tube toward the base of the platform. Rooks also seemed to understand the idea that a heavier stone will be more likely to knock the platform over. In this same test, rooks showed they understood that they needed to pick a stone of a shape that would roll easily. Rooks also show the ability to work together to receive a reward. In order to receive a reward, multiple rooks had to pull strings along the lid of a box in order for it to move and them to reach the reward. Rooks seem to have no preference regarding working as a group comparative to working singly. They also seem to have a notion of gravity, comparable to a six-month-old baby and exceeding the abilities of chimpanzees. Although they do not use tools in the wild, research studies have demonstrated that rooks can do so in cognition tests where tools are required, and can rival, and in some circumstances outperform, chimpanzees. Relationship with humans Farmers have observed rooks in their fields and thought of them as vermin. After a series of poor harvests in the early 1500s, introduced a Vermin Act in 1532 "ordeyned to dystroye Choughes (i.e. jackdaws), Crowes and Rokes" to protect grain crops from their predations. This act was only enforced in piecemeal fashion, but passed the Act for the Preservation of Grayne in 1566 that was taken up with more vigour and large numbers of birds were culled. Francis Willughby mentions rooks in his Ornithology (1678): "These birds are noisome to corn and grain: so that the husbandmen are forced to employ children, with hooting and crackers, and rattles of metal, and, finally by throwing of stones, to scare them away." He also mentions scarecrows "placed up and down the fields, and dressed up in a country habit, which the birds taking for countrymen dare not come near the grounds where they stand". It was some time before more observant naturalists like John Jenner Weir and Thomas Pennant appreciated that in consuming ground-based pests, the rooks were doing more good than harm. Rookeries were often perceived as nuisances in rural Britain, and it was previously the practice to hold rook shoots where the juvenile birds, known as "branchers", were shot before they were able to fly. These events were both a social occasion and a source of food (the rook becomes inedible once mature) as rook and