Seed Dispersal by Rooks (Corvus frugilegus) -with Focus on Non-Native Species

Seed dispersal is an essential ecological function, and many plants depend on dispersal mediated by animals (zoochory). Zoochory is important for the natural succession and regeneration of plant communities but may also play a role in the dispersal of non-native and invasive species with damaging ecosystem effects. The rook (Corvus frugilegus) is an omnivorous species eating a broad variety of seeds and therefore potential to disperse a wide range of seeds in both natural and urban habitats. In this study seed dispersal by rooks in Central and Northern Jutland, Denmark was examined through examination of regurgitation pellets and vegetation studies. The aim of the study was to investigate i) to what extent rook regurgitation pellets found under rookeries contain seeds; ii) which seed species are found, including whether pellets contain seeds of non-native species; iii) if the plant species found in the regurgitated pellets were found in the vegetation under rookeries. Regurgitation pellets were collected from April to June beneath rookeries. In total 124 seeds representing 8 taxa were found in 153 pellets. Most of the seed species were cereals and other dry-fruited species, mainly weeds and ruderal species. The study showed that Danish rooks canact as seed dispersers. Cereals and other dry-fruited species such as weeds, and ruderal species were the dominant seeds found in rook pellets. No non-native species were found. However, this does not exclude the possibility of the rooks being able to disperse them. The lack of exotic fruit found in the pellets of Danish rooks may be due to waste management in Denmark, not having open waste dumps and open compost heaps with spill overs from the kitchen is not recommended. A vegetation survey under rookeries showed that only Stellaria media was found both in regurgitation pellets and in the vegetation beneath rookeries, suggesting that many dispersed seeds are unable to germinate or survive under the tree canopies at the rookeries.