Agustina Gómez Laich

Pushed for time or saving on fuel: fine-scale energy budgets shed light on currencies in a diving bird.

Animals may forage using different currencies depending on whether time minimization or energy maximization is more pertinent at the time. Assessment of net energy acquisition requires detailed information on instantaneous activity-specific power use, which varies according to animal performance, being influenced, for example, by speed and prey loading, and which has not been measured before in wild animals. We used a new proxy for instantaneous energy expenditure (overall dynamic body acceleration), to quantify foraging effort in a model species, the imperial shag Phalacrocorax atriceps, during diving. Power costs varied nonlinearly with depth exploited owing to depth-related buoyancy. Consequently, solutions for maximizing the gross rate of gain and energetic efficiency differed for dives to any given depth. Dive effort in free-ranging imperial shags measured during the breeding season was consistent with a strategy to maximize the gross rate of energy gain. We suggest that the divergence of time and energy costs with dive depth has implications for the measurement of dive efficiency across diverse diving taxa.

Environmental and operational variability affecting the mortality of Black-browed Albatrosses associated with long-liners in Argentina

Abstract The effects of different environmental and operational factors on the incidental capture of Black-browed Albatross (Thalassarche melanophris) in long-line fishing operations were analysed. This is the most commonly captured seabird by Argentine long-line fishing vessels, and significant decreases in its populations have been mainly attributed to long-line fishing practices. The estimated mean rate ± s.d. of by-catch for the analysed period (1999–2003) was 0.03 ± 0.39 birds per 1000 hooks. Black-browed Albatrosses were mainly caught during day settings. Higher capture rates were observed during autumn and winter. The effect of the length of long-lines on the incidental capture of Black-browed Albatrosses was also analysed, showing that higher capture rates occurred when short long-lines were deployed. Seasonal differences in the distribution of captures were observed, being widely distributed to the north of the shelf-break during autumn—winter (i.e. non-breeding season) and mostly concentrated in southernmost latitudes, closer to the presumed breeding area in the Malvinas (Falkland) Islands during spring—summer. Mortalities during winter were mainly associated with the Patagonian Toothfish (Dissostrichus eleginoides) fishery, while those observed during summer were associated with long-liners targeting Kingklip (Genypterus blacodes) on the Patagonian Shelf.

Spatio-temporal variation in mortality rates of White-chinned Petrels Procellaria aequinoctialis interacting with longliners in the south-west Atlantic

The White-chinned Petrel Procellaria aequinoctialis is the second most commonly captured species by Argentinean longliners. The severe declines that this species has experienced in some of its populations (e.g. South Georgia Islands) have been principally attributed to incidental mortality associated with longliners. In this study we analyse the spatio-temporal variability in the mortality rates of White-chinned Petrels on the Patagonian Shelf and the effects that environmental and operational variability have on such mortality. The average capture rate (± 1 SD) for the period 1999–2003 was 0.014 ± 0.090 White-chinned Petrels for every 1,000 hooks deployed. Higher capture rates were observed when short longlines were deployed. Capture rates were not affected by the wind speed or by the time to the full moon. The distribution of the captures differed throughout the year. During autumn–winter most captures took place in the north of the Patagonian Shelf, whereas during spring–summer incidental captures occurred principally to the south between 45°S and 50°S. Resumo El Petrel Barba Blanca Procellaria aequinoctialis constituye la segunda especie mas frecuentemente capturada por la flota palangrera Argentina. Los importantes decrecimientos poblacionales observados en algunas poblaciones de esta especie (e.g. Islas Georgias del Sur) han sido principalmente atribuidos a la mortalidad incidental asociada a embarcaciones palangreras. En este trabajo se analizo la variacion espacio- temporal en las tasas de captura incidental del Petrel Barba Blanca a lo largo de la Plataforma Continental Argentina y se estudio el efecto que diferentes variables ambientales y operacionales tienen sobre la mortalidad incidental de esta especie. La tasa de captura promedio (± d.s) durante el periodo 1999–2003 fue de 0.014 ± 0.090 Petreles Barba Blanca cada 1.000 anzuelos. Mayores tasas de captura fueron registradas al utilizar palangres cortos. No se observo un efecto de la intensidad del viento ni de la distancia a la luna llena sobre las tasas de captura. La distribucion de las capturas difirio a lo largo del aao. Durante el otoao-invierno la mayoria de las capturas estuvieron localizadas al norte de la Plataforma Continental Argentina, mientras que durante los meses de primavera-verano las capturas estuvieron localizadas principalmente entre los 45°S y 50°S.

Use of natural and anthropogenic resources by Olrog's Gull Larus atlanticus : implications for the conservation of the species in non-breeding habitats

We studied the exploitation of crab-beds and fishing grounds by Olrog’s Gulls Larus atlanticus in non-breeding areas along the coast of Buenos Aires province, Argentina. During 2004 and 2005, censuses were performed in different areas of Mar Chiquita coastal lagoon and Mar del Plata harbour. Additionally, from April to August 2005 the movements of five non-breeding individuals were studied by means of radio-telemetry. At both study sites the highest numbers of Olrog’s Gulls were observed between June and August. A total of 278 radio-tracked locations (from 407 samples) were registered. All the tracked individuals showed strong site fidelity, with 96% of the radio signals registered in the vicinity of the lagoon’s mouth, associated with both crab-beds and areas where sport-fishing activities took place. Conservation issues in nonbreeding areas should be tackled in the near future, given the conservation status of this species (Vulnerable) and the fact that each year several Olrog’s Gulls are being killed because of their interaction with sport-fishing activities.

Foraging behaviour and diet of American Oystercatchers in a Patagonian intertidal area affected by nutrient loading

Abstract Eutrophication increases the biomass of opportunistic green macroalgae that covers intertidal zones, and macroalgal blooms may affect the intertidal invertebrate community and predation of invertebrates by shorebirds. In San Antonio Bay, Argentina, eutrophication from the discharge of wastewater from a coastal town produces periodic macroalgal blooms. Our aim was to assess if macroalgal blooms affect the foraging behaviour and diet of the American Oystercatcher (Haematopus palliatus). A macroalgal transplant experiment was performed in order to evaluate how epifaunal species respond to a macroalgal canopy. The availability of prey for Oystercatchers, and their foraging behaviour and diet, were analysed in two paired channels with different nutrient loadings. Oystercatchers generally ate the most profitable prey and avoided prey with a profitability value lower than the mean rate of energy intake. During the macroalgal blooms, Oystercatchers avoided two prey species with high profitability values, shifting their foraging strategy and feeding onto a suboptimal prey but with a high encounter rate. Our results suggest that nutrient loadings and the macroalgal blooms that they generate have effects on the diet and foraging behaviour of Oystercatchers, which results in an increase of the average rate of energy intake of Oystercatchers foraging along the channel subject to a macroalgal bloom.

Repeated observations of a Cape Gannet Morus capensis on the coast of Patagonia, Argentina

1 Department of Biology, University of Washington, Box 351800, Seattle, WA 98195-1800, USA, and the Wildlife Conservation Society, 2300 Southern Boulevard, Bronx, NY 10460, USA 2 Biologia y Manejo de Recursos Acuaticos, Centro Nacional Patagonico – CONICET, Boulevard Brown 2915, Puerto Madryn, Chubut, Argentina 3 Centro Universitario Leonardo da Vinci, Rodovia BR 470, Km 71, N° 1040, Santa Catarina, Brazil 4 Universidad Nacional de la Patagonia San Juan Bosco, Boulevard Brown 3700, Puerto Madryn, Argentina * Corresponding author, e-mail: gar@u.washington.edu

The eldest sibling is the lousiest in an obligate brood-reducer seabird

ABSTRACT Previous studies on vertical transmission of lice on terrestrial birds have shown that the intensity of parasitism can vary within broods in relation to the hatching order of chicks. In species where the hatching order has an important effect on chick survival, lice would benefit from living on the host with the highest survival prospects. In the present work, we test this hypothesis using as model lice from the Imperial Shag, an obligate brood reducer. Our specific aims were to investigate how infestation by Eidmanniella pellucida varies in relation to the age, the order of birth and the hatching date of chicks. We observed that chicks were infested by their parents during their first days of life, mainly by lice in nymphal stage. The first chick to hatch was the most infested. Infestation was also affected by hatching date, increasing as the season progressed, reaching a maximum at the peak of the breeding season and decreasing gradually after that. The age of the chick was unrelated to the intensity of infestation. Our results suggest that lice would prefer the chick that is more likely to survive and highlights the adaptive strategies of lice according to the ecology of their hosts.