usual feeding areas inducing a diminution in flock size and take off distances. Dunlin (Calidris alpina) seems to be the most vulnerable species whereas Eurasian Shelduck (Tadorna tadorna), although a protected species in France, shows a great fear of man. Globally disturbances lead to an under-use of space the consequence of which on the acquisition of energy reserves by birds will have to be studied.