THE EFFECT OF INTRODUCED SPECIES ON RAPTORS

Biological invasions are considered one of the major threats to the Earth's biota, and their prevention and control are widely recommended. A critical step is to gather information on the effects of introduced species on native species. In such analysis, it is important to consider both the negative effects and the fact that many nonnatives have become key components of existing ecosystems. The effects of nonnatives are particularly worrisome for raptors because raptors have high trophic positions and their ecological role can structure native communities. We here examine the effects of introduced species on raptors, as well as the interest in studying these effects, through a review of the published literature. The numbers of studies on raptors and introduced species as individual topics are rapidly increasing, but despite this we found few articles relating the two topics and fewer still with a clear aim of studying this relationship. Although the number of published reports we found was low, articles indicating negative effects outnumbered articles showing positive ones. Negative effects identified included decrease in native prey and direct or indirect poisoning via poisons aiming to protect productive introduced species from predators or to control introduced pests. Positive effects identified included extension of distributional range facilitated by introduced species or nonnative species as a food source. Very importantly, native raptors can become dependent on introduced species, and any proposed control of the nonnative/introduced species merits careful evaluation. In conclusion, the effects of nonnative species on this key group of top predators and scavengers have been poorly considered, but merit special attention and specific design in future studies.