Andrea Raya Rey

Geographical variation in egg size dimorphism in rockhopper penguins

All crested penguins present a unique reversed hatching asynchrony: the larger second-laid egg (B-egg) hatches before the smaller first-laid egg (A-egg). Although both eggs often hatch, the A-chick generally dies of starvation within days after hatching. However, within rockhopper penguins, the population at the Falkland Islands is unique in that some birds manage to raise both chicks. Although it has been suggested that the egg size dimorphism between A- and B-eggs may explain how long both eggs and chicks survive, this hypothesis has never been explicitly tested. We expect that both eggs are retained longer in the less dimorphic clutches than in the more dimorphic ones. In this paper, we have compiled egg measurements for three rockhopper penguin species (Eudyptes chrysocome, E. filholi and E. moseleyi) in order to compare the intra-clutch egg size dimorphism among these species. Furthermore, we have collected new data to compare egg size dimorphism between two populations of E. chrysocome (Falkland Islands versus Staten Island). A-egg volumes are more variable between species and populations than B-egg volumes. E. chrysocome and especially the population from the Falkland Islands produces the largest A-eggs and the least dimorphic eggs. Nevertheless, as differences in A-egg volumes between species and between the populations of Falkland Islands and Staten Island are stronger and more significant than differences in egg dimorphism, we suggest that A-egg volume, more than egg dimorphism, could be one of the factors influencing the prevalence of twins. A large A-egg and/or reduced egg dimorphism is probably necessary to enable rockhopper penguins to raise two chicks, but other reasons may also be involved which enable them to keep both eggs and chicks.

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.

Comparative foraging behaviour of sympatric Humboldt and Magellanic Penguins reveals species-specific and sex-specific strategies

Abstract How closely related marine organisms mitigate competition for resources while foraging at sea is not well understood, particularly the relative importance of interspecific and intraspecific mitigation strategies. Using location and time—depth data, we investigated species-specific and sex-specific foraging areas and diving behaviour of the closely related Humboldt (Spheniscus humboldti) and Magellanic (S. magellanicus) Penguins breeding in sympatry at Islotes Puñihuil in southern Chile during the chick-rearing period. The average duration of foraging trips was <20 h and did not differ significantly between species or between sexes of each species. Magellanic Penguins made significantly deeper and longer dives than Humboldt Penguins. Males of both species made significantly longer dives than females. Total distance travelled per foraging trip was significantly greater for males than for females, and females made more direct trips (less sinuous) than males. Foraging effort was concentrated in waters up to 15 km to the west and south-west of the colony. The overlap in density contours was lower between species than between sexes within a species. In general, dive characteristics and foraging areas differed more between Magellanic and Humboldt Penguins than between the sexes of each species. In contrast to the findings of studies of flying seabirds, the foraging behaviour of these penguins differs more between species than between sexes.

Pelagic swarms and beach strandings of the squat lobster Munida gregaria (Anomura: Munididae) in the Beagle Channel, Tierra del Fuego

The present article is the first formal record of pelagic swarms and beach strandings of the squat lobster Munida gregaria in the Beagle Channel, southern South America. To describe size composition and natural diet of beach strandings and swarms, samples from strandings were taken in April 2007, March 2008 and March 2010. Samples from swarms were taken in May 2007 and April 2010. Also, during November 2008 and January 2009, two acoustic surveys were carried out to describe both, horizontal distribution and school metrics of swarms. Pelagic swarms and beach strandings were composed of 100% individuals of the morph gregaria of M. gregaria. Mean size of males and females in both, beach strandings and swarms, were similar. The diet of pelagic M. gregaria was composed mainly of crustaceans, unicellular algae and small macroalgae, sediment and particulate organic matter. Swarms of pelagic Munida took the shape of extended layers of varying density and height. Their positions in the water column were also variable: swarms were found at different depths, from the subsurface layer to near the sea bottom. Occasionally, some large swarms occupied most of the water column. In the Beagle Channel, SW winds during spring tides could be a forcing factor for M. gregaria strandings. The absence of shoaling animals in the Beagle Channel between 1997 and 2002 and the recent occurrence of swarms are coincident with their appearance in other locations in Patagonia. In consequence, we hypothesize that the factor influencing the formation of swarms must be acting at a regional scale.

Prey Search Behavior of the Imperial Cormorant (Phalacrocorax atriceps) during the Breeding Season at Punta León, Argentina

Abstract. Behavior by a foraging seabird during the breeding season can be examined by analyzing time invested throughout the foraging route to determine the presence of Area-Restricted Search (ARS) as well as other characteristics related to the shape of the foraging path and activity (flying, resting or diving). Forty-six Imperial Cormorants (Phalacrocorax atriceps), 18 males and 28 females breeding at Punta León, Argentina (43°04′S; 64°2′W), were fitted with GPS loggers recording one foraging trip (sampling interval: 1 second) in 2004, 2005, 2007 and 2008. Trip duration was longer, on average, for females (6.3 ± 1.9 h) than males (5.3 ± 1.6 h) (Mann-Whitney U test z 1,45 = 2.23, P = 0.026), but year had no significant effect on any of the path characteristics. ARS was detected in 43 individuals, 22 of which made smaller-scaled searches nested within larger ARS areas. Search scale was not correlated to maximum distance reached and did not differ between sexes nor years. Cluster analysis separated four types of behavior: short direct return trips (N = 7), long direct return trips (N = 31), random flight searches (N = 6) and loops (N = 2), with each behavioral type present in both sexes. Behavioral variability within a population may be due to differences in targeted prey type and spatio-temporal stability during the season, as well as to individual physiological constraints and life-history traits linked to how individuals search for food at sea.

Population Trend and Breeding Biology of Gentoo Penguin in Martillo Island, Tierra Del Fuego, Argentina

Abstract Data on population size and some aspects of the breeding biology of Gentoo Penguins (Pygocelis papua) have been studied as part of a long-term monitoring program at Martillo Island in the Beagle Channel, Tierra del Fuego. The colony of Gentoo Penguin on Martillo Island is the only one reported in Argentina and has been monitored regularly since 2000. Timing and hatching success were similar to those reported at other colonies in the South Atlantic Ocean/Antarctic Peninsula region. A maximum of twelve nests were recorded during the 2006/2007 season, with an average breeding success of 1.0 chicks/nest. The Gentoo Penguin colony at Martillo Island increased by 19% in the past 13 y, while other colonies in the south Atlantic region and the Antarctic Peninsula have been decreasing or stable.

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 experience and foraging behaviour of Imperial Shags (Leucocarbo atriceps) in Argentina

Abstract Breeding success depends on efficient foraging behaviour by breeding individuals. However, foraging skills are acquired over time and foraging behaviour is expected to be optimised over the course of successive breeding events. In 2008, 32 Imperial Shags (Leucocarbo atriceps) breeding at the Punta León colony, Argentina, either with prior breeding experience (4 males and 9 females) or without (10 males, 9 females), were fitted with tracking devices to record one foraging trip during the early chick-rearing period. Birds did not differ in the maximum distance from the colony or duration of foraging trips, but males spent more time flying than females. Inexperienced individuals spent more time diving than experienced individuals, and inexperienced males in particular spent more time flying and performed more dives than other birds. Experienced males and females differed in the areas that they searched most intensively, and inexperienced males used different areas from experienced males. This study shows the importance of considering sex-and age-related differences when studying behavioural aspects, such as foraging patterns in seabirds.

New records of South American sea lion Otaria flavescens predation on southern rockhopper penguins Eudyptes chrysocome at Staten Island, Argentina

Predation by fur seals and sea lions has been identified, among others, as a potential cause of the declines in rockhopper penguin populations. Here, we report a multiple predation event of southern rockhopper penguins Eudyptes chrysocome by South American sub-adult male sea lions Otaria flavescens at Staten Island, Argentina. The sea lions attacked and preyed on penguins mostly using a wait and rush tactic at sea, but in some cases, penguins were also pursued on land. Although observations suggested that only a few sea lions are involved in predation, further research is necessary to elucidate the importance of this predation in the rate of population decline.

Distribution and Density of Kelp Geese and Flightless Steamer Ducks Along the Beagle Channel, Tierra del Fuego, Argentina

Abstract We describe the distribution and estimate the density of the Flightless Steamer Duck (Tachyeres pteneres) and the Kelp Goose (Chloephaga hybrida) along the Beagle Channel, Tierra del Fuego, during the summer season (February and March) 1997. Using a 10-min transects method from a vessel; we estimated density and evaluated its relation with different characteristics of habitats. The study area was divided a priori into six zones. Due to the scarcity of information about these species, we reviewed previous literature to evaluate seasonal movements and made comparisons with other regions of Tierra del Fuego. Differences in habitat distribution compared with the previous studies in the same area are reported. In the Beagle Channel, the Flightless Steamer Duck was more abundant than the Kelp Goose. The observed distribution seems to be a result of a preference for the inner waters of the Beagle Channel, at the western sector of the study area. In spite of the difference in the distribution of the two waterfowl, both preferred similar habitats. The preferred habitat was protected coasts such as small bays, inlets, or sectors of the islands sheltered from the prevailing winds and currents. The geese moved during autumn and winter from the Beagle Channel and Staten Island to the Atlantic coast. In terms of difference in density between areas, the Kelp Geese were twenty times more frequent in Staten Island than around the Beagle Channel, while Flightless Steamer Duck were twice as dense in Staten Island than the Beagle Channel.