Nora Lisnizer

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.

Spatial and temporal variation in population trends of Kelp Gulls in northern Patagonia, Argentina

Abstract Many populations of seabird species with opportunistic or generalist feeding habits have expanded worldwide, possibly because they are using additional food resources provided by human activities. The Kelp Gull (Larus dominicanus) is a generalist feeder that often feeds on urban and fish waste and its populations have been expanding in several regions of the southern hemisphere. In Patagonia, Argentina, it is the most abundant species of gull. However, population trends have been reported for only a few colonies and there has been no evaluation of population changes at a regional scale. In this study we provide an update on the distribution and size of Kelp Gull colonies along 1800 km of coastline of northern Patagonia, and assess population trends over a period of 15 years (1994–2008) at different spatial scales (colony, coastal sector, region). In northern Patagonia, Kelp Gulls currently breed in 68 colonies, which range in size from a few to 11 000 breeding pairs. Ten new sites were colonised in the study period. Most colonies (74%) are increasing and the overall population increased by 37% (from 52 784 to 72616 pairs), at an annual growth rate of 2.7%. Two of the four coastal sectors showed significant annual increases (5%), whereas the other two remained stable. Our results confirm the expansion of populations of Kelp Gulls along a long section of the coast of northern Patagonia, although the observed trends varied with the spatial scale considered.

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.

Transfer processes drive population dynamics of kelp gull colonies in Patagonia: Implications for management strategies

Abstract The dispersal of individuals among breeding sites is considered to be one of the key processes in seabird population dynamics. The kelp gull (Larus dominicanus) is the most abundant gull in coastal Argentina, although its population dynamics in the region remains poorly understood. This article aims to address aspects of kelp gull demography along a wide coastal sector (~1800 km) in northern Patagonia to improve our understanding of population changes and contribute to the design of management strategies and monitoring programmes. Modelled scenarios suggest that annual increases of 10–20% are high for the species, and 29% of 62 evaluated colonies presented growth rates within this high reference range. Transfer processes among colonies (e.g. source–sink) contributed to the growth of at least six kelp gull colonies. These processes have been instrumental in the growth of small, and in some cases recently established colonies, which had generally higher growth rates and were found near large and long-established colonies. These are the first studies of kelp gull demography on the coasts of Argentina aimed at understanding the population dynamics of this species in a metapopulation context.

Variation in the Size of Eggs of Kelp Gulls (Larus dominicarius) at Two Colonies in Patagonia, Argentina

Abstract Although several studies have reported basic information about the size of Kelp Gull (Larus dominicarius) eggs, no attention has been paid to the comparison of patterns of intra-clutch variation at different breeding sites. Here, the variation in egg size of Kelp Gulls at two colonies from Patagonia, Argentina, was analyzed. The objectives were to characterize egg size variation in Kelp Gulls breeding at a recently established colony in Punta Loma that primarily relies on natural prey; and to evaluate if patterns of intra-clutch variation in that colony differ from those at Vernaci Sudoeste Island, a larger and well-established colony with access to supplementary food in the form of fishery waste. In two-egg clutches, first-eggs were larger than second-eggs. Neither average egg size nor intra-clutch patterns differed between study sites. Also, in two-egg clutches, egg size decreased as date of laying increased, probably due to younger birds laying smaller eggs later in the season. The pattern of intra-clutch variation in three-egg clutches differed between sites. Three-egg clutches at Vernaci Sudoeste Island presented similar sizes for first- and second-eggs and these were larger than third-eggs. This pattern contrasted with the steady decrease in relation to laying order that was observed at Punta Loma. Also, second-and third-eggs from Vernaci Sudoeste Island were larger than corresponding eggs from Punta Loma. Our data suggest that differences in egg size between colonies could be the consequence of enhanced food availability at Vernaci Sudoeste Island in the form of discards generated by trawl fisheries. Future studies to evaluate age of birds and inter-annual environmental stochasticity are needed to elucidate the effect of these factors on egg size variation.

Demographic and breeding performance of a new kelp gull larus dominicanus colony in Patagonia, Argentina

Summary. Understanding the processes involved in the establishment and persistence of new seabird colonies is important for improving conservation and management strategies. Over the past few decades, kelp gull Larus dominicanus numbers have increased in Patagonia, Argentina, and new colonies have been reported. We studied a recently established colony to analyse aspects of its population dynamics and breeding biology. The number of breeding pairs at Punta Loma increased from 13 to 233 in the seven years after the colony was established (2004–2011) and the number of chicks fledged per nest was low (< 1 chick per nest) compared to that of other long-established kelp gull colonies in the region. Modelled estimates of abundance assuming closed population dynamics for the Punta Loma colony were lower than observed (70% lower or more), suggesting that the observed growth cannot be explained by local productivity alone. Immigration from other colonies was likely to be the main factor responsible for the observed growth, being considerably higher than local recruitment. This study constitutes the first characterisation of demographic processes occurring during the initial years following colony establishment in kelp gulls. The main findings include rapid population growth driven by immigration and poor breeding performance potentially linked to a high proportion of young breeders. Our results highlight the key role of source-sink dynamics on the growth and persistence of new seabird colonies.

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.

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