We studied the migration of Magellanic penguins near the southern tip of the breeding distribution, and for the first time found evidence of partial migration for this species within the same colony. ...Forty‐three percent of the penguins studied stayed within ~ 290 km of the colony (residents), while others went northwards as far as 2000 km. All penguins spent the same amount of time at sea and traveled similar total distances, but residents experienced colder waters (2°C lower) and habitats with lower Chlorophyll‐a concentrations than migrants. The two habitats are inhabited by different prey items, consequently offering the penguins distinct prey options. We have shown high variability in the non‐breeding dispersion behavior of Magellanic penguins within the same colony; nonetheless, further research is required to understand the proximate and ultimate causes, and the consequences, of this behavior.
The Magellanic penguin Spheniscus magellanicus is a top predator and a major consumer of marine resources in the Patagonian Continental Shelf and worldwide. It is the most migratory of the Spheniscus ...penguins, but until recently, its migration route was only partially known. Our aims with regard to the Magellanic penguin breeding on Isla Quiroga, Argentina, were: 1) to compare the distribution during the winter period between sexes and 2) in case that habitat is segregated, to evaluate possible proximate causes like competitive exclusion and/or habitat specialization. In March 2017 and 2018, prior to migration, we equipped 26 penguins with MK3/4 geolocators, which were recovered in late September/early October. Penguins dispersed northwards up to 29°S and southwards up to 56°S, near the Beagle Channel, being distributed over 2158 ± 50 km of latitudinal range and showing a large‐scale distribution pattern across longitudes in waters within the continental shelf. We found a longitudinal segregation between sexes in their winter grounds, with males closer to the 200‐m isobath and further from the coastline than females. Morphological and physiological differences between sexes might allow males to dive deeper at a lower cost than females, which could result in a more offshore path for males. This spatial segregation was supported by bulk blood stable isotope values and estimated isotopic niche, which differed between males and females at their arrival from winter breeding grounds, but not while penguin breed and behave as central place foragers in the colony. For the first time in this species, we combined two independent tools, geolocation and stable isotope data, and find that sexual segregation in habitat use could potentially generate an optimal winter foraging strategy for both sexes, precluding potential intersex competition for food.
In birds, possible explanations for a bias in brood sex ratio include differential cost of rearing nestlings of different sexes, and different parental fitness returns related to offspring sex. We ...studied brood sex ratio of Magellanic penguins,
Spheniscus magellanicus
, in Puerto Deseado for 3 years. Our objectives were to compare the growth curves and energetic costs of rearing nestlings of different sexes, and to evaluate the possible implications of environmental and parental condition in the establishment of a bias in the brood sex ratio. We also investigated the relationship between hatching order and sex, and its impact on brood survival. Asymptotic mass was 11.41% higher for males than for females. The energetic cost of feeding male nestlings was slightly higher than for feeding females, but the difference in energy requirements was only 2.6% of the total energy budget. During the 3 years, brood sex ratio was 0.53, and almost constant within years over the raising period, showing no sex allocation during feeding. Sea surface temperature, which is linked to higher prey abundance when colder, explained brood sex ratio at fledging. The sex ratio was male-biased during the coldest year. Parental body condition was not an important variable explaining brood sex ratio. There was no bias in nestling sex with respect to hatching order and nestling survival was not related to nestling sex. We conclude that, even though the cost of feeding male offspring is higher, it only involves a small fraction of total cost of raising nestlings and might not be responsible for an adaptive bias in the sex ratio of nestlings for this species. However, during good oceanic conditions, females might bias their brood sex ratio towards males, thereby potentially gaining an advantage by raising good-quality males.
Egg laying is one of the most important phases in a female bird's breeding cycle. Its cost is high because eggs contain all the resources needed for the development of an embryo. Variation in size ...and quality of eggs can have important long‐term consequences for offspring survival. Hatching asynchrony is known to influence sibling competition in many bird species. Last‐hatched chicks will have a competitive disadvantage throughout the pre‐fledgling period because they are smaller. The aim of this study was to analyze the effect of hatching asynchrony and egg size variation on the growth and fledging success of Magellanic penguin Spheniscus magellanicus chicks after disentangling the effects of parental condition. We simultaneously manipulated egg size dimorphism, hatching asynchrony and parental condition by performing a cross‐fostering experiment, creating broods with controlled egg size dimorphism and hatching asynchrony in a colony of Magellanic penguins located in Isla Quiroga, Santa Cruz, Argentina. We found that hatching asynchrony had a negative effect on last‐hatched chicks, but this disadvantage was mitigated by egg size dimorphism in their favor. Moreover, females in good condition invest more in second than in first chicks, which, added to a greater investment by foster fathers, leading to offspring fledging in good condition. On the contrary, for the first‐hatched chicks, we found that body condition of the biological father was an important factor for their growth. We conclude that raising more than one chick seems to be a decision based on parental condition throughout the breeding season.
•Forage fishes constitute key species in marine food webs and their biomass largely fluctuates between years.•The Magellanic penguin is a conspicuous top predator of the Southwest Atlantic Ocean that ...feeds upon forage fish.•Magellanic penguin isotopic niche size increases with decreasing abundance of forage fish.•Magellanic penguin trophic preferences indicate the abundance of forage fish.
As marine ecosystems are harvested or modified by anthropogenic or natural factors, there is an increasing demand for indicators of trophic web health or status. The Magellanic Penguin (Spheniscus magellanicus) is a widely distributed species that forages in the Patagonian Shelf. During breeding, this species is a central-place forager that feeds mainly on schooling fish, with Argentine anchovy (Engraulis anchoita) being the dominant prey in the north and Fuegian sprat (Sprattus fuegensis) in the south of the Argentine Patagonian distribution (40–55°S). Like most forage fish, both prey species display large natural interannual recruitment fluctuations. We used stable isotope analysis of adult Magellanic penguin blood obtained at twelve colonies along its Patagonian latitudinal range to assess changes in isotopic niche and in trophic level as a response to interannual changes in abundance and spatial segregation of forage fish size classes, respectively. Magellanic penguins showed large isotopic niche fluctuations among breeding seasons, explained by the contribution of forage fish in their diet. Furthermore, the size of the isotopic niche negatively correlated with forage fish biomass estimated from acoustic surveys and with their contribution in penguin diet. We defined an isotopic niche size threshold that indicates low abundance of forage fish in nearby feeding grounds. In addition, the trophic level of Magellanic penguins increased with latitude, which corresponds to the size-distribution of both main forage fish species, showing that penguins from different colonies target different size classes of their main prey. We present here a simple and easy to implement indicator to monitor the status of the base of the food web in one of the most productive marine areas in the world, which constitutes the feeding ground of a diverse group of high trophic level predators and sustains large-scale fisheries.
The current information about the diet composition of the rock shag (
Phalacrocorax magellanicus
) in the SW Atlantic coast comes mainly from conventional pellet or stomach content analysis from a ...few locations situated in northern Patagonia (Chubut Province, Argentina). In this work, we studied the diet of breeding rock shags over several years at a colony from southern Patagonia (Ría Deseado, Santa Cruz Province, Argentina) using a combined technique of conventional diet assessment (pellet analysis) and stable isotope analysis of carbon and nitrogen. Our results confirm the importance of benthic prey and the low inter-annual variability in the diet of the rock shag. These results coincide with previous research in relation to the exploitation of slow moving, predictable, but low-energy density prey. The stable isotope mixing models, which was informed with prior data obtained from pellet analysis, allowed for the detection of subtle differences between the diet of adults and chicks, consisting in the incorporation of higher proportions of cephalopods, an energy-rich prey, in the diet of chicks. By comparing our results with the diet of the red-legged cormorant, which breeds in sympatry in the Ría Deseado Estuary and whose diet composition is strongly pelagic, we suspect a certain level of trophic resource partitioning between these rock shag and red-legged cormorant.
In birds, the adaptive significance of hatching asynchrony has been under debate for many years and the parental effects on hatching asynchrony have been largely assumed but not often tested. Some ...authors suggest that hatching asynchrony depends on the incubation onset and many factors have been shown to influence hatching asynchrony in different species. Our objective was to analyze the exact timing of the onset of incubation and if this affects hatching asynchrony; and, in addition, which other factors (brood patch development, incubation position, adult body condition, intra‐clutch egg dimorphism, laying date and year) affect hatching asynchrony in Magellanic penguins Spheniscus magellanicus. We first estimated the eggshell temperature at which embryo development starts, with a non‐destructive and novel method. We then recorded individual egg temperatures in 61 nests during incubation, and related them, and other breeding parameters, to hatching asynchrony. We also observed incubation positions in 307 nests. We found a significant positive relationship between hatching asynchrony and the temperature that the first‐laid egg experienced during egg laying and between hatching asynchrony and the initial brood patch area. We also found a negative relationship between hatching asynchrony and the difference in temperature between second and first‐laid eggs within a clutch, measured after the egg‐laying period was finished. We ruled out position of the eggs during incubation, adult body condition, egg volume, laying date, and study year as factors influencing hatching asynchrony. The egg temperature during laying and the difference in temperature between eggs of a clutch are determinants of hatching asynchrony in Magellanic penguins.
The use of combined conventional and stable isotope analyses to study the diet of seabirds has become very frequent. Unfortunately species and tissue-specific Trophic Discrimination Factors (TDF), ...necessary to run stable isotope mixing models in the most performing way, are lacking for a wide number of seabird species. We assessed the process of inspecting and selecting the most adequate TDFs by running mixing region simulations with three different TDFs scenarios. This was carried out in a combined dietary study of a widespread but poorly studied seabird from the Americas: the Neotropic Cormorant (
Phalacrocorax brasilianus
), at a breeding colony from coastal Patagonia. The mixing models were run with the best fitting carbon and nitrogen TDFs (whole blood), which were those obtained with R package SIDER, a Bayesian inference-based model predicting the TDFs of consumers considering their ecology and phylogenetic relatedness. We found that cormorants fed on rather mobile fish of a fairly variable ecological spectrum, both benthic and pelagic, and showed low prey diversity. Our results coincide with the overall generalist and opportunistic piscivorous habit found at different coastal areas along its broad distribution range. Despite some differences found in the proportion estimates of the main prey between the two methods, their combination through the incorporation of prior information into the mixing models provides a comprehensive trophic profile. Finally, the use of SIDER, alongside the inspection and comparison of different potential TDF values, offered a simple and effective framework to calculate and select the most adequate specific TDFs to be employed in stable isotope mixing models.
Kelp Gull is the most abundant gull species in the Southern Hemisphere, occurring in South America, Africa, New Zealand, Australia, Sub-Antarctic Island, and Antarctica Peninsula. There is no ...consensus about the number of subspecies; some studies proposed two and others six subspecies. Previous genetic studies with this species show low genetic diversity at mtDNA, in contrast to the high variability found in the nuclear gene. Thus, this study proposed to evaluate the subspecies of Kelp Gull through mtDNA, recovering the demographic history and population genetic structure throughout the South Hemisphere. For this, we sequenced Cytochrome
b
in 98 samples of Kelp Gull from Brazil, Argentina, and Antarctica, and added to the dataset 20 haplotypes available in GenBank. Bayesian Phylogeny did not support a clade in any subspecies proposed. However, it is possible to observe the genetic population structure of Kelp Gull in the Southern Hemisphere based on haplotype frequency. In addition, there is evidence that Kelp Gull lost genetic diversity, following population expansion during Holocene around 2500–3000 years ago.
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