Sluice River and the Ducks

Earlier in the month I walked down Station Road, turned left on the Portmarnock Road, saw a gap in traffic, increasingly rare, and darted across the road, so that I would have a good view of the wild life preserve. The Sluice River empties into Portmarnock Sound here, and there is a wide expanse of wetlands which is home to a lot of birds. The Canada geese have gone for the summer, but we always have the ducks, which normally congregate opposite the petrol station, a rich source for treats from various people.
I was surprised to see all the female ducks tightly huddled on the near side of the Sluice River. The males were either swimming aimlessly around in the river, or sitting, mostly alone, amongst the grass on the opposite bank. How curious! Especially when the males normally won't let anyone near their partner.