Langholm's birds and voles

Key findings

• Only two hen harrier pairs attempted to breed in 2004, only one breeding successfully.
• Pipit abundance continues to be stable.
• Red grouse numbers have not recovered.

Numbers of harriers have continued to fall since the peak in 1997. In 2004, only two pairs attempted to breed (see Figure 1), well below the 13 pairs for which the Langholm Special Protection Area (SPA) was designated. One of the pairs failed during incubation when the clutch of five eggs disappeared. The second pair successfully reared three chicks from a clutch of six eggs. With increasingly long data sets now available to us, some of the relationships described between hen harrier numbers, breeding success and their chief prey appear to have changed.

Few harriers turned up to breed in 2004 in spite of high vole numbers (see Figure 2). For the last four years, vole abundance has been a poor predictor of both the number of harriers and their subsequent breeding success. The two breeding females in 2004 were the same as those that bred in 2003, suggesting that either there were few potential recruits or Langholm was no longer attractive.

Figure 1. The number of breeding male and female harriers at Langholm, 1992-2004

	Males
	Females

Figure 2. Numbers of small mammals and pipits at Langholm in spring

	Pipits (right axis)
	Small mammls (left axis)

Small mammal data are presented per 100 trap nights. In 2001, data were collected six weeks later than usual owing to Foot & Mouth Disease

Meadow pipit abundance has been stable over the last five years and now appears to be at levels similar to those observed at the start of the study. Over the 13 years, pipit abundance has been negatively correlated with the numbers of breeding female harriers, suggesting that harriers themselves may be regulating pipit abundance.

Despite fewer harriers, red grouse abundance has not recovered. Counts on 10 areas, each of 50 hectares, produced an estimate of only 4.4 and 4.8 grouse per 50 hectares during spring and summer respectively (see Figure 3). It is likely - but not proved - that in the absence of gamekeeping, grouse numbers may be limited by predation from foxes and crows. Numbers of predators have increased since grouse keepering on the moor stopped in 1998. Our data on carrion crows show a steady annual increase over the last five years.

Unfortunately, we have no measures of fox abundance, except numbers killed, for the period of the Joint Raptor Study. In 2002 we started counts of fox scats along 29 kilometres of transects walked monthly. These show an increase over the last three years. It is likely that higher numbers of predators following cessation of keepering will be impacting upon ground-nesting birds, including both red grouse and hen harriers.

Figure 3. Average number of red grouse (young and adults) counted at Langholm on 10 50-hectare areas in July from 1992 to 2004