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COPYRIGHT 2005 Wilson Ornithological Society
Nest predation is a major cause of nestling mortality in avian species (Ricklefs 1969, Skutch 1985, Martin 1988, Rotenberry and Wiens 1989, Weatherhead and Blouin-Demers 2004). The intensity of predation pressure can affect the evolution of life history traits (Cody 1971, Clark and Wilson 1981, Slagsvold 1982, Nilsson 1984, Stutchbury and Morton 2001), and high nest predation generally results in selection for individuals that can reduce their investment in each breeding attempt (Slagsvold 1982, Lundberg 1985). This is particularly true of small birds, which are usually unable to protect their nests against predators. Some researchers have investigated this theory by comparing island and mainland populations, because predation pressure on islands often differs from that of mainland populations (Higuchi 1976, Loiselle and Hoppes 1983, George 1987, Sieving 1992). Higuchi (1976) reported that some life history traits of one insular subspecies of the Varied Tit (Parus varius owstoni) differed from those of the mainland subspecies (P. v. varius) and that predation pressure differed between the two populations.
We report extremely low nesting success in one insular subspecies (P. v. namiyei) of the Varied Tit and compare certain life history traits with those of two populations studied by Higuchi (1976), each of which is subjected to different predation pressure. We also discuss whether the differences in predation pressure could be responsible for the variation in life history traits among three different subspecies of Varied Tits.
METHODS
P. varius occurs on the Japanese mainland and islands, the southern Korean Peninsula, and Taiwan. The species is divided into eight subspecies across its range (Ornithological Society of Japan 2000). P. v. varius occurs on the mainland of Japan and the southern Korean Peninsula, P. v. namiyei is found on three northern islands (Niijima, Toshima, and Kozushima; Fig. 1) of the Izu Archipelago, and P. v. owstoni occurs on three southern islands (Miyake, Mikura, and Hachijo).
[FIGURE 1 OMITTED]
Study site.--The study site was Kozushima Island, Tokyo, Japan (18.87 [km.sup.2]; 34[degrees] 12' N, 139[degrees] 08' E; population ~2,100). The island is part of Fuji-Hakone-Izu National Park, but has a residential area that occupies about 10% of the island. The dominant vegetation is broadleaved evergreen forest, mostly Castanopsis cuspidate, Machilus thunbergii, and second-growth Alnus sieboldiana. Patches of cedar (Cryptomeria japonica) plantations are interspersed throughout the island. The climate is temperate, with a mean annual rainfall of 2,535 mm and a mean annual temperature of 17.4[degrees]C. Mean temperature and rainfall on Miyakejima Island and the adjacent mainland are 16.5[degrees]C, 1,832 mm and 17.5[degrees]C, 2,907 mm, respectively (Japan Meteorological Agency, www.jma.go.jp/JMA_HP/jma/indexe.html).
Field observations.--We erected 137 nest boxes in...
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