Originally posted and adapted from a RSPB Centre for Conservation Science and Vogelbescherming Nederland blog.
Insufficient reproduction as a consequence of predation is a major determinant of population decline in ground-nesting birds. Malcolm Burgess and colleagues discuss their latest study on the effectiveness of using electric fences as a preventative measure.
A common driver of the decline of ground-nesting meadow birds, especially waders, is insufficient reproduction caused by high predation levels. While productivity is low both in and outside of nature reserves, it usually differs between them.
Outside nature reserves, agricultural activities have negative impacts on their breeding success and are the main cause of low productivity of chicks. Within nature reserves, where the negative agricultural impacts are minimized, predation of nests and chicks affect nesting success and account for the low productivity of nests.
Our study looked at breeding wader populations in two nature reserves in England and the Netherlands where previous monitoring data showed us that red foxes were the main predators of wader nests as well as a predator on chicks. We investigated the effectiveness of temporary ditch-side electric fencing used in both these countries in efforts to reduce nest and chick predation.
Excluding the fox
We used temporary ditch-side electrical fences covering an area of 62 hectares in England and covering 107 hectares in the Netherlands to exclude foxes from the main wader nesting areas during the breeding season. We monitored the predator dynamics before and after fencing, which showed us that foxes were successfully excluded from areas with functioning electrical fences, and the nests of black-tailed godwits and lapwings across both reserves.
Both study sites across all years showed that godwit and lapwing nest survival was substantially higher within areas enclosed by ditch-side electric fences. Brood survival, which was assessed for godwits in the Netherlands, was also higher within the fenced area across all years; likely a result from the reduced number of foxes accessing the fenced areas.
Our study therefore demonstrated that electric fencing – provided that it is regularly maintained along its entire length and for the entire breeding period – has a positive effect on nest and brood survival.
Survivors on the move
Wader broods remained inside the larger fenced area in the Netherlands (107 ha) but moved out of the smaller fenced area in England (67 ha). We therefore recommend fencing an area as large as possible, containing high-quality habitats and breeding waders to:
- Protect more nests and especially chicks
- Minimize the area of high quality breeding habitat left exposed to ground-predators outside the fence
- Limit the effect of a potential increase in predation pressure outside the fence
- Increase cost effectiveness, since the cost of fencing material per meter decreases as fence length increases.
However, we also caution against making a fenced area too large: for fencing to be functional it must be well-maintained throughout the breeding season along its entire length. As vegetation grows, electrical earthing occurs and wire stands can also become broken, so regular checks of the entire fence line are required which incurs labour costs.
Fencing: not for the long term
Although our study clearly illustrates that temporary ditch-side electric fencing can improve wader productivity in lowland grasslands, electric fences remain an expensive conservation intervention. We hope electric fences are used as a temporary tool to increase wader productivity, buying the time required to find more natural solutions to reducing predation to apply at landscape scales.
Drivers of predator populations
Our results provide a glimpse into a more sustainable natural solution: the annual variability in nest survival showed the same trend inside and outside of fenced areas, with years of low or high survival inside fences mirroring the outside. This indicates that in both countries, factors other than fox predation and agricultural activities also impact wader nest survival variably across years.
We suggest that factors regulating predator populations and predator behaviour are at least partly responsible for the observed annual variation in nest survival; such factors could include annual variation in the abundance of voles or other prey species, or related elements such as varying local abundance of different predator species, changes to predator behaviour, prey behaviour and vegetation structure as a result of flooding.
A better understanding of what drives predator pressure on ground-nesting birds is the required next step to find more sustainable natural solutions to manage predators at a landscape scale in areas where breeding waders are increasingly concentrated in discrete patches of suitable habitat.
Read the full research: “Do ditch-side electric fences improve the breeding productivity of ground-nesting waders?” in Issue 3:2 of Ecological Solutions and Evidence.