Experimental analysis of novelty responses in a bird assemblage inhabiting a suburban marsh

Suburban areas in the Pampas region of Argentina are inhabited by several bird species that sharply differ in their ability to exploit human-modified, urban areas. This bird assemblage includes species restricted to natural grasslands (e.g., Great Pampa Finch, Embernagra platensis (J.F. Gmelin, 1789)) as well as generalist, highly cosmopolitan species such as House Sparrow, Passer domesticus (L., 1758). We explored the role of certain aversive responses to novelty in shaping the marked differences in ecological plasticity among species in the assemblage. In field experiments, we tested for differences in feeding in the presence of artificial objects near feeders regularly replenished with seeds. In spite of their granivorous diet, some non-urbanized species did not use the feeders, possibly because of an extreme degree of aversion to novel situations. The group of birds that visited the feeders included both urbanized (N = 8) and non-urbanized (N = 2) species. We found that the presence of novel objects discouraged visitation to an otherwise attractive food source, although neophobia was weak for most species. However, we found unexpectedly high levels of neophobia in highly generalist, urbanized species such as House Sparrow and Shiny Cowbird, Molothrus bonariensis (J.F. Gmelin, 1789). This response is discussed in the context of the influence of post-fledging development in a relatively simple and predictable ecosystem versus that in urban areas.