Alejandro Gatto

DIVING BEHAVIOR AND FORAGING AREAS OF THE NEOTROPIC CORMORANT AT A MARINE COLONY IN PATAGONIA, ARGENTINA

Abstract The Neotropic Cormorant (Phalacrocorax brasilianus) is a widespread and abundant species distributed throughout the Neotropics. We report on diving behavior and foraging areas of Neotropic Cormorants in inshore marine waters of Patagonia, Argentina. Mean dive duration was 18.9 ± 5.3 sec and differed significantly among birds. Maximum dive duration was 43 sec. Birds spent 58–79% of their time at sea underwater. Mean recovery time at the surface between successive dives was 6.7 ± 1.5 sec, and was also significantly different among individuals. Mean diving efficiency (mean dive duration time/mean recovery time) was 2.6 ± 0.5 (range: 0.5–4.6). We were able to locate birds while feeding on 112 of 215 occasions. Almost 90% of mapped locations (68 feeding trips) were within 2.5 km of the colony. However, we did not receive a signal on 103 occasions, suggesting that foraging may also occur in waters outside the inlet where the colony was located. High variability in dive duration and recovery time is congruent with flexible foraging techniques and diet, as Neotropic Cormorants feed on both bottom and pelagic schooling fish.

Feeding Behavior and Habitat Use in a Waterbird Assemblage at a Marine Wetland in Coastal Patagonia, Argentina

Abstract Wetlands are critical foraging areas for many waterbird species, and their relatively high productivity often determines the coexistence of several species using food resources for breeding and/or refueling during migration. Between 18 October and 20 December 2000, we gathered information on foraging habitat use and feeding techniques of sixteen waterbirds during the austral spring at Malaspina inlet, Chubut, Argentina. We quantified the utilization by waterbirds of ten foraging habitat types and seven feeding techniques on seven fixed survey stations along the coastline, representing the different coastal habitats of the Malaspina inlet. The waterbird assemblage was structured in three main guilds: shallow water frequenters (three cormorants, two terns, a grebe, and two steamer-ducks), hard habitat peckers (two gulls, an egret, and an oystercatcher) and soft habitat frequenters (two oystercatchers, a sandpiper, and a duck). These differed greatly in their use of habitats and feeding techniques, suggesting clear differences in the use of food resources. Most of the groups defined used almost exclusively one feeding technique or habitat type. This fact and the low resource utilization breath values suggest the existence of a relatively high degree of specialization within this waterbird assemblage.

Foraging Patterns of Breeding Olrog’s Gull at Golfo San Jorge, Argentina

Abstract The spatial distribution and use of feeding areas by Olrog’s Gull (Larus atlanticus) breeding within a 34 km2 inlet at Golfo San Jorge, Argentina was investigated. Radio-transmitters were deployed on eight breeding adult birds during the late incubation period in 2001. Feeding areas were identified by means of radio-telemetry on the basis of 93 bird locations during a total of 89 foraging trips, and by direct observation of instrumented birds on 23 occasions. Both telemetry and visual data indicated that Olrog’s Gull fed almost exclusively within the inlet. In all, 85% of mapped locations (N = 93) were within 3 km of the colony, near the mouth of the inlet. The birds were consistent in the use of one particular area, and most of the tracked birds foraged mainly in one or two areas. Mean number of trips per day was 4.1 ± 0.99 (range = 1-9) and mean trip duration was 109 ± 31.2 min (range = 15-645 minutes). Both variables differed significantly among individuals. Gulls foraged at all states of the tide, although all eight individuals were more likely to forage during mid and low tides than during high tides. The small foraging range of Olrog’s Gull is defined by the spatial extension of intertidal habitats with crabs, being their main prey during the breeding season. Our results confirm the relatively high ecological specialization of Olrog’s Gulls shown in previous diet studies and their dependence on intertidal areas with grapsid crabs.

Provisioning of mates and chicks by Cayenne and Royal Terns: resource partitioning in northern Patagonia, Argentina

Abstract Cayenne (Thalasseus sandvicensis eurygnathus) and Royal Terns (Thalasseus maximus) breed in mixed colonies in Argentina. This paper presents the first detailed information on their breeding diet and assesses differences and overlap between species in the type and size of prey. During 2004 and 2005, observations of prey delivered to mates and chicks were carried out at Punta León, Patagonia. The diet of Cayenne and Royal Terns comprised nine and 10 prey species respectively. Fish comprised >99% of the prey of both species of tern in the two study years. Both species had a fairly specialised diet based on pelagic schooling fish, mostly Argentine Anchovy (Engraulis anchoita) and two species of silversides (Odontesthes spp.). Despite observed overlap in trophic resources, our results showed that Argentine Anchovy was the main prey for Royal Terns, whereas the two species of silversides together with Anchovy comprised the bulk of the diet for Cayenne Terns. Fish delivered by Cayenne Terns were significantly smaller than those by Royal Terns. Results suggested that both type and size of prey may be important factors permitting food partitioning between the two species of tern during the breeding season.

Relevance of forage fish in the diet of Magellanic penguins breeding in northern Patagonia, Argentina

ABSTRACT We quantified the trophic niche of Magellanic penguins (Spheniscus magellanicus) breeding and moulting in Golfo San Jorge, Argentina, through conventional stomach content and stable isotope analysis. A total of 112 adults were flushed during the early and late chick stages of 2011 and 2012 at Isla Vernacci Norte, and at least 15 prey taxa were found, including fishes, cephalopods, crustaceans and polychaetes. Overall, Argentine anchovy (Engraulis anchoita) showed the highest contribution in terms of importance by mass (68.1–85.3%, depending on chick stage and year), except for the old chick stage in 2011 when the shortfin squid (Illex argentinus) was the main prey consumed (56.0%). Based on carbon and nitrogen isotopic values from a total of 256 blood samples, corresponding to young and old chicks and to adults of both sexes sampled throughout the incubation, chick and moult stages at the above mentioned colony and years, Bayesian mixing model outputs showed that Argentine anchovy was always the main prey (48–86%). Bayesian mixing model outputs obtained from adults of both sexes and their chicks during the late chick stage of 2013 at Isla Vernacci Norte, Isla Tova and Isla Leones also showed that Argentine anchovy was the main prey consumed. This is the first comprehensive assessment of Magellanic penguin diet composition in northern Patagonia, quantifying the relative contribution of prey in the diet of adults and chicks at different stages of the annual cycle and years, and confirms the relevance of a forage fish such as the Argentine anchovy in its trophic ecology.

Assessing the trophic niche of South American Terns integrating conventional and isotopic methods

Abstract Conventional dietary studies combined with stable isotope analysis allowed the characterisation of the trophic niche of South American Terns (Sterna hirundinacea) breeding in Argentina. Direct observation of prey deliveries during mate-and chick-provisioning showed that the diet of South American Terns comprised at least 18 prey items, mainly pelagic schooling fish with smaller proportions of marine invertebrates. Argentine Anchovy (Engraulis anchoita) was the main fish prey. Adults delivered a higher proportion of fish and smaller prey to their chicks than to their mates. Analysis of stable isotope ratios in blood samples, using Bayesian stable isotope mixing models, indicated that adult Terns used a higher proportion of marine invertebrates for self-feeding than for mate-or chick-provisioning. Analyses of stable isotopes ratios in blood samples from chicks were consistent with the determination of diet from direct observation, and indicated differences from adults in both the proportion of different prey in the diet and trophic niche. In addition, isotopic niche analysis showed that chicks had a significantly higher trophic position compared with self-feeding adults during both mate-provisioning and chick stages. The results highlight the importance of combining stable isotope and conventional methods to adequately assess the food requirements of a population during the breeding season.

Animal Diversity, Distribution and Conservation

In this chapter, we summarize the ecological information available on the species of arthropods, reptiles, terrestrial birds and mammals known to occur at Peninsula Valdes, within the context of the Monte and Patagonia eco-regions. Two hundred species of insects and spiders, 12 species of reptiles, 139 species of birds and 23 species of native mammals inhabit today the island-like peninsula. We describe the community structure, distribution and abundance of the different taxa according to current knowledge. As the Peninsula Valdes region is a World Natural Heritage Site and a provincial protected area of high importance for the conservation of biodiversity and the regional economy, we found relevant to summarize knowledge on the effects of human activities on different components of biodiversity. Habitat degradation, grazing by domestic sheep and poaching are major threats to wildlife, although Peninsula Valdes still harbours some of the most abundant populations of wild species in Patagonia. It is a priority to implement the management plan available for Peninsula Valdes, taking into account the interactions between biodiversity, the different human activities and the physical environment. At the same time, it is necessary to identify and implement actions to conserve wild species and habitats, and also to develop programmes for the coexistence of responsible human activities and healthy wildlife populations.

Using Morphometry and Molecular Markers for Sexing South American, Cayenne and Royal Terns Breeding in Patagonia, Argentina

Abstract. The first information on the morphometry and sexual size dimorphism of the sympatric South American (Sterna hirundinacea), Cayenne (Thalasseus sandvicensis eurygnathus) and Royal (T. maximus maximus) terns from the Patagonia region in Argentina is provided, and a discriminant analysis to sex the three species is used. Morphological characters were obtained from South American Terns (n = 83), Cayenne Terns (n = 63) and Royal Terns (n = 20). All species were sexed using polymerase chain reaction-based molecular techniques. Sexes in the three tern species were only slightly dimorphic in size. Male Cayenne and South American terns were significantly larger than females in bill length, bill depth and head length. Royal Terns, in contrast, showed a high overlap in most morphological measurements, with head length being the only measurement that differed significantly between sexes. Head length correctly sexed 89% of South American Terns and 75% of Royal Terns, while a function including bill depth and head length correctly sexed 78% of Cayenne Terns. Our results provide a valuable tool for rapid sexing in the field of these three Patagonian terns, although reliable sexing in Cayenne and Royal terns should be preferentially achieved using a combination of morphometric and molecular sexing.