Grey-headed woodpecker colour. The typical woodpecker markings are small and not particularly conspicuous. It has a grey head with black moustache, and the male has a red crown. It has a shorter neck, slimmer bill and slightly rounder head than the green woodpecker. Calls made by the European green woodpecker and grey-headed woodpecker resemble each other. The far-carrying territorial song of the grey-headed woodpecker is more melodic and cleaner than the explosive "laughter" of the green woodpecker. The call series consists of ten to fifteen utterances of declining pitch and gradual slowing. The verse may appear melancholic and "dying". The territorial song
An Essay on the Nature and Significance of Economic Science on economic methodology in generating a range of tightly-argued, radical implications from a simple definition, for example in admitting an "aspect" of behaviour (rather than a list of behaviours) but not limiting the subject-matter of economics, provided that the influence of scarcity impinges on these (pp. 16–17). The broad behavioural definition is credited for its consistency with the expanding boundaries of economics decades later. In this Robbins both narrows the definition of economics, thereby demonstrating the usefulness of deduction, and opens up the subject-matter of economics. Robbins's "Essay" is one of the most-cited works on the methodology and philosophy of