Browsing by Author "Campos, Ana R."
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- Can thin-billed prions Pachyptila belcheri breed successfully on an island with introduced rats, mice and cats? The case of New Island, Falkland IslandsPublication . Catry, Paulo; Silva, Mónica C.; MacKay, S.; Campos, Ana R.; Masello, Juan F.; Quillfeldt, Petra; Strange, Ian J.Small burrowing petrels nesting on islands rarely survive introductions of mammalian predators. On New Island, a population of around two million pairs of thin-billed prions nests despite the presence of introduced ship rats, house mice and feral cats. Understanding the mechanisms of such coexistence is important, as it is important to establish a baseline for future monitoring. To do this, prion breeding success was determined for 7 years and in several habitats. Breeding success was high, except for the small fraction of the population that nests in tussock Poa Xabellata stands, where several lines of evidence suggest significant predation by rats. Such high breeding success possibly resulted from predator swamping in this highly seasonal environment. This study suggests that introduced mammals do not currently depress thin-billed prion breeding success on New Island. However, cats and rodents might have future harmful eVects if external factors depressed the prion population or allow a signiWcant population growth of predators on New Island.
- Competition among european robins Erithacus rubecula in the winter quarters: Sex is the best predictor of priority of access to experimental food resourcesPublication . Campos, Ana R.; Catry, Paulo; Ramos, Jaime; Robalo, Joana IsabelCompetition for resources by individuals of different sexes, ages, body sizes or geographical originsmay have varied implications, from demography to the evolution ofmigratory systems. European robins Erithacus rubecula display segregation by habitat in relation to sex, age, body size and geographic origin in the winter quarters. Here we report on an experiment to investigate the existence of asymmetries in the priority of access to food resources among unconstrained individuals in their natural environment. Feeders with mealwormswere provided in an areawith a high density of wintering robins and, after 15 days of provisioning, were replaced by a spring trap thatwas operated during a whole day. The first individuals to be caught in each trap were heavier and had higher fat andmuscle scores than last-caught individuals. Based on this and on behavioural observations, we conclude that first-caught individuals had priority of access to feeders. First- and lastcaught individuals did not differ in body size, wingtip shape or age ratios. However, whilst 35% of the first-caught individuals weremales, only 6%of the last-caught individuals weremales. This suggests that sex is an important predictor of the outcomes of competition in an area where multiple robin populations coexist in winter, while, at least on sites where no strictly sedentary individuals are present, geographic origin may be relatively unimportant.
- How do Robins Erithacus rubecula resident in Iberia respond to seasonal flooding by conspecific migrants?Publication . Campos, Ana R.; Catry, Paulo; Tenreiro, Paulo; Neto, Júlio M.; Pereira, António C.; Brito, Rui; Cardoso, Helder; Ramos, Jaime; Bearhop, Stuart; Newton, JasonInexistente
- Population census and nesting habitat selection of thin-billed prion Pachyptila belcheri on New Island, Falkland IslandsPublication . Catry, Paulo; Campos, Ana R.; Segurado, Pedro; Silva, Mónica C.; Strange, Ian J.Seabirds have the potential to be used as indicators for monitoring changes in the southern oceans. However, many species and populations are still poorly known. The thin-billed prion (Pachyptila belcheri) is the most abundant seabird species around the Falkland Islands, but this far, no detailed censuses of its populations had been carried out. In this study, we developed a methodology, based on standard field methods combined with a Geographical Information System, to census the biggest known colony (New Island) of this species. Data were also collected on nesting habitat preferences. Results indicate that there are 1,081,000 (95% confidence limits: 815,000–1,346,000) apparently active nest-burrow entrances on New Island South which, given the very high occupancy rates by known breeders, should correspond to a similar number of nesting couples. We present quantitative evidence that this result can be extrapolated for the entire island, giving an overall estimate of 2 million pairs. Prions have an almost ubiquitous distribution on New Island, but they are more frequent in areas with steeper slopes (excluding cliffs). Habitats dominated by introduced grass species generally hold higher densities of nests in comparison to most native formations.
- Provenance does matter: Links between winter trophic segregation and the migratory origins of European robinsPublication . Catry, Paulo; Campos, Ana R.; Granadeiro, José Pedro; Neto, Júlio M.; Ramos, Jaime; Newton, Jason; Bearhop, StuartAmongst migratory species, it is common to find individuals from different populations or geographical origins sharing staging or wintering areas. Given their differing life histories, ecological theory would predict that the different groups of individuals should exhibit some level of niche segregation. This has rarely been investigated because of the difficulty in assigning migrating individuals to breeding areas. Here, we start by documenting a broad geographical gradient of hydrogen isotopes (δ (2)H) in robin Erithacus rubecula feathers across Europe. We then use δ (2)H, as well as wing-tip shape, as surrogates for broad migratory origin of birds wintering in Iberia, to investigate the ecological segregation of populations. Wintering robins of different sexes, ages and body sizes are known to segregate between habitats in Iberia. This has been attributed to the despotic exclusion of inferior competitors from the best patches by dominant individuals. We find no segregation between habitats in relation to δ (2)H in feathers, or to wing-tip shape, which suggests that no major asymmetries in competitive ability exist between migrant robins of different origins. Trophic level (inferred from nitrogen isotopes in blood) correlated both with δ (2)H in feathers and with wing-tip shape, showing that individuals from different geographic origins display a degree of ecological segregation in shared winter quarters. Isotopic mixing models indicate that wintering birds originating from more northerly populations consume more invertebrates. Our multi-scale study suggests that trophic-niche segregation may result from specializations (arising in the population-specific breeding areas) that are transported by the migrants into the shared wintering grounds.
- Winter segregation of migrant European robins Erithacus rubecula in relation to sex, age and sizePublication . Catry, Paulo; Campos, Ana R.; Almada, Vítor Carvalho; Cresswell, WillBirds often show some form of social segregation during winter, both at large geographical scales (a consequence of differential migration) and at the regional or local level, when comparing different habitats or micro-habitats. However, our understanding of the mechanisms underlying such patterns is still poor. These issues have been rarely investigated in migratory Old-World passerines, particularly with respect to differences between the sexes. In this study, we show that female European robins Erithacus rubecula (sexed by molecular techniques) greatly outnumber males in southern Iberia, which confirms that this species is a differential migrant with a strong latitudinal segregation of the sexes. Furthermore, sex, age and body size influence the habitat distribution of robins in winter. Subordinate birds (females, juveniles and small individuals) were generally more common in habitats with a greater shrub development, and comparatively scarce in woodlands with relatively little undergrowth. Birds wintering in woodlands were in better condition (assessed by breast-muscle scoring) than birds wintering in shrubland. These results are consistent with the hypothesis that proposes that social dominance, mediated by differences in size and experience, is important in determining the habitat segregation of sex and age classes. The alternative hypothesis (habitat specialization), although not specifically supported by our findings, cannot be ruled out on the basis of the available evidence.