17/02/22
I’ve been watching the herons on Moscow Island. They’re early breeders, aiming to have their chicks hatched just when the frogs are coming to the water to breed offering a plentiful food supply for the youngsters. Heronwatch begins at the weekend, and the birds are putting on a show already. Their courtship rituals are worth seeing. At first, single male herons are seen standing on their chosen nest, giving ‘advertising’ calls and occasionally looping round the site in display flight. Once the females arrive the colony is alive with posturing, beak-clacking birds – the courtship display has to break down their usual antisocial territorial behaviour patterns. Ritualised posturing is a key to this. The Stretch Display, with sky-pointing beak, is performed to attract a mate. Once a female alights near the nest, the male will drive her away using aggressive postures and threat calls. Usually she flies away, but returns several times, with the aggressive display lessening each visit, until she is allowed to alight on the nest itself. We’ve already seen pairs mating, and there may well be eggs in the nests.
I have to admit, I’m rather worried about the poor creatures. Herons like to nest high in mature trees, and being large birds, they build big nests. They reuse nests from year to year, so the ungainly stick structures get bigger and bigger as more sticks are added with each season’s occupation. Nest refurbishment is part of the courtship behaviour – the males bring sticks to the females, who add them to the nest. Sometimes it’s a really good stick and the female looks well pleased, fiddling with it and poking about until it’s in just the right place. Sometimes it’s a mere twig, and she looks at it as if she’s thinking ‘You got that at the petrol station, you cheapskate’! However, we had howling winds yesterday and they’re forecast to be worse tonight and tomorrow – imagine sitting in an armchair-sized heap of sticks thirty feet up in the top of a tree with a gale blowing at 60 miles an hour, and you can see my concern. Nests could be blown out of the branches, or, indeed, whole trees toppled. Herons usually avoid flying in high winds, having a large wing area for their weight, They’re in real danger of being blown out of control and whipped into the branches, so a long period of rough weather can leave them hungry, or drive them to leave their eggs unbrooded. If they lose eggs they will lay again, but if the nest is lost it means a month or so of hard work to establish a new one, which can mean they miss the boom-time for feeding the new chicks unless another vacant nest is available. If a tree is lost it could take two or three nests with it.
20/02/22.
Well, Heronwatch started yesterday, and I was down to the Boathouse to see how the herons had weathered the storm. One nest on the screens is fine, with an occupying pair of herons clinging on grimly in the wind with spraddled legs and their long chest and median feathers whipping around. They don’t look very comfortable, but they’re sticking to it. The other nest with a camera on it has gone - completely and utterly gone, with not a stick left. The unlucky pair that was showing interest in it will have to go back to house-hunting. I have heard there is evidence that herons are adapting to wilder weather by choosing lower nest sites with more cover, where the nest will be more protected in high winds than in the traditional treetop locations, and the Ellesmere heronry seems to be following this pattern. It’s a sensible adaptation to the extreme weather events we’re experiencing these days. Let’s hope the herons so unceremoniously evicted by Storm Eunice have a flexible attitude to their ideal home!