Out and about and interesting warbler

Dale airfield: 4 Chiffchaff on track up. Flock of 10 Chough and 20 Ravens. 6 White wagtails, 4 Wheatear. Mixed flock of 50 linnet and 20 Goldfinch. Lots of gulls sheltering 150+ GBBs. Only wader was a Ruff in top NW corner (been a good year for these!), it flew off heading in direction of the Gann. Kete-St Anns-Mill Bay. Alba wagtails passing regularly, 3 White at lighthouse. 4 Wheater and Kestrel. Incredibly brief view of what appeared to be a chiffchaff-sized warbler with a yellow rump!!! in the steep scrubby valley by the private quay at the bottom of the row of cottages. Spent 30mins waiting and watching but nothing, nipped down to Mill Bay and then came back for another look.