Heavy weather taking its toll on country's wildlife

It seems that the owl's predicament was due to a collapse in the number of short-tailed voles that are an important food source for many predators like owls. They are common throughout Britain and periodically there are plagues of them, but they are currently in short supply.

It's one of nature's mysteries, but from time to time their numbers dramatically increase over one, two or three years. Just as mysteriously, such plagues suddenly disappear and they become scarce for a while. I suspect the current collapse in the population is due to last year's appalling summer, and that has led to a lot of hungry owls this winter.

Female owls need to be a certain weight before they lay eggs, and they had a particularly poor breeding season last year as a result of not having enough voles to eat.

My friend, who is a keen ornithologist, told me 2012 was the worst breeding year for barn owls he can ever remember and that a lot of the nest boxes he had erected for them remained empty.

Buzzards also eat a lot of voles, and the one that attacked the owl probably did so because he too was starving.

Predators like buzzards have to be very hungry and desperate to consider attacking another predator, even a smaller one like a barn owl, because of the risk of being injured.

Apart from making things very difficult for farmers and reducing their profits, last year's wet summer caused all kinds of other problems in the Scottish countryside.

While bees and butterflies, like voles, have struggled for survival, slugs and snails thrived.

Slugs are causing a lot of damage to autumn-sown crops, but it is the dramatic increase in the snail population, or rather a particular small mud-snail called Limnaea truncatula that has caused major problems for livestock farmers.

That snail is an intermediate host for liver fluke that can cause serious illness and death in cattle and sheep.

Sub-clinical levels of infection leads to dairy cows yielding less milk, while beef and sheep don't grow as fast and take longer to fatten.

Liver fluke have a complicated life cycle that can be briefly explained as follows.

The adult fluke live in the bile ducts of sheep and cattle, damaging the livers of the host animals. They produce large numbers of eggs that pass into the intestines and thence out of the body in droppings. If the eggs fall on dry ground they die quickly, but in wet areas they can remain viable for up to five months.

The development of the embryo within the egg is inhibited by low temperatures, so that eggs tend to accumulate on pastures during the winter and hatch out in large numbers when the temperature rises in late spring and early summer.

From those eggs emerge an active larvae called a miracidium that swims through the water looking for the body of a snail to enter.

There it develops into the next stage called a cercaria, which emerge from the snail to become encysted upon grass leaves. There they wait for grazing sheep and cattle to ingest them, before migrating from the gut to the bile ducts in the liver where they develop into egg-laying females and start the cycle all over again.

The last two wet years have created ideal conditions for both snails and fluke to multiply to unprecedented levels.

Losses among sheep have been high in some areas, despite dosing with flukicides, as the animals soon become re-infected. Indeed, many sheep farmers have started the practice of dosing every three weeks to contain the problem.

Heavy fluke infestation has also led to more barren ewes than usual and fewer twins and triplets.

Early results from ultra-sound scanning of pregnant sheep indicate that many farms are in line to produce a lot less lambs this spring. I know of several farms where scan results are 30% lower than usual.

Of course, scanning sheep is a bit like counting chickens before they hatch, as the weather at lambing has such a big influence on the final results.

Here's hoping for an early, warm spring.