Puzzling Garden Warbler

Enjoyed a superb ringing session yesterday morning with 43 birds trapped at Lower Bruckland Ponds.  I never knew this place was such a fuel station for migrating passerines, but clearly it is.  As ever with ringing I wouldn't have had a clue half these birds were there without the nets. The more ringing I do the more I realise field counts are way off the mark, especially when it comes to migration.

It was mostly Warblers; 11 Chiffchaff, six Willow Warbler, one Blackcap, one Whitethroat, one Sedge Warbler and best of all a Garden Warbler.  Garden Warblers are scarce around here, so it was a complete surprise!

What a beaut!

This is only the second Garden Warbler I've ever handled (the other a spring bird) so am not experienced in ageing them. In fact I thought it was a 3 (this years young) at first, until I looked closer at its eyes...

The reddish tones to the iris makes this an adult (age code 4), would be more grey-brown if it was a 3.

Another look at the tail showed that although the feathers were quite pointy tipped, they're broad and abraded...

Not too sure what's going on with the tail though to be honest...

The main reason why I thought it was an young bird was because of that darker and obviously fresher central tail feather.  Many first-year passerines moult the odd or a few tail feathers during their post juvenile moult, which is what I thought had happened here - but other features make this an adult bird so that can't be the case!?  Also look at the middle tertial at the top of the photo, that's another darker and newer feather.  I keep looking at the other central tail feather too because to me that looks almost like a juvenile feather, much browner and narrower than the rest of the tail. Could this be a '5' (born last year) that failed to moult its two central tail feathers in Africa during the winter, but has since replaced one of them!?  

I really hope someone experienced with the moult cycle of Garden Warblers reads this and gives me their thoughts. I am probably way of the mark but surely it can't be a younger bird with an iris that colour and so much wear on the feathers??

Thankfully having handled many ten's of Sedge Warblers it was easy to age this bird as an adult (age code 4)...

Sedge Warblers didn't breed at the Ponds this year so it's definitely a migrant.

Looks like we are in for a few wet days now....