Watching out for those welcome parasites

EYE ON NATURE:IT'S HALF A CENTURY since the great onset of change from Ireland's era of mixed farming ­– that happily tangled menagerie of livestock (cattle, horses, sheep, pigs, poultry) and patchwork of small-scale crops, managed and rotated in a close-hedged maze of hay-meadows, paddocks and unsprayed arable acres. The sheer complexity of it all, its mix of habitats, animals, plants and farming operations, provided a golden age of biodiversity, a fair human balance with the rest of nature.

Since then, the great cloak of ryegrass, Lolium perenne, has spread across Ireland – 3.4 million hectares of it, or some 80 per cent of our farmland. Its emerald monoculture has replaced natural grasslands and grazed heathland to provide the basic fodder of intensive farming.

What this does to nature became an urgent question only in the wake of Rio’s global agreements. Given the (now scarcely credible) goal of halting the loss of species by 2010, the EU Commission looked for tools to measure the impacts of its farming policies. But even the scientists scarcely knew where to begin. One key meeting, held in Ireland in 2004, agreed only on the priority of finding the right “biological indicators” with which to judge how CAP was performing in the field.

Five years later, Ireland’s Ag-Biota project, funded by the Environment Protection Agency, has come up with some answers. Led by UCD’s School of Biology and Environment and partly manned by PhD research students, it has used widespread field study and experiments at the sites of Teagasc’s grassland research. It confirmed some of Ireland’s losses so far – bumblebees down by half in 30 years, for example, and many birds hit by the loss of hedgerows in which to nest. “Landscape simplification and degradation”, says its report, along with rising use of chemicals, has brought similar declines to those common across Europe.

Birds are a good indicator of landscape change, since farms with a rich range of habitats, bounded by hedges and walls, have the greatest variety of avian species. Dairy farms not only value the shelter of hedgerows, but have an abundance of flies and other dung-loving insects to feed the birds – but not the variety of arthropods of grassland with a greater range of plants and lengths of sward.

“Arthropods” are simply the insects, plus spiders, millipedes, and so on, all with jointed legs – the general multitude of creepy-crawlies that mean so much to the ecosystems of a healthy countryside. How do you choose which to identify and count (for counting is vital both to science and bureaucracy) as a way of judging ecosystem health? In what the Ag-Biota team see as “one of the most ecologically meaningful insights” of their work, they zeroed in on two groups of insects that live by parasitism ­the ruthless-seeming lifestyle that plays such a big part in nature’s population balance and control. Tiny parasitic wasps lay their eggs inside caterpillars and aphids, for example, along with spider eggs and the grubs of dung-breeding flies. Their own abundance and diversity, even in intensive agriculture, gives the strongest indication of how their wider host species are doing.

A second useful group of parasites are the “cuckoo” bumblebee species, thick-skinned in every sense. They are solitary bees that invade the nests of specific conventional bumblebee species, fight off the defenders, and lay eggs for their hosts to rear. They have undergone the most obvious losses in recent years and become another front-line indicator of bumblebee decline.

“Ag-Biota” was coined as merciful shorthand for the title of the final report: “Monitoring, Functional Significance and Management for the Maintenance and Economic Utilisation of Biodiversity in the Intensively Farmed Landscape.” The widely-appeciated value of bumblebees as pollinators gives meaning to “Economic Utilisation of Biodiversity”. We also know the good work that earthworms do as well, but this needed special inquiry, given a recent suggestion that their functions could be carried out by fewer species. In fact, as Ag-Biota’s earthworm experiments show, three different groups of species do very different jobs, all of them essential (even to conserving the carbon in the soil).

Much of the new knowledge from the Ag-Biota project will find a use in the Rural Environment Protection Scheme (Reps), in which thousands of smaller farmers are already enrolled. Dairy farmers should welcome the conclusion that better management of wildlife habitats may be more important than cutting down on intensive husbandry. The virtues of diversity, however, in plants that make up the sward of grassland and the arthropods they support, have values for nature and farmers both. Ag-Biota's work has just opened the door to longer-term field experiment, in which Lolium perenneshould be far from the only grass in town.

Eye on Nature

A treecreeper has fed on our window sill more than once. Is this unusual?Keith Lamb, Clara, Co Offaly

It is indeed. It must have found some small insects there.

In a wild place on our land I discovered two burrows freshly dug. They were about 40cms wide and had a large area of spoil, more than for rabbits. There was another burrow about 10 feet above the bank. Does this sound like badgers?John A Connolly, Wexford

Yes, it does.

The otter which used to swim in the canal which enters Tralee Bay at Blennerville was recently killed by a car on the main road nearby. I last saw it in mid-March. Someone spotted it breaking through the ice on the canal during the snowy spell earlier in the year. It seemed not worried by humans but was curious about us.

Geoff Stacey, Tralee, Co Kerry

First swallow of the year spotted on March 29th on Howth golf course.

Brian Lynch, Sutton, Dublin, 13

The female red-breasted merganser identified in Eye March 28th was likely to be the very similar female goosander which was sighted earlier on the same river at Glanmire.

Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo. E-mail : viney@anu.ie. Include a postal address.