Trophic transfer of heavy metals and avian feeding ecology in an urban brownfield

Background/Question/Methods

The objective of this study is to assess the habitat quality of a polluted urban forest. Urban wildlands provide valuable habitat for resident and migrating birds; however, it is vital to determine if these habitats impart a greater risk than benefit to the species they attract. We focused on avian feeding ecology and the trophic transfer of heavy metals at a forested brownfield in Liberty State Park (LSP) in Jersey City, New Jersey. Previous research has shown that insectivorous house wren nestlings are accumulating heavy metals at LSP. In order to determine how metals are entering the house wrens’ food chain and if these metals are biomagnified, we collected invertebrate samples from nesting sites throughout our study area and analyzed the samples for metal load. To further investigate avian feeding ecology at LSP we studied avian use of native versus non-native fruiting plants. Non-native fruiting plants can benefit birds as a food source; however, the resulting dissemination of their seeds can facilitate invasion. We conducted point counts at fifty sites and recorded the number of birds that fed from native and non-native fruits. Fruit samples from five species of native and non-native plants were collected and tested for heavy metals.

Results/Conclusions

Preliminary results of the invertebrate metal analysis show that metal concentrations are generally higher in predatory invertebrates than in herbivorous invertebrates.  Results for Cr, Cu and Pb were above the minimum detection level for most samples. Results for Cd were below the minimum detection level for most samples. Preliminary results of the fruit metal analysis show interspecific and intraspecific variation in metal load among fruits from different locations within the site.  Cd was detected in white mulberry, autumn olive, wild grape and porcelain berry, but was not detected in black cherry. Pb and Cu were detected in all five plant species. Cr was not detected in significant amounts for any species. No significant differences were found between avian use of native and non-native fruiting plants.  The most common species of birds found feeding on both types of fruits were American robins and grey catbirds.  Overall, birds preferred large fruiting trees, such as non-native white mulberry and native black cherry, over smaller shrubs or vines.  Therefore, avian preference of fruiting plants at LSP is more likely based on plant morphology than plant origin.