Friday, 27 August 2010

Don’t blame the crows.

Redshank, Fox predating a nest at night, the fabulous Turov Marshes in Belarus.

I’ve spent too much time in the office recently. Today’s office was at Berney Marshes, looking at the results of this year’s breeding season for waders. On the face of it, it’s been a fairly good year with 157 pairs of Lapwing and 130 pairs of Redshank. However, productivity is the key issue and this was way below target. Berney is at the leading edge of our understanding of breeding waders, with much research being undertaken. Data-loggers placed into nests chart the time of day a predation event takes place. 92% of Lapwing and 71% of Redshank nest predations occur at night. This points to mammalian predators rather than avian.  Nest cameras on some nests take snaps as the predator strikes. The majority of snaps of Lapwing nest predations show Foxes as the predator. Perhaps contrary to general perception, most studies do not show crows as a major nest predator.

Once the nests hatch, chicks are a tasty snack for a wider variety of diners. At this stage, bird predators are a more significant predator and may include Marsh Harriers, Kestrels, Grey Herons or Buzzards. But predation is a highly complex issue, with a whole range of interacting factors. Habitat quality, weather, wetness and the abundance of prey (for both predator and prey) all play a part in the story.

Fox activity within a site has been shown to vary considerably between years. This may be related to the abundance of primary prey such as voles. Removal of Foxes is not always the answer, for example, it may allow mustellid predators to increase instead.
Many natural floodplain systems that have high numbers of breeding waders have cyclical patterns of productivity. They are good for waders some years, good for wildfowl, grebes and terns in others. Research on our reserves is instructive but understanding how these natural systems work is just as important. We cannot expect our nature reserves to deliver high wader productivity every year, but by managing the factors that are within our control, achieving some success in more years than not should be possible.

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