Meeting Report: The Dumfriesshire Rook Census and Tracking the Greenland White-fronted Goose

4 November 2016
Dr Larry Griffin (Principal Research Officer, WWT Caerlaverock Wetland Centre)

About 40 members and guests attended this meeting to hear a lecture by Dr Larry Griffin, Principal Research Officer at the Wildfowl and Wetlands Trust Caerlaverock reserve. Dr Griffin's lecture was entitled The Dumfriesshire Rook Census and Tracking the Greenland White-fronted Goose.

The first part of the lecture was devoted to ongoing research on the white-fronted geese, whose global population has fallen from 35,500 in 1999 to only 18,000 in 2015. Small numbers winter in our area on the Ken-Dee marshes and near Stranraer, but this population has also fallen from 1100 to 400 over a similar period. Shooting is not thought to be the problem as this is now banned throughout their range except in England and Wales. Low breeding productivity seems to be a major issue, as only about 20% of pairs normally produce any young. Various possible explanations are being investigated, using satellite-tracking tags to locate the geese in their remote west Greenland breeding areas. These tags can also detect whether a goose is flying, walking or stationary, which in turn can give information on whether it is actually nesting.

One possible cause for the decline in numbers was thought to be competition for nest sites with Canada Geese, which have recently colonised west Greenland, but this is has been discounted as the two species of geese use different areas. Current theories now favour an unfavourable climate cycle. Snowfall in west Greenland follows a fifty-year cycle, and at present it is in a high-snowfall phase which leaves the birds insufficient snow-free time to breed. It is hoped that as the cycle becomes more favourable, goose numbers may increase.

The second part of Dr Griffin's lecture was devoted to the survey of nesting rooks in Dumfriesshire. The first census of breeding rooks was carried out as long ago as 1908, making the Dumfriesshire survey the longest-running of any county in Britain. Rooks can be distinguished from crows by their whitish face and bill, and the shaggy feather 'trousers' on their legs. They breed colonially in trees — 'rookeries', usually deciduous although they will also use Scots pines.

The latest census, in 2015, recorded 13,135 nests in 350 rookeries, a slight increase over the previous census in 2010. However, prior to that numbers had shown a sharp decline, from about 25,000 in 1993 to about 10,000 in 2010, whereas numbers had increased up to 1993. Possible causes for the recent decline include shooting, poisoning, and changes in land use, including increased housing development. Predation of young rooks by ravens or birds of prey may also be a factor. The results of the next census are awaited with interest to see if the recent increase in numbers is maintained.