Monday, 18 July 2011

The A B C of wet grassland management

Well, the S, W, P of grassland management actually – sward, water and predation. With the breeding season fading fast, last week involved a fair amount of reviewing how it all went. Breeding waders have fared badly this spring on a lot of wet grassland reserves due to the dry conditions and the resultant increased impact of various predators, as noted here before.

However, Cantley Marshes is a shining example of a careful and considered approach to understanding the issues on a site and finally delivering the goods. When I first looked at Buckenham and Cantley in 2005 it supported 119 pairs of waders, but numbers were declining and Lapwing productivity was way below the target figure of around 0.7 fledged chicks per pair to maintain a stable population.

An initial habitat ‘audit’ identified clear problems: the sward was too long and dominated by rushes, and the grassland was drying out too early in spring. A programme of rush control and improved grazing (with clear targets for spring sward height) was put in place. Improvements were made to the water regime; low spots hemorrhaging water into ditches were identified and blocked, and additional water features were created to hold winter rainfall.

With the habitat looking better, waders increased, but not to target levels and productivity remained low. Two years of study of predation rates followed. With data loggers placed in the nests (to determine the time of predation) and nest cameras overlooking selected nests, it was clear that predation was an issue. Surveys of crow and fox numbers showed both to be above critical levels, but with the loggers pinpointing nocturnal predation and the cameras taking lovely snaps of Foxes, the main culprit was becoming clear, although as on other sites, the overall predation picture was complicated and varied from year to year.

2011 was the year when it all came together. It took a while you may say, but this was a careful step by step approach of evidence gathering and problem solving. Achieving ideal habitat condition is critical. Following further tinkering with the water regime, the fields held high water levels into the spring despite the dry conditions. With these high water levels reducing the ingress of ground predators, combined with a targeted early season reduction of Foxes, the number of waders and their hatching success both increased. The end of season result was a total of 161 pairs of waders and a minimum productivity total of 0.8 chicks per pair of Lapwings.

Waders are under pressure in the lowland wetlands where they were once so common. But how many of our wet grassland nature reserves simply fail their S W P?

1 comment:

Paul Tout said...

I'm glad to see that the RSPB is coming round to targetted predator reduction. Here it's obvious, that as with Carrion Crows, killing a fox before February or March is of absolutely no use whatsoever. I used to tell the people managing partridges in Italy: let the winter do its worst and THEN hit them (crows and foxes) when they're down. I still think there's a lot to be done on crow predation though I accept that you0ve done your homework well in this case. I think they're well in the frame for declines of birds nesting in open dry habitats in this part of Italy, especially Lesser Grey Shrikes and Stone Curlews. I actually don't think the adult (crow) pairs have the time or the firepower to overcome the two (or more) adult shrikes or curlews on guard but the gangs of thuggish subadult crows hang about all summer with nothing much else to do than learn their bushcraft.