Comparisons of species diversity, density and niche use of the terrestrial avifauna of Gull Island and South Head, Witless Bay, Newfoundland

Vassallo, Monique Ida (1979) Comparisons of species diversity, density and niche use of the terrestrial avifauna of Gull Island and South Head, Witless Bay, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Islands usually have lowered species diversity relative to similar areas of mainland. Such changes in species diversity usually lead to changes in bird density and niche use. A study was done on the terrestrial avifauna of Gull Island and the adjacent mainland, South Head, Witless Bay, Newfoundland, to investigate this. It also examined possible specific effects of changes in species diversity on the density and niche use of the island avifauna. -- Gull Island had a lower bird diversity than South Head as well as an absence of congeners. Total bird density was also lower on the island. The Northern Waterthrush, Boreal Chickadee and Gray-cheeked Thrush were more abundant on the island, presumably as a response to lowered competition. The Fox Sparrow and Pine Siskin had similar densities at each area. The other species had higher densities on the mainland. -- Niche shifts were noted in breeding and foraging habitats of some selected island populations. The Fox Sparrow and Northern Waterthrush shifted their selection of breeding habitat towards the predominant habitat types of Gull Island. The foraging niche of the Boreal Chickadee showed similar flexibility. -- The Boreal and Black-capped Chickadees were found in the same foraging habitat on South Head. They coexisted by exploiting different areas of the vegetation. On Gull Island only the Boreal Chickadee was present. It shifted its foraging towards some of the areas exploited by the Black-capped Chickadee on the mainland and broadened its foraging range in other areas. In all three chickadee populations seasonal changes were noted in foraging behavior. -- This study supports the hypothesis that species diversity changes on Gull Island led to corresponding changes in density and niche use of all species examined.

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