Vasilios Liordos

Sex Determination of Great Cormorants (Phalacrocorax carbo sinensis) using Morphometric Measurements

Abstract Great Cormorant (Phalacrocorax carbo) is monomorphic in plumage such that sexes cannot be separated by plumage characteristics. In contrast, it displays sexual size dimorphism, with males generally being larger than females. Sexual dimorphism and variability in size of the continental Great Cormorant (P. c. sinensis) was studied in Greece to develop useful sexing techniques using morphometric measurements. Body mass, wing, culmen, and tarsus length of 81 birds controlled under license were measured during the wintering season in 1999-2002. The sex of each bird was determined by dissection and gonadal inspection. Forward stepwise discriminant analyses were performed to provide reliable functions that would enable the prediction of sex of a bird. Differences in size between adult and juvenile birds were not significant in both sexes, whereas males were larger than females in all measurements. Body mass (19.2%) and culmen length (11.1%) were the most dimorphic variables of those looked at followed by tarsus (6.5%) and wing (6.1%) length. Although wing length was the least dimorphic variable, it also displayed the lowest coefficient of variation (2.3%) thus being the best single measurement for separating the sexes. Three discriminant functions that correctly classified 92.6-95.1% of Great Cormorants of this sample were produced. These functions were reliable (similar accuracy for discriminant analysis and jackknife validation) and seasonally unbiased, as body mass was excluded from the analyses. The function including wing and culmen length as variables showed somewhat lower accuracy when tested with a new sample from The Netherlands suggesting that the obtained functions should be applied with caution to other populations, especially within the area of overlap between the sexes, unless inter-population sources of variation (e.g., geographic variation, hybridization, inter-observer bias) are sufficiently understood.

Sexual differences in the diet of great cormorants Phalacrocorax carbo sinensis wintering in Greece

Sexual differences in the diet of the great cormorant, Phalacrocorax carbo sinensis, were studied in four Greek wintering areas, the Amvrakikos Gulf, the Axios and Evros Deltas and the Messolonghi Lagoon, through the analysis of stomach contents. Great cormorants are birds sexually dimorphic in size, with males being generally larger than females. Although similar prey species were found in the stomachs of both sexes in all the studied areas, significant differences were observed with respect to the proportion of species taken. Male birds ate higher proportions of large fish species such as grey mullets, European sea bass, Dicentrarchus labrax, and Prussian carp, Carassius gibelio, while female birds took higher proportions of smaller species such as big-scale sand smelt, Atherina boyeri, and black goby, Gobius niger. As a consequence, male great cormorants were found to feed on significantly larger prey than did females by means of fish standard length and body mass. There was no significant difference between the sexes in the mass of food found in stomachs.

Spatial Patterns of Winter Diet of the Great Cormorant in Coastal Wetlands of Greece

Abstract Diet of the Great Cormorant (Phalacrocorax carbo) was studied in three coastal wintering areas (Axios and Evros Deltas, Messolonghi Lagoon) of Greece, in order to assess spatial differences and commercial value of prey. Thirteen birds were collected from the Axios Delta, 28 from the Evros Delta, and 16 from Messolonghi Lagoon. Pellets were collected from the Evros Delta (26) and Messolonghi Lagoon (30). A variety of fish taxa were found in the samples, but only one or two dominated in Great Cormorant’s diet, either by numbers or biomass. Grey mullets (Mugilidae and Golden Grey Mullet Liza aurata) were the most important prey by numbers and biomass in the Axios Delta; Giebel (Carassius auratus gibelio) dominated by numbers and biomass in the Evros Delta; whereas Boyer’s Sand Smelt (Atherina boyeri) was most important by numbers and Mugilidae by biomass at Messolonghi Lagoon. Differences found in diet between areas are probably due to differences in prey species composition and abundance. Fish of high commercial value contributed in low proportions in Great Cormorant’s diet, by numbers and biomass, being highest at Messolonghi Lagoon (22.4% by numbers, pellets; 11.5% by biomass, stomachs). The small overlap between the bird’s diet and valuable prey suggests minimal competition with fisheries.

Low mercury contamination in Mediterranean gull Larus melanocephalus chicks in Greece

Mercury (Hg), a toxic heavy metal harmful to animals, commonly occurs in Mediterranean ecosystems. Mediterranean gull Larus melanocephalus numbers have declined considerably in Greece since the 1990s. Mediterranean gull chicks’ back feathers were therefore collected from three Greek colonies in different years between 1999 and 2009 to assess Hg pollution in this larid. Hg concentrations varied with arithmetic means ranging between 815 ng g−1 dry weight (dw) (Lafri Lagoon in 2000) and 1264 ng g−1 dw (Evros Delta in 2000), and values were independent of chick age, although significant among-year and among-site variations were found. Hg concentrations in Greek Mediterranean gull chick feathers were generally low and in fact lower than those associated with adverse effects in other bird species. Comparisons with other studies revealed that Hg concentrations in Mediterranean gulls from Greece were mostly lower than those found in other gull species elsewhere in the world. This study presents the first data on Hg contamination in the Mediterranean gull. The results might be useful in understanding and evaluating the birds’ exposure to this highly toxic pollutant and its impact on both local populations and the wider ecosystem.

Habitat and Temporal Variation in Diet of Great Cormorant Nestlings in Greek Colonies

Abstract Diet of Great Cormorant (Phalacrocorax carbo sinensis) nestlings was studied during four consecutive breeding seasons (1999-2002) at three Greek colonies (Axios Delta, and Lakes Kerkini and Mikri Prespa) in order to assess variation and commercial value of prey. A variety of fish taxa were found in nestlings’ regurgitates in each area and season, but only one or two dominated by numbers or biomass. Black Goby (Gobius jozo), Round Sardinella (Sardinella aurita) and Twaite Shad (Alosa fallax) were the most important prey in the Axios Delta; Bleak (Alburnus alburnus), Giebel (Carassius auratus gibelio) and Roach (Rutilus rutilus) at Lake Kerkini; Chalcalburnus belvica and Giebel at Lake Mikri Prespa. Nestling diet varied both seasonally (but only at Lake Kerkini significantly so) and annually (significantly in the Axios Delta and at Lake Mikri Prespa). Temporal changes can be attributed to changes in prey availability and abundance and confirm this bird’s opportunistic behavior. Between-colonies, differences in diet were significant, probably due to differences in habitat and prey species diversity and composition. The low consumption of valuable fish prey by Great Cormorant nestlings (<10%, numbers and biomass) suggests minimal competition with human interests.

Efficiency and Accuracy of PCR-Based Sex Determination Methods in the European Phalacrocoracidae

The applicability of simple PCR-based approaches for sex discrimination in the three European Phalacrocoracidae species was tested, using 93 individuals of known sex and two sets of primers (1237L/1272R and 2550F/2718R) for the amplification of the avian sex-specific chromo-helicase-DNA-binding protein gene. We evaluated the accuracy of each set of primers in providing the correct sex for each individual. The first primer set did not produce reliable results. The second provided a band pattern for each sex, easily distinguishable with agarose gel electrophoresis, which correctly identified all the individuals, even in samples of low DNA yield. The amplification products were sequenced and aligned revealing important nucleotide diversity among Phalacrocoracidae species. Compared with morphometric discriminant analysis and DNA-fingerprinting techniques previously applied, the PCR-based sexing with the 2550F/2718R primers is more accurate, less invasive and widely applicable to both adults and chicks, using a variety of DNA sources such as blood, tissue, feathers, egg shells and others.

Reproductive performance of the great cormorant (Phalacrocorax carbo sinensis) in three Greek colonies

Several breeding parameters of the great cormorant (Phalacrocorax carbo sinensis) were studied in Greece in 2001 and 2002 and were found to be generally higher at Lake Kerkini than in the other colonies. Fledging success (proportion of hatched eggs that led to fledged nestlings) was significantly higher at Lake Kerkini and in the Axios Delta in both years than at Lake Mikri Prespa in 2002. Mean fledgling production (the number of young fledged per initiated clutch) was significantly higher at Lake Kerkini than at Lake Mikri Prespa in 2002. The high fledgling production (2.15–2.75 fledglings on average in this study), the high food availability and the low initial population density allowed the total Greek breeding population to grow at a fast rate (19.0% per annum) in the 1990s. Given the scarcity of information on great cormorant nesting in Greece, basic breeding parameters are important for modelling population dynamics.

Postnatal growth of the great cormorant Phalacrocorax carbo sinensis (Aves: Phalacrocoracidae) in northeastern Mediterranean wetlands

Abstract Postnatal growth of nestling great cormorants Phalacrocorax carbo sinensis was studied at two northeastern Mediterranean wetlands, the Lakes Kerkini and Mikri Prespa, northern Greece. A method for constructing growth curves from only two visits to bird colonies was used. Logistic growth parameters re-calculated from the logarithmic equation fitted well to the actual growth data of initial-final measurements of body mass, bill length, bill + head length, and tarsus length. Growth rates (K) did not significantly differ between colonies for all variables: body mass (0.205 and 0.206 day−1 at Lakes Kerkini and Mikri Prespa respectively), bill length (0.131 and 0.147 day−1), bill + head length (0.109 and 0.121 day−1) and tarsus length (0.201 and 0.215 day−1). Asymptotic values (A) did not significantly differ between colonies for body mass (2126.7 g and 2128.95 g) and bill length (70.57 and 68.83 mm) but did so for bill + head (147.89 and 151.51 mm) and tarsus length (75.42 and 71.31 mm). The inflection point (T) was similar for body mass (16.6 and 16.4 days) and tarsus length (7.9 and 7.1 days) but significantly different for bill (13 and 11.2 days) and bill + head length (12.2 and 11.1 days). Climatic conditions and food availability were not considered as factors greatly affecting the observed intercolony variation, and therefore other proximate and ultimate factors should be further examined. The proposed method is very helpful because growth curves can be constructed with the allocation of the smallest amount of time and effort, while at the same time keeping the disturbance of vulnerable breeding avian populations to the minimum level. Furthermore, and provided that other factors are controlled, this method could be used for the monitoring of the influence of spatial and temporal variation of ecological conditions on nestling growth.