The effects of predator control on breeding moorland birds

Key points

• Lapwing, golden plover, curlew, red grouse and meadow pipit bred on average three times more successfully when predator control was performed.
• As a result, the populations increased in subsequent years.
• In the absence of predator control, the populations declined.

Background

Control of generalist predators such as foxes and crows is commonly performed to protect livestock and game birds, but its potential to contribute to conservation of other wildlife is not well understood. Birds that nest on the ground such as curlew, lapwing and golden plover are particularly vulnerable to predation, and long-term fox and crow populations increases in recent decades may have increased predation pressure.

What they did

Fletcher and colleagues ran an experiment for eight years to look at the effects of controlling predators on five species of ground-nesting birds that breed on moorland. They included four different moorland sites, in two pairs. In one pair, one site received predator control for the whole experiment and the other did not. In the other pair, one site received predator control for four years and one did not, then the sites were swapped for the remaining four years of the experiment. On all four sites the numbers of breeding birds and estimates of breeding success were made.

This approach allowed them to compare how the birds did on the same piece of moorland when predator control was or was not happening. They could also compare between the two areas that did and did not receive predator control on the same year.

What they found

Predator control techniques reduced the abundance of foxes by 43% and crows by 78%, but no change was detected in already low stoat and weasel abundance.

Birds were monitored to see how many breeding pairs fledged young each year – this means that the pair successfully reared at least one of their chicks until it was able to fly.

For lapwing, golden plover and curlew, more than three times as many pairs fledged young when predators were controlled than when they were not. For meadow pipits, twice as many pairs fledged young.

During the period of predator control, there was an increase in breeding success that led to a significant increase in numbers of lapwing and golden plover the following year. As curlew take longer to mature to breeding age, a three-year lag period was allowed, and after this a similar positive response to predator control was detected. When predators were not controlled, the abundance of these species dropped – there were fewer birds each year than there had been the year before. The table below shows the size of these changes. They did not detect any effect of predator control on meadow pipit, skylark or snipe.

What does this mean?

In summary, when predators were controlled, lapwing, golden plover, curlew, meadow pipit and red grouse all bred better than on the same moorland when predators were not controlled. For lapwing, golden plover, curlew and red grouse this led to more birds breeding on the moor in subsequent years. Where habitat is favourable, the application of predator control may be important for conserving some ground-nesting bird species.

Read the original abstract

Fletcher, K.L., Aebischer, N.J., Baines, D., Foster, R., & Hoodless, A.N. (2010). Changes in breeding success and abundance of ground-nesting moorland birds in relation to the experimental deployment of legal predator control. Journal of Applied Ecology, 47: 263-272.

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