Yellowhammer (Emberiza citrinella)
The Yellowhammer is certainly a territorial species and, because the breeding sites are usually along hedgerows or other thin strips of vegetation, these defended areas are linear. In a study in England, each male’s territory was about 60m long, and stretched up to 10-15m into the adjacent field, covering about 2000m² in all. Other studies in optimum habitat have come up with a similar figure, but in less suitable habitat a territory may encompass as much as 20,000m²; it all depends on how much hedgerow is available and how much ground is covered by the adjacent crop, if any. Perhaps surprisingly in view of this variation, territories are only used for pair formation and nesting, with the birds travelling to neutral areas to find food.
As far as feeding is concerned, the Yellowhammer is a species thoroughly set in its ways. It almost always forages on the ground (e.g. 90% of observations year round), and most of its pecking movements are directed downward. It has a diet of seeds that it greatly favours, such as grasses, and others, such as Crucifers (Cruciferae) that it simply will not touch. In common with all other buntings it hunts for insects during the breeding season, and will pick up berries in late summer and autumn, but that is the extent of its dietary adventure.
Males and females are socially monogamous, although extra-pair copulations are frequent. The most desirable males, and those most likely to sire young outside their formal relationship, are the males with the largest amount of reddish plumage on the face. These are usually older birds that have learnt to seek out plants with right chemistry to produce this hue (carotenoids). Most display is on the ground. The female builds a nest low down, well hidden in vegetation, and after a short incubation period the young leave the nest early, usually before they are able to fly.