I have noticed a great deal of activity in the local rookeries over recent days, as pairs add sticks to their nests and indulge in a spot of petty theft from those left unattended. There is a real sense of excitement, with the first eggs likely to be laid within the next two weeks. Since Norfolk is a county dominated by agriculture it should come as no surprise that we have such a large population of breeding rooks. The most recent survey, carried out by the British Trust for Ornithology in the mid-1990s, estimated that there were 17,600 nests located in 340 rookeries spread across the county. This represents an increase on previous figures, perhaps a reflection of a run of mild winters, coupled with the ban on stubble burning and the increasing number of outdoor piggeries. These last two changes will have increased the amount of food available to these farmland specialists. My own impression is that they have continued to increase and that there are now many more rookeries to be found within the county. Some of these are small, numbering a few pairs, such as the one alongside the B1108 just outside Watton or that close to the heart of Wymondham. Most rookeries sit high in tall deciduous trees and at this time of the year, before bud-burst, the large nests are obvious. Others are in conifers and I recall one in hawthorn scrub at Bunwell. I have also heard of a few rooks nesting on the pylons that run alongside the Norwich southern bypass at Keswick.
Although rookeries may seem noisy, disorganised affairs, there is a structure and hierarchy to them. Dominant birds, typically well-established pairs that have bred together over several seasons, will occupy nests at the centre of the rookery. Presumably this gives them the greatest protection from predators and the elements. Less-experienced pairs, usually young birds, are forced to nest on the periphery of the colony and these are more likely to fail through a combination of position and lack of experience on the part of the birds themselves. Although both members of the pair construct and defend the nest, it is the female who incubates the eggs and broods the chicks. During this period, as Gilbert White noted in his journal of 1775, the male provides the female with food. Although the breeding season diet is dominated by invertebrates, the rook is omnivorous and has developed a reputation for taking grain. Despite this, rooks are tolerated across much of the county, though some are still shot each year and the loud thump of a gas gun remains commonplace. Not that such measures seem to have halted the increase of this wonderful bird.