I arrived at the West Park lake just as this pair of swans were coming to the end of the co-ordinated routine which is their pre-mating ritual. For perhaps a quarter of a minute, the cob mounted the pen, his weight half submerging her in the water.
Then a brief reprise of the pre-mating ritual as they paid attention to one another. Necking takes on new meanings when performed using necks as long and flexible as these.