Wednesday 12th January 2022

Tristis Chiffchaff

The first ringing session of the year, with perfect weather, wind strength and direction. The reedbed is currently both unproductive and underwater so I concentrated on the area downwind of the sewage works. This proved to be a good call and 65 birds were trapped with 44 Chiffchaff, including 3 tristis and 2 UK control collybita. Also 6 Goldcrest, 3 Bullfinch, 3 Blue Tit, 3 Great Tit, 3 Robin, 1 Dunnock, 1 Blackbird and 1 Wren.

Two of the tristis were classic birds with olive limited to the margins of their flight feathers and tail and completely lacking in yellow tones except in the underwing coverts. A few years ago, the third bird would have been relegated unceremoniously to the form colloquially known as fulvescens, showing more olive on the mantle, a hint of yellow in the supercilium, undertail coverts and around the thighs. It was assumed that these birds were intergrades from the zone of overlap between tristis and abietinus. However, all the mtDNA analyses done on these birds for me by Martin Collinson’s team at Aberdeen University have come back as 100% tristis. Whilst this method only gives the maternal ancestry, I think it unreasonable to assume that hybridisation only occurs between male abietinus and female tristis.

The current thinking seems to be that if it looks like a tristis, sounds like a tristis and has tristis DNA then that’s what it is. Fortunately, all the birds were attracted into the net using a tristis song lure and gave the soft, short ‘peep’ call on release, which, as far as I am concerned seals the deal! I have posted photos of all three birds and a collybita Chiff below for comparison purposes.

tristis 1 with more olive than usual and a hint of yellow in the eyestripe.
tristis 1 – note hint of yellow in the undertail coverts and around the thighs.
tristis 1 – yellower underwing coverts than usual
tristis 2 – a ‘classic’ example
tristis 2 – note lack of yellow tones apart from faint underwing coverts.
tristis 3 – another ‘classic’ bird
tristis 3 – no yellow here either
collybita Chiff for comparison
collybita breast and underwing coverts

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