In sexually size-dimorphic bird species, rearing costs of sons and daughters usually differ and may be important in the evolution of offspring sex ratio adjustment. Raptors have reversed sexual size dimorphism and the smaller males are sometimes found to be overrepresented in food-poor territories or years. As a raptor with small reversed sexual dimorphism (6% in body mass), the European Honey Buzzard Pernis apivorus is expected to show little or no brood sex ratio bias in relation to environmental conditions. We molecularly sexed 311 chicks of 195 broods in and around The Netherlands, during 1996–2014. We examined which environmental factors explained brood sex ratio variation best. Overall, sex ratio was not biased (all nests pooled: 50.8% females) but more females were produced in years when on average Honey Buzzards bred earlier (32% sex ratio change over a ten-day range in annual mean laying date). Within-year laying date variation, hatching order, abundance of wasp (Vespinae) nests (main food source) and summer weather did not explain sex ratio variation. In the Veluwe and Drenthe (1974–2014), Honey Buzzards laid eggs earlier when the spring was warmer, which resulted in a c. 9-day advance in laying date over 40 years. As warm spring weather was also a predictor of a higher density of wasp colonies, we expected female chicks to benefit more from growing up in wasp-rich years than males, if the sex ratio biases were adaptive. However, this differential growth benefit was not noticeable in chick body mass; chick body mass was best explained by negative effects of relative laying date (within a year) and hatching order. The potential benefit for female nestlings (compared to males) of growing up in years with warm springs, when egg laying occurs early and wasp colonies are more abundant, remains unknown.
{"title":"Brood Sex Ratio in European Honey Buzzards Pernis apivorus is Related to Spring Phenology","authors":"Kees H. T. Schreven, R. Bijlsma, C. Both","doi":"10.5253/arde.2022.a10","DOIUrl":"https://doi.org/10.5253/arde.2022.a10","url":null,"abstract":"In sexually size-dimorphic bird species, rearing costs of sons and daughters usually differ and may be important in the evolution of offspring sex ratio adjustment. Raptors have reversed sexual size dimorphism and the smaller males are sometimes found to be overrepresented in food-poor territories or years. As a raptor with small reversed sexual dimorphism (6% in body mass), the European Honey Buzzard Pernis apivorus is expected to show little or no brood sex ratio bias in relation to environmental conditions. We molecularly sexed 311 chicks of 195 broods in and around The Netherlands, during 1996–2014. We examined which environmental factors explained brood sex ratio variation best. Overall, sex ratio was not biased (all nests pooled: 50.8% females) but more females were produced in years when on average Honey Buzzards bred earlier (32% sex ratio change over a ten-day range in annual mean laying date). Within-year laying date variation, hatching order, abundance of wasp (Vespinae) nests (main food source) and summer weather did not explain sex ratio variation. In the Veluwe and Drenthe (1974–2014), Honey Buzzards laid eggs earlier when the spring was warmer, which resulted in a c. 9-day advance in laying date over 40 years. As warm spring weather was also a predictor of a higher density of wasp colonies, we expected female chicks to benefit more from growing up in wasp-rich years than males, if the sex ratio biases were adaptive. However, this differential growth benefit was not noticeable in chick body mass; chick body mass was best explained by negative effects of relative laying date (within a year) and hatching order. The potential benefit for female nestlings (compared to males) of growing up in years with warm springs, when egg laying occurs early and wasp colonies are more abundant, remains unknown.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":" ","pages":"1 - 18"},"PeriodicalIF":0.4,"publicationDate":"2022-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45696950","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tim Temizyürek, Michelle Johannknecht, Peter Korsten
Hatching asynchrony is a frequent phenomenon in altricial birds and can lead to brood reduction due to sibling competition. There are a number of adaptive hypotheses to explain its occurrence, relating hatching asynchrony to sibling competition and timing of breeding. Incubation prior to clutch completion (early incubation) is the main cause of hatching asynchrony. We used temperature loggers inside the nests of breeding Blue Tits Cyanistes caeruleus to provide a detailed account of female incubation over most of the egg-laying period. We relate this early incubation to the time interval between clutch completion and hatching as well as hatching asynchrony. Our study shows the frequent occurrence of early incubation during the beginning of the laying period, with all females showing more early incubation towards clutch completion. At first, early incubation mostly occurs at night, but as egg laying progresses, it also occurs during the day. However, overall there was more nocturnal than diurnal early incubation. These results were obtained using two different methods for quantifying incubation from temperature profiles, which we compared and cross-validated in this study. Moreover, the amount of early incubation related negatively to the time between clutch completion and first hatching and positively to the extent of hatching asynchrony. While we did not directly investigate the mechanisms driving variation in early incubation, the exceptionally cold March/April period followed by a warm May in our study year may explain the comparatively great amounts of early incubation we observed. We hypothesise that spring temperatures may influence the amount of early incubation, with warmer springs resulting in more early incubation and consequently shorter times from clutch completion until first hatching as well as increased hatching asynchrony. Such a mechanism of adjustment of incubation time and hatching asynchrony may also be important for the adaptation of birds to climate change.
{"title":"Incubation before Clutch Completion Predicts Incubation Time and Hatching Asynchrony in the Blue Tit Cyanistes caeruleus","authors":"Tim Temizyürek, Michelle Johannknecht, Peter Korsten","doi":"10.5253/arde.2022.a6","DOIUrl":"https://doi.org/10.5253/arde.2022.a6","url":null,"abstract":"Hatching asynchrony is a frequent phenomenon in altricial birds and can lead to brood reduction due to sibling competition. There are a number of adaptive hypotheses to explain its occurrence, relating hatching asynchrony to sibling competition and timing of breeding. Incubation prior to clutch completion (early incubation) is the main cause of hatching asynchrony. We used temperature loggers inside the nests of breeding Blue Tits Cyanistes caeruleus to provide a detailed account of female incubation over most of the egg-laying period. We relate this early incubation to the time interval between clutch completion and hatching as well as hatching asynchrony. Our study shows the frequent occurrence of early incubation during the beginning of the laying period, with all females showing more early incubation towards clutch completion. At first, early incubation mostly occurs at night, but as egg laying progresses, it also occurs during the day. However, overall there was more nocturnal than diurnal early incubation. These results were obtained using two different methods for quantifying incubation from temperature profiles, which we compared and cross-validated in this study. Moreover, the amount of early incubation related negatively to the time between clutch completion and first hatching and positively to the extent of hatching asynchrony. While we did not directly investigate the mechanisms driving variation in early incubation, the exceptionally cold March/April period followed by a warm May in our study year may explain the comparatively great amounts of early incubation we observed. We hypothesise that spring temperatures may influence the amount of early incubation, with warmer springs resulting in more early incubation and consequently shorter times from clutch completion until first hatching as well as increased hatching asynchrony. Such a mechanism of adjustment of incubation time and hatching asynchrony may also be important for the adaptation of birds to climate change.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"110 1","pages":"1 - 20"},"PeriodicalIF":0.4,"publicationDate":"2022-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48532341","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"Conspecific Density as a Driver of Offspring Body Condition in Three Cormorant Colonies in Denmark","authors":"T. Bregnballe, M. Frederiksen","doi":"10.5253/arde.v109i1.a26","DOIUrl":"https://doi.org/10.5253/arde.v109i1.a26","url":null,"abstract":"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.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"109 1","pages":"593 - 608"},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48566265","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Gagliardi, D. Preatoni, S. Volponi, A. Martinoli, M. Fasola
Breeding Great Cormorants Phalacrocorax carbo have been rapidly increasing in Italy since the 1990s, and have settled their colonies in sites already used by other colonial waterbirds. We investigated the patterns of interference between Grey Herons Ardea cinerea and Great Cormorants, the two species most prone to competition due to their similar preference for nest sites. The analysis of long-term population trends in colonies with both species compared to colonies without Cormorants, showed that the number of Grey Heron nests gradually decreased following the settlement of Great Cormorants. The two species exhibited a gradual spatial segregation in nest location, both horizontally and vertically, within the same colony. In some heronries we found clear examples of interaction, but we also report cases where the interaction was less clear. Thus, although Great Cormorants might be competitively dominant over Grey Herons for nest site occupancy in many of their shared colonies, the spatial competition dynamics might also be influenced by factors affecting population dynamics in the wider environment. We envisage specific observations and focus on areas with an apparent abundance of trees suitable for nesting by both species.
{"title":"When Gate Crashers Show Up: Does Expansion of Great Cormorant Phalacrocorax carbo in North-Western Italy Affect Breeding Site Selection in Grey Heron Ardea cinerea?","authors":"A. Gagliardi, D. Preatoni, S. Volponi, A. Martinoli, M. Fasola","doi":"10.5253/arde.v109i2.a25","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a25","url":null,"abstract":"Breeding Great Cormorants Phalacrocorax carbo have been rapidly increasing in Italy since the 1990s, and have settled their colonies in sites already used by other colonial waterbirds. We investigated the patterns of interference between Grey Herons Ardea cinerea and Great Cormorants, the two species most prone to competition due to their similar preference for nest sites. The analysis of long-term population trends in colonies with both species compared to colonies without Cormorants, showed that the number of Grey Heron nests gradually decreased following the settlement of Great Cormorants. The two species exhibited a gradual spatial segregation in nest location, both horizontally and vertically, within the same colony. In some heronries we found clear examples of interaction, but we also report cases where the interaction was less clear. Thus, although Great Cormorants might be competitively dominant over Grey Herons for nest site occupancy in many of their shared colonies, the spatial competition dynamics might also be influenced by factors affecting population dynamics in the wider environment. We envisage specific observations and focus on areas with an apparent abundance of trees suitable for nesting by both species.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"109 1","pages":"583 - 591"},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46156932","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In Israel, which is a bottleneck for some six hundred million migrating birds, the drainage of the Hula Lake in the north resulted in serious conflicts between fish-eating birds and the intensive fish farming and agriculture that became established on the reclaimed land. Implementation of various deterrence methods, including lethal control, failed to solve these conflicts. We followed the concept that only by understanding the biology of the organism in question could the tools (indications) for effective and sustainable management be devised that would solve such conflicts while helping the preservation of natural assets such as wetlands and their inhabitants. We demonstrated this concept in the solutions reached in the case studies of pelicans and cormorants and their interactions with intensive commercial fish ponds. We studied the physiological condition, food preference and energy demands, and ecological constraints of Great White Pelican Pelecanus onocrotalus, Great Cormorant Phalacrocorax carbo and Pygmy Cormorant Microcarbo pygmeus. As a result, we suggested different management solutions that are currently implemented with the full cooperation of the fishermen and the nature preservation authorities. Based on assessment of visual acuity to detect and catch fish under water Great Cormorants were effectively pushed towards Lake Kinneret where they could hunt more profitable fish than in the turbid fish ponds. The established roosts there were not controlled such as to lead the birds away from the fishponds. In case of the pelicans, part of the drained Hula valley was reflooded and extra fish was provided. Both measures effectively reduced the damage at the fish farms. We have shown that such solutions are economically helpful for fishermen and enable the preservation of the wetland habitat.
{"title":"Experimental Biology in Conflict Resolutions: The Case of Pelicans and Cormorants in Israel","authors":"Z. Arad","doi":"10.5253/arde.v109i2.a30","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a30","url":null,"abstract":"In Israel, which is a bottleneck for some six hundred million migrating birds, the drainage of the Hula Lake in the north resulted in serious conflicts between fish-eating birds and the intensive fish farming and agriculture that became established on the reclaimed land. Implementation of various deterrence methods, including lethal control, failed to solve these conflicts. We followed the concept that only by understanding the biology of the organism in question could the tools (indications) for effective and sustainable management be devised that would solve such conflicts while helping the preservation of natural assets such as wetlands and their inhabitants. We demonstrated this concept in the solutions reached in the case studies of pelicans and cormorants and their interactions with intensive commercial fish ponds. We studied the physiological condition, food preference and energy demands, and ecological constraints of Great White Pelican Pelecanus onocrotalus, Great Cormorant Phalacrocorax carbo and Pygmy Cormorant Microcarbo pygmeus. As a result, we suggested different management solutions that are currently implemented with the full cooperation of the fishermen and the nature preservation authorities. Based on assessment of visual acuity to detect and catch fish under water Great Cormorants were effectively pushed towards Lake Kinneret where they could hunt more profitable fish than in the turbid fish ponds. The established roosts there were not controlled such as to lead the birds away from the fishponds. In case of the pelicans, part of the drained Hula valley was reflooded and extra fish was provided. Both measures effectively reduced the damage at the fish farms. We have shown that such solutions are economically helpful for fishermen and enable the preservation of the wetland habitat.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"228 ","pages":"659 - 666"},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41311811","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. Bregnballe, Jesper Tofft, Jana Kotzerka, A. Lehikoinen, Pekka Rusanen, C. Herrmann, O. Krone, H. Engström, Kalev Rattiste, Jurgen Reich, S. Kouzov
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.
{"title":"Occurrence and Behaviour of White-Tailed Eagles Haliaeetus albicilla in Great Cormorant Phalacrocorax Carbo Sinensis Colonies in Countries around the Baltic Sea","authors":"T. Bregnballe, Jesper Tofft, Jana Kotzerka, A. Lehikoinen, Pekka Rusanen, C. Herrmann, O. Krone, H. Engström, Kalev Rattiste, Jurgen Reich, S. Kouzov","doi":"10.5253/arde.v109i2.a24","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a24","url":null,"abstract":"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.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"109 1","pages":"565 - 582"},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43798771","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Govedič, Teja Bizjak Govedič, Ana Pajtnar, G. Torkar
The foraging of Great Cormorants Phalacrocorax carbo in Alpine rivers is a relatively recent phenomenon. Wintering populations in Slovenia increased in the 1980s. In the 1990s, the increase affected the upper sections of rivers where the habitats of Grayling Thymallus thymallus and trout Salmo and Oncorhynchus spp. are located. The upper section of the Soča River system is known as one of the biogeographic hotspots for (sub)alpine rivers, where several endemic or rare fish species are found. The aim of this study is to evaluate the diet of the Cormorants in this area and to compare it to some other threats to the fish fauna of the river. A total of 75 Cormorant stomachs were examined. Of these, 68 (90.7%) contained fish or recognisable fish remains. The birds' diet consisted of eight species of fish: Marble Trout, Rainbow Trout, Common Nase, Vairone, Common Chub, Italian Chub, Italian Barbel and Bullhead. The increase in numbers and the diet of Cormorants in the river basin of Soča is discussed in the context of the increase of other threats to this ecosystem, such as fish stocking, gravel extraction and tourism, especially angling and water sports. A more comprehensive environmental assessment of all these factors is needed, as their increase runs parallel with the arrival of the Cormorants in the upper section of the river. There is therefore reason to believe that Cormorants are only a small part of a larger problem in the conservation of the river ecosystem.
{"title":"Great Cormorants Phalacrocorax carbo in the Subalpine Soča River System, Slovenia: The Possible Effect of Avian Predators in a Sensitive Biogeographic Region for Fish","authors":"M. Govedič, Teja Bizjak Govedič, Ana Pajtnar, G. Torkar","doi":"10.5253/arde.v109i2.a12","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a12","url":null,"abstract":"The foraging of Great Cormorants Phalacrocorax carbo in Alpine rivers is a relatively recent phenomenon. Wintering populations in Slovenia increased in the 1980s. In the 1990s, the increase affected the upper sections of rivers where the habitats of Grayling Thymallus thymallus and trout Salmo and Oncorhynchus spp. are located. The upper section of the Soča River system is known as one of the biogeographic hotspots for (sub)alpine rivers, where several endemic or rare fish species are found. The aim of this study is to evaluate the diet of the Cormorants in this area and to compare it to some other threats to the fish fauna of the river. A total of 75 Cormorant stomachs were examined. Of these, 68 (90.7%) contained fish or recognisable fish remains. The birds' diet consisted of eight species of fish: Marble Trout, Rainbow Trout, Common Nase, Vairone, Common Chub, Italian Chub, Italian Barbel and Bullhead. The increase in numbers and the diet of Cormorants in the river basin of Soča is discussed in the context of the increase of other threats to this ecosystem, such as fish stocking, gravel extraction and tourism, especially angling and water sports. A more comprehensive environmental assessment of all these factors is needed, as their increase runs parallel with the arrival of the Cormorants in the upper section of the river. There is therefore reason to believe that Cormorants are only a small part of a larger problem in the conservation of the river ecosystem.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"109 1","pages":"395 - 415"},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41550873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mennobart R. van Eerden, Stef van Rijn, M. Kilpi, A. Lehikoinen, V. Lilleleht, Karlis Millers, A. Gaginskaya
Great Cormorants Phalacrocorax carbo in the eastern Baltic are expanding in numbers. Eight colonies in Estonia, Finland and the Russian Federation were investigated in 2007. Brood size and condition of large nestlings were determined and indicate that food provisioning was not a limiting factor. Food items consisted of both pelagic and benthic prey, with marked differences among the colonies. Eelpout Zoarces viviparus and Roach Rutilus rutilus were the most important prey according to fish mass. For pelagic prey this was Sprat Sprattus sprattus. Additional data in later years support the conclusion that the species experienced a rapid expansion at the time of investigation. Two factors are likely to have contributed to improved conditions for Cormorants in this part of the eastern Baltic. First, the low abundance of predatory fish such as Cod Gadus morhua and Pikeperch Sander lucioperca as a result of overfishing by commercial fisheries as well as climate change has, most likely, caused small benthic and pelagic prey fish to thrive. Second, increased eutrophication has probably fuelled the fish production. Based on fish species taken and the number of Cormorants present, the conclusion seems justified that any interaction between Cormorants and fisheries is unlikely at the scale of the Finnish Gulf, although locally measurable effects of Cormorant consumption on commercial yield may exist. As a visible, relatively new apex predator to the system, the Great Cormorant may well be an indicator of the ecological condition of the system. Monitoring of Cormorants (numbers, distribution, food, breeding success) may therefore provide useful data which can be used to assess the recovery of the benthic and pelagic parts of the food web.
波罗的海东部的Phalacrocorax carbo大Cormorants数量正在增加。2007年对爱沙尼亚、芬兰和俄罗斯联邦的八个殖民地进行了调查。确定了大型雏鸟的繁殖规模和状况，表明食物供应不是一个限制因素。食物包括上层和海底猎物，各殖民地之间存在显著差异。根据鱼类数量，黄鳝和Roach Rutilus Rutilus是最重要的猎物。对于远洋猎物，这是Sprat Sprattus Sprattus。后来几年的额外数据支持了这样一个结论，即该物种在调查时经历了快速扩张。有两个因素可能有助于改善波罗的海东部这一地区的珊瑚礁状况。首先，由于商业渔业的过度捕捞以及气候变化，Cod Gadus morhua和Pikepers Sander lucioperca等掠食性鱼类的丰度较低，很可能导致小型底栖和中上层掠食性鱼类茁壮成长。其次，富营养化加剧可能助长了鱼类生产。根据所采集的鱼类种类和存在的Cormorant数量，得出的结论似乎是合理的，即在芬兰湾的规模上，Cormorant与渔业之间不太可能发生任何互动，尽管当地可能存在Cormorant消费对商业产量的可测量影响。作为该系统中一种可见的、相对较新的顶级捕食者，大Cormorant很可能是该系统生态状况的指标。因此，对Cormorants的监测（数量、分布、食物、繁殖成功率）可以提供有用的数据，用于评估食物网中底栖和中上层部分的恢复情况。
{"title":"Expanding East: Great Cormorants Phalacrocorax carbo Thriving in the Eastern Baltic and Gulf of Finland","authors":"Mennobart R. van Eerden, Stef van Rijn, M. Kilpi, A. Lehikoinen, V. Lilleleht, Karlis Millers, A. Gaginskaya","doi":"10.5253/arde.v109i2.a5","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a5","url":null,"abstract":"Great Cormorants Phalacrocorax carbo in the eastern Baltic are expanding in numbers. Eight colonies in Estonia, Finland and the Russian Federation were investigated in 2007. Brood size and condition of large nestlings were determined and indicate that food provisioning was not a limiting factor. Food items consisted of both pelagic and benthic prey, with marked differences among the colonies. Eelpout Zoarces viviparus and Roach Rutilus rutilus were the most important prey according to fish mass. For pelagic prey this was Sprat Sprattus sprattus. Additional data in later years support the conclusion that the species experienced a rapid expansion at the time of investigation. Two factors are likely to have contributed to improved conditions for Cormorants in this part of the eastern Baltic. First, the low abundance of predatory fish such as Cod Gadus morhua and Pikeperch Sander lucioperca as a result of overfishing by commercial fisheries as well as climate change has, most likely, caused small benthic and pelagic prey fish to thrive. Second, increased eutrophication has probably fuelled the fish production. Based on fish species taken and the number of Cormorants present, the conclusion seems justified that any interaction between Cormorants and fisheries is unlikely at the scale of the Finnish Gulf, although locally measurable effects of Cormorant consumption on commercial yield may exist. As a visible, relatively new apex predator to the system, the Great Cormorant may well be an indicator of the ecological condition of the system. Monitoring of Cormorants (numbers, distribution, food, breeding success) may therefore provide useful data which can be used to assess the recovery of the benthic and pelagic parts of the food web.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"109 1","pages":"313 - 326"},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48821982","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Day-fresh Great Cormorant pellets were collected at a huge single winter roost at Kreupel island in Lake IJsselmeer, The Netherlands. The roost is situated on a sandy island, 3 m above the water level and is regularly used by 1000–8000+ Cormorants. By examining pellets and thus reconstructing the previous day's meal of Cormorants gathering at the roost, we explored spatio-temporal differences in the diet of individual birds. We found that structural differences in pellets (size, colour and structure) are related to their content (fish species and fresh mass of a daily meal). Structurally larger and lighter coloured pellets contained larger and coarser fish and represented a higher total fish mass. Pellets of different size and structure were non-randomly distributed at the roost. Birds positioned centrally in the roost produced on average larger pellets than birds at the edges. Cormorants having few or no food remains in their pellets were more frequently recorded on the edge of the roost than in the centre and in particular, they were more likely to be located to the rear of the roost. The same was true for pellets showing a bloody signature which may be linked to either injury by sharp fin rays or to a parasite induced effect. Pellet data were corroborated by observations of differential distribution of faecal splashes of Cormorants, showing that individuals in the centre of the roost produced most guano. Clear diet differences existed within the roost between birds in the centre and elsewhere in the roost, whereas smaller differences existed between the front, edge and rear of the roost. Our data suggest a social hierarchy based on higher foraging success of birds returning earlier to the roost and settling in the centre, hereby forcing later arriving and less successful Cormorants towards the edge, rear and front position. We conclude that position at the roost is a reflection of previous foraging success, possibly caused by differences in dominance between Cormorants during the period of communal foraging. From a methodological point of view, our study demonstrates that, because of structural differences in pellets and spatial differences in occurrence, it is important to collect pellets randomly if one is to describe a proper diet sample by using pellets at any given site. Especially in marshlands and under trees and bush growth with a lot of litter, the likely collection of larger, more conspicuous pellets will cause a bias towards the larger fish species and sizes. Also sampling only at edge locations or specifically at the centre of a roost may give biased results, as this may result in an under- or overestimation in reconstructed fish uptake (e.g. fish size, mass, species) from the waterbody under study.
{"title":"Social Hierarchy within Communal Foraging Flocks of Great Cormorants Phalacrocorax carbo as Reflected by Differences in Prey Composition and Food Intake at the Roost","authors":"Mennobart R. van Eerden, Stef van Rijn","doi":"10.5253/arde.v109i2.a23","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a23","url":null,"abstract":"Day-fresh Great Cormorant pellets were collected at a huge single winter roost at Kreupel island in Lake IJsselmeer, The Netherlands. The roost is situated on a sandy island, 3 m above the water level and is regularly used by 1000–8000+ Cormorants. By examining pellets and thus reconstructing the previous day's meal of Cormorants gathering at the roost, we explored spatio-temporal differences in the diet of individual birds. We found that structural differences in pellets (size, colour and structure) are related to their content (fish species and fresh mass of a daily meal). Structurally larger and lighter coloured pellets contained larger and coarser fish and represented a higher total fish mass. Pellets of different size and structure were non-randomly distributed at the roost. Birds positioned centrally in the roost produced on average larger pellets than birds at the edges. Cormorants having few or no food remains in their pellets were more frequently recorded on the edge of the roost than in the centre and in particular, they were more likely to be located to the rear of the roost. The same was true for pellets showing a bloody signature which may be linked to either injury by sharp fin rays or to a parasite induced effect. Pellet data were corroborated by observations of differential distribution of faecal splashes of Cormorants, showing that individuals in the centre of the roost produced most guano. Clear diet differences existed within the roost between birds in the centre and elsewhere in the roost, whereas smaller differences existed between the front, edge and rear of the roost. Our data suggest a social hierarchy based on higher foraging success of birds returning earlier to the roost and settling in the centre, hereby forcing later arriving and less successful Cormorants towards the edge, rear and front position. We conclude that position at the roost is a reflection of previous foraging success, possibly caused by differences in dominance between Cormorants during the period of communal foraging. From a methodological point of view, our study demonstrates that, because of structural differences in pellets and spatial differences in occurrence, it is important to collect pellets randomly if one is to describe a proper diet sample by using pellets at any given site. Especially in marshlands and under trees and bush growth with a lot of litter, the likely collection of larger, more conspicuous pellets will cause a bias towards the larger fish species and sizes. Also sampling only at edge locations or specifically at the centre of a roost may give biased results, as this may result in an under- or overestimation in reconstructed fish uptake (e.g. fish size, mass, species) from the waterbody under study.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"109 1","pages":"549 - 563"},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48980845","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"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","authors":"L. Marion, Pierrick Marion","doi":"10.5253/arde.v109i2.a8","DOIUrl":"https://doi.org/10.5253/arde.v109i2.a8","url":null,"abstract":"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.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"109 1","pages":"353 - 366"},"PeriodicalIF":0.4,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43423812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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