Red-necked grebes usually nest as isolated pairs with more than between neighbouring nests, although semi-colonial nesting may occur in suitable sites, where up to 20 pairs each defend a linear territory. Semi-colonial breeding is more likely to occur in prime locations, such as large floating mats of vegetation with no connection to the shoreline. Such sites, safe from most predators and large enough to provide some wind and wave protection, have grebes nesting much closer than shoreline breeders, down to . Pairs nesting in these colonies produce larger clutches of eggs, which hatch earlier in the season and result in larger broods. The territory is defended with various threat displays, including wing-spreading, hunching, and bill-thrusting; pairs breeding in colonies are more aggressive, less likely to leave the nest unguarded and show a greater tendency to move out of sight of the colony when not incubating. Breeding is often in loose association with gulls or other colonial water birds.