Space utilization by a cormorant (Phalacrocorax carbo L.) colony in a multi-wetland complex in relation to feeding strategies

In this study, we investigated the response of inland breeding cormorants Phalacrocorax carbo to a complex spatial configuration of feeding habitats in relation to social and individual feeding strategies. The numbers of feeding trips outside the colony site (Lake Grand-Lieu, western France), where only solitary fishing is used by cormorants, and the number of birds fishing on the lake where social fishing predominates were investigated during the breeding season and compared with the fledging period. From the investigation of feeding trip traffic, we identified three major habitats used by cormorants in the vicinity of the colony site (< 25 km around the colony site) that accounted for 94.1 of the IN flights and 92.0% of the OUT flights (n = 1745 arrivals and 2404 departures respectively), and notably one area that accounted for 58% of total flights although it is the furthest away. No fundamental change in the relative significance of these feeding grounds for solitary fishing cormorants was found throughout the breeding season, even in a between-years comparison (1996-2001), in contrast to what has often been found elsewhere. Although the peak of foraging activity in the surrounding habitats and also within the lake waters largely coincided with the time when the majority of young had fledged, the index of cormorant numbers (ratio between bird numbers at a given time and that for a baseline date) on the lake remained at a high level until late August compared to movements outside the lake, as a result of regular social fishing (84.9 +/- 4.0% of fishing numbers). From these findings, we discuss factors governing the selection of feeding grounds throughout the breeding season in relation to energy considerations, feeding strategies and food resources.     

Growth and survival of neotropic cormorant (Phalacrocorax brasilianus) chicks in relation to hatching order and brood size

We investigated chick development and feeding rate in the neotropic cormorant, Phalacrocorax brasilianus, in a colony in Central Chile. The year of our study was characterized by relatively good foraging conditions. Brood sizes varied from two to five chicks, and hatching was asynchronous, with gaps of 0 to 6 days between the youngest and the oldest chick. Egg size declined over laying order in three-egg clutches, but not in four-egg clutches. Hatch weight did not vary with hatching position, irrespective of brood size. Chicks increased mass on average by 60 g/day between 8 and 20 days of age. Growth rates and survival to fledging depended on hatching position only in broods of four, where D-chicks grew slower and showed a higher pre-fledging mortality. There was a non-significant tendency that also A-, B-, and C-chicks in broods of four grew slower than in smaller broods. Average number of fledglings was 2.76. Feeding frequency decreased with chick age between the ages of 10–40 days. Four-chick broods received more feeds per day than smaller broods, leading to a similar per-chick feeding frequency across all brood sizes. D-chicks were clearly disadvantaged in growth and survival, and facultative brood reduction occurred.     

Diet analysis in piscivorous birds: What can the addition of molecular tools offer?

In trophic studies on piscivorous birds, it is vital to know which kind of dietary sample provides the information of interest and how the prey can be identified reliably and efficiently. Often, noninvasively obtained dietary samples such as regurgitated pellets, feces, and regurgitated fish samples are the preferred source of information. Fish prey has usually been identified via morphological analysis of undigested hard parts, but molecular approaches are being increasingly used for this purpose. What remains unknown, however, is which dietary sample type is best suited for molecular diet analysis and how the molecular results compare to those obtained by morphological analysis. Pellets, feces, and regurgitated fish samples of Great Cormorants (Phalacrocorax carbo sinensis) were examined for prey using both morphological hard part analysis and molecular prey identification. The sample types and methods were compared regarding number of species detected (overall and per sample) as well as the prey species composition and its variability among individual samples. Via molecular analysis, significantly higher numbers of prey species were detected in pellets, feces, and fish samples. Of the three sample types, pellets contained the most comprehensive trophic information and could be obtained with the lowest sampling effort. Contrastingly, dietary information obtained from feces was least informative and most variable. For all sample types, the molecular approach outperformed morphological hard part identification regarding the detectable prey spectrum and prey species composition. We recommend the use of pellets in combination with molecular prey identification to study the diet of piscivorous birds.     

Seed germination and seedling survival in a colony of the common cormorant,Phalacrocorax carbo

Germination and seedling survival of some woody plants were examined in a colony of the common cormorant at Unoyama, central Japan. The germination ofQuercus serrata andPinus densiflora was less successful in the colony than outside the colony. The percentage of germination success was negatively correlated with the amount of cormorant faeces scattered on the ground and also with the soil water conent. Most of the germinated seedlings inside of the colony died with symptoms such as necrosis spreading from the edge of leaves. Saplings ofQ. serrata also tended to die more in the colony than outside the colony. The survival rate ofQuercus glauca seedlings with scattered faeces on their leaves and/or on the the surrounding soil was significantly lower than the rate of those free of faeces. These results suggest that in the cormorant colony, germination of seeds and seedling survival are greatly inhibited due to both the direct and indirect effects of cormorant faeces.     

UNIQUE ISLAND HABITATS MAY BE THREATENED BY DOUBLE-CRESTED CORMORANTS

Abstract: Double-crested cormorant (Phalacrocorax auritus) populations on the Great Lakes expanded greatly during the past 2 decades. On Lake Erie, the number of breeding cormorants increased from 174 birds (87 nests) in 1979 to 26,542 (13,271 nests) in 2000. In 2000, 81% of the breeding population was on 2 western-basin islands (East Sister and Middle Islands). The plant communities on these islands represent some of the last remnants of Carolinian vegetation in Canada. Our study is the first to quantitatively assess the relationship between the distribution of nesting cormorants and forest health. On East Sister Island, 2 measures of forest cover were obtained using infrared aerial photographs and ground-based measurements of leaf area index. These measures of forest cover were correlated (r_s = 0.70, P < 0.001), which validated the use of remotely sensed data to assess forest cover. Cormorant nest density was negatively correlated with tree cover on both East Sister and Middle Islands. Temporal comparisons of Middle Island data indicated a reduction in tree cover from 1995 to 2001, and these reductions coincided with a large increase in the island's cormorant population. Although correlational in nature, our results suggest that cormorants may be detrimentally affecting island forests.     

Avian Predation on Steelhead is Consistent with Compensatory Mortality

Numerous factors such as predation, disease, injury, and environmental conditions (e.g., river flows, hydropower operations) can influence survival rates of fish. Although mortality due to predation is commonly assumed to be additive and result in a directly proportional reduction on survival rates, compensatory processes may work to counteract or negate the effects of predation mortality on survival rates. We applied a random effects model to a long-term, mark-recapture-recovery data set on anadromous steelhead (Oncorhynchus mykiss) from the Snake River Basin in the northwestern United States to assess whether avian predation mortality constitutes an additive or compensatory source of mortality. Specifically, our assessment focused on predation mortality due to double-crested cormorants (Phalacrocorax auritus) and Caspian terns (Hydroprogne caspia) on colonies in the Columbia River estuary. In addition, we evaluated several candidate environmental indices to examine potential interactions between the effects of predation versus environmental conditions on steelhead survival rates. Average predation rates were 3.3% for the double-crested cormorant colony and 17.0% for the Caspian tern colony. For both colonies, the estimated correlation between the predation rate and survival rate of steelhead was near zero, indicating that mortality due to avian predation is compensatory. Models that included variables for river flow, juvenile migration timing, and an index of forage biomass in the ocean accounted for 56–59% of the variation in steelhead survival, whereas avian predation rates accounted for <1% of the variation. Management efforts to reduce the abundance of the bird colonies are unlikely to improve the survival or conservation status of steelhead; however, results indicate that steelhead survival could be improved by hydropower management decisions that increase river flows and reduce juvenile migration delays. © 2020 The Wildlife Society.     

普通鸬鹚鸟卵溶菌酶与巢密度及卵顺序和新城疫病毒母源抗体关系

亲鸟可通过母体作用向鸟卵传递不同的免疫物质,用于免疫防御,对提高子代生存率至关重要。本研究在青海湖鸬鹚岛共采集60枚普通鸬鹚(Palacrocorax carbo)鸟卵,并同时记录巢密度和卵顺序,通过血凝抑制试验和溶解实验分别测定鸟卵溶菌酶浓度和新城疫病毒(Newcastle disease virus,NDV)母源抗体效价。对鸟卵溶菌酶浓度与巢密度进行Pearson相关分析,利用单因素方差(One way ANOVA)分析鸟卵溶菌酶浓度与卵顺序关系,利用t检验分析新城疫病毒阳性鸟卵与阴性鸟卵溶菌酶浓度差异性,对新城疫病毒阳性鸟卵抗体效价与溶菌酶浓度进行Spearman相关分析。(1)不同窝的鸟卵溶菌酶浓度与巢密度呈正相关性(r=0.886,P0.000 1);(2)同一窝内鸟卵溶菌酶浓度随着卵顺序的增加而增加(F=3.95,P0.05),且新城疫病毒阳性鸟卵的溶菌酶量高于阴性鸟卵(t=4.08,df=58,P0.001);(3)在新城疫病毒阳性鸟卵中,其新城疫病毒抗体效价与溶菌酶含量呈负相关关系(r=﹣0.840,P0.001)。上述结果表明,亲鸟会根据繁殖密度和卵顺序来调节向鸟卵分配的溶菌酶,同时会调节向鸟卵中传递抗新城疫病毒母源抗体和溶菌酶浓度,从而使免疫防御作用最大化。     

Evidence of dominant parasympathetic nervous activity of great cormorants (<Emphasis Type="Italic">Phalacrocorax carbo</Emphasis>)

The characteristics of autonomic nervous activity were examined on captive great cormorants Phalacrocorax carbo hanedae, using a power spectral analysis of heart rate variability. Heart rates were calculated from recordings of the electrocardiograms of the birds via embarked data loggers. We investigated the effects of blockades of the sympathetic or parasympathetic nervous systems using the indices of autonomic nervous activity such as high frequency (0.061–1.5 Hz) component, low frequency (0.02–0.060 Hz) component and the low frequency power component to high frequency power component ratio. Resting heart rate (85.5 ± 6.1 bpm) was lower than the intrinsic heart rate (259.2 ± 15.3 bpm). The heart rate drastically increased after the injection of the parasympathetic nervous blocker, on the other hand it slightly decreased after the injection of the sympathetic nervous blocker. The sympathetic, parasympathetic and net autonomic nervous tones calculated from heart rate with and without blockades were 40.9 ± 27.6, −44.5 ± 7.4 and −29.5 ± 9.0%, respectively. The effect of the parasympathetic nervous blockade on low frequency and high frequency power was greater than that of the sympathetic nervous blockade. Those data suggested that the parasympathetic nervous activity was dominant for great cormorants.     

The family prosthogonimidae (Trematoda) in Australia

The family Prosthogonimidae (Trematoda) in Australia. International Journal for Parasitology 3: 853–862. The family Prosthogonimidae has previously been known in Australia by three species of Prosthogonimus Lühe, 1899 (from birds) and by Coelomotrema Angel, 1970 (from marsupials). Two new genera are now proposed: Cylindrotrema cygni from Cygnus atratus (Latham) (caecum), and Mawsonotrema eudyptulae from Eudyptula minor (Forster) (liver). Prosthogonimus vitellatus Nicoll, 1914 is recorded from three new hosts, Gymnorhina tibicen leuconota (Latham), Phalacrocorax melanoleucos (Vieillot) and Chlidonias hybrida (Pallas), and the species is redescribed from 11 specimens from the first of these. The life history, not known for any Australian species, is discussed.

The only plump-bodied genera in the family are Coelomotrema, Cylindrotrema and Mawsonotrema, all of which are confined to Australia.

Mawsonotrema differs from all other members of the family in the position of the genital pore, which is away from the anterior end of the body, lying against the anterior border of the acetabulum.