Great Cormorant Phalacrocorax Carbo Sinensis Research Articles

Identification of Contracaecum rudolphii (Nematoda: Anisakidae) in Great Cormorants Phalacrocorax carbo sinensis (Blumenbach, 1978) from Southern Italy

In this study, four dead great cormorant Phalacrocorax carbo sinensis (Blumenbach, 1978) specimens, collected from the coasts and lakes of Southern Italy, were examined by necropsy for the detection of Contraceacum sp. The adults and larvae found were subjected to morphological analysis and molecular identification by PCR-RFLP. A total of 181 Contracaecum specimens were detected in all of the four great cormorants examined (prevalence = 100%), showing an intensity of infestation between nine and ninety-two. A co-infestation by adult and larval forms of Contracaecum rudolphii was found only in one of the great cormorants examined. Following molecular investigations, 48 specimens of C. rudolphii A and 38 specimens of C. rudolphii B were detected, revealing co-infestation solely for the great cormorant from Leporano Bay (Southern Italy). Our results showed an opposite ratio between C. rudolphii A and C. rudolphii B in Pantelleria and in Salso Lake (Southern Italy) compared to what was reported in the literature, probably due to migratory stopovers and the ecology of the infested fish species, confirming the role of Contracaecum nematodes as ecological tags of their hosts.

Migration Patterns and Recorded Emigration of the Great Cormorant Phalacrocorax carbo sinensis in the Largest French Colony of Lac de Grand-Lieu: Density-Dependent Factors Operating at Different Time and Geographical Scales

The number of wintering Great Cormorants Phalacrocorax carbo sinensis in France has strongly increased since the 1970s, mainly due to the protection of the ‘continental’ sinensis subspecies in countries north of France. This increase has led to the establishment of a pioneering inland breeding colony in western France, while previously only the largely marine ‘Atlantic’ P. c. carbo subspecies occurred on the Channel coast. The marine subspecies was attracted and bred in this new inland settlement of sinensis, which rapidly became the largest colony in France. This paper analyses the migration pattern of birds from this colony by analysis of the dispersal of colour-ringed birds between 1989 and 2008. Interestingly, besides a classic south-west migration pattern, birds from this colony also displayed a pattern heading north-east, up to countries such as The Netherlands, from where the founders (sinensis) of this colony probably originated. Sightings and recoveries revealed that about 25% of the adults and 19% of the first-year birds headed north-east. Due to this north-east migration direction, the overall annual dispersal point was located only 50 km south-west of the colony, although in December and January this midpoint was located about 320 km south-west of the colony. The birds largely avoided Brittany, presumably to avoid competition with individuals of the carbo subspecies, and the main wintering areas of sinensis from other colonies, both in France (east, centre and south) and in Spain. Over the years 1989–2008, in the breeding period, the mean dispersal distance was shorter for adults than for young birds (54 km vs. 144 km, respectively) but in winter adult birds migrated further than young ones (305 km vs. 221 km, respectively). The mean annual dispersal distance in winter varied from 106 km to 527 km (all age-classes taken together). Migratory distance was not related to mean winter temperature. For adults, dispersal distance correlated with the annual number of breeding pairs in the Grand-Lieu colony between 1990 and 2003, but not between 2004–2008. Emigration (breeding in another colony) was recorded up to 2011 to 11 inland colonies and one coastal colony (founded more recently than Grand-Lieu), nine of them in France, two in Spain and one in The Netherlands. Annual emigration rate was negatively related to colony size in Grand-Lieu. The study points to the existence of density-dependent effects on distribution patterns of Cormorants outside the breeding season but also suggests connectivity and interaction among colonies that are hundreds of kilometres apart.

Natural Regulation of the Baltic Population of the Great Cormorant Phalacrocorax carbo sinensis: The Interplay between Winter Severity and Density Dependence

After a period of continuous increase and range expansion, the Baltic Great Cormorant population has stabilised in large parts of its range in recent years. Ringing recoveries reveal that considerable proportions of the population winter in areas that can be affected by prolonged frost periods. There is evidence that winter severity is an important density-dependent regulation factor: if the population is large, ice cover of coastal and inland water surfaces during harsh winters affects the population by reducing the availability of food resources. As long as the population remained small, however, it was not affected even by very cold winters, since the remaining accessible food resources were presumably still sufficient. The analysis presented here uses the average winter temperature in Germany as a proxy for winter severity in the frost-affected parts of the wintering areas of Baltic Cormorants. The Baltic Cormorant population in 1980–2016 is estimated from annual counts in Denmark, Schleswig-Holstein, Mecklenburg-Western Pomerania, Estonia, Finland and Gotland, which account for about 50% of the total population. The interplay between winter severity and density dependence is analysed using a linear and a non-linear regression model approach. The non-linear model gives a better description of the relationship between the size of the Baltic breeding population during the year (n), the winter temperature Tn, and the population size during the previous year (n–1). According to the model, a population of less than 41,400 breeding pairs would not suffer declines during even the coldest winters recorded since 1882. In 1989, the Baltic Cormorant population exceeded for the first time the threshold value for density-dependent regulation caused by severe winters. The winter 1995/96 was then the first one cold enough to cause a population decline. According to the model, during the years 2002/2003, 2005/06, 2008/09, 2009/10 and 2010/11 the winters have been cold enough to reduce population numbers. Furthermore, the model shows that the regulative winter effect is restricted to the low temperature range.

Conspecific Density as a Driver of Offspring Body Condition in Three Cormorant Colonies in Denmark

Density-dependent depletion of prey during the breeding season may affect breeding performance and colony development in seabirds and colonial waterbirds. Breeding Great Cormorants Phalacrocorax carbo sinensis are central place foragers, so parental flight distances to profitable foraging grounds and thus parental provisioning of offspring are likely affected by local food availability. Chick body condition in a given colony may therefore be influenced by the distance to feeding areas, changes in fish stocks and fish distribution as well as the number of Cormorants from neighbouring colonies using the same feeding areas. At three Danish Great Cormorant colonies with overlapping foraging ranges and variable access to shallow marine areas, Vorsø (VO), Mågeøerne (MA) and Stavns Fjord (SF), we investigated variation in mean chick body condition (n = 9697) in relation to colony location, year, colony size and estimated density of foraging conspecifics during 1993–2007. Foraging areas available to VO colony parents had the highest theoretical densities of conspecifics and the VO chicks were invariably in poorer condition than the chicks at the other two colonies. Chick body condition was negatively correlated with estimated foraging density, especially within a foraging range of 20 km. Body condition between all three colonies was weakly correlated over the years, suggesting that changes in macro-environmental conditions (e.g. fish density) only had moderate impacts on food availability, independently of Cormorant numbers. We conclude that both the geographical location of colonies, the size of the colony itself and the nearest neighbouring colonies and the associated variation in density of foraging Cormorants were major drivers of variation in chick body condition between colonies and years.

Time Shift in the Exploitation of Fish Stocks by Great Cormorants Phalacrocorax carbo at Lake IJsselmeer: How Wintering Birds began Competing for Fish with Breeding Conspecifics

Monthly aerial bird counts showed a strong increase in the number of wintering Great Cormorants Phalacrocorax carbo sinensis since the late 1990s at Lake IJsselmeer but not at Lake Markermeer-IJmeer. Compared to the 1980–1990s, breeding numbers also increased in this part of the system. The resulting increased exploitation of fish stocks was thought to have been possible because of a long-term increase in the stock of Ruffe Gymnocephalus cernuus, despite a clear overall decline of total estimated fish biomass in the lake during the same period. The most likely cause of these shifts was thought to be the intensive commercial fishing regime, removing the large predatory fish first, followed by a strong reduction of stocks of large Bream Abramis brama, in turn paving the way for increases in the stocks of Ruffe. Increased predation by Cormorants on the enhanced stocks of small fishes was possible because of ameliorated underwater visibility in Lake IJsselmeer. Starting in 2000, there was a strong shift in both temporal habitat use and associated fish consumption by Cormorants towards the winter period. The local breeding birds, exploiting the same age- and size-structured community of fishes in the spring, thus face an already-depleted food resource. Compared to the 1980–1990s, fish consumption by Cormorants in winter increased by a factor of ten, whereas that by breeders did so by a factor of 1.6. Our calculations showed that the actual harvest of available fish stock by wintering and breeding Cormorants together was c. 5% in 1985–2000 and c. 15% in 2001–2015. The disproportionate division of the overall consumption (‘harvest’) of the fish stock towards the wintering birds is a strong argument for direct competition with their conspecifics breeding locally. In conclusion, we calculate that because of the increased winter exploitation initiated by the activities of an intensive commercial fishery, the fish consumption in summer and early autumn by breeding Cormorants and their offspring was suppressed by a factor of six.

Occurrence and Behaviour of White-Tailed Eagles Haliaeetus albicilla in Great Cormorant Phalacrocorax Carbo Sinensis Colonies in Countries around the Baltic Sea

The recovery of the Baltic White-tailed Eagle Haliaeetus albicilla population since the 1980s is a conservation success story. However, the re-establishment of this predator in coastal and lake areas appears to affect Great Cormorants Phalacrocorax carbo during the breeding season. We collated published and unpublished records of White-tailed Eagle occurrence and interactions with Cormorant colonies as well as records of Cormorant anti-predator responses and effects on Cormorant breeding performance. We found evidence for immediate direct effects (mainly kleptoparasitism, predation of eggs and offspring) and indirect effects (facilitating nest predation by mainly gulls and corvids). Repeated disturbance from hunting White-tailed Eagles was also inferred to trigger changes in selection of nest sites, to cause complete abandonment of colonies and lead to regional redistributions of breeders. However, there are also observations of ‘unproblematic’ coexistence with White-tailed Eagles breeding inside Cormorant colonies. There is some evidence to suggest that nesting opportunities for Cormorants may become further restricted as White-tailed Eagle numbers continue to increase, and we argue that this – in some regions – will impose limitations on the distribution and size of breeding populations of Cormorants.

GPS-Tracking of Great Cormorants Phalacrocorax carbo sinensis Reveals Sex-Specific Differences in Foraging Behaviour

Great Cormorants Phalacrocorax carbo sinensis are considered generalist predators feeding in a variety of marine and freshwater habitats on many different prey species. Recently however, there is increasing evidence that even seemingly generalist species can often be regarded as a diverse group of individual specialists sometimes induced by sex-specific foraging behaviour. To test whether this also holds true for Great Cormorants, the present study characterised the at-sea distribution and examined the time budgets of provisioning Great Cormorants by deploying GPS-loggers on 11 nesting males and females during the breeding season of 2012. Additionally, pellets were collected from underneath the nests of these tagged birds for detailed diet analysis, based on the otoliths and fish bones recorded within them. Diverse foraging patterns were recorded, ranging from exclusively freshwater feeding, to offshore foraging, with the furthest recorded distance from the colony being 28 km at sea. Time budgets during foraging trips revealed relatively long periods of resting ashore (55% of the trip ± 23%), followed by foraging (31 ± 18%), and time spent in flight (15 ± 11%). Flatfishes dominated in the diets of these Great Cormorants, indicating benthic-foraging strategies when foraging in saltwater (feeding on discards could be ruled out). The males in this study avoided freshwater foraging habitat and preferred offshore waters with a sandy bottom or nearshore waters alongside rocky breakwaters and within harbours. Females foraged in all habitat types, but proportionally more in inland freshwater bodies. Females spent more time on foraging than did males, particularly in marine habitats, whilst males rested more. It is proposed that these differences might have been caused by sex-specific foraging strategies, possibly resulting from competition at foraging sites.

Vocal behaviour of the Great Cormorant Phalacrocorax carbo sinensis during the breeding season

ABSTRACT Capsule Great Cormorants Phalacrocorax carbo sinensis use vocal communication during the breeding season, with males being particularly vocal earlier in the breeding cycle and showing individual variation in some calls, which could be used for individual recognition. Aims To identify and describe vocal behaviour of Great Cormorants, to link calls with observed behaviours and to explore if the calls had potential for individual recognition. Methods We followed 21 nesting pairs of Great Cormorants by videoing and recording their vocal behaviour throughout the breeding season. We linked calls with observed behaviours, and measured the acoustic characteristics of the calls using signal analysis tools in Matlab. Results We identified and measured acoustic characteristics of six different call types: courtship, landing, nest building, nest relief, jumping, and chick begging calls. Five of these call types were linked to distinctive breeding behaviours. Vocal signalling occurred between the male and female, and between parents and offspring. Males showed higher vocal activity than females and used a larger repertoire of calls. The courtship call was the most common call type in both sexes. These calls also differed acoustically between the sexes; male calls were longer in duration than female calls (617 ms versus 323 ms) and had wider bandwidth (763 Hz versus 473 Hz). Conclusion Great Cormorants use vocal communication for social interactions. Males were vocally more active and had a larger repertoire of calls than females, and calls differed between the sexes. Calls of males also differed individually and could, therefore, function for individual recognition in this species.

Cormorants have negligible seascape-scale impacts on benthic vegetation communities

Great cormorant Phalacrocorax carbo sinensis populations in the Baltic Sea have rapidly expanded since the 1990s, raising concerns about their ecosystem impacts. Nutrient runoff from colonies, as well as cormorant predation on fish, can affect surrounding producer communities. Past studies have found cormorant impacts on producers in the immediate vicinity of colonies, but the importance of cormorants over a larger spatial scale is unknown, especially compared to other environmental variables. We used an extensive underwater vegetation inventory dataset (~18000 data points along the Finnish coast) to determine the effects of cormorant colonies on macroalgae and plants. We compared community structure and species abundance/occurrence in near-colony (<5 km from a colony) and control (>10 km from a colony) points, and determined the importance of cormorant influence (using an index incorporating colony size and distance from the colony) in near-colony sites. We found no significant differences in community structure between near-colony and control points in most habitats, and adding the cormorant index only infinitesimally improved statistical models after incorporating other environmental factors. However, the abundance of several species did differ; in particular, the foundation species bladderwrack Fucus vesiculosus and eelgrass Zostera marina were either less likely to occur in near-colony points or were negatively correlated with cormorant index, possibly due to the effects of nutrient enrichment from colonies. Our findings confirm that cormorants can have effects on some producer species, but highlight that these effects are negligible when taking into account the scale and magnitude of other bottom-up and top-down processes occurring in the Baltic Sea.

Genetic identification and insights into the ecology of Contracaecum rudolphii A and C. rudolphii B (Nematoda: Anisakidae) from cormorants and fish of aquatic ecosystems of Central Italy.

Contracaecum rudolphii (s. l.) is a complex of sibling species of anisakid nematodes having the fish-eating birds belonging to the Family Phalacrocoracidae as final hosts. The great cormorant Phalacrocorax carbo sinensis is parasitized by C. rudolphii A and C. rudolphii B. Adults and L4 specimens of C. rudolphii (s. l.) (N = 3282) were collected in cormorants from brackish and freshwater ecosystems of Central Italy. Third-stage larvae of Contracaecum (N = 882) were obtained from the fish species Dicentrarchus labrax, Anguilla anguilla, Aphanius fasciatus, Atherina boyeri, Leuciscus cephalus, Barbus barbus, and Carassius carassius captured in the same geographical areas of cormorants' standings. Contracaecum rudolphii A and C. rudolphii B were identified by a multilocus genetic approach: allozymes, sequences analysis of the mtDNA cox2, and ITS region of rDNA gene loci. Differential distribution of the two parasite species was observed in different aquatic environments. Contracaecum rudolphii B outnumbered C. rudolphii A in wintering cormorants from freshwater ecosystems; the opposite trend was found in cormorants from brackish water. Analogously, C. rudolphii A larvae were more prevalent in brackish water fish, while C. rudolphii B larvae were found infecting only freshwater fish. The findings seem to confirm that C. rudolphii A and C. rudolphii B would have a life-cycle adapted to brackish and freshwater environments, respectively. A differential feeding behavior of wintering cormorants, the ecology of the infected fish species, and abiotic factors related to early stages of the parasites are supposed to maintain the distinctiveness of the two parasite species' life cycles in the two different aquatic ecosystems.

Differences in the diet of breeding Cormorants Phalacrocorax carbo sinensis in an inland colony: the effect of years, breeding stages and locations within the colony

Abstract A study of the diet of the Great Cormorant Phalacrocorax carbo sinensis (fish species and size) in (1) different seasons (years), (2) breeding stages (incubation and chick rearing), and (3) breeding areas (center and edge) in the colony in the Dzierżno-Duże Reservoir (southern Poland) was carried out. Overall, 147 pellets of the Great Cormorant were analysed. The low values of the indexes of Levin (Bi) and Shannon (H’) showed a limited trophic spectrum in the diet of the Great Cormorant. Roach (Rutilus rutilus) with a percentage index of relative importance (%IRI) of 62.89, perch (Perca fluviatilis) (%IRI = 22.63) and carp (Cyprinus carpio) (%IRI = 10.43), were the most common prey. Evident changes in the diet between 2003 and 2014, with less roach and more perch and ruffe in 2014 were found. They could be probably related to changes in the fish community. Differences in the food of cormorants between breeding stages reflected dietary requirements of the chicks. During the breeding season younger chicks require feeding with smaller fish than older chicks. The proportion of fish species found in the cormorant diet differed between the edge and the centre of the colony. We concluded that the impact of Great Cormorants on native fish assemblages may be dependent on the location within the colony, development state of the chicks and season, not just fish availability.

Where do wintering cormorants come from? Long‐term changes in the geographical origin of a migratory bird on a continental scale

Abstract Populations of migratory birds often mix to a considerable extent in their wintering areas. Knowledge about the composition of wintering populations is highly relevant to management, not least for species such as the great cormorant Phalacrocorax carbo sinensis, prone to conflicts with human interests. However, few studies have been able to estimate long‐term changes in winter population composition. We use 30 years of ringing and recovery data (1983–2013) from all major breeding populations of cormorants in continental Europe (except the Black Sea region) to estimate partitioning probabilities (i.e. the probabilities of moving to specific wintering areas) using a Bayesian capture–mark–recovery model. Combining these results with information on breeding numbers and reproductive output in a population model, we estimate the size and composition of wintering populations in Europe and North Africa. Partitioning probabilities showed some variation over time, but were similar for first‐winter and older birds. Cormorants from the western part of the breeding range tended to winter progressively further west over time. This may be a density‐dependent response to the recent growth of more easterly breeding populations. All wintering populations grew rapidly over the study period, and their composition showed pronounced changes. All wintering populations were composed of birds from many different breeding populations, but the proportion of cormorants of more easterly origin increased markedly over time in most wintering areas. Policy implications. Cormorant wintering populations in Europe consist of mixtures of birds of different breeding origins. These mixtures are also highly variable over time. These factors reduce the chances of successfully limiting conflicts in specific wintering areas through, for example, regulation of breeding numbers in one breeding area. The dynamic nature of cormorant winter populations means that conflicts are best addressed when and where the conflict occurs, or on the scale of the entire continental population. It is unlikely that the latter will be cost‐effective and politically realistic.

Stable isotope analysis reveals the feeding distribution of wintering Great cormorant Phalacrocorax carbo sinensis along a marine-continental Mediterranean gradient

Harmonizing biodiversity conservation and natural resource management often requires anticipating the potential impact that certain species can cause through their exploitation of specific resources. During the winter 2008/2009 we studied the feeding ecology of the Great Cormorant Phalacrocorax carbo sinensis in SE Spain, in order to determine its dependence on different food sources available along an oceanic-continental gradient (open sea-freshwater bodies). Trophic niche was assessed using C and N stable isotopes, applying up-to date metrics and analytical tools.Isotopic signatures revealed high mobility patterns for cormorants, illustrating differences between roosting and feeding areas (spatially well separated). Cormorants roosting in open sea move to inland freshwater bodies, their trophic niche overlapping that of individuals settled there. Similarly, individuals settled around transitional waters (coastal lagoon), seem to divide the predation pressure between different food sources along the marine-continental gradient. Recently in Spain, the Great Cormorant has been devoid of legal protection due to its supposed impact on fisheries. Our methods provide a useful and non-invasive tool that can be used as a first step for assessing such interaction. On the basis of its dispersed feeding distribution and expected predation pressure the cormorant does not seem to represent a serious threat to recreational or commercial fisheries which would justify downgrading its protection.

Age effects on reproductive success, nest-site location, and offspring condition in the Great Cormorant Phalacrocorax carbo sinensis

Breeding performance of many vertebrate species is known to improve over the early stages of the life cycle, which has been commonly attributed to the progressive improvement in competences and increasing investment in reproduction. While there is a large body of evidence for age-related variation in fecundity within bird populations, much less is known on whether and how age affects other traits related to reproduction. The aim of this study was to test for age-related patterns in fecundity, nest-site location, offspring condition and brood sex ratio in a long-lived colonial waterbird, the Great Cormorant (Phalacrocorax carbo sinensis). For this purpose we collected data on 180 breeding attempts of 100 Great Cormorants aged two to 11 years. We found a progressive increase in reproductive output with age and we showed that older individuals nested closer to the colony centre and in higher nesting densities. We also found that parental age was positively related to physiological condition of offspring (measured with whole-blood haemoglobin concentration and plasma glucose concentration). There was no indication for age-related adjustments in brood sex ratio in our cormorant population. Our results indicate a great complexity of the processes which produce age-related improvements in reproductive performance within avian populations.

Helminth parasites of the lesser great cormorant Phalacrocorax carbo sinensis from two nesting regions in the Czech Republic.

Parasitological examinations of 102 specimens of the lesser great cormorant Phalacrocorax carbo sinensis (Blumenbach) from two nesting regions in the Czech Republic (South Bohemia and South Moravia) were carried out at the Institute of Parasitology, Czech Academy of Sciences (previously the Czechoslovak Academy of Sciences) in the years 1987-1992. In them, a total of 19 species of helminth parasites was found, including Trematoda (11 species), Cestoda (2), Nematoda (4) and Acanthocephala (2), which can be divided into three main groups regarding their host specificity: parasites specific for cormorants (Phalacrocorax spp.) (37%), those parasitic mainly in cormorants (16%) and non-specific parasites (47%). Of the 19 species recorded, 100% were found in South Moravia, but only 47% of these 19 species in South Bohemia. The higher number of helminth species in cormorants from South Moravia and a higher proportion of non-specific species may be associated with the presence of the large Nové Mlýny water reservoir, in addition to better ecological and environmental conditions in this warmer region. Scanning electron microscopical examination of three common nematode species parasitising cormorants, Contracaecum rudolphii Hartwich, 1964, Desmidocercella incognita Solonitsin, 1932 and Syncuaria squamata (von Linstow, 1883), revealed some taxonomically important, previously unreported morphological features, such as the cephalic structures, numbers and distribution of male caudal papillae or the shapes of spicules.

Maximizing dietary information retrievable from carcasses of Great Cormorants Phalacrocorax carbo using a combined morphological and molecular analytical approach.

Avian carcasses can provide important information on the trophic ecology of birds. Usually, the number of carcasses available for examination is limited and therefore it is important to gain as much dietary information per specimen as possible. In piscivorous birds and raptors, the stomach has been the primary source of dietary information, whereas the gut (intestine) has so far been neglected as it usually contains only a few morphologically identifiable hard parts of prey. Molecular approaches have the potential to retrieve dietary information from the gut, although this has not yet been verified. As well as identifying the prey, it is important to estimate any secondary predation to avoid food web errors in dietary analyses. The assignment of accidentally consumed prey is notoriously difficult regardless of the prey identification approach used. In the present study, morphological and molecular analyses were, for the first time, combined to maximize the dietary information retrievable from the complete digestive tract of Great Cormorants Phalacrocorax carbo sinensis. Moreover, a novel approach based on predator–prey size ratios was applied to these piscivorous birds to minimize the number of samples that might contain secondarily predated prey. The stomach contents of the examined birds were found to provide the most dietary information when morphological and molecular analyses were used in combination. However, compared with the morphological approach, the molecular analysis increased the number of fish species detected by 39%. The molecular approach also permitted the identification of fish DNA in the Cormorant guts. Predator–prey size ratios derived from morphological analysis of fish hard parts can reduce the incidence of potential confounding influence of secondarily predated prey by 80%. Our findings demonstrate that a combination of morphological and molecular approaches maximizes the trophic information retrievable from bird carcasses.

Selective predators or choosy fishermen? Relation between fish harvest, prey availability and great cormorant (Phalacrocorax carbo sinensis) diet

The increase in numbers and range of the continental subspecies of great cormorant Phalacrocorax carbo sinensis in Europe has led to a growing number of conflicts with commercial fisheries and recreational angling. We investigated the dietary preferences (fish species and size classes) of wintering cormorants in two freshwater basins in Northern Italy, using pellet analysis and data on fish community composition. First, we compared cormorant diet (biomass of fish species consumed) with the annual harvest by professional fishing (biomass/year). Second, we compared diet with a measure of prey availability: direct fish sampling with nets of different mesh size. Cormorants preyed mainly on cyprinid fish. A comparison of pellet analysis and commercial fishing data showed that some fish species consumed by cormorants did not occur in the commercial harvest. Using only species that occurred in the diet and in the commercial harvest, there was no relationship between the amount of fish of different species taken. A positive correlation between pellet analysis data (consumed) and data from scientific fish sampling (available) showed that cormorants exploited fish resources on the basis of prey availability. Comparing the size of fish collected from nets and fish consumed by cormorants also showed that birds were selective with respect to prey size, picking mostly small individuals (< 110 g). We conclude that potential effects of cormorants on commercially important fish will mainly depend on habitat type (fish ponds, natural deep lakes, others), and that in the natural lakes in Lombardy cormorants mainly concentrate on species which are of limited value for commercial fishing.

Local Heterozygosity Effects on Nestling Growth and Condition in the Great Cormorant.

Under inbreeding, heterozygosity at neutral genetic markers is likely to reflect genome-wide heterozygosity and, thus, is expected to correlate with fitness. There is, however, growing evidence that some of heterozygosity-fitness correlations (HFCs) can be explained by ‘local effects’, where noncoding loci are at linkage disequilibrium with functional genes. The aim of this study was to investigate correlations between heterozygosity at seven microsatellite loci and two fitness-related traits, nestling growth rate and nutritional condition, in a recently bottlenecked population of great cormorant Phalacrocorax carbo sinensis. We found that heterozygosity was positively associated with both nestling traits at the between-brood level, but the individual (within-brood) effects of heterozygosity were non-significant. We also found that only one locus per trait was primarily responsible for the significant multi-locus HFCs, suggesting a linkage disequilibrium with non-identified functional loci. The results give support for ‘local effect’ hypothesis, confirming that HFCs may not only be interpreted as evidence of inbreeding and that genetic associations between functional and selectively neutral markers could be much more common in natural populations than previously thought.

Late-breeding Great CormorantsPhalacrocorax carbo sinensisproduce fewer young of the more vulnerable sex

We examined the brood sex ratio and offspring body mass in relation to the timing of breeding and brood size in the Great Cormorant Phalacrocorax carbo sinensis. The brood sex ratio was not related to brood size but it was significantly related to the hatching date, with a decreasing proportion of males in the brood in the course of the season. Male chicks had significantly lower body mass if they hatched later in the season, whereas there was no such relationship for female offspring. Assuming that environmental conditions deteriorate with progress of the breeding season, and male offspring may be more vulnerable to poor environmental conditions, the observed decline in the proportion of male offspring late in the season may be adaptive.

Is it always beneficial to breed in the centre? Trade-offs in nest site selection within the colony of a tree-nesting waterbird

In most of colonial avian species, central parts of the colonies offer higher safety in terms of predatory pressure. However, in heterogeneous habitats, nest sites of high physical quality are likely to offer effective protection against predators or adverse weather conditions regardless of their location within the colony. The aim of this paper was to investigate whether nest site selection in a tree-nesting waterbird, the Great Cormorant Phalacrocorax carbo sinensis, depends on the within-colony location of sites, their physical quality or a combination of these components. The study was conducted during 2010–2011 in a cormorant colony in central Poland. We found that early-breeding individuals preferred nest sites in the central parts of the colony and located high off the ground. The high quality of pairs nesting in these locations was confirmed with good body condition of nestlings, measured by their body masses and plasma concentrations of glucose and urea. A similar spatial pattern was found for the daily nest survival rate and reproductive success. It was found that the central nesting sites associated with high nesting densities were better protected against predators, while the physical quality of nesting sites determined the probability of nest collapse before the conclusion of breeding activities. The two-way process of assessing nest site attractiveness (nest site location vs. physical quality) suggests that, under the limitation of the most attractive nesting sites (good-quality central sites), tree-nesting waterbirds may trade central nesting locations for the high-quality sites at the peripheries of the colony.