Predator control and moorland birds

Key findings

• The Upland Predation Experiment has completed the final year of collecting breeding success data and has one more spring of breeding abundance data to be collected. The analysis of all the data are in progress from which firm conclusions will be drawn.
• Gamekeepers continue to reduce abundance of foxes and crows on the long-term keepered site and on the new keepered site. Fox and crow abundance have increased to pre-keepering levels where we have stopped controlling them.
• Waders and meadow pipits show a tendency for greater breeding success on sites with predator removal, but the trend in numbers of breeding pairs is not yet clear.
• Black grouse and grey partridges also show a tendency for better breeding success in the presence of predator removal, but the low numbers of these species means that analysis may not be conclusive.

2007 was the seventh year of the Upland Predation Experiment based at Otterburn in Northumberland. This project, funded by the Uplands Appeal, aims to test whether predator removal by moorland gamekeepers (ie. killing foxes, crows, stoats and weasels) improves numbers or breeding success of moorland birds other than red grouse. Species of conservation concern in the UK, such as golden plover, curlew, lapwing, skylark and black grouse, are of particular interest. The project consists of four plots, each about 12 square kilometres (1,200 hectares), on which bird numbers and breeding success have been monitored since 2000.

There are two long-term plots which have remained under the same regime for the duration of the project; Ray Demesne has a full-time keeper, and Emblehope acts as an unkeepered comparison (see Figure 1). The other two plots were switched over, so that Otterburn had a fulltime keeper from autumn 2000 to autumn 2004, and Bellshiel was the unkeepered comparison. In the autumn of 2004, predator control started on Bellshiel and stopped on Otterburn. The switch-over allows us to look at breeding success and abundance on the same plot with and without predator removal.

Predator indices from 2007 on Ray Demesne continue to indicate low numbers of all the main predators compared with the long-term unkeepered plot. In this third spring since keepering started on Bellshiel, the indices for foxes were 78% lower (from foxes seen per hour during spring lamping) and crows 87% lower (from carrion crows seen per hour on counts from March to August), compared with the average during unkeepered years.

The stopping of predator control on Otterburn was linked to an increase in foxes to pre-keepering levels, and to an increase in crows, but this is 25% lower than in 2000 before keepering started. Although stoats and weasels are also culled on the predator removal plots, the abundance indices show no consistent trends. The abundance of large raptors (peregrine, hen harrier, goshawk and buzzard) is similar across all plots.

Figure 1. Diagram of the experimental design of the Upland Predation Experiment

	Keepered
	Unkeepered
	Break in keepering and data collection in 2001 owing to Foot & Mouth Disease

On Ray Demesne in the years with predator control, 53% of the 247 nesting attempts by curlew, golden plover and lapwing were successful compared with 28% of the 39 nesting attempts in 2000 without predator control (see Figure 4). On the unkeepered Emblehope plot (see Figure 5), only 12 (21%) out of 56 nesting attempts by waders were successful over the same period. In 2007 only two (6%) out of 31 nesting attempts by waders were successful on the Otterburn plot, compared with 61 (71%) out of 86 attempts in the years when the plot was keepered (see Figure 2).

The opposite trend occurred on Bellshiel (see Figure 3) with five (63%) out of the eight wader nesting attempts were successful in 2007 compared with only four (8%) out of the 51 attempts during the unkeepered phase. Compared with numbers of breeding pairs in the baseline year, golden plovers on Otterburn and lapwings on Ray Demesne may have increased slightly, but curlews declined on all plots during the first half of the experiment (see Table 1).

On Otterburn since 2006, numbers of curlew have been stable. Meadow pipits seem to breed better with predator control, but the small number of nests that we find each year (on average 60 nests across the four plots) means that this trend will become clear only with more data (see Figure 2). Meadow pipit abundance shows no trend in relation to predator control, with numbers generally increasing regardless of treatment.

For all gamebird species, breeding success in 2007 was poor because of weather. Over the whole project, black grouse hens had on average 0.7 young per hen (18 hens) without predator control, but 3.9 young per hen (15 hens) with predator control. On Otterburn, grey partridges produced 4.9 young per pair (24 pairs) without predator control and 6.9 young per pair (43 pairs) with predator control. We have more data for red grouse and over the duration of the project on average 84% of hens had broods on Ray Demesne in years with predator control compared with the unkeepered plot, Emblehope, which had an average of 44% of hens with broods over the same time period.

Our findings suggest that predator removal may improve the breeding success of some species of ground-nesting birds in addition to red grouse. By the nature of the study, the numbers of pairs of most species are small and therefore demonstrating effect on breeding numbers is difficult. The figures and conclusions in this report are provisional. A final analysis of the project will be completed in 2008.

Figure 2. Otterburn plot: percentage of pairs that fledged young for curlew, golden plover, lapwing, meadow pipit and red grouse, 2000-2007 (no data for 2001 owing to Foot & Mouth Disease)

Keepered
Unkeepered

Figure 3. Bellshiel plot: percentage of pairs that fledged young for curlew, golden plover, lapwing, meadow pipit and red grouse, 2000-2007 (no data for 2001 owing to Foot & Mouth Disease)

Keepered
Unkeepered

Figure 4. Ray Desmesne plot: percentage of pairs that fledged young for curlew, golden plover, lapwing, meadow pipit and red grouse, 2000- 2007 (no data for 2001 owing to Foot & Mouth Disease)

Keepered
Unkeepered

Figure 5. Emblehope plot: percentage of pairs that fledged young for curlew, golden plover, lapwing, meadow pipit and red grouse, 2000- 2007 (no data for 2001 owing to Foot & Mouth Disease)

Keepered
Unkeepered