title: How important are seabirds in the diet of black rats on islands with a superpredator?
abstract: This study assessed the impact of introduced black rats (Rattus rattus) on Cory's shearwater (Calonectris diomedea borealis) in a multi-invaded insular ecosystem where rats are mesopredators. We hypothesized that black rats should have little impact on Cory's shearwaters in the presence of cats as superpredators. Stomach contents and stable isotope analysis (SIA) in tissues of black rats were analyzed to assess the trophic ecology and the importance of Cory's shearwater in their diet. We also studied the isotopic signature in tissues of house mouse (Mus domesticus) to confirm previous data showing no predation of this species on Cory's shearwaters. For both rodent species, temporal variation in diet composition in response to the availability of seabird prey was evaluated, and short- and long-term consistency in diet was tested using different tissues from the same individual. For black rats a Bayesian isotope mixing model (SIAR) was applied to determine the relative contribution of each prey to the individual diet. SIA of mouse tissues varied between the Cory's shearwater breeding and non-breeding periods. However, no significant differences were found in diet and SIA for black rats. In contrast, individuals of both species showed a strong consistency in diet which apparently benefited their body condition index. Although black rats supplement their diet with Cory's shearwater eggs and chicks (8.3% in stomach contents and 10.6% in the SIAR model), their current impact on the Cory's shearwater population appears to be small, probably due to several factors including the small size of the rat population and a high level of rat predation by cats.
authors.affiliation: Animal Health Department, Veterinary Faculty, Regional Campus of International Excellence "Campus Mare Nostrum", University of Murcia, 30100 Espinardo, Murcia, Spain; Island Ecology and Evolution Research Group (IPNA-CSIC), Astrofísico Francisco Sánchez 3, 38206 La Laguna, Tenerife, Canary Islands, Spain; Portuguese Society for the Study of Birds, Avenida João Crisóstomo, 18-4°Dto, 1000-179 Lisboa, Portugal. Electronic address: shparejo@gmail.com.
authors.forename: Sandra
authors.initials: S
authors.lastname: Hervías
authors.affiliation: Marine and Environmental Research Center (IMAR/CMA), Department of Life Sciences, University of Coimbra, Apartado 3046, 3001-401 Coimbra, Portugal.
authors.forename: Filipe R
authors.initials: FR
authors.lastname: Ceia
authors.affiliation: Portuguese Society for the Study of Birds, Avenida João Crisóstomo, 18-4°Dto, 1000-179 Lisboa, Portugal.
authors.forename: Tânia
authors.initials: T
authors.lastname: Pipa
authors.affiliation: Island Ecology and Evolution Research Group (IPNA-CSIC), Astrofísico Francisco Sánchez 3, 38206 La Laguna, Tenerife, Canary Islands, Spain.
authors.forename: Manuel
authors.initials: M
authors.lastname: Nogales
authors.affiliation: Animal Health Department, Veterinary Faculty, Regional Campus of International Excellence "Campus Mare Nostrum", University of Murcia, 30100 Espinardo, Murcia, Spain.
authors.forename: Rocío Ruiz
authors.initials: RR
authors.lastname: de Ybáñez
authors.affiliation: Marine and Environmental Research Center (IMAR/CMA), Department of Life Sciences, University of Coimbra, Apartado 3046, 3001-401 Coimbra, Portugal.
authors.forename: Jaime A
authors.initials: JA
authors.lastname: Ramos
mesh_terms: D000818:Animals; D001394:Azores; D001717:Birds / Q000502:physiology*; D002415:Cats / Q000502:physiology*; D004032:Diet; D017753:Ecosystem; D020387:Food Chain; D062312:Islands; D051379:Mice; D051381:Rats / Q000502:physiology*
keywords: Calonectris diomedea borealis; Insular ecosystem; Mesopredator; Prey selection; Rodent feeding behaviour