A nest and a swan song on the river

I was at the wheel of my boat, steering round a bend in the river. A small island appeared up ahead with a couple of willow trees and an odd object on its shoreline — a brown mound capped with white, like an enormous bun with icing on it. 

It took me a couple of seconds to realise it was a swan’s nest on which the brooding swan had fallen fast asleep. I got closer and saw that the nest was over a metre in diameter and made of dead reeds. The swan didn’t wake up.

Swans lay an average of four eggs which take about 36 days to hatch. Behind these statistics lie some more interesting facts. A female swan, or pen, will have her first clutch when she’s three to five years old and it will be below the average number of eggs, often only one or two. Then, each year, as she matures and the parenting skills of herself and her mate increase, the clutch size will grow, eventually reaching seven or even eight.

The pair will stop breeding when she is 12 to 14. However, the pair, which could have a life expectancy of another 10 years or more, remain together and continue to defend a territory. Or at least this is what usually happens. There are occasional divorces and occasional bereavements. A swan that loses a mate, for whatever reason, usually finds another, often a younger replacement, quite soon.

The choice of a little river island as the nest site was also interesting. The island was obviously a natural defence. Adult swans don’t really have any predators in Ireland — though I have seen video footage of a white-tailed eagle in Kerry making a rather half-hearted attack on one.

However, cygnets are quite vulnerable. There is a long list of creatures that will kill them if they get a chance, including hooded crows and herons, mink and, when the cygnets are very young, even brown rats. And I have heard credible reports of large pike attacking them from below.

And cygnets remain vulnerable for a long time. It takes between 120 and 150 days for them even to learn to fly.

This limits the range of the species in northern Europe and Asia where autumn ice forms before the young can fly away to escape it. The mute swan is probably the heaviest bird in the world that can achieve flight and the achievement is at the very fringe of what’s possible. They require at least 50 metres of open water as a take-off runway.

The distance required for landing is less and they sometimes become trapped by mistakenly landing on a body of water that’s too small from which to take off. In bad visibility they also sometimes make the mistake of landing on a wet road in the belief that it’s a river. In that situation they are completely helpless unless somebody rescues them.

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