Deserts, difficult and demanding to live in, the people of the Arabic Peninsula needed to know the detailed facts of the nature surrounding them. With the expansion of caliphate and the urban cultures that followed in the urban centres, such a knowledge was not a necessity anymore, but it constituted one of the two main sources for the interest in nature which arose among intellectuals, the other being the translated works of mainly Aristotle’s zoology. These two sources were integrated in the description of nature and augmented with original observations. The chapter on birds from the encyclopaedia of the Iḫwān al-Ṣafāʾ is presented here as an example of this development.