Much binding in the Marsh!!

 Yesterday was the last day of August and the weather was perfect for the beautifully-put-together team. The first net round was suitably impressive with a good number of Blackcaps and other warblers. On returning from a later round I was met with the news that we had ringed our FIFTH Grasshopper warbler of the season. Since we don't even average one per season this was a really special moment---but the faces of the team betrayed they thought this wasn't going to be the key moment of the day.......

Liz had extracted an 'interesting' bird and Pete and Kev agreed but asked me to open the bag and see what I thought--always an exciting prospect. I took out a bird and after only a few seconds the experience I'd had in Poland over several years with this species confirmed in my mind that we had a MARSH WARBLER !!! I quickly confirmed a couple of key measurements the team had taken then alerted the site's top birder Steve to give his opinion.

This was our group's first and the site's Marsh Warbler and one of only a handful ever seen in Staffordshire ever--so we had to be sure. In the end it was relatively straightforward so I have produced a few pictures to illustrate why it was a Marsh and not a very similar Reed Warbler.

First the whole bird--slighly more olive green tinge rather than browner Reed, especially on the rump. At 70 mm the wings are longer, as is the primary projection--the distance between the longest wing feather and the secondaries. The face is plainer and the bill is marginally shorter with a slightly steeper forehead. There were some additional features:-

In Poland where I have been very fortunate to have ringed dozens, one of the first and quickest features to see is the claw colour. The right hand claws are creamy-white in the Marsh and dark horn colour in the left hand Reed.

One of the definitive features needs a couple of measurements. Firstly the wing length--in this bird 70mm. Second is the length of the so-called notch on the inner web of the 2nd primary wing feather:-

I've shown the measurement with the white lines. In this bird it was 9mm--there is a diagnostic table we use which shows the ration of wing length to notch length--and this confirmed our ID. Simply put Reed has shorter wings and longer notch, Marsh have longer wings and shorter notch!

The colour of the rump is also a useful supplementary feature--but having seen quite a few pictures of the two birds below, cameras vary immensely in the colour shown in the final picture. Fortunately this shot shows a realistic view of the subtle difference. The right hand bird is a Marsh with a slightly more olive tinge to the rump than the more rusty tones of the left hand Reed.

Last but by no means least there was one other feature-- of absolutely NO use in the field. Our friend Rob who rings hundreds of Marsh Warblers in Poland always gets us to check for tongue spots. When reed-bed warblers are in the nest, they have two dark spots right at the base of their tongues which gives the adults a target to aim for when pushing food in. In Reed Warblers these spots last for a few months after fledging--but by this time of year are always lost in Marsh Warblers. This bird had no spots...QED

So we were able to release the bird with a cast iron ID after a relatively short time to allow it to get on with it's life and migration. Who knows where it came from but north eastern Europe would be the most probable given that it's a relatively common bird out there. Perhaps someone--(my friend in Poland??) may re-catch it next summer and put a piece in the jigsaw.......

As the excitement subsided, we had time to reflect on what a great job trainee Liz did in suspecting this was a potential Marsh warbler and bringing it to everyone's attention--nice one Liz!!

The rest of the session quickly got back underway and we ended with a satisfying total of 123 new birds--64 of which were Blackcaps. One of these showed a feature  I've been talking about--the replacement of the crown feathers at this time of year to black in males and brown in females. The latter is tricky to show as sometimes the colour change is a tad subtle--but in this case it's pretty obvious:-

Finally for this post we recaptured a Marsh Tit which demonstrated beautifully an ageing feature which not everyone is aware of given that lots of ringers don't come across many examples of this species:-

I have marked the outer few greater coverts with the white square-and you can see quite clearly they are longer and paler tipped than the same feathers nearer the body. This clearly shows that this bird still retains some of its longer pale-tipped juvenile coverts but has moulted in some of the shorter non-tipped adult greater coverts--proving this was a juvenile bird.

August ended with a bang--September is a month of mass bird movement with many species exiting the UK before bad weather starts so we are hoping for more exciting days in September.