This RSPB page detailing their Cirl Bunting Project gives more details about the reasons for their decline and what is being done about it. The Cirl Bunting
is like a small Yellowhammer, 15-16.5 cm in length (wing-span 22-22.5 cm) with a thick seed-eater's bill. The male has a bright yellow head, with a black crown, eyestripe and throat, and a greenish breast band across its otherwise yellow underparts, and a heavily streaked brown back. The female is much more like the Yellowhammer, but has a streaked grey-brown rump and chestnut shoulders.