Browsing by Author "Matias, Rafael"
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- Brood-guarding behaviour in Cory’s Shearwaters Calonectris diomedeaPublication . Catry, Paulo; Matias, Rafael; Vicente, Luís A.; Granadeiro, José PedroBrood-guarding (or the continual attendance at the nest by one parent) has been relatively little studied in altricial birds. Parental investment in brood-guarding is often highly variable within a species, and the study of such variability may contribute to the understanding of the functions and regulation of this behaviour and of the tradeoffs involved in the choice between attending the nest and leaving to forage. In some colonial birds, it has been found that early nesting pairs attend their chick for longer than later nesting counterparts, giving rise to the synchronisation hypothesis that suggests that early pairs prolong broodguarding in order to reduce the probability of nest predation by a dilution effect. In this paper, for the first time we test the prediction that burrow-nesting colonial birds subject to little predation pressure should not display a seasonal decline in brood-guarding duration. The growth assistance hypothesis suggests that brood-guarding may allow the provision of frequent small meals and the efficient use of energy by chicks with poor homeothermic capabilities, resulting in improved early chick-growth. Finally, the chick-protection hypothesis predicts that chicks in more exposed nests should be brood-guarded for longer. Data collected at two Cory’s Shearwater Calonectris diomedea colonies situated in contrasting environments supported the synchronisation hypothesis, as there was no seasonal trend in brood-guarding duration. Contrary to the growth assistance hypothesis, chicks brood-guarded for longer periods did not have an improved growth (in one colony there was even a negative effect of brood-guarding on early chick development). Finally, we found no difference in brood-guarding between nests with contrasting levels of exposure to potential predators and weather. Despite confirming the prediction of the synchronisation hypothesis, more research is needed to identify the main factors underlying the variability of brood-guarding observed in this and other studies.
- Brood-guarding duration in black-browed albatrosses Thalassarche melanophris: temporal, geographical and individual variationPublication . Catry, Paulo; Phillips, Richard A.; Forster, Isaac P.; Matias, Rafael; Lecoq, Miguel; Granadeiro, José Pedro; Strange, Ian J.In birds, the period spent brooding or guarding young chicks is highly variable, but such variation has seldom been studied. Previous single-year studies of Antarctic petrels Thalassoica antarctica and grey-headed albatrosses Thalassarche chrysostoma revealed a pronounced seasonal decline in brood-guarding duration and gave rise to the ‘synchronisation hypothesis’, which suggests that some of the variation in the length of the brood-guarding stage is related to predictable seasonal changes in the risk of chick predation. We tested the predictions of this and three other hypotheses in a two-site, four-year study of the black-browed albatross T. melanophris. The existence of a pronounced seasonal decline in broodguarding duration was apparent at both sites, and in years of contrasting food availability, providing further support for the ‘synchronisation hypothesis’. Alternative explanations for this pattern are that short brood-guarding periods for latehatched chicks result from a seasonal decline in food availability or from the fact that early nesting birds are of higher individual quality. However, these explanations are at odds with the absence of a seasonal decline in early chick growth or in probability of chick survival. Furthermore, adult quality (measured as past reproductive performance) had a weak and inconsistent effect on the duration of brood-guarding. Weather changes explained some of the variation in broodguarding, but there were no differences between regions of contrasting climates. Individual pairs displayed a degree of inter-annual consistency in brood-guarding duration and, at least in some years, longer brood-guarding resulted in higher fledging probability. We speculate that a higher investment in brood-guarding increases the cost of reproduction, which counteracts other selective pressures that would otherwise lead to longer brood-guarding durations.
- Low breeding success and sharp population decline at the largest known Falkland skua colonyPublication . Catry, Paulo; Almeida, Ana Pereira; Lecoq, Miguel; Granadeiro, José Pedro; Matias, RafaelThe Falkland skua Stercorarius antarctica antarctica is a poorly known seabird. Demographic studies at the largest known colony of this taxon revealed a sharp population decline (47%) in just 5 years, between 2004 and 2009. The decline seems to be linked with a chronic low breeding success in the recent years and is consistent with a situation of virtually zero recruitment. The ultimate causes of the decline are, as of yet, unknown, but plausible explanations are examined and discussed. The reported population trends should be the cause of some concern, and more research and monitoring are desired.
- Moult strategies of Cory’s Shearwaters Calonectris diomedea borealis: The influence of colony location, sex and individual breeding statusPublication . Alonso, Hany Rafael de Drummond Ludovice Garcia; Matias, Rafael; Granadeiro, José Pedro; Catry, PauloThe replacement of old feathers is essential for birds, but it is also an energy-demanding task. As moult usually does not coincide with other stressful events in its annual cycle, such as reproduction and migration, the bird can optimise its use of time and energy allocated to different activities. There are very few studies comparing the moult strategies of populations with similar breeding calendars but occurring in areas of different habitat quality. Cory’s Shearwaters Calonectris diomedea have a partial moult–breeding overlap, an unusual phenomenon among pelagic seabirds. We have compared the moult schedules in Cory’s Shearwater colonies located in distinct environments (pelagic vs. coastal) and show that moult–breeding overlap is less extensive on Selvagem Grande, situated in deep oceanic waters, than on Berlenga, situated on the continental shelf. Colony attendance of failed breeders, most of which were moulting, was lower at Selvagem Grande than at Berlenga, which suggests that the feeding areas of birds from the former site are more distant from the colony. Failed breeders started to moult earlier than individuals still raising a chick, and breeding status had a stronger influence on determining the onset of wing-feather moult than colony location. Despite published evidence that internal circannual rhythms and external cues, such as variation in daylength, are important factors regulating moult schedules, it is clear that birds retain a considerable flexibility that allows them to respond to external factors in order to strategically manage time and energy in a way that is thought to maximise their fitness.
- Predicting the distribution of a threatened albatross: The importance of competition, fisheries and annual variabilityPublication . Catry, Paulo; Lemos, R. T.; Brickle, Paul; Phillips, Richard A.; Matias, Rafael; Granadeiro, José PedroThe ability to predict the distribution of threatened marine predators is essential to inform spatially explicit seascape management. We tracked 99 individual black-browed albatrosses Thalassarche melanophris from two Falkland Islands’ colonies in 2 years. We modeled the observed distribution of foraging activity taking environmental variables, fisheries activity (derived from vessel monitoring system data), accessibility to feeding grounds and intra-specific competition into account. The resulting models had sufficient generality to make reasonable predictions for different years and colonies, which allows temporal and spatial variation to be incorporated into the decision making process by managers for regions and seasons where available information is incomplete. We also illustrated that long-ranging birds from colonies separated by as little as 75 km can show important spatial segregation at sea, invalidating direct or uncorrected extrapolation from one colony to neighboring ones. Fisheries had limited influence on albatross distribution, despite the well known scavenging behavior of these birds. The models developed here have potentially wide application to the identification of sensitive geographical areas where special management practices (such as fisheries closures) could be implemented, and would predict how these areas are likely to move with annual and seasonal changes in nvironmental conditions.
- Prey-switching to fishery discards does not compensate for poor natural foraging conditions in breeding albatrossPublication . Kuepfer, Amanda; Votier, Stephen C; Sherley, Richard; Ventura, Francesco; Matias, Rafael; Anderson, Orea; Brickle, Paul; Arkhipkin, Alexander; Catry, PauloFishery discards supplement food for many seabirds, but the impacts of declining discards are poorly understood. Discards may be beneficial for some populations but have negative impacts by increasing bycatch risk or because they are junk-food. The Falkland Islands support > 70% of global black-browed albatross Thalassarche melanophris populations, which feed on discards. However, the effect of discards on population demographics, and implications of fishery management changes, are unknown. We analysed stomach contents of black-browed albatross chicks across eight breeding seasons (2004-2020) from New Island, Falkland Islands, to assess variation in discard consumption and how this relates to foraging conditions and breeding success. Across years, 68%-98% of samples contained natural prey, whilst 23%-88% of samples contained fishery discards. Discard consumption was positively related to fishery catches of hoki Macruronus magellanicus and sea surface temperature anomalies SSTA (degrees C), and negatively related to breeding success. These results suggest a diet-switching behaviour for Falkland Islands albatrosses, whereby birds switch from preferred natural prey to suboptimal discards when environmental conditions, and hence natural feeding opportunities, are unfavourable. Crucially, this study highlights that fishery discards do not compensate for poor natural foraging conditions for breeding albatrosses in the long term.
- Searching for a breeding population of Swinhoe’s Storm-petrel at Selvagem Grande, NE Atlantic, with a molecular characterization of occurring birds and relationships within the HydrobatinaePublication . Silva, Mónica C.; Matias, Rafael; Ferreira, Vânia; Catry, Paulo; Granadeiro, José PedroLong-distance dispersal plays a critical role in population dynamics, particularly in species that occupy fragmented habitats, but it is seldom detected and investigated. The pelagic seabird Swinhoe's Storm-petrel, Oceanodroma monorhis, breeds exclusively in the NW Pacific. Individuals have been regularly observed in the Atlantic Ocean since the 1980s, but breeding has never been confirmed. In this study, we searched for evidence of breeding of Swinhoe's Storm-petrels on Selvagem Grande Island, NE Atlantic, between 2007 and 2013. During this period, six individuals were captured, sexed and characterized molecularly for two mitochondrial loci, cytochrome oxydase I and the control region, to confirm species identity, survey genetic diversity and estimate evolutionary relationships within the Hydrobatinae. These individuals were confirmed to be Swinhoe's Storm-petrels, and all except one are females. Phylogenetic analyses suggest sister relationship with Matsudaira's Storm-petrel and dismiss misidentifications with other dark rump species. Patterns of genetic variation suggest that dispersal occurred likely by more than a single female. Despite the record of a pair duetting in a burrow, breeding could not be confirmed. Swinhoe's Storm-petrels are regularly occurring at Selvagem Grande, but capture/recapture patterns suggest that a possible breeding population is small and likely not self-sustaining. In seabirds, long-distance dispersal events may facilitate colonization of new habitats created in the context of predicted climate change impacts on the marine ecosystems.
- Spatial and temporal aggregation of albatross chick mortality events in the Falklands suggests a role for an unidentified infectious diseasePublication . Ventura, Francesco; Granadeiro, José Pedro; Matias, Rafael; Catry, PauloIn the context of environmental change, determining the causes underpinning unusual mortality events of vertebrate species is a crucial conservation goal. This is particularly true for polar and sub-polar colonial seabirds, often immunologically naïve to new and emerging diseases. Here, we investigate the patterns of black-browed albatross (Thalassarche melanophris) chick mortality events unrelated to predation recorded between the 2004/05 and 2019/2020 breeding seasons in four colonies across the species range in the Falklands. The prevalence of these mortality events was highly variable across years, causing the death of between 3 and 40% of all chicks in the studied plots. With few exceptions, mortality was patchily distributed. Using clustering methodologies, we identified the spatio-temporal mortality clusters based on the nest locations and chick death date. Using generalised linear models and generalised additive mixed-effects models we found that chicks nearer the first mortality event were predicted to die before those in more distant nests. The probability of death increased with age and was highest for chicks close to nests where a chick had died previously. Our findings, along with the symptoms consistently exhibited by most deceased chicks in the study, strongly suggest the prevalence of a widespread infectious disease, potentially with a common aetiology, both in areas with regular and with very rare human presence. Understanding the causes driving these disease-related mortality events, which seem different from the outbreaks documented in the literature, is a conservation priority for the Falklands black-browed albatross population, which comprises over 70% of the species global population.
- The diet of Atlantic Yellow-legged Gulls (Larus michahellisatlantis) at an oceanic seabird colony: estimating predatory impact upon breeding petrelsPublication . Matias, Rafael; Catry, PauloThe diet and breeding ecology of Yellowlegged Gulls (Larus michahellis atlantis) were studied on Selvagem Grande, North Atlantic in the nesting season of 2007. We collected and analyzed 715 pellets from adults. The most frequent prey were White-faced Stormpetrels (Pelagodroma marina; present on 40.8% of all pellets) and the endemic land snails (Theba macandrewiana; present on 36.5% of all pellets). Other birds, namely Cory’s Shearwaters (Calonectris diomedea), Macaronesian Shearwaters (Puffinus assimilis), Bulwer’s Petrels (Bulweria bulwerii), and Band-rumped Storm-petrels (Oceanodroma castro) were relatively less frequent, but overall, seabirds were present in ca. 50% of all pellets, representing an estimated 60.4% of all mass consumed by gulls. We estimate that the contribution of seabirds to the overall caloric balance accounted for 82.5% of all energy consumed. The number of gull pairs breeding on Selvagem Grande was 12 on 2005 and 2007. Breeding success was low (0.92 and 0.25 juveniles per breeding pair, respectively). Us ing a simple bioenergetics model, we estimate the breeding gull population to have the potential to consume approximately 4,847 adult/sub-adult seabirds in 3.5 months in order to meet its energetic requirements. The importance of the estimated predation levels is discussed and some management actions are suggested.
- The diet of feral cats at New Island, Falkland Islands, and impact on breeding seabirdsPublication . Matias, Rafael; Catry, PauloWe studied the diet of feral cats (Felis catus) on New Island, Falkland Islands, through the analysis of 373 scats collected during the austral summers of 2004/2005 and 2005/2006. The most frequent prey were three introduced mammals (house mice Mus musculus, ship rats Rattus rattus and rabbits Sylvilagus sp.) and the thin-billed prion Pachyptila belcheri (each season present on ca. 21% of the analysed scats). These represent the Wrst systematic data on feral cat diet for the Falklands. A simple bioenergetics model suggests that cats could be eating in the region of 1,500–11,000 prions per season, representing <1% of the local adult and subadult population. Predation on other seabirds nesting on New Island (several penguin species, albatrosses and cormorants) was unimportant, with the possible exception of white-chinned petrels Procellaria aequinoctialis, which nest locally in very small numbers. For each prion eaten, cats were estimated to have killed 1.1–1.9 ship rats during the summer season, and probably more in autumn and winter. Knowing that ship rats are prion predators, it is conceivable that, on the whole, cats are having a positive impact on the prion population, a scenario predicted by general theoretical models. Thus, considering the available information, we would not recommend the implementation of any eradication programme on New Island that would target cats in isolation. Nevertheless, it would be prudent to consider some local action targeting cats and rats around the small New Island white-chinned petrel colony.