Originally Posted by Dave Appleton
Really interesting new feature Ashley! Would be interested to know how robust you think this should be, and whether there's any overlap or variation (other than young Willows being black as you've already said).
Last weekend I watched a few Marsh Tits - at least I believe they were all Marsh Tits - and one or two seem to have very slight brownish tones to the bristles. Not as clear as in your photos by any means, but browner than the black cap.
Have a look and see what you think: http://gobirdingeu.blogspot.co.uk/20...arsh-tits.html
Can't respond on your blog post as it doesn't accept anon comments. One other possibility to bear in mind, is if a tit (either species) has been feeding on flowers or catkins with brownish pollen which could change the colour of the nasal bristles.