Assessing the rook population in the Yare valley has long been a favourite ritual of my springs. Since the nests are coarse bundles of sticks in the bare treetops it is easy to combine the serious census work with the season’s wider pleasures: the sounds of first chiffchaffs or blackcaps, the lemon wings of male brimstone butterflies, and the year’s first glamorous colour from primroses, marsh marigolds and walls of blackthorn blossom.
However, by the time I reached the third of my 30 rookeries, I sensed that this year would be different. A site that had once held 100 nests was completely empty. Thereafter, each old place revealed the new story of absence.
The most telling came in two strips of mainly alder carr that fringe the valley where the rivers Waveney and Yare converge. This is England’s largest area of lowland grazing marsh and, since rooks are primarily consumers of grassland invertebrates, the whole sea-like expanse of uninterrupted green has traditionally been heaven for the birds.
There are six rookeries either side of Haddiscoe Island, which average 283 nests each. In combination and until 2007 they held 1,697 pairs, probably the highest rook density in East Anglia. Ten years later their combined total is 696, a fall of 59%.
The most compelling moment was when I reached Thorpe Hall near Haddiscoe, where 340 pairs once nested. Its five-acre alder coppice is probably my favourite rookery anywhere, and in its pomp some of the trees were smothered in a continuous layer of nests.
It is the only site where I’ve found rooks nesting in the tops of hawthorn bushes. Such was their urge to share the raucous, joy-filled traffic that it seemed as if birds would nest anywhere just to be part of it. This spring there is not one.
The decline across all 30 rookeries is not so steep, with a fall of just 42% from 3,253 pairs to 1,890. It is hard to know exactly what has happened during the 10 years, but I suspect it could be drier springs and summers. One fact, however, is definite: something is amiss with the Yare valley rooks.
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