Thursday 10 January 2019

A Great Northern Diver on the River Thames 9th January 2019

Today I drove the length of the county, from my home in the extreme northwest of Oxfordshire, south  to Beale Park which lies by the River Thames just in Berkshire, the river hereabouts forming the county line between Berkshire and  Oxfordshire.

It took about an hour to drive to Beale Park and my reason for going was to see a juvenile Great Northern Diver that was first found on a lake just a few metres adjacent to the river but latterly has taken  an apparent preference for the river and is to be found anywhere along an approximate mile stretch of the river either side of Beale Park and is easily viewable from the grass towpath that runs beside the river.

In pleasant sunshine but chastened by a raw and cold wind I left the car at a deserted and closed Beale Park at just after twelve noon, and made my way along a muddy track, past the lake to the flat grassy towpath. In direct contrast the opposite bank of the river, in Oxfordshire, rose steeply, a thickly wooded slope ascending to the skyline.

River Thames dividing Berkshire from Oxfordshire
The river at this time of year is relatively undisturbed compared to the plethora of craft that take to it in the summer months and similarly the towpath was free of much disturbance. I encountered just a couple of local birders and a dog walker during my two hour visit. This lack of disturbance probably encouraged the diver to frequent the river where the fishing was possibly better than on the lake. 

On reaching the river bank I was very fortunate to immediately come across the diver swimming in the middle of the river, diving for food and, due to its location, currently in Berkshire. I followed it, as by means of a series of leisurely dives, and exhibiting some interesting behaviour, it slowly moved downriver, in the direction of the town of Pangbourne and thus deeper into Berkshire.

Maybe a touch of indigestion?

Note how low in the water it can sink its body.The water is literally washing
over its body behind its neck

'Snorkelling' where it swam along on the surface looking below
the water for any likely fish to catch
Two scullers also coming down river caused it to dive and double back underwater and I then found myself following the diver up river until we were in Oxfordshire! The diver was relatively unconcerned about my presence and continued steadily fishing whilst moving further upriver. Each time it was underwater I tried to move along the towpath to a spot where I anticipated it would surface. Sometimes I got it right and at other times not so, but generally myself and the diver remained in reasonably close contact.

The diver continued feeding for the entire two hours I observed it  and on two occasions I saw, what was for me, a unique event, although subsequent research on my part has shown it is not so unusual. I have watched  countless Great Northern's diving and fishing and they always seem to consume their prey underwater before surfacing but twice this diver brought a large fish to the surface in order to deal with it and then swallow it. The first fish was a Tench, judging by the fins and the diver took some time to manouevre it into its bill in order to swallow the fish head first.The second fish was a Pike which looked a little on the large size but this I believe went down the same way as the Tench

The above two images are of the diver swallowing a Tench

Here the diver has caught a Pike.
For the next couple of hours I discreetly followed the diver along the river, concealing my outline by utilising the clumps of bramble and small trees growing on the bank to disguise my presence to a degree, although the diver knew I was there.

A spot of feather maintenance. Note the length of its body

Preening and showing the intricate scaly patterning of juvenile feathers on its
mantle and wing coverts

Watching a small aircraft passing over
Great Northern Divers are comparatively rare inland and especially so on rivers, preferring to remain on the sea around our coast. or if they do come inland usually finding large reservoirs or open bodies of water more to their liking. Undoubtedly the nearby lake had proved the original attraction as it flew along the Thames Valley. It is thought that most Great Northern's that occur around our coast and inland originate from Iceland.

I watched this large bird, its size making its movements when resting on the water's surface almost ponderous although it is supremely adapted to a virtually exclusive aquatic existence. It has a formidable sized bill that is long, dagger shaped and at this time of year pale grey, requiring a large head and powerful neck to support it. The forehead has a curious ridge of feathers that is very distinctive and looks like a large bump when seen sideways on. 

The diver's long, flat, torpedo shaped body can be held low in the water, so low that water sometimes flows over its back where it joins the neck and the diver and water become almost as one. The legs and feet are placed very far back, almost at the end of its body to give it the power to propel itself  rapidly as it hunts its prey underwater.

This bird is a juvenile, as are most that are found inland, told by the prominent scaling all over the upperparts, each feather immaculate and precisely aligned with its neighbour. Its eyes, prominent in a pale face,  shone ruby red in the bright sunshine and it will be two years before it reaches maturity and commences to breed. 

Inevitably while wandering along the riverbank I came across other waterbirds. Four very wary Mandarin Ducks, two males and two females, and up to now hidden in an overhanging mess of twigs and branches on the far bank that swept down into the cold dark green waters of the river, briefly and unexpectedly emerged from their concealment. As still as a statue, a Grey Heron stood on the far bank, and black, sinister looking Cormorants, craning their sinuous necks in anxiety at my presence, perched on the skeleton of a dead tree, fallen haphazardly across the bank and partially into the water, while Little Grebes swam furtively into quiet backwaters, hoping not to be noticed.

There were many alder trees growing in wetter parts of the hinterland between the towpath and the lake, their twiggy upper branches thick with plump catkins still maintaining a solid and  unopened compactness, but it will not be long before they burst and these had attracted half a dozen Siskins, the males already commencing to sing. A couple of Lesser Redpolls were an unexpected  find, rising up into the sky with their distinctive calls, from a birch tree.

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