In the centre of Slipper Mill Pond, a saline lagoon just across the county border, a female Canada goose is incubating her eggs on a large floating platform. To the south, a smaller raft is occupied by the gander and two great black-backed gulls, the female sitting tight on a scrappy nest of broken twigs and dried grasses while her partner stands beside her, bathed in sunshine.
Although at first glance it appears a serene scene, subtle body language hints at underlying tensions between the two nesting pairs. The female goose’s sleek black and white head rests on her shoulder, but her eyes are open and alert. On the adjacent platform, the gander stands sentinel, staring down the great black-backs. The female gull shifts on her nest. Her mate shuffles his feet, his neck slightly arched. The gander takes a step forward, tossing his head.
Great black-backs are the largest gull species in the UK – formidable, heavy-set birds with powerful blunt-tipped bills. Though they have similar wingspans to Canada geese, the latter’s average weight is a hefty 4.6kg to the gulls’ average 1.7kg.
Canada geese are notorious for their antagonistic behaviour and over the past three years they have repeatedly exerted their dominance over this pair of seabirds. The great black-backs first nested on the Slipper pond in 2012, claiming the largest of the pond’s three nesting rafts and rearing two chicks. They have returned each spring, successfully fledging young in all but 2015. In 2017, the Canada geese arrived, ousting the gulls from their prized central platform. Both species form lifelong pair bonds and are loyal to their nest sites, so, although the gulls attempt to stake a claim to their preferred breeding ground in early February, for the third year running they have been relegated to the smaller southern raft as soon as the geese arrived at the end of March.
Just as the gander is about to lunge at the male gull, he is distracted by a passing mute swan. Head pumping, he plunges into the water ready to defend his territory, but this cob’s mate is tending their nest on neighbouring Peter Pond and he’s in full sail, his wings raised and neck snaked back in a threat display known as busking. Powering through the water he pursues the Canada goose who, having met his match, paddles furiously towards the safety of his own nest platform.
• This article was amended on 3 May 2019. The photograph of the great black-backed gull replaced an earlier image.