BIOMONITORING HEAVY-METALS USING THE BARN-OWL (TYTO-ALBA-GUTTATA) - SOURCES OF VARIATION ESPECIALLY RELATING TO BODY CONDITION

The feasibility of using the Barn Owl (Tyto alba guttata) to monitor e nvironmental quality in the Netherlands was investigated, using Cd, Cu , Pb, Mn, and Fe as indicators for environmental contamination. Throug hout 1992, bird-watchers, volunteers, and officials submitted 53 birds . The age and geographical distribution of these birds formed a repres entative sample of the population. The following interrelationships we re investigated: cause of death, nutrient reserve, age, time of death, place of death, body measurements, sex, condition, and heavy metal co ncentration in kidney, liver, and tibia. Twenty-eight animals had died after collisions. Fifteen Barn Owls died of exhaustion. In total, twe nty-four birds were exhausted, with coccidiosis or other parasitic gas trointestinal infections. The condition of the birds showed that as th e birds' condition worsened, fat reserves were depleted before protein reserves. Significant linear relationships were found between decreas ing protein reserves and decreasing dry weights of the liver, kidney, flight muscle and heart, but not of the tibia. An asymptotic, nonlinea r relation was observed between dry organ weight and fat reserve. This suggested that fat reserves were only found when protein reserves exc eeded 15% of the body mass at starvation. Concentrations of Cu and Fe in liver and kidney rose as protein reserves fell; the total content o f Cu and Fe per organ, however, remained constant. The Mn concentratio n of these organs remained constant; Mn content increased with increas ing organ sizes. Neither Cd nor Pb showed a clear relationship with pa rameters of body condition. The ratio between the organ content of Pb or Cd and the dry organ weight, however, revealed some birds from cont aminated habitats. The findings suggested that concentrations of envir onmental contaminants Should be measured on a dry weight basis. Furthe rmore, depending on the pharmacokinetic characteristics of a contamina nt, the total content of that contaminant per organ can be more inform ative than the concentration. In this one year sample of Barn Owls, no indications were found of toxic levels of Cd, Cu, Pb, Mn, or Fe in th e Netherlands. It is concluded that the Barn Owl is a suitable biomoni tor. Furthermore, a network of volunteers can produce an informative s ample of the Barn Owl population without interfering with the populati on.