Heavy Effects on Tengmalm's Owl Food Influences Their Breeding

Abstract from the Journal of Applied Ecology
22nd July 1996

A study by Birger Hornfeldt and Erik Nyholm from Umea, Sweden, has tried to find a direct effect on the Tengmalm's Owl by the gross heavy metal pollution from a smelter in Northern Sweden.

The study was for two two-year periods representing two different vole population cycles.

These charming owls breed in nest boxes so the study provided what the owlish estate agent would describe as about 200 'des reses' in three areas at kilometre intervals along roads and tracks. The three areas were less than 13 km, between 13 and 22 km and more than 22 km from the smelter.

The four main parameters of breeding that were measured did decrease the closer the owls were to the smelter - population density, clutch size (except in one year), breeding success and viability of the egg/chick. The amount of arsenic, cadmium, lead and mercury in the prey increased the closer they were to the smelter but these metals did show an increase in the livers of the owl chicks (except for arsenic).

The trapping of small mammals revealed that in two of three years the study area near the smelter had smaller populations than the control area at more than 22 kms. They concluded the effect on the owl's breeding was not direct; rather it was caused by heavy metal and sulphur dioxide pollution effects on the prey.

Chris Mead