Thursday, 3 March 2011

Squelch index

Breeding waders will occupy a lot of work time over the coming couple of months. Pre-season reflection has involved reviewing the current state of our knowledge and updating species action plans, and the Snipe has received a lot of attention.

There has been a massive decline in numbers, with the Snipe now almost entirely restricted to nature reserves in middle England. 90% of Snipe now breed in just 3% of the available land. Take Hertfordshire as an example. Looking at ‘The Birds of Hertfordshire’ (Sage 1959), the opening line states “There is little doubt that the Snipe is a widespread breeding bird over the county as a whole”. Nowadays, there is not one single breeding pair, the last confirmed breeding was in 1998.

The problem is the ever drier countryside. Snipe require soft soil conditions where high water tables enable them to probe for worms, which form 90% of the diet. As the soil dries, worms go deeper into the soil and it becomes harder to probe. There is a link between Snipe success and late summer available worm biomass.

Snipe have a long breeding season - but only if habitat conditions remain favourable. Early nests have a higher predation rate, so a female Snipe that starts early and can get in at least two nesting attempts is more likely to raise young. An incubating female Snipe will feed for 10 minutes or so every hour or so. Ideally she will walk off the nest and feed in the near vicinity. If soils are hard, she may have to fly to feeding areas and ultimately it is the hardness of the soil that determines when she stops breeding. When the eggs hatch, the male will take the first two chicks, the female the second two. Unusually for waders, Snipe feed their chicks. If conditions are good, the adult will feed both, in poor years just one, or none, will survive. Enter here the Squelch Index. If you walk across the grass and your weight causes water to ooze up out of the ground, it is likely to be good for Snipe. The Squelch Index must remain high well into July or even August to allow Snipe to have a good breeding season. Most of the countryside is now rock hard.

Add to that the problems of grassland management - nest trampling by livestock (1+ cow per hectare results in >40% of nests being lost) and of grass mowing before August, and you will understand why the Snipe is between a rock (hard soil) and a hard place.

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