Browsing by Author "Croxall, John P."
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- Factors affecting the solution of a parental dilemma in albatrosses: At what age should chicks be left unattended?Publication . Catry, Paulo; Phillips, Richard A.; Forcada, Jaume; Croxall, John P.With rare exceptions, avian offspring are continuously attended by one parent for at least the first few days after hatching. The duration of this phase of the nesting cycle is regulated by a trade-off between the benefits of brooding/guarding and those of foraging.We manipulated offspring age in grey-headed albatrosses, Thalassarche chrysostoma, by swapping chicks between nests. Parents given chicks 6 days older than their own shortened brooding by only 1.2 days, and parents given chicks 6 days younger than their own extended brooding by 1.4 days. Despite being relatively unresponsive to chick age, parents adjusted brooding in relation to calendar date and to chick condition. The results suggest that adults do not use chick age per se as a cue, but instead probably use an internal timer, and fine-tune the decision to end brooding according to date and chick mass. The duration of brood guarding did not correlate with adult body condition, suggesting that adults had a sufficient safety margin to allow them to respond to chick needs without compromising their own residual reproductive value. Chick survival at the end of brood guarding was strongly dependent on calendar date (early and late chicks suffered higher mortality), which suggests that greyheaded albatrosses benefit from breeding synchronously. We conclude that the length of the brood-guarding period is dependent on chick condition and seasonal variation in chick predation risk.
- Foraging behaviour of four albatross species by night and dayPublication . Phalan, Ben; Phillips, Richard A.; Silk, Janet R. D.; Afanasyev, Vsevolod; Fukuda, Akira; Fox, James; Catry, Paulo; Higuchi, Hiroyoshi; Croxall, John P.We integrated information from satellite transmitters, GPS loggers and wet/dry activity loggers to compare the at-sea behaviour of 4 sympatric albatross species by night and day: wandering Diomedea exulans, grey-headed Thalassarche chrysostoma, black-browed T. melanophrys and light-mantled sooty Phoebetria palpebrata (in total, 350 foraging trips by 101 individuals). Trip duration, distance and maximum range varied more within species between stages (incubation, broodguard and post-brood) than between species at the same stage, implying that reproductive constraints are more important than interspecific competition in shaping foraging behaviour. Wandering albatrosses spent more time on the water in fewer, longer bouts than other species. The proportion of time spent on the water was similar among the 3 smaller species. The partitioning of foraging activity between day and night varied little between species: all landed and took off more often, but spent less time overall on the water during the day than at night. This supports observations that albatrosses forage most actively during daylight, even though many of their fish and squid prey approach the surface only at night. Albatrosses were more active on bright moonlit nights, seem to have no fixed daily requirement for sleep, rest or digestion time on the water, can navigate in darkness, and are probably unhindered by the slight reduction in mean wind strength at night. They are probably less active at night because their ability to see and capture prey from the air is reduced and it is then more energy-efficient for them to rest or to catch prey using a ‘sit-and-wait’ foraging strategy.
- Foraging strategies of grey-headed albatrosses Thalassarche chrysostoma: Integration of movements, activity and feeding eventsPublication . Catry, Paulo; Phillips, Richard A.; Phalan, Ben; Silk, Janet R. D.; Croxall, John P.We identified a range of foraging strategies adopted by grey-headed albatrosses Thalassarche chrysostoma rearing chicks at Bird Island, South Georgia, by simultaneously using satellite telemetry, wet/dry activity recorders and stomach temperature loggers. The albatrosses foraged mostly over oceanic waters, probably associated with the Polar Front north of South Georgia, and also over shelf-slope waters around the Antarctic Peninsula. After leaving the colony, birds commuted to areas with predictable prey concentrations, where they remained for several days. During search periods, birds landed more often and had a higher intake rate, but spent the same proportion of time in flight as on commuting days. Although intake rates were particularly high in shelf-break waters around the Antarctic Peninsula (only one individual foraged in this area), prey were also consumed in reasonable quantities during commuting flights. While at sea, birds spent most (81%) of the day flying, and most (94%) of the night resting on the water. A considerable proportion (26% by mass) of prey was consumed during darkness. The majority of prey were detected and captured during search flights, but 35% were located while sitting on the sea surface. Many ingestion events (up to 27% of the overall food intake) showed temperature signatures characteristic of fluids, suggesting that albatrosses may feed on gelatinous and rapidly digested prey (e.g. salps and jellyfish) much more often than previously suspected. Diet samples delivered to the chicks comprised mostly squid (particularly Martialia hyadesi) and Antarctic krill Euphausia superba.
- Framework for mapping key areas for marine megafauna to inform Marine Spatial Planning: The Falkland Islands case studyPublication . Augé, Amélie A.; Dias, Maria P.; Lascelles, Ben; Baylis, Alastair M.M.; Black, Andy; Boersma, P. Dee; Catry, Paulo; Crofts, Sarah; Galimberti, Filippo; Granadeiro, José Pedro; Hedd, April; Ludynia, Katrin; Masello, Juan F.; Montevecchi, William A.; Phillips, Richard A.; Pütz, Klemens; Quillfeldt, Petra; Rebstock, Ginger A.; Sanvito, Simona; Staniland, Iain J.; Stanworth, Andrew J.; Thompson, Dave R.; Tierney, Megan; Trathan, Philip N.; Croxall, John P.Marine Spatial Planning (MSP) is becoming a key management approach throughout the world. The process includes the mapping of how humans and wildlife use the marine environment to inform the development of management measures. An integrated multi-species approach to identifying key areas is important for MSP because it allows managers a global representation of an area, enabling them to see where management can have the most impact for biodiversity protection. However, multi-species analysis remains challenging. This paper presents a methodological framework for mapping key areas for marine megafauna (seabirds, pinnipeds, cetaceans) by incorporating different data types across multiple species. The framework includes analyses of tracking data and observation survey data, applying analytical steps according to the type of data available during each year quarter for each species. It produces core-use area layers at the species level, then combines these layers to create megafauna core-use area layers. The framework was applied in the Falkland Islands. The study gathered over 750,000 tracking and at-sea observation locations covering an equivalent of 5495 data days between 1998 and 2015 for 36 species. The framework provides a step-by-step implementation protocol, replicable across geographic scales and transferable to multiple taxa. R scripts are provided. Common repositories, such as the Birdlife International Tracking Database, are invaluable tools, providing a secure platform for storing and accessing spatial data to apply the methodological framework. This provides managers with data necessary to enhance MSP efforts and marine conservation worldwide.
- Senescence effects in an extremely long-lived bird: The grey-headed albatross Thalassarche chrysostomaPublication . Catry, Paulo; Phillips, Richard A.; Phalan, Ben; Croxall, John P.Studies attempting to document reproductive or other pre-lethal senescence effects in wild birds typically face an array of problems, including flaws in statistical analyses, non-adaptive philopatry to deteriorating environments, confounding effects arising from cohort heterogeneity and differential death rates of phenotypes and the frequent pairing of old birds to younger mates. Furthermore, recent studies suggest that birds could maintain a high level of physical fitness until old age, before being struck by a catastrophic illness leading quickly to their demise. The presence of terminally ill individuals in most datasets (and their greater incidence in older age categories) may therefore provide a false impression of progressive senescence in cross-sectional analyses. This study was designed explicitly to avoid all the known pitfalls linked to the demonstration of progressive senescence in wild populations, and involved one of the very longest-lived bird species.We show that, during incubation, old (aged 35 years and over) male grey-headed albatrosses Thalassarche chrysostoma make longer foraging trips, and have lower daily mass gains, than experienced mid-aged individuals (aged up to 28 years). This is, to our knowledge, the first report documenting reduced foraging performance with old age. Hatching and breeding success of pairs composed of two old individuals were reduced in comparison to mid-aged pairs. Overall results were very similar when analyses were repeated using only individuals known to have survived 1 or 2 years beyond field measurements (hence probably not suffering from the effects of an advanced terminal illness). We conclude that extremely long-lived individuals usually experience some degree of general physical deterioration, leading to reduced foraging and breeding performance, long before their final demise.
- Sustained fast travel by a gray-headed albatross (Thalassarche chrysostoma) riding an antartic stormPublication . Catry, Paulo; Phillips, Richard A.; Croxall, John P.A Gray-headed Albatross (Thalassarche chrysostoma) was recorded traveling, in the course of a foraging trip, at a minimum average ground speed of >110 km h–1 for ~9 h with virtually no rest. A er taking into account the sinuosity of albatross fl ight, actual mean ground speed was predicted to be ≥127 km h–1, achieved in association with high tailwinds during an Antarctic storm. Despite its high speed and the storminess of the sea, the albatross still managed to successfully locate and capture prey at a rate comparable to that achieved under less extreme conditions. This individual’s performance suggests that albatrosses have the capacity to maintain positive energy budgets while quickly covering long distances and taking advantage of the strong winds that are frequent in the Southern Ocean.