Frugivory and seed dispersal by redwings Turdus iliacus in southwest Iceland

We studied consumption of wild fruits by redwings Turdus iliacus coburni at two sites on the southwest coast of Iceland, just prior to the autumn migration. During this period the principal study site offers c. 800 000 fruits ha-1: most of these are of Empetrum nigrum (c. 90% of fresh weight), but fruits of Vaccinium uliginosum, Arctostaphylos uva-ursi, Vaccinium myrtillus and Rubus saxatilis are also present. Redwings regularly consumed the fruits of all these species except R. saxatilis. At both study sites E. nigrum fruits were the most important component of the redwing diet (70 - 80% of fruits ingested), followed by V. uliginosum (c. 20%). Neither species was consumed as predicted on the basis either of overall relative abundance of fruits or of relative frequency of occurrence of fruiting plants in two hundred$0.3\ {\rm m}^{2}$plots. In another forty$0.3\ {\rm m}^{2}$plots, the number of E. nigrum fruits consumed over a seven-day period was not significantly correlated with the number of fruits initially present. Empetrum nigrum seed width is positively correlated with fruit size, and the mean width of seeds in droppings suggests that redwings prefer large E. nigrum fruits (which have a higher pulp-to-seed weight ratio) to small E. nigrum fruits. Despite the predominance of E. nigrum, redwing droppings tend to contain a mix of seeds of different species, the most frequent combination being E. nigrum and V. uliginosum.