Profils comportementaux, individuels et de couple, au sein d'une population nidificatrice de grèbes huppés Podiceps cristafus L.

From early March to late August 1987, a sample of some sixteen Great Cresteel Crebes breeding pairs has been thoroughly followed, in order to draw pair and individual behavioural profiles, and to get intimate knowledge of personal success or failure stories, as well as of social interactions within the group. The ultimate goal is to refine the undertstanding of the recruitment process. The sample is part of a local population whose numbers fluctuate between 70 and 80 individuals, a population which had been fastly expanding in the early eighties. The habitat is an old meander of the river Meuse on the Belgian-Dutch border, isolated upstream from the main artificial river-bed but still in communicaton with it downstream; it covers 4.40 Ha ; right and left banks develop respectively 656 and 766 m; they are irregularly fringed with willow and alder shrubs and trees, offering less nesting opportunities than required by postulating pairs in spring. Thus, competition for nest sites and territories is high and late settlers have to wait. until successful birds leavc with their chicks or until unsuccessful pain eventually give up after several nesting attempts. It is so far possible to distinguish three successive waves of breeding cycles : the first wave settlers mate, select nest site and defend a territory from late March; part of the breeding pairs is replaced in June by a second wave; a third one, initiated in late July and in August, might produce young reaching autonomy as late as in October. This general outline allows the expression of individual divenity in aggressivity, diligence, persistence or tactics, which may be important for success or failure. Each breeding wave begins with a phase characterized by repeated copulations, continuing for days or weeks, and which probably ensures maturation and synchronization of pair-members. This phase is shortened for birds of the second and third waves, who are already synchronized before winning a nest site. The quick succession of breeding pairs on the nest and territories is to be taken into account when taking a census of a breeding population or when evaluating breeding success and check recruitment. It is argued that population dynamics study as well as habitat and population management have to gain in a better knowledge of behaviour, through an integrated approach of both the population and the individual and social levels.