Larus Atlanticus Research Articles

Effect of urbanization on individual condition of a threatened seabird: the Olrog’s Gull Larus atlanticus

Effect of urbanization on individual condition of a threatened seabird: the Olrog’s Gull Larus atlanticus

Where are you from? Isotopic tracing of juvenile Olrog’s Gulls from Mar Chiquita during the wintering season

ABSTRACT Individual traits such as age-class can have profound effects on space utilisation by individual birds, with juvenile birds more often exhibiting dispersive movements. We studied the origin of juvenile Olrog’s Gulls Larus atlanticus, a threatened species, using stable isotopes ratios of carbon (δ13C), nitrogen (δ15N) and sulphur (δ34S). We analysed feathers from individuals captured in the wintering season at Mar Chiquita Coastal Lagoon, Argentina, and the potential trophic sources of their breeding sites at Bahía Blanca and San Blas. Mean δ13C was similar for trophic sources and mean δ15N was higher for Bahía Blanca. The δ34S showed a greater variation among prey species than among sites. The mean contributions of the main colonies resulted in assigning 37.5% individuals as from Bahía Blanca, 16.7% from San Blas, and 45.8% undetermined. Results indicate that Mar Chiquita coastal lagoon attracts juvenile Olrog’s Gulls dispersing from the two main breeding grounds of the species. This work is one of the first approaches to study the origin of dispersive juvenile larids through the application of stable isotope analysis. This isotopic approach allows obtaining trophic and movement information when it is not possible to use other tools.

Innovative problem-solving in a threatened gull species, the Olrog's Gull (Larus atlanticus).

Innovation, a process that plays an important role in the ecology and evolution of species, is considered an expression of behavioral flexibility in animals. Here we analyzed innovative problem-solving ability and performance enhancement through learning in the Olrog's Gull (Larus atlanticus), under controlled processes and experimental conditions. Trials were undertaken with nine adult individuals captured at a highly urbanized coastal area of Argentina. Each individual was presented with a Plexiglas box that could be opened by pushing or pulling two lids, each lid leading to a separated food reward. We measured problem-solving ability through consumption latency and the number of solved lids. As explanatory variables, we measured contact rate, as a measure of persistence, and the number of effective contacts. The results showed that the contact rate and effective contacts did not affect variables related to problem-solving ability during the first confrontation of the individuals with the closed box. Consumption latency decreased significantly throughout the trials, and with increasing contact rate and effective contacts. The number of solved lids increased through the trials independently of the contact rate and the total effective contacts with the box. Although persistence did not influence individuals' performance during the problem-solving test; this variable affected individuals' ability to solve the task throughout trials. Learning was evidenced by the decrease in the resolution time across experiments, suggesting that successful individuals improved their performance probably through a trial-and-error process. Evaluation of behavioral responses of a threatened seabird to a novel problem-solving task adds knowledge to previous field studies and provides a better understanding of the ability of individuals to adjust their foraging behavior in highly urbanized areas used during the non-breeding season.

Factors affecting individual foraging behavior in a threatened seabird: Olrog’s Gull (Larus atlanticus) as a case study

The analysis of feeding strategies in animals is one of the most important topics in foraging ecology. The individual’s foraging behavior depends on both the individual’s own actions and the behavior of other foragers. Here we analyse the effect of the sex and group size on the foraging behavior of immature Olrog’s Gull (Larus atlanticus Olrog, 1958), endemic to the Atlantic coast of southern South America and regionally listed a threatened species. Birds were captured, banded, sexed, and aged during the non-breeding season in Mar Chiquita coastal lagoon, Argentina. The foraging behavior was quantified by observations made on individuals of known identity, recording the size of foraging groups, as well as prey size and type. Foraging parameters estimated were foraging effort, capture rate, and foraging efficiency. Males spent more time in agonistic behavior and captured larger prey. With an increase in group size, the capture rate, the capture of small crabs by males, and the foraging effort were higher. The agonistic behaviors, size of consumed prey, and foraging effort were affected by individual identity. Our study pinpoints factors underlying variation in the foraging behavior of Olrog’s Gulls and illustrates the importance of modelling individual variation when analyzing foraging behavior.

HEMATOLOGIC METRICS FROM OLROG'S GULL (LARUS ATLANTICUS) DURING THE NONBREEDING SEASON IN ARGENTINA.

Ecophysiology and conservation studies often require the prior establishment of baseline physiologic metrics. For instance, expected reference intervals for health metrics are valuable tools for veterinarians and conservationists who monitor the health status of endangered populations and species. This study establishes reference intervals for hematologic metrics in free-ranging Olrog's gull (Larus atlanticus) during the nonbreeding season. Fifty-six gulls (immature and adults) were captured and studied in Mar del Plata and neighboring coastal areas (Buenos Aires, Argentina) during the winter of 2018 (n = 22) and 2019 (n = 34). Hematocrit, red blood cells (erythrocytes), hemoglobin, mean cell volume, mean cell hemoglobin (MCH), MCH concentration, white blood cells (WBC; leukocytes), heterophils, lymphocytes, eosinophils, monocytes, and basophils were analyzed. Additionally, the variability of hematologic metrics according to body weight, sex, age, and calendar year was examined. Hematologic metrics were in line with those reported in other seabird species. Males had greater body weight and MCH than females. The heterophil to lymphocyte ratio and lymphocyte levels were higher in adults than in immatures. Hematocrit, WBC, heterophils, and basophils also varied significantly between calendar years. The results highlight the importance of appropriate metrics and reference intervals for monitoring the health status of this threatened species, and it is recommended to implement such comparative assessments among populations.

Chlorpyrifos and persistent organic pollutants in feathers of the near threatened Olrog's Gull in southeastern Buenos Aires Province, Argentina.

The use of bird feathers to assess environmental contamination has steadily increased in ecotoxicological monitoring programs over the past decade. The Olrog's Gull (Larus atlanticus) is a species endemic to the Atlantic coast of southern South America, constituting one of the three threatened gull species listed in the entire American continent. The aim of this study was to assess the exposure to Persistent Organic Pollutants (POPs) and chlorpyrifos in the Near Threatened Olrog's Gull through the analysis of body feathers sampled at the Mar Chiquita coastal lagoon, the main wintering area of the species in Argentina, controlling for sex and age class. Chlorpyrifos showed the highest concentrations among all contaminants and groups of individuals (X¯=263ngg-1), while among POPs the concentration of organochlorine pesticides was higher than polychlorinated biphenyls and polybrominated diphenyl ethers, likely indicating the current use of these agricultural contaminant in the region. The highest values of total POP concentrations (males X¯=280ngg-1, females X¯=301ngg-1) were found in juvenile gulls, likely as a consequence of the incorporation of pollutants during the breeding season. Subadult and adult birds showed difference between sexes in the concentration of contaminants, with higher levels in males than females. The results highlight the need to include birds of different sex and age classes in order to better understand the variation in pollutants loads. The present study provides relevant information to improve the conservation status of the Olrog's Gull and new insights about the environmental health of the Mar Chiquita coastal lagoon, Argentina, a MAB-UNESCO World Biosphere Reserve. However, there is a continued need for long-term monitoring programs focusing on this threatened species to understand the effects of pollutants on its population.

Distribution of Olrog’s GullLarus atlanticusfrom Bahía San Blas during the non-breeding period: signals of partial migration

SummaryThe Olrog’s GullLarus atlanticusis an endemic and threatened species of the south-western Atlantic. Little is known about its movements during the non-breeding period. The objective of this study was to analyse the migration of the species by tracking adults from Bahía San Blas (Buenos Aires province, Argentina) with geolocators and using information of sightings of ringed gulls. Differences between males and females were evaluated using tracking data and ringed data were used to determine age differences. A single core area (kernel 50%) from 21 tracked birds was identified. This area included the study colony and also other breeding colonies located up to 300 km to the north. The range area (kernel 95%) included coastal areas up to 1,000 km from the colony. All sightings of ringed gulls (n= 41) occurred north of the breeding colony, however 12 adult individuals were sighted during the winter in its breeding grounds. Our results suggest the occurrence of partial migration behavior in Olrog’s Gull. The migration pattern reported here implies than during the non-breeding season, breeding and wintering areas away from the nesting grounds should be considered as one system in the design of conservation strategies for this regionally threatened gull.

SERUM BIOCHEMISTRY VALUES FOR THE OLROG'S GULL (LARUS ATLANTICUS): A STUDY BASED ON FREE-LIVING INDIVIDUALS.

Analysis of serum parameters provides information about body condition, nutritional state, and health status of individuals/species, and has broad application in ecological research and veterinary diagnosis. This study establishes baseline values for serum chemistries of the Olrog's gull (Larus atlanticus). Glucose, urea, uric acid, total protein, globulin, albumin, cholesterol, triglyceride, calcium, and phosphorus concentrations were determined, as was the activity of the following enzymes: alkaline phosphatase, creatine phosphokinase, aspartate aminotransferase, and alanine aminotransferase. Thirty nonbreeding gulls (juvenile and subadult individuals) were captured and studied in Mar Chiquita Reserve (Buenos Aires, Argentina) during the wintering periods 2016 (n = 17) and 2017 (n = 13). In general terms, most values for the parameters reported were in line with those previously described for other seabirds. The year had a significant effect on several of the biochemical parameters evaluated, and the sex had a significant effect on the alkaline phosphatase and calcium. This study has defined the serum biochemical reference signatures for free-ranging Olrog's gulls during the nonbreeding period, and contributes to the knowledge of the overall health status of this threatened and endemic species.

Use of winter habitat at an early age: spatial ecology and association with human activities of juvenile Olrog’s GullLarus atlanticus

SummaryOlrog’s GullLarus atlanticusis an endemic species of the Atlantic coast of southern South America and is currently listed as ‘Near Threatened’ on the IUCN Red List. The species breeds in coastal wetlands of Buenos Aires and Chubut provinces of Argentina and during winter migrates northwards as far as southern Brazil. During the breeding season the species is considered to have a specialised diet, foraging mostly on crabs. However, during the non-breeding season the gull presents a wider dietary spectrum (including fish) as a result of a potential association with commercial and sport fishing activities. The main goal of this study was to analyse the habitat use and overlap with natural and anthropogenic food resources of juvenile Olrog’s Gull during the winter in Mar Chiquita Lagoon, Buenos Aires. Twenty-two GPS devices were deployed during the winters of 2013 and 2014. A total of 1,088 fixes was gathered by GSM (both seasons combined). Analysis showed that the individuals were (kernel 95%) distributed in a limited area along the mouth of the lagoon. The core area (kernel 50%) covered only 0.3 km2and was located in the south of the mouth. The overlap between juveniles and crab densities was lower than expected, while the overlap between juveniles and fishing effort was higher than expected during weekdays and lower during weekends. These results are of value for the further development of marine conservation measures for wintering areas which have so far been somewhat neglected while addressing the conservation status of the species.

Evaluation of neophobia in a threatened seabird: Olrog’s Gull (Larus atlanticus) as a case study

ABSTRACTBehavioural differences between individuals are expected when animal face novel stimuli. Aversion responses in such situations are called neophobia. Here, we assessed the degree of neophobia towards objects with respect to social context and age in Olrog’s Gulls (Larus atlanticus). The responses of individuals in trials in which a novel object was placed at a feeding station were compared with those of individuals in trials without a novel object. In the presence of a novel object, gulls consumed food in less than 60% of the cases. We found one type of object where gulls expressed a high degree of aversive response. The probability of a gull consuming bait from a feeding station was higher in juveniles than sub-adults, and increased also with the number of adults close to the feeding station. Consumption latency was higher during treatment trials than during the control trials. The degree of neophobia in juveniles decreased with increasing numbers of individuals close to the station. Our study demonstrated the potential relevance of neophobia in understanding foraging behaviour and potential conservation concerns in this near-threatened species.

Field Sexing Olrog's Gull (Larus atlanticus) Using Morphometry

Olrog's Gull (Larus atlanticus) is a vulnerable species; however, no study has addressed the relationship between body measurements and sex. To provide an easy and reliable work tool to identify the sex of individuals, adult Olrog's Gulls (n = 111) were weighed, several measurements were taken, and the sexes were determined using DNA analyses. All measurements showed significant differences between sexes, with males being significantly larger (Range = 4.0-15.1%) in all measurements. Logistic regression models were selected using the Akaike information criterion and were validated using leave-one-out cross validation. The best set included three models. Model 1 performed best and included head-bill length, bill depth, wing length and body mass as independent variables, and was closely followed by model 2, which contained the same variables with the exception of wing length. Model 3 included head-bill length, body mass and wing length as independent variables. Model 1 was 1.3 and 2.1 times more likely to be the best model than models 2 and 3, respectively. Model 1 correctly assigned the sex in 94.6% of all birds and 93.4% of females. Model 2 performance was marginally better and correctly assigned the sex in 95.5% of all birds and 95.1% of females. The correct classification of males was 96.0% in both models. Results demonstrate the validity of these measurements, which can be easily taken in the field to reliably determine the sex of Olrog's Gulls.

Persistent organic pollutants in sediments, intertidal crabs, and the threatened Olrog's gull in a northern Patagonia salt marsh, Argentina

Persistent organic pollutants (POPs) are of great concern for the environment. In this study we (a) determine levels and distribution of OCPs, PCBs, and PBDEs in sediments and two crab species (Neohelice granulata and Cyrtograpsus altimanus), (b) assess bioaccumulation in crabs, and (c) explore the occurrence of POPs in the Near Threatened Olrog's gull (Larus atlanticus) chicks and eggs in one of the most important salt marsh environments in the South West Atlantic. Sediments, crabs, and gull chicks and eggs showed POPs presence at low levels; being α-endosulfan, PCB-153, and BDE-47 the most represented compounds. In sediments, pollutant concentrations were lower than those reported in Canadian guidelines for the protection of the aquatic life. POP bioaccumulation was recorded in crabs, suggesting a risk to upper trophic level predators. Further studies are needed to understand the trophic effects of POPs in San Blas bay, particularly on the threatened Olrog's gull.

Bird diversity and conservation in the southern coast of Santa Catarina state, Brazil

Coastal lagoons and their surrounding habitats often harbour high biodiversity and some of the most threatened ecosystems in the world. However, in the Neotropics the biodiversity is often poorly described, lacking even inventories of species which therefore limits the assessment of threats and the stablishment of efficient conservation measures. We present here lists of bird species recorded at ten sites along the under-studied coastal lagoons of southern Santa Catarina, Brazil, collected mainly from October 2012 to March 2018. We present quantitative data for endemic and threatened species, identify migratory status and highlight distributional novelties. In total, we recorded 229 species encompassing 63 families, including twelve species of conservation concern, 11 endemic to the Atlantic Forest or Pampas zoogeographical provinces and 38 migrants. We provide new records of seven rare species in Santa Catarina (Larus atlanticus, Calidris pusilla, Aramides ypecaha, Bubo virginianus, Limnornis curvirostris, Phacellodomus ferrugineigula and Pseudocolopteryx flaviventris) and report the first evidence of occurrence of Schoeniophylax phryganophilus for the State. Based on our findings, we discuss the regional diversity and conservation of the avifauna.

Effect of Feeding Technique and Prey Characteristics on the Feeding Rate of Olrog's Gulls (Larus atlanticus)

The Olrog's Gull (Larus atlanticus) is a species that feeds almost exclusively on intertidal crabs. The influence of feeding technique, food source, and habitat characteristics on the feeding rate of breeding individuals was examined at Bahia San Blas, Argentina, from September to December 2007. Olrog's Gulls used four feeding techniques, with more prey captured by pecking than by peck-digging, head submergence, or up-ending. Olrog's Gulls fed throughout the tidal cycle using different intertidal zones when they were exposed and covered by water. However, feeding techniques used in exposed intertidal areas (pecking and peck-digging) resulted in significantly higher feeding rates. Feeding rate increased with average prey density and was higher when feeding in structured environments, characterized by the presence of rocks or oysters and high densities of the intertidal crab Cyrtograpsus altimanus. The burrowing crab Neohelice granulata is the main component of the Olrog's Gull diet during most of the breeding cycle. Although average density of N. granulata in feeding patches was lower than that of C. altimanus, body size of the former was significantly larger and energy density of individuals higher, resulting in a higher energy profitability of unstructured habitats. Prey switching toward C. altimanus during the young chick stage observed in previous studies may result from the need to feed chicks with smaller prey.

Enteric bacteria in Olrog’s Gull (Larus atlanticus) and Kelp Gull (Larus dominicanus) from the Bahía Blanca Estuary, Argentina

The Bahía Blanca Estuary in Argentina is under the effect of chronic microbiological pollution with untreated raw sewage and the pathogens associated with it. In this estuary, there are breeding colonies of Olrog’s Gull (Larus atlanticus) and Kelp Gull (Larus dominicanus), where parents feed chicks and themselves on prey and food items foraged at or near sewage outfalls and refuse tips where they can be exposed to pathogens of human and animal origin. The objective of this study was to assess the role of Olrog’s Gull and Kelp Gull as carriers of zoonotic pathogens of faecal origin. Bacterial recovery from faecal samples of both gull species was positive for Salmonella enterica var. Typhimurium, Salmonella enterica var. Gallinarum, Escherichia coli, Shigella dysenteriae, Enterobacter cloacae and Klebsiella pneumoniae. The prevalence and diversity of pathogens varied between gull species, and Olrog’s Gull tested positive for a wider range of pathogens than Kelp Gull. Escherichia coli was the most prevalent bacteria in chicks and adults of both gull species, followed by Salmonella spp. in Olrog’s Gull chicks, and Enterobacter cloacae and Shigella dysenteriae in Olrog’s Gull adults. The potential use of these gull species as sentinels of microbiological pollution in the Bahía Blanca Estuary is proposed.

The diet of Olrog's Gull (Larus atlanticus) reveals an association with fisheries during the non-breeding season

In this study, we used stable-isotope analysis to determine the importance of different food resources in the diet of an endemic gull species of the Atlantic coast of southern South America during the non-breeding period. We compared the isotopes 15N and 13C in the blood of Olrog's Gulls (Larus atlanticus) of different ages with those in potential prey of the Gulls. We also determined the abundance of Olrog's Gull in their wintering areas and attending coastal fisheries operations in a small region of Argentina. An isotope-mixing model showed differences in the isotopic signatures of adult, subadult and juvenile Gulls. Although the isotope-mixing model showed crabs as the main prey, it also showed that demersal and pelagic fish may be important in the diet. We speculate that the demersal and pelagic fish in the diet, shown by their isotopic signatures in the Gulls, may be taken in association with coastal fisheries, particularly bottom otter-paired trawling. At-sea observations showed that Olrog's Gulls were one of the most-common birds attending fishing operations of the Argentine coastal fishing fleet, taking advantage of fish mostly made available through hauling operations.

Enteric Infections by Trematodes and Nematodes in Olrog's Gull, Larus atlanticus

Trematodes and nematodes can be pathogenic helminths of birds. Every year during the breeding season, there is variable mortality among chicks from the largest Olrog's gull (Larus atlanticus) colony in Argentina. During two consecutive breeding seasons of Olrog's gull, we studied epidemiological and pathological aspects of infections by digeneans (Microphallidae) and nematodes (Acuariidae) in Olrog's gull chicks. Prevalence of nematode infection was 80.3% in 2005 and 89.2% in 2006, and mean intensity was 23.7 in 2005 and 50.8 in 2006. The risk for infection rose 34.3% and the intensity of infection 6.7% for every increase of 1 mm in head-beak length. The nematodes occupied the proventricular glands and caused disruption of their structure and mild inflammatory proventriculitis. Prevalence of digenean infection was 97.0% in 2005 and 97.3% in 2006. In 10-day-old live chicks, prevalence was 98.0% in 2006 and 95.3% in 2007. Infection was associated with severe catarrhal enteritis, lymphocyte/eosinophil-rich inflammatory responses, extensive fibroblast proliferation around the parasites, and disruption of the architecture of the adjacent crypts.

Enteric Infections by Trematodes and Nematodes in Olrog's Gull, Larus atlanticus

Enteric Infections by Trematodes and Nematodes in Olrog's Gull, Larus atlanticus

A Survey for Avian Influenza from Gulls on the Coasts of the District of Pinamar and the Lagoon Salada Grande, General Madariaga, Argentina

In the present study, fecal samples obtained from kelp gulls (Larus dominicanus), brown-hooded gulls (Larus maculipennis), and Olrog's gulls (Larus atlanticus) on the coast of the District of Pinamar, and grey-hooded gulls (Larus cirrocephalus) on the coast of the Lagoon Salada Grande and surrounding wetlands, General Madariaga, Buenos Aires Province, Argentina, were tested for evidence of avian influenza virus over a period of 3 yr. This surveillance in free-living wild birds in the Buenos Aires Province started in October 2008. Additional samples, which included cloacal swabs, tracheal swabs, or pooled organs, were obtained from sick or dead gulls that arrived at the Fundaci6n Ecol6gica Pinamar or were provided by the Direcci6n de Seguridad en Playas, Municipalidad de Pinamar. Samples were pooled according to date, species, and area. Pooled samples were inoculated in 9- to 11-day-old eggs, and after 5 days, allantoic fluids were tested for evidence of hemagglutination. None of the samples was positive for avian influenza viruses.

Spatial patterns in the use of foraging areas and its relationship with prey resources in the threatened Olrog’s Gull (Larus atlanticus)

Olrog’s Gull Larus atlanticus is a threatened species which feeds during the breeding season almost exclusively on crabs. We studied the use of foraging areas and its relationship with prey resources in Olrog’s Gulls breeding at Bahia San Blas, Argentina. Feeding areas were identified by radio-tracking 10 and 12 birds in 2006 and 2007, respectively (458 and 574 foraging trips, respectively) and monitoring 120 color-marked individuals during 2007 (3,447 locations). Feeding habitats were classified using dominant substrate and structural characteristics, and prey availability was assessed by sampling 2,220 1-m2 quadrates distributed throughout gull potential feeding areas. Both telemetry and monitoring of marked individuals indicated that gulls used 20 km of coastline but foraged mainly in three sectors located between 1.5 and 7 km north of the colony. During both years, the use of feeding areas varied throughout the breeding cycle, with a higher use of areas closer to the colony during the chick stage. Results showed a differential distribution of crab species depending on habitat type, with a dominance of Cyrtograpsus altimanus in structured environments and Neohelice granulata in muddy substrates with vegetation. During incubation, gulls mostly used areas characterized by high densities of N. granulata, while during the early chick stage they mostly used sectors with high densities of C. altimanus. Prey size varied among crab species, C. altimanus being significantly smaller. Changes in Olrog’s Gull use of coastal areas appear to be determined by the seasonal change in trophic requirements of adults and chicks, given the spatial segregation of their prey in relation to habitat characteristics.