Wednesday 13 December 2023

A Great Northern Diver visits Farmoor 12th December 2023

On a Monday, in the late afternoon with the sun just slipping below the trees I left Farmoor Reservoir for my home. Not ten minutes later D rang to tell me about a Great Northern Diver that was out in the middle of the larger basin that is known as Farmoor 2. I had just crossed the toll bridge at nearby Eynsham but fortuitously there is a roundabout a few hundred metres beyond the toll where I was able to about turn the car and head back to the reservoir, while at the same time putting the news out so other birders would be aware of the diver's presence. Sadly this sometimes does not happen at Farmoor for reasons best left unsaid.

Dusk was rapidly approaching and it was by no means certain the light would hold to enable me to find the diver. To attempt to walk around the reservoir at this late hour would guarantee failure so with the kind permission of Mark, one of the Thames Water Rangers, I was able to drive around but even then, stopping at various points, I could not find the diver. It was only, having almost completed  the full circuit and returning down the causeway, that I saw two birders obviously looking at something. It had to be the diver. Stopping the car I jumped out and there was the elusive bird swimming not too far out from the causeway.

There was no chance of a photo as the light had virtually gone but I had at least seen it Remarkably B, another local birder actually made it to the reservoir on his bike just as I was leaving and managed to see it virtually in the dark. Top effort!

I resolved to return to the reservoir the next morning but the weather, unlike yesterday was foul. A pall of grey, wet mist was settled  upon the reservoir creating an overall dankness but there was cause for optimism as it became obvious there was better weather to come as the light improved and some insipid sunlight began to shine through the dispersing mist and cloud.

The diver however was nowhere to be seen as I walked a third of the way up the central causeway. It certainly was not where I had last seen it yesterday. Looking for a large dark bird on the silvery waters of the reservoir was made complicated by the fact that a number of Cormorants were energetically and communally fishing, their dark profiles superficially similar to that of the diver. 

The Cormorants, up to twenty, kept close company feeding in what can only be described as a mass frenzy, frantically diving after trout with which the reservoir is stocked by Thames Water at huge expense. When an individual Cormorant caught a fish and surfaced with it all the other ones would converge and a free for all commenced, the bird with the fish frantically endeavouring to swallow its prize as quickly as possible to avoid being mugged by its 'friends'. If the captured fish was large and proved hard  to swallow it resulted in the particular Cormorant swimming in a very unnatural manner with head and distended neck held vertically out of the water while its body remained completely submerged as it endeavoured to force the fish down its gullet.This often took some minutes but was usually successful.

Then another Cormorant would catch a fish nearby  and the entire flock would hurtle over there in a confusion of thrashing wings and paddle feet noisily slapping the water. It was as if the birds became swept up in a communal hysteria. Subtle it certainly was not. Every Cormorant for itself with no quarter given. I have only seen this phenomenon here on the reservoir and can only wonder if it occurs elsewhere. 

In the past a Cormorant has even been found choked or starved to death here, unable either to regurgitate or swallow a large trout which had become stuck in its throat.

Eventually I espied the diver over towards the far side of the larger basin and walked round to be closer, although on arriving opposite I found it was a fair way offshore, loosely in the company of two Great Crested Grebes. The diver submerged and anticipating where it might re-surface I walked another thirty metres along the perimeter track and sure enough the diver surfaced roughly where I had anticipated and crucially much closer to me. Now for some photos.

It fed intermittently but for the most part lethargy held sway as it drifted dreamily on the water with eyes closed and in no apparent hurry to feed or do anything but idle the time away.

It indulged in some light preening, rolling over onto its side in the water to reveal pristine white underparts, then came a bit of snorkelling, where it dipped only its bill, forehead and eyes under the water but did not dive. Presumably it was looking for passing fish.

This latest individual to visit the reservoir is a juvenile, as are the majority that arrive here, told by the pale fringes to its upperpart feathers which produce a  neat  and distinctive scalloping effect. A plumage of predominantly greyish brown and white was evident for most of the time in the dull light but when the sun made a belated entrance the bird was transformed as head and neck were rendered a paler brown, highlighting the wine red eyes. The red in their eyes is a pigment in the retina that filters light below the water and aids the diver as it hunts its prey below the surface.

Its large bill and  head contributed to an overall impression of a big, bulky bird, almost ponderous in its movements as it cruised the reservoir. It is a bird that has evolved to live an almost exclusively waterborne existence. When it did submerge there was no hasty Cormorant like jump and dive but rather a bend of head and neck and an elegant glide below the surface.

Great Northern Divers do not breed until they are three years old so this bird will not gain its adult breeding plumage until 2025.They do not breed in Britain, only coming here from October to May to mainly winter on the coast but sometimes can be found inland on sizeable lakes or reservoirs.This bird possibly was blown inland by the gales of last weekend and found sanctuary at Farmoor as have others that have been discovered inland lately, such as at Frampton and Draycote in the neighbouring counties of  Gloucestershire and Warwickshire respectively.

Worldwide the majority of the population breeds from the Aleutian Islands, Canada and northern USA to southern Greenland and winter along both the western and eastern seaboards of the USA as far south as Mexico. In North America they are known as Common Loons and their eerie haunting call is a favourite mood creator for countless films, sometimes in a wildly inappropriate context.

The only European breeding population is in Iceland which is probably the origin of the bird now at Farmoor. Around four thousand individuals annually winter around Britain,  mainly off the coast of northwestern Scotland with others wintering on the coasts of northern, eastern and southwest England, Wales and Ireland

Let's hope this bird will make its winter home at Farmoor.

They have often done so in the past.

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