Counting frogs and tadpoles' teeth
Two springs ago, on 171 selected bits of the map 500m square, 405 water bodies were surveyed for spawn, with three return visits to check on frog numbers and accumulating spawn. Everything was carefully estimated, including dimensions and depth of the water. There was spawn in half the water bodies and three-quarters of the survey squares, with the greatest occurrence in Mayo, Sligo and Donegal.
Most obviously, the frogs of Ireland have adapted to the loss of ponds by moving to the ditches that drain our grassy fields: 86 per cent of them, no less, were breeding in these habitats (even in the west, where, confusingly, “ditches” are the banks above them, and the dug-out bits are the “drains”) and fewer than 5 per cent were in farmland ponds.
This is not exactly a novel discovery: the concentration of Irish frogs in ditches and at the sides of streams in bogs was noted by scientists three decades ago. Intensive study of the species has extended even to the variable number of a tadpole’s teeth. But the new survey makes Ireland one of the few countries with a robust headcount of Europe’s common frog.
With an average of about two dozen per hectare, we come nowhere near Finland’s teeming densities (up to 80 per hectare) or even those of good habitats in Scotland. But it’s a healthy population, even sometimes “explosive” in breeding compared with the frogs of continental Europe (a figure of 1,000 eggs per clump of spawn spans, like all averages, some wide extremes).
Frogs control slugs and midge larvae. The adults help feed our otters, badgers herons and kestrels. The tadpoles feed dragonfly larvae and great diving beetles – and goldfish.
Which is why, if you have fish in your pond, you won’t get any frogs.
Eye on Nature Your notes and queries
Can you settle a long-standing dispute? Does spring start on February or March 1st? Sinead Quinn, Wicklow town
Ireland follows the old Celtic calendar and has spring starting on February 1st. The Met Office here follows the calendar used by the rest of Europe, which has it on March 1st.
Recently in the fields of Clonliffe College I saw a bird of prey flying from tree to tree being mobbed by crows, magpies and seagulls. Was it looking for eggs or a nesting site for itself? Nicola Main, Fairview, Dublin
It was probably looking for eggs or small birds. Other birds will always mob a raptor that invades their territory.
A friend in Dalkey has been charmed all winter by the antics of a flock of bullfinches. Recently a flock of smaller birds appeared. They have red patches on either side of the head, red breasts, with flashes of white or yellow on wings, and dull brownish backs. Geraldine Monaghan, Parnell Road, Dublin
They were goldfinches.
* Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo, or email firstname.lastname@example.org. Please include a postal address