Rock Shags Research Articles

Anthropogenic debris in Kelp Gull and other seabird nests in northern Patagonia, Argentina

Anthropogenic debris is used as nesting material by many seabirds and may result in negative impacts. We assessed the frequency of occurrence of debris (>5 mm) in Kelp Gull (Larus dominicanus) nests at six locations along 2400 km of the Argentine coast, at different distances from urban centres, and in nests of other seven seabird species nesting syntopically. Frequencies in Kelp Gull nests were in general relatively low, ranging between 3.3 and 37.5%, and differed significantly among colonies. No relationship was found between frequency and distance to urban centres. Debris were recorded with frequencies of less than 19.2% in nests of Olrog's Gulls (L. atlanticus), Dolphin Gulls (L. scoresbii), Imperial Cormorants (Leucocarbo atriceps) and Magellanic Penguins (Spheniscus magellanicus), but not in nests of Neotropical Cormorants (Nannopterum brasilianus), Rock Shags (Leucocarbo magellanicus) and Southern Skuas (Catharacta antarctica). This information obtained along a wide coastal sector provides a baseline for future monitoring.

First record of the runt eggs of the Imperial Cormorant <em>Phalacrocorax atriceps</em> and the Rock Shag <em>P. magellanicus</em> in the San Jorge Gulf, Argentina

[The present study describes for the first time the abnormally small (runt) eggs of the Imperial Cormorant (IC) and Rock Shag (RS) observed during the breeding seasons of 1990/91, 1992/93, 1993/1994, 1994/95 and 1996/97 on the Isabel Island (45°07’S, 66°30’W) and the Galiano Island (45°06’S, 66°25’W), located in the northern San Jorge Gulf, Argentina. The frequency of occurrence of IC runt eggs was 0.2% (n = 995) and their average volume was significantly lower than normal eggs (t = 17.4, P< 0.0001, n = 824). The runt eggs were more spherical than those of normal size (Shape Index: 70.6 vs 64.5 for CI and 74.9 vs 63.9 for RS). The volume of the RS runt egg was 21.1 cm3. The cutoff between normal and runt eggs is between 30 and 35 cm3 for the IC and between 24 and 30 cm3 for the RS. The volume of the runt egg was 42.1% and 53.4% the average volume of the two remaining eggs of the clutch for CI and RS, respectively. None of the consistently observed IC runt eggs hatched and it seems that none of the eggs showing a volume lower than the proposed cutoff is destined to hatch]. [Article in Italian]

The diet of adult and chick rock shags (Phalacrocorax magellanicus) inferred from combined pellet and stable isotope analyses

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.

Phylogeography and genetic structure of two Patagonian shag species (Aves: Phalacrocoracidae)

We compared the phylogeographic and genetic structure of two sympatric shag species, Phalacrocorax magellanicus (rock shag) and Phalacrocorax atriceps (imperial shag), from Patagonia (southern South America). We used multilocus genotypes of nuclear DNA (microsatellite loci) from 324 individuals and mitochondrial DNA sequences (ATPase) from 177 individuals, to evaluate hypotheses related to the effect of physical and non-physical barriers on seabird evolution. Despite sharing many ecological traits, the focal species strongly differ in two key aspects: P. magellanicus has a strong tendency to remain at/near their breeding colonies during foraging trips and the non-breeding season, while P. atriceps exhibits the converse pattern. Both species showed similar mtDNA genetic structure, where colonies from the Atlantic Coast, Pacific Coast and Fuegian region were genetically divergent. We also found similarities in the results of Bayesian clustering analysis of microsatellites, with both species having four clusters. However population differentiation (e.g. Fst, Φst) was higher in P. magellanicus compared to P. atriceps, and average membership probabilities of individuals to specific clusters (Q-values) were also higher in the former. Phalacrocorax magellanicus has strong phylogeographic structure, consistent with the impact of Pleistocene glaciations, with diagnostic haplotypes associated with each of the three mentioned regions. The same pattern was not as evident for P. atriceps. Migration rate estimators were higher for P. atriceps than for P. magellanicus; however both species followed an n-island-like model of gene flow, this implies that dispersal occurs across the continental land mass that separates Atlantic and Pacific Oceans. Our results supported the hypothesis that non-physical barriers are important drivers of the genetic and phylogeographic structure in seabirds, and also that physical barriers constitute effective but not absolute impediments to gene flow.

SEROSURVEY FOR SELECTED INFECTIOUS AGENTS IN TWO SYMPATRIC SPECIES OF CORMORANTS (PHALACROCORAX ATRICEPS AND PHALACROCORAX MAGELLANICUS) FROM COASTAL PATAGONIA, ARGENTINA

We conducted a serologic survey for selected infectious agents on two sympatric cormorants, the Imperial Cormorant (Phalacrocorax atriceps) and the Rock Shag (Phalacrocorax magellanicus). Blood was collected from 267 Imperial Cormorants and 106 Rock Shags at 17 colonies along the Patagonia Atlantic shore during nine breeding seasons (1994, 1999-2001-2005-2008-2010). Antibodies to four pathogens were common to both species and frequently observed: avian paramyxovirus type 1 (56% of Imperial Cormorants and 56% of Rock Shags); avian adenovirus (67% of Imperial Cormorants and 40% of Rock Shags); infectious bronchitis virus serotypes IBV-41, IBV-46, IBV-99, and IBV-JMK (53% of Imperial Cormorants and 64% of Rock Shags); and Salmonella pullorum (18% of Imperial Cormorants and 7% of Rock Shags). Antibody prevalence for these pathogens varied significantly between species, except for avian paramyxovirus type 1. Exposure to avian paramyxovirus type 1 and all serotypes of infectious bronchitis virus varied significantly among seasons in both species. In contrast, the sporadic occurrence of positive titers suggest that cormorants had occasional exposure to Aspergillus spp. (3% of Rock Shags, only in 2000), avian paramyxovirus type 3 (5% of Rock Shags, only in 2008), Chlamydophila spp. (1% of Imperial Cormorants, only in 2010), and avian reovirus (1% of Rock Shags, only in 1999; 29% of Imperial Cormorants, in 2008 and 2010). Both species were antibody negative for avian encephalomyelitis virus, avian influenza virus, avian laryngotracheitis virus, avian paramyxovirus type 2, and infectious bursal disease virus. We provide the first information on pathogen exposure, indicated by detection of antibody in blood samples, for two sympatric species of South Atlantic cormorants. To determine major causes of morbidity and mortality in these birds future efforts should focus on necropsy surveys in cormorant colonies.

Marine protected areas, spatial scales, and governance: implications for the conservation of breeding seabirds

AbstractAs in many regions worldwide, seabird colonies in Argentina are important conservation targets of marine protected areas (MPAs). Seabirds are wide ranging, often crossing jurisdictional boundaries during foraging. Using a recently designated MPA as a case study, this article discusses the challenges of protecting breeding seabirds given their spatial requirements and use of different jurisdictions. Seabirds breeding at the MPA have distinct foraging strategies. Rock Shags and Olrog's Gulls forage inshore within the MPA. Imperial Cormorants, Magellanic Penguins, and Southern Giant Petrels, in contrast, often feed beyond the MPA's jurisdiction, traveling into provincial, federal, or international waters where they can be affected by fisheries and oil development. This indicates the need of management actions beyond MPA boundaries. The large scale and connectivity of marine ecosystems and the variety of economic pressures require the participation of stakeholders and several government agencies in conservation issues, and thus integrated coastal management and marine spatial planning appear as options to complement the use of MPAs. Although MPAs are a valuable tool to conserve breeding seabirds, increased efforts are needed to design new governance structures and complementary strategies for spatial protection so as to deal with the biological, social, and political complexities of marine systems.

Low seasonal variation in the diet of Rock Shags (Phalacrocorax magellanicus) at a Patagonian colony in Argentina

The characteristics of the food sources exploited by seabirds are one of the main factors determining the abundance and distribution of those birds. Determination of the diet over the year and between breeding and non-breeding seasons is important in understanding the food sources and their potential relationship with seabird population dynamics. We studied seasonality in the diet of the Rock Shag (Phalacrocorax magellanicus), a seabird endemic to southern Argentina and Chile, at a colony at Punta Loma, Chubut, by analysis of pellets (regurgitated casts) collected weekly during two consecutive non-breeding and breeding seasons in 2002 and 2003. We identified 19 prey-types in the diet. Polychaetes were the most common item, being present in 80–90% of the samples. Fish were also dominant in both non-breeding and breeding seasons (present in 60–80% of the pellets), especially species of Patagonotothen, Ribeiroclinus and Helcogrammoides. Crustaceans and cephalopods were also present in the diet, but to a lesser extent. There was a high overlap in dietary composition between non-breeding and breeding seasons, although more crustaceans and cephalopods were consumed during the non-breeding season in 2002. Results indicate that the food sources of Rock Shags are present in their feeding areas throughout the year, although many of these species are restricted in their availability, are of small size and have low energy content.

Foraging behaviour and habitat partitioning of two sympatric cormorants in Patagonia, Argentina

Radiotelemetry was used to assess the distribution and diving behaviour of Rock Shags Phalacrocorax magellanicus and Red‐legged Cormorants Phalacrocorax gaimardi breeding in sympatry, and Rock Shags breeding in isolation. When breeding in sympatry there was little overlap in the foraging locations of the two species, with the highest densities of each species separated by 10 km. Red‐legged Cormorants fed significantly closer to the breeding colony than did Rock Shags and undertook shorter foraging trips, making almost twice as many foraging trips per day as Rock Shags. Rock Shags breeding in isolation had a shorter foraging range than the birds breeding in sympatry with Red‐legged Cormorants and foraging trip duration was significantly shorter. However, the number of feeding trips per day was similar between areas of sympatry and allopatry. Differences in the foraging ecology of Rock Shags in areas of sympatry and allopatry may be due to interspecific competition, which forces niche differentiation. The distance between foraging sites, the speed of movement of the prey, a species tendency to move into prey‐depleted areas and the length of the breeding season (during which the birds are constrained to be in the same area) may play critical roles in determining the extent to which differential area use by competitors is a strategy that benefits both parties.

Colony and nest site fidelity of the rock shag (Phalacrocorax magellanicus)

The rock shag (Phalacrocorax magellanicus) is an endemic species from southern Argentina and Chile. In Argentina, the population is distributed along the Patagonian coast in 143 small colonies (5–377 pairs). We studied colony and nest site fidelity of rock shags at Punta Loma, Patagonia, Argentina. We banded 37 adults from December 2001 to June 2003, during two breeding and two non-breeding seasons. Nest site fidelity was extremely high during consecutive breeding and also non-breeding seasons. The high percentage of banded birds residing in the colony in consecutive seasons suggests that rock shags are highly faithful to breeding sites and supports the idea of low post-breeding dispersion.

Sex determination of adult Rock Shags by molecular sexing and morphometric parameters

Male and female Rock Shags (Phalacrocorax magellanicus) are not obviously sexually dimorphic in plumage or size and are thus difficult to distinguish in the field. We evaluated the utility of two different DNA-based techniques for sexing adult Rock Shags. We found that the primer set 2550F/2718R (originally tested in three individuals of P. carbo), with minor differences in the forward primer, provided a consistent and simple sexing method for Rock Shags. Moreover, we obtained three reliable discriminant functions for sexing adults from three different colony sites between 42° to 47°S in coastal Patagonia, Argentina. Discriminant analysis of five external characters of adult birds indicated that head, bill, and wing lengths were the most accurate variables for use in a discriminant function model, predicting the sex of 80–86% of the birds. Males were significantly larger than females for all body measurements except for bill depth. Rock Shags showed less marked sexual dimorphism than other phalacrocoraciid species.

TEMPORAL PATTERNS IN THE DIET AND FOOD PARTITIONING IN IMPERIAL CORMORANTS (PHALACROCORAX ATRICEPS) AND ROCK SHAGS (P. MAGELLANICUS) BREEDING AT BAHÍA BUSTAMANTE, ARGENTINA

We studied the diet of Imperial Cormorants (Phalacrocorax atriceps) and Rock Shags (P. magellanicus) at Bahia Bustamante, Argentina, between 1992 and 1994. We analyzed pellet casts (1887 from Imperial Cormorants and 799 from Rock Shags) and regurgitations of stomach contents (260 from Imperial Cormorants and 24 from Rock Shags). Imperial Cormorants and Rock Shags fed on at least 22 and 21 different types of prey, respectively. The main prey species during all study years were fish: Engraulis anchoita for Imperial Cormorants and Patagonothen sp. for Rock Shags. For both species, the consumption of the main food categories as estimated by pellet analysis was similar among years. A significant relationship was found between Imperial Cormorant and Rock Shag diets during the three years, while the diet overlap index was relatively high. During all years, Imperial Cormorants consumed a significantly larger proportion of pelagic or demersal fish than did Rock Shags, while Rock Shags consumed benthic fish in a greater proportion than did Imperial Cormorants. Mean maximum diving depth, determined using capillary tube depth gauges, of Imperial Cormorants (24.4 m ± 18.8 SD) was significantly greater but more variable than that of Rock Shags (9.3 m ± 4.1 SD).

Foraging Behavior and Feeding Locations of Imperial Cormorants and Rock Shags Breeding Sympatrically in Patagonia, Argentina

Although there have been several studies of the foraging behavior of the Imperial Cormorant (Phalacrocorax atriceps) and the Rock Shag (Phalacrocorax magellanicus), none document the feeding performance and the use of feeding areas by these birds breeding in mixed or adjacent colonies. We studied birds nesting sympatrically in two colonies at Malaspina Inlet, Patagonia, Argentina. Both colonies were located on islands separated by 2.2 km: Vernacci Oeste, inside Malaspina Inlet and Vernacci Este at the mouth of the inlet. Rock Shags from both islands and Imperial Cormorants from Vernacci Oeste fed inside the inlet, and showed similar dive duration, surface interval and foraging range. Imperial Cormorants from Vernacci Este foraged outside the inlet and showed longer dive duration, surface interval and foraging range. Imperial Cormorants made longer foraging trips than Rock Shags (4.9 ± 1.9 vs. 1.9 ± 0.7 h) regardless of its colony. There was no overlap between the foraging areas used by Imperial Cormorants from the two colonies. Despite Rock Shags from both islands feeding inside the inlet, there was a little overlap in their foraging locations (3-22%). Rock Shags and Imperial Cormorants breeding in the same colony showed an overlap in their foraging areas, being lower at Vernacci Este than at Vernacci Oeste. Although both species are usually described as having different diving capacities, we found that their diving behavior was similar when feeding in areas of similar environmental conditions.

Breeding Habitat Requirements of the Imperial Cormorant and Rock Shag in Central Patagonia, Argentina

Abstract We studied the habitat requirements and nest site characteristics of Imperial Cormorants (Phalacrocorax atriceps) and Rock Shags (P. magellanicus) in northern Golfo San Jorge, Argentina. Colonies of both species were only located on islands. We characterized nesting habitat at 15 and 31 islands with and without Imperial Cormorant colonies, and 19 and 27 islands with and without Rock Shag colonies, respectively. The probability of finding nesting cormorants and shags was independent of island size. Both cormorants and shags nested on only 18% of islands or islets closer than one km to the mainland, but nested in between 35% and 52% of islands located further offshore. All Imperial Cormorant and Rock Shag colonies were located on bare, rocky substrate. All colonies of both species were located more than 50 m from shrubs. The mean slope of the substrate where colonies were located was significantly greater for Rock Shags than for Imperial Cormorants (73° vs. 3°). Orientation of cliffs and steep slop...

Foraging behaviour and feeding locations of Rock Shags Phalacrocorax magellanicus from a colony in Patagonia, Argentina

During 1996 and 1997, foraging Rock Shags Phalacrocorax magellanicus were studied at Punta Loma, Argentina using radio‐transmitters deployed on ten adult shags during the chick‐rearing period. Rock Shags undertook 2.6 ± 0.6 sd trips per day. The mean duration of a feeding trip was 2.6 ± 0.7 hours. A bird spent 36% of daylight hours away from the colony on feeding trips, diving for 92% of the foraging trip, and made a mean of 106 dives per foraging trip. Foraging trip duration was strongly correlated with the total number of dives made in one foraging trip. Rock Shags fed mainly in water less than 10m deep with a gravelly sand bottom and within 5 km of shore. Mean foraging range was 3.8 ± 2.6 km and 2.6 ± 2.3 km for 1996 and 1997, respectively. These results suggest a high foraging effort (diving time per foraging trip) for Rock Shags, presumably associated with poor food conditions close to the colony. Comparison is made with other Phalacrocorax species.

Diving Behavior of Rock Shags at a Patagonian Colony of Argentina

-The diving behavior of ten adult Rock Shags (Phalacrocorax magellanicus) foraging at Punta Loma, Patagonia, Argentina was studied, using radiotransmitters deployed during two chick-rearing periods. Shags dived continuously during foraging trips, spending 75% of their time at sea underwater. Mean dive duration was 47 ? 14 sec while mean subsequent surface interval was 14 + 6 sec (N = 11,212 dives). During both seasons, there was a weak linear relationship between dive duration and recovery time. Only four of the birds showed a positive and significant linear function between these diving parameters. Recovery time at the surface was independent of the previous dive time only during low tides. Dive efficiency (dive time/recovery time) was the highest reported for a foot-propelled diver (mean = 3.7 and 4.2 for 1996 and 1997, respectively). Food resources located in shallow waters at Punta Loma allowed the shags to optimize their searching period underwater by decreasing the energetic costs associated with diving. Received 11June 1999, accepted 24July 1999.

Molecular Variation and Biogeography of Rock Shags

Molecular analysis of the present genetic structure of Rock Shags indicates significant population subdivision probably caused by vicariant disjunction associated with the Llanquihue Glaciation (35,000-15,000 ybp). The formerly continuous population was forced into refugia on the Pacific and Atlantic coasts, where they remained without contact for approximately 20,000 years. With amelioration of the climate and consequent glacial retreat, populations recolonized rocky shorelines in the central portion of the present day range and introgressed considerably. The Chubut and Falkland populations serve as genetic sources for the others, whereas the Fuegian population acts as a genetic sink. The population that is resident on Isla Chiloe is enigmatic and in nonequilibrium, possibly the result of indirect effects by a yet unsampled population.

Diving Patterns of Full-Grown and Juvenile Rock Shags

Information on diving patterns was obtained for full-grown and juvenile Rock Shags (Phalacrocorax magellanicus) feeding in Port Stanley Harbour, Falkland Islands. Birds dived mainly in, or just outside, beds of giant kelp within 50 m of the shore where the water depth varied from 1-6 m. Mean dive and recovery times were 28 sec and 10 sec respectively, diving rate was 1.8 dives/min and birds spent 75% of the time underwater. Full-grown and juvenile birds both showed a highly significant positive relationship between dive time and water depth. Full-grown individuals also showed a significant increase in recovery time with increasing dive time, but for juveniles recovery time was independent of dive time. This resulted in full grown birds attaining a rate of diving that was 30-50% higher than that of juveniles in shallow water.

Molts of the Rock Shag and New Interpretations of the Plumage Sequence

The Rock Shag (Phalacrocorax magellanicus) was found to be similar in molt patterns to other cormorants studied. It was previously thought that two predefinitive plumages occur in this species; this study shows there is only one predefinitive plumage, which is polymorphic and geographically variable. In addition, although the alternate and basic plumages were thought to be very distinct in aspect, I found that these plumages are similar, and specimens previously thought intermediate between alternate and basic plumage combine individual and geographical variation. Differences in frequencies of juvenal plumage phases and adult plumage variants between Chilean and Argentinian coastal populations suggest evolution in isolation by populations separated by a vicariance event such as the Llanquihue Glaciation (20,000 to 10,000 ybp).