In search of otters

The possibility of otters along the Ock has intrigued me for a while - apparently mink used to be common, but something must explain why it is now a stronghold of water voles and young moorhens (another favourite of mink) and otters have been reported along the Thames at Iffley meadows and at Radley Lakes in north Abingdon. Also, BBOWT have reported that an otter spraint has been found at one of their reserves through which Sandford Brook - a tributary of the Ock flows. 
So I've been checking out various possible places where otters may leave spraints, which they use for marking territory and beneath the bridge, where the Ock flows under the A34 I found this:

It is defiantly, not dog (I've seen and stood in enough of that to know what that is), but it could be an otter spraint or mink scat.  There are two tests to tell them apart:

1. Smell: An otter spraint can smell of jasmine or lavender , a mink scats just smells awful.
2. Contents: An otter spraint will contain fish bones and scales, whilst a mink scat contains mammal fur.

I didn't recall in horror when I smelt it, so it probably wasn't mink, so I took it home and a dissected it on the kitchen table - the contents of it are obviously fish:

Whilst dissecting, it produced an even stronger grassy smell, definitely otter.

The territory of an otter can vary - depending upon the size of the population and the abundance of food - from 1 to 20 miles, so this could be the same otter that was reported by BBOWT - if it is, then it may risk crossing the Marcham road, a busy road to the west of Abingdon.

The return of otters to English water ways has to be one of the conservation success stories of recent years. It was almost extinct in central England with only a significant population in the west  and fragmented populations elsewhere.  It was not until the banning of certain pesticides along with the 1979 otter hunting ban has the population recovered and this record of a spraint can be added to the increasing numbers recorded elsewhere in Oxfordshire.

Hedge Life

Although they look bare:

 The hedgerows on either side of Mill Road are alive with the sounds of songbirds.  A Dunnock, a rather drab little bird has a wonderful song:

So does the Robin, previously a regular in our garden, this year they have been conspicuous by their absence, so it's good to see the a few of them singing in the hedge.

Birds are not the only sign of the arrival of spring, a clump of snowdrops have sprung up under the hedge.

Great crested grebe

This is a first for me on the river Ock, a great crested grebe

I suspect this one has migrated from the coast and is just stopping off before finding a suitable lake,  where they can frequently be seen and where they breed and raise young during the spring and summer.  I imagine if I go back tomorrow it may not be there.
It's easy to take grebes for granted, they are now fairly common and most large lakes will support at least one pair, I saw two on Longmead lake today.  

But back in the Victorian era they were nearly driven to extinction as their splendid plumage was prized for hats and clothing.  In 1860, the population was reduced to 42 breeding pairs.
To protest against this the 'Fur, Fin and Feather Folk' group was formed in 1889, changing it's name in 1904 to 'Royal Society for the Protection of Birds', which now has over 1 million members - including myself
The RSPB now put the population of great crested grebes as 9,400

References
RSPB: http://www.rspb.org.uk/about/history/
Arkive: http://www.arkive.org/great-crested-grebe/podiceps-cristatus/info.html
RSPB Handbook of British Birds

First water vole post of 2010....

The river is still very high (but not on flood watch), as is the ditch running through the centre of the Ock meadow

Which itself is water logged:

Previously, both the river and the ditch have been locations of water voles in 2009, but as the pictures show, it's very unlikely that there are any water voles there now.

However, on Sandford Brook, flowing to the north east of the Ock meadow there are what looks like water vole burrows in the bank of the stream:

This is the site where I saw signs of feeding last year:

http://viewsoftheock.blogspot.com/2009/06/return-to-stream.html

If these are water vole burrows, they may not be inhabited and could be remains of a extinct colony.

But a close up of one of them may show signs of feeding and possibly footprints

Perhaps not enough evidence to yet make a conclusion, but it is somewhere to keep an eye out as spring approaches.

River foam

The high water at the weekend  has resulted in foam being produced on the river along the Ock valley walk:

I've noticed this before on the Ock and other rivers and thought this blog would be an opportunity to try and research it.  The foam seems to be made by surfactants - 'a substance that reduces surface tension' (Oxford English Dictionary).  The resulting reduction in surface tension and the faster flowing water creates bubbles which are moved by the wind and the currents to the calm parts of the river where they accumulate - resulting in the foam, in this case forming by one of the weirs.

There appear to be two possible causes of these surfactants,  natural organic material - decomposing plants and animals, the rate of this could be caused up by an increase in temperature or pollution or man made material - detergents for example.
As there is not a lot of it  and there has been a sudden increase in temperature and water flow, coupled with the lack of industry along the river (especially any which are likely to produce detergents) it is probable this foam is natural - although it doesn't look like it.  I hope to go back at the weekend to see if it had dispersed. 

This article proves a remarkable amount of foam can occur naturally (if a man-made dam is considered natural) without any pollution: http://www.dundeeonline.com/articles/12.1.2003.html

As always, if anyone knows anything more about this, I'd be very interested to hear.

References:
http://www.in.gov/idem/wqsurvey_025surfacefoam.pdf
http://www.duluthstreams.org/understanding/foam.html

After the snow...

As expected, now the snow has almost melted, the river is very high

And it appears to have burst it's banks, causing slight  flooding on the Ock meadow

The ditch running along the Ock meadow is also very high, contributing to the flooding:

On the meadow itself are a series of holes, maybe made by field voles?

And the predators are out, making the most of the first feeding opportunity for nearly two weeks. A heron by the ditch - maybe after a displaced water vole?

A kestrel seeking out small mammals on the meadow

A  flood watch has been issued for the Ock

http://www.environment-agency.gov.uk/homeandleisure/floods/34681.aspx?area=061WAF17Ock&page=1&type=Town&term=abingdon

And 32 other rivers in the 'Thames' area:

http://www.environment-agency.gov.uk/homeandleisure/floods/34678.aspx?type=Region&term=Thames

Update 18/1/2010: The river Ock in no longer on flood watch


http://www.environment-agency.gov.uk/homeandleisure/floods/34681.aspx?area=061WAF17Ock&page=1&type=Town&term=abingdon

 

Garden Birds

With the cold weather continuing, numerous birds have visited the garden. Some regulars, some not
A first for our garden are redwings.  A winter migrant that is normally found in hedgerows and judging by internet postings  they (and fieldfares) are moving into gardens in their droves.

Collard doves have become more frequent visitors over the past few months, especially now they have mastered the bird feeder:

Blackcaps are very rare visitors, so I took the opportunity to try and get a picture - even if it meant I was late for work

Two goldfinches enjoying the same feeder some time later, although the number of goldfinches in our garden has declined.  In previous years we've had up to 10 , now we are lucky if we get a maximum of 4 (maybe they've just found a better source of food).

This is all practice for the RSPB's Big Garden Bird Watch at the end of the month: http://www.rspb.org.uk/birdwatch/
It will be interesting to see if the visiting redwings and fieldfares remain long enough to be counted and to see if anyone else has seen a decline in goldfinch numbers.

Since my previous post, several articles have subsequently been written about this spell of cold weather including this one by Simon Moss: http://news.bbc.co.uk/today/hi/today/newsid_8455000/8455832.stm
It seems I am wrong about the impact on some birds of prey, Simon Moss argues that the cold weather will increase their food supply as more animal succumb to the cold.  Although I haven't seen any red kits or buzzards in recent weeks - perhaps I have not been looking hard  enough.