Ship rats Rattus rattus on the Shiant Islands, Hebrides, Scotland

Key, Gillian; Fielding, Alan H.; Goulding, M. J.; Holm, R. S.; Stevens‐Wood, Barry

doi:10.1017/s0952836998276096

Cited by 8 publications

(18 citation statements)

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“…This suggests higher productivity is the principal driver for the small home range sizes and high rat densities observed on Big South Cape Island/Taukihepa. This mirrors the results from the Shiant Islands, Scotland, where ship rats were in higher densities (22-85 rats/ha) and heavier on the island with a large puffin colony, in contrast to rats trapped on the immediately adjacent island without seabirds (Key et al 1998). Similarly, very heavy ship rats (mean adult weight: 246 g) were trapped in white-chinned petrel Procellaria aequinoctialis colonies on Ile de Possession, southern Indian Ocean (Jouventin et al 2003).…”

Section: Discussionsupporting

confidence: 82%

“…There is evidence for increased population densities, larger body sizes and reduced reproductive rates in rodents on islands (Key et al 1998;Innes 2005), which have been attributed to the 'island syndrome' (Adler & Levins 1994;Russell et al 2011b) as a response to reduced dispersal, competition and predation. Although this effect is recognised, marine subsidies from dense aggregations of seabirds are also known to lead to increased population densities and other changes in population parameters in various animals including rodents (Stapp & Polis 2003;Mulder et al 2011;Ruffino et al 2013), which may be a confounding factor.…”

Section: Introductionmentioning

confidence: 99%

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Home range and population density of black rats (Rattus rattus) on a seabird island: a case for a marine subsidised effect?

Harper¹,

Rutherford²

2016

NZ J Ecol

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Rodents on islands are known to exhibit differing spatial ecology than is seen in mainland habitats and in the case of invasive rats this may affect their impacts on native species. Ship rats' (Rattus rattus) home range size and population densities were measured on Big South Cape Island/Taukihepa, an island with a dense seabird colony, near South-west Stewart Island. Home ranges for both male and female rats were much smaller than had been recorded for virtually all sites in New Zealand. Female home ranges remained at 0.06 ha through a breeding season whereas male home ranges increased in size and also overlapped with more males later in the season. Ship rat population density ranged from 6.5 ha -1 in December to 36.4 ha -1 by late summer and remained high through autumn. The peaks in measured population densities are among the highest recorded in New Zealand. High populations densities, small home ranges and heavy mean body weights are suggested to be due to high primary productivity attributable to the dense seabird population rather than because of the 'island syndrome'. Further comparisons with other New Zealand islands and mainland sites did not clearly support nor negate the 'island syndrome' in ship rats in New Zealand, although large increases in population densities on Big South Cape Island/Taukihepa did not influence home range sizes.

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Section: Discussionsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Home range and population density of black rats (Rattus rattus) on a seabird island: a case for a marine subsidised effect?

Harper¹,

Rutherford²

2016

NZ J Ecol

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“…Field work was conducted during a single visit to the islands from 22 to 28 August 2000. Although rats are present on Eilean Mhuire (Key et al . 1998; Maclennan, Ferguson & Buxton 2000) all work was conducted on Eilean an Tighe and Garbh Eilean.…”

Section: Methodsmentioning

confidence: 99%

“…Rats have been implicated in the historical declines of puffins and other seabirds on the Shiant Islands and elsewhere in Britain (Lockley 1953; Harris 1984; Lovegrove, Williams & Williams 1994). Key et al . (1998) found feathers in faeces of Shiant Islands rats, but suggested that this mostly reflected scavenging of birds killed by gulls.…”

Section: Introductionmentioning

confidence: 99%

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Stable isotopes reveal evidence of predation by ship rats on seabirds on the Shiant Islands, Scotland

Stapp

2002

Journal of Applied Ecology

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Summary1. Introduced predators are a major threat to native island populations, yet direct evidence of predation is often lacking, especially when it is difficult to detect by traditional dietary methods. 2. Historical declines of nesting seabirds on the Shiant Islands, Outer Hebrides, roughly coincided with the accidental introduction of ship rats Rattus rattus in c . 1900. Rats have been implicated in declines of seabirds, but the Shiant population is one of two remaining naturalized R. rattus populations in Britain, prompting calls for their protection. 3. Live-trapping studies with stable isotopes and gut content analysis were used to investigate whether ship rats prey on Shiant Islands seabirds. Another aim of this study was to determine whether marine-derived foods subsidize rat populations, permitting higher densities, greater productivity and larger body size than expected from terrestrial resources alone. 4. Comparisons of stable carbon and nitrogen isotopic signatures of rat tissues with those of seabirds, marine invertebrates, marine algae and land-based foods revealed that seabirds and other marine prey were the primary source of protein for rats living in colonies or near the shore. These results were corroborated by gut content analysis, and suggest a greater role for active predation of seabirds by rats than has previously been apparent at this locality. 5. Seabird colonies and especially coastal areas supported higher numbers of rats than more inland habitats. Coastal and colony-dwelling rats were more active reproductively and were larger than those living inland. 6. Although rats are capable of surviving solely on terrestrial foods, their ability to use marine prey may buffer populations during lean times, i.e. outside the seabird nesting season, and may in part explain their success and status as pests on islands world-wide. Overall, this work reveals the value of stable isotopes in identifying predation by exotic species, but also underscores potential uncertainties inherent in all diet-based methods in distinguishing predation from scavenging.

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