Territory in the Great Crested Grebe Podiceps Cristatus Re‐examined.

Summary. This paper summarizes observations on territorial behaviour in the Great Crested Grebe in Oxfordshire and Berkshire and compares them with those of Venables & Lack (1934, 1936) in Surrey. On all waters, each breeding pair defended at least the immediate nest‐site but the area of the defended water adjoining this varied considerably. Such variation is probably affected by population density, distribution and availability of nest‐sites, the topography and the frontage of water before each nest‐site, as well as the degree of aggressiveness of individual pairs. The territories are taken up by already mated pairs and are often deserted when the young hatch, but a few pairs stay in the territory with the brood. More observation is needed on “colonialism” in the species because it appears to vary locally. Some possible functions of territorial behaviour are discussed but no definite conclusions can yet be drawn.