Omnivorous Bird Research Articles

Bird communities and the structure of urban habitats

We examine relationships between bird communities and habitat structure along a gradient of urban habitats in Vancouver, B.C. Bird species diversity, evenness of species abundances, and numbers of species increase with foliage height diversity and total vegetation as they do in "natural" habitats. Few ecological niches for birds are enhanced by man-made features of the urban environment. Bird species diversity is actually inversely related to the apparent increase in habitat diversity contributed by elements of the built environment. While limited to a few niches, food provided by man has a major effect on density and distribution of birds in urban areas. Therefore, despite declining natural productivity and species diversity, total bird density does not decline across the Vancouver urban gradient. Overall, available habitat and food in highly urbanized environments strongly favour the few cavity-nesting, ground-feeding graminivorous or omnivorous bird species that have already come to dominate.

Predation on Potato Moth, Phthorimaea Operculella (Lepidoptera: Gelechiidae), by the Western Silvereye, Zosterops Gouldi (Aves: Zosteropidae).

The omnivorous bird, the western silvereye, eats the larvae of potato moth, preferring the larger third and final fourth instars. An examination of the gizzard contents shows that silvereyes eat proportionally fewer third-instar larvae when the density of the moth population is low, despite the equal abundance of third and fourth-instar larvae. With increasing moth density, the third- instar larvae become increasingly attractive. It is inferred that the level of crop infestation determines whether the smaller third-instar larvae are as profitable as energy sources as the fourth-instar larvae.