Whilst ringing at Sabkhat Al Fasl on 17 March 2017 we caught two Chiffchaffs with one appearing to be the normal abietinus type and the one a rather duller paler looking bird, recalling slightly Siberian Chiffchaff tristis. I was uncertain of its racial identity so sent the photo to Alan Dean who has extensive knowledge of these birds. Alan mentioned the bird showed the right shade of brown in the upperparts but only a hint of buff wash on the breast and flanks. There is a lack of yellow away from the ‘shoulder’ and wing-edges and a lack of olive in the crown and mantle matching tristis. Alan also mentioned the bird appears greyer (less brown) above and whiter (less buff) below, but at this time of year tristis is in body moult (also some tertials and tail feathers) and can appear like the bird I trapped. I was completely unaware that the plumage changed so much due to moult in the spring. The bill and legs often appear very black but this feature is variable. If the bird calls the most distinct call is a thin, piping monosyllabic ‘peep’, but this bird was not calling. The Siberian Chiffchaff is a vagrant to Saudi Arabia with this bird being the second record for the Country after another bird trapped and ringed at the same location in January 2015. Records are rare or very rare from Kuwait (probably no confirmed records), Qatar and the UAE but they are regular wintering birds in Oman. Identity of Chiffchaffs in the Middle East is very complicated with Mountain Chiffchaffs nearby, which look quite like tristis, and a series of taxa with intriguing combinations of abietinus or intermediate plumage but tristis-like calls (the brevirostris/caucasicus/menzbieri group). Alan Dean who is an expert on many things including Chiffchaffs suggested it may be a tristis but said he was unfamiliar with the brevirostris/caucasicus/menzbieri subspecies at this time of year and sent the photos onto Jose Luis Copete. Jose Luis very kindly commented on the bird as well, indicating it was probably a tristis and ruled out other Chiffchaffs occurring in the Middle East as they show green tones on the mantle and as well as evident traces of yellow below. Jose Luis also added that brevirostris shows less green and has a longer primary projection which the trapped bird does not show. He also sent me his paper on Iberian Chiffchaffs with many photos of various subspecies and my bird clearly matches Siberian Chiffchaff rather than the other possible subspecies. I would like to thank Alan and Jose Luis for their very helpful comments on this bird and taking the time to answer my question on its racial identify.