The Crayfish Cruncher - 30th March 2026

Great Northern Divers, almost invariably immature birds, are a reasonably regular visitor to my local Farmoor Reservoir during the winter months, usually only single birds but sometimes two together.

This winter it wasn't until five days ago that one graced the concrete bowl of delights, being discovered on the larger basin in the late afternoon of the 26th of March..Better late than never.

I went the next morning, Friday  to see it, a day of gloom, low cloud and blustery cold wind but forty plus Sand Martins flickering across the troubled reservoir waters and a singing Willow Warbler in the hedgerow were re-assurance that the Spring, despite the cold and grey was truly here.

At first I was unable to locate the diver as it demonstrated a remarkable facility for giving one the slip, travelling long distances underwater to surface unexpectedly far from where it submerged. A behavioural trait I have noticed before with this species,

Finally, once it was found I kept an eye on it but even so it managed to evade me once again. This  of course may say more about my observational skills than the diver's elusiveness.Later that morning after the yacht club took to the water the diver flew and relocated to the adjacent smaller basin the other side of the central causeway and here it has remained undisturbed ever since. Thankfully the strong wind and resulting waves have deterred the paddle boarders who use this smaller basin from taking to the water.When they do I suspect the diver will depart. 

The following day, Saturday, such is the reach of social media, saw many birders coming to view the diver and take its photograph and it was only today, Monday that I returned to the reservoir, not so much to see the diver as to discover what early migrants if any were out and about on the reservoir.

Hirundines have been making a welcome appearance these last few days mainly in the morning, chiefly Sand Martins but with a few Swallows amongst them and today I added House Martin to my year list as a couple flew in the lee of the strong north wind under the trees at the western end of the reservoir.

I stood here with Dave, another Farmoor regular and chatted and birded, glad to be out of the worst of the wind that had buffeted me on the exposed causeway. We watched a pair of Grey Wagtails, prospecting nest sites their  beauty and elegance, rendering them surely one of the most underated of birds.

Hirundines flew around us and above the nearby trees and water works, the Sand Martins churring calls a cheery counterpoint to the grey skies. A Cattle Egret and then a Great Egret flew south and north respectively, later a Sparrowhawk mobbed by a crow flew past at tree top height, the crow, emboldened, almost touching the raptor but the sparrowhawk's superior flying ability allowed it to evade the crow's unwelcome attentions with consumate ease. Later a repeated single note call came from the sky.It was naggingly familiar but at first I could not place it but then, of course, it came to me. It was a Little Ringed Plover, a newly arriving migrant that flew over us but was reluctant to land and disappeared to the south east.

It is little incidents like this that keep one enthused and coming back for more on what is after all an unexceptional and for much of the time unexciting inland reservoir.

The diver, meanwhile remained well offshore as more Farmoor regulars joined us but slowly we drifted away, each with our own priorities and preferences. I made my way down off the reservoir to the Thames Path by the river, glad to be out of the nagging wind. The blackthorn blossom still remained pristine white if a little battered amongst the slowly greening hawthorns as the wistful refrain of a Willow Warbler's song came from the tops of the trees to be answered by another a little further away.The songs were muted as if the strong wind deterred the birds from anything bolder but unequivocally it was the melancholy but welcome song of a Willow Warbler and a little later I saw one of the birds snatching flies from the twigs and leaves as it sang.

I returned to the perimeter track to find the diver was now relatively close in, diving and feeding on the alien Signal Crayfish that infest the reservoir to the detriment of our indigenous crayfish. It would surface with a crayfish in its formidable bill and shake it vigorously, softening it up, sending bits of disintegrating crayfish flying in the air before the unappetising crustacean was swallowed whole. One can only presume the diver's stomach must have powerful digestive juices to dissolve the carapace and armouring that protects the crayfish.

I watched the diver consume a number of crayfish before it settled, obviously with appetite satisfied and floated idly on the water. 

The sun came out briefly making the diver look very different on the blue water

It closed an eye and slept and I ruminated on what a strange life it must be to spend almost your entire life on and underwater apart from dragging your body a few feet onto land to nest at the very edge of the water.

This individual will not breed this year as it is only in its second year of life and retains its juvenile plumage of dull grey brown upperparts and silky white underparts.It is only in its third year in Spring it will assume the glory of fully black and white adult plumage.

How long this bird will remain at Farmoor is unknown but surely will not be longer than a month, probably less. We will have to wait and see but in the meantime it is welcome to remove as many of the alien and invasive crayfish as it can.