Songbird Use of Native and Invasive Fruit in the Northeastern USA

Fruit is consumed by songbirds, yet whether or not it comprises an important component of habitat quality depends on the extent to which it is used by birds. In addition, there is evidence fruits of exotic invasive species may be nutritionally inferior to fruits of native species, so the influence of plant invasion on bird body condition is of interest to managers. Birds that consume invasive fruits may also serve as seed vectors, and consumption of fruits of invasive species may exacerbate invasion. Thus, the extent to which songbirds consume fruits of native versus invasive plant species, influence of plant invasion on bird body condition, and extent to which birds exhibit foraging behaviors that elevate their potential to act as dispersers of invasive species have important implications for habitat management. To understand bird use of native and invasive fruits and the potential role of birds in dispersing invasive plants, we observed bird foraging, measured body condition indices of birds captured in mist nets, measured available fruits of native and invasive plants, and calculated indices of seed dispersal for bird species based on fruit handling and consumption, within 16 shrubland sites in western Massachusetts, USA. Our findings indicate that birds use fruit extensively (57% of foraging events), use varied among species, and frugivorous species at our sites generally chose the fruit of native species, especially Prunus, over fruits of invasive species. Body condition indices were negatively related to the proportion of invasive fruit in most cases. In general, birds were better dispersers for native fruits than for invasive fruits. Our findings support the value of native fruit resources as a component of habitat quality, and, conversely, suggest that nonnative plant invasion may lead to reduced habitat quality for songbirds.

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