Population dynamics of black-tailed Godwits in the light of heavy metal pollution

PhD ceremony: Ms. M. Roodbergen, 14.45 uur, Academiegebouw, Broerstraat 5, Groningen

Thesis: Population dynamics of black-tailed Godwits in the light of heavy metal pollution

Promotor(s): prof. T. Piersma

Faculty: Mathematics and Natural Sciences

In the thesis of Maja Roodbergen the population level effects of diffuse pollution, in the form of heavy metals, on Black-tailed Godwits breeding on contaminated soils in The Netherlands are studied. In a polluted and a reference site, concentrations of heavy metals in soil, earthworms, feathers and eggs of Black-tailed Godwits were measured and population studies were conducted. Although heavy metals were transferred from soil to Black-tailed Godwits, this did not seem to have an effect on population parameters studied. In both sites reproduction was too low for populations to be stable.

The collated data on reproduction and survival in meadow birds showed that population declines in meadow birds are caused by reduced nest success and chick survival, not adult survival. Population growth rate in meadow birds is most sensitive to adult survival. However a chronic reduction in reproduction can lead to population declines. Using population models Roodbergen recommends to focus conservation efforts mainly on reproduction. In Black-tailed Godwits reproduction needs to be at least doubled. To reach this, several reproductive parameters, specifically chick survival, the proportion breeding and nest success, need to be increased simultaneously.

In The Netherlands, at least c. 14% of the Dutch breeding population of Black-tailed Godwits is confronted with heavy metal levels above Maximum Permissible Concentrations for secondary poisoning. Although it is not likely that heavy metals are a driving factor in population declines of meadow birds, they may pose a greater risk in the future, as concentrations of heavy metals in Dutch soils have increased. Roodbergen recommends to raise groundwater levels in fields on peat soils with management agreements. Next to being beneficial for breeding meadow birds, this can diminish risks of heavy metal pollution, except in areas with high soil concentrations of Mercury. Applying Calcium may also decrease heavy metal exposure.