Adrián Schiavini

Sexual differences in the foraging behaviour of Magellanic Penguins related to stage of breeding

Abstract Understanding the foraging behaviour of seabirds and its plasticity is vital to establish their role in marine food webs and their use as indicators of change in the availability of prey. The foraging behaviour of penguins is known to differ with locality, sex, stage of breeding and between years. We studied the diving behaviour of breeding Magellanic Penguins (Spheniscus magellanicus), using time-depth recorders, during incubation and brooding in the 2003–04 and 2004–05 breeding seasons at Isla Martillo, Tierra del Fuego, Argentina. Foraging trips during the incubation period were longer than those during the brooding period for both sexes in both years of the study. Sex-related differences in foraging behaviour were observed during the incubation stage. During the incubation stage females performed longer foraging trips than males, foraging effort was lower, and did not dive as deep as males in both years. Foraging success was lower for females than males during incubation only in 2003. Our results suggest that sexual differences, expressed as differences in the foraging parameters of males and females, only develop when Fuegian Sprat (Sprattus fuegensis), the main prey in this locality, is not abundant close to the colony. Females may be extending the volume of water they can exploit by extending the duration of trips (horizontal distance), whereas males do so by diving deeper (vertical distance). Our results show the fundamental differences in foraging strategies between the sexes in Magellanic Penguin are a consequence of environmental conditions not morphological differences between sexes.

Occurrence of hourglass dolphin (Lagenorhynchus cruciger) and habitat characteristics along the Patagonian Shelf and the Atlantic Ocean sector of the Southern Ocean

The hourglass dolphin, Lagenorhynchus cruciger, is one of the smallest cetaceans found in Antarctic waters. Although frequently observed, this is one of the least studied species of dolphin. In this study, we investigate the occurrence of hourglass dolphin in the South-West Atlantic and Southern Ocean from 42°S to 63°S and characterize the oceanographic and environmental features associated with their occurrence. Sighting data were collected during two scientific cruises in December 2009 and January and February 2011 and integrated into a geographical information system with environmental variables such as sea surface temperature, ocean colour, depth, distance to oceanographic fronts and distance from shore. We used a principal component analysis (PCA) to identify patterns in data and a non-hierarchic cluster analysis (K means) to classify observations into groups. A total of 19 sightings (96 individuals) were recorded. Group size ranged from one to twelve dolphins (mean 5.05). We could differentiate two groups in relation to the environmental conditions where animals were found, one group occurring in shallow coastal waters and the other occurring in deeper and colder waters further offshore. The present study contributes novel information on environmental measures associated with hourglass dolphin distribution in the South-West Atlantic and Southern Oceans. Additionally, it includes relatively high sighting clusters of this species in two highly productive and biodiverse areas (Burdwood Bank/Isla de los Estados and the South Shetland Islands).

Breeding biology of Magellanic Penguins (Spheniscus magellanicus) at the Beagle Channel: interannual variation and its relationship with foraging behaviour

AbstractInterannual variation in seabird foraging or reproductive behaviour may reflect fluctuations in marine resources. In this study, we evaluated different foraging and breeding parameters of Magellanic Penguins (Spheniscus magellanicus) from Martillo Island in the Beagle Channel, and the relationships between these parameters at different stages within the season (incubation, early and late chick-rearing) over three consecutive breeding seasons (2006–2007, 2007–2008 and 2008–2009). In 2007, we observed greater adult foraging effort (longer foraging trip duration and vertical travel distance, VTD) and lower chick feeding frequency, together with a slower growth rate and later fledging date of chicks, which we suggest was linked to lower food availability near the colony that year. The increased foraging effort appeared to be compensated by enhanced feeding activity (e.g., number of wiggles per dive). However, this increase did not coincide with a larger amount of food load brought to colony, which may have been due to a change in the type or size of prey consumed by the penguins. Magellanic Penguins from Martillo Island showed great plasticity in foraging behaviour, as evidenced by changes in consumed prey type or increased foraging effort and feeding activity when the consumption of their main prey item, Sprattus fuegensis, seemed to decrease. Moreover, during this particular breeding season, although the growth rate of chicks was lower, the breeding success remained constant throughout the study period, suggesting that the penguins managed to compensate for the apparent decrease in Fuegian sprat.ZusammenfassungDie Brutbiologie von Magellanpinguinen (Spheniscus magellanicus) im Beagle-Kanal: Variation zwischen Jahren und ihre Beziehung zum Nahrungserwerbsverhalten. Interannuale Variation im Nahrungserwerbs- und/oder Fortpflanzungsverhalten von Seevögeln könnte Schwankungen im marinen Ressourcenangebot widerspiegeln. In dieser Studie haben wir unterschiedliche Nahrungs- und Brutparameter von Magellanpinguinen (Spheniscus magellanicus) auf der Martillo-Insel im Beagle-Kanal sowie die Beziehungen zwischen diesen Parametern in unterschiedlichen Stadien der Brutsaison (Bebrütung, frühe und späte Kükenaufzucht) in drei aufeinanderfolgenden Brutsaisons (2006–2007, 2007–2008 und 2008–2009) ausgewertet. Im Jahr 2007 haben die Altvögel mehr Aufwand in die Nahrungssuche investiert (längere Nahrungstrips und längere vertikale Wegstrecken, VTD) und die Küken weniger häufig gefüttert, und die Küken wuchsen langsamer und flogen später aus. Wir schlagen vor, dass dies mit einer geringeren Nahrungsverfügbarkeit in der Nähe der Kolonie in diesem Jahr zusammenhängt. Der höhere Nahrungssuchaufwand wurde offenbar durch eine erhöhte Nahrungsaufnahme (z. B. Anzahl der Bewegungen pro Tauchgang) ausgeglichen. Dieser Anstieg stand jedoch nicht mit einer größeren zur Kolonie gebrachten Nahrungsmenge in Einklang. Dies könnte auf eine Veränderung des Typs und/oder der Größe der von den Pinguinen aufgenommenen Nahrung zurückzuführen sein. Magellanpinguine von der Martillo-Insel zeigen große Plastizität in ihrem Nahrungserwerbsverhalten. Diese offenbart sich anhand von Veränderungen des konsumierten Nahrungstyps und/oder der Steigerung des Nahrungssuchaufwands und der Nahrungsaufnahme, wenn der Verzehr der Hauptnahrung der Pinguine, Sprattus fuegensis, scheinbar abnimmt. Zudem blieb in dieser bestimmten Brutsaison der Bruterfolg über den gesamten Untersuchungszeitraum hinweg konstant, obwohl die Wachstumsrate der Küken niedriger war. Dies deutet darauf hin, dass die Pinguine den offensichtlichen Rückgang ihrer Hauptbeute ausgleichen konnten.