PARENT SESSION

(06-06) Impact of polluted river floodplains on the Little Owl, Athena noctua vidalii : a field study.

Groen, Niko¹, De Jonge, Jolande^*,1, Boudewijn, Theo², Van den Brink, Nico³, ¹ Institute for Inland Water Management/RIZA, Lelystad, The Netherlands² Bureau Waardenburg, Culemborg, The Netherlands³ Alterra, Wageningen, The Netherlands

ABSTRACT- In the 70s, the floodplains of the large rivers in the Netherlands were severely contaminated with organic compounds and heavy metals, which were deposited as polluted silt during floods. Model studies showed that these contaminants are still posing risks to birds which depend on the river forelands for their food. However, little is known about actual effects of these contaminants in the field situation. In 1998 a study was been started to assess the possible risks of pollution in river floodplains on little owls (Athene noctua vidalii), by studying a population in the polluted Rhine basin and a population in an unpolluted reference area in the east of the Netherlands. The little owl was selected because this species is found both in and beyond river forelands and they are also very territorial. Several biological breeding parameters were recorded weekly such as number, volume and weight of eggs, eggshell thickness, brooding time, hatching date and number of hatchlings. Of the chicks, mass changes, biometric development, survival rate and fledgling success rate were recorded. During each nest check the number of prey animals in the nesting box were counted and weighed. An infrared camera recorded the prey items brought to the nest. The contamination patterns of prey animals and soil samples collected in the territories were measured. Preengland oil and feathers were analysed and some eggs and a dead little owl were also collected for analysis. By combining and integrating various approaches, we try to establish whether or not pollution in river forelands has a negative effect on little owls there. These effects of contamination will be discussed in relation to other factors that might affect the functioning of little owls, like for instance flooding of floodplains. Preliminary results show that birds from the polluted area have a delay in the timing of breeding, a lower clutch size and a lower breeding success. Furthermore their preenoil contained elevated levels of PCB and DDE. Earthworms of the contaminated area showed high levels of heavy metals. In contrast to the model study, in which heavy metals were expected to pose the highest risk, it appears from the field study that PCBs and p,p-DDE are of major concern

Key words: Athena noctua vidalii, pollution , rivers, ecotoxicology