Yellowhammers have experienced a considerable decline over the past 25 years

Yellowhammers (Emberiza citrinella) are resident all year round, except in north and northwest parts of Scotland (Highlands of Scotland and certain lowland areas i.e. Inner Hebrides and Orkneys), where they are summer visitors only. They are a part of the Buntings family, which are characterised to a degree by their finch-like appearance; yet for a slightly different bill structure and flatter heads, they are different. They are also renowned for their lengthy bodies and tails, which give them a memorable aspect. Unfortunately, Yellowhammers have experienced a considerable decline over the past 25 years, and therefore have been classified on the Red List as a species of considerable conservation concern. Much of this decline has been put down to variable farming practicing, such as the sowing of crops in autumn, thus reducing supply over winter. In the UK alone there are 710,000 breeding pairs, which put the population of Yellowhammers at a considerably low level. Yellowhammers feed mainly on seed and insects.

Source: Garden Bird
http://voice.gardenbird.co.uk/all-about-the-yellowhammer/