Cormorant papers:

references, abstracts and comments. Where there is no abstract, an abstract has been written, where abstracts are too long they have been abridged. Abstracts in languages other than English have been translated into English. CRGB = Cormorant Research Group Bulletin. The comment is personal, it points out errors and possible follow-ups, it is begun: CP:

Note the following lists on the web:


N, O, P, Q, R, S, T, U, V, W, X, Y, Z, Å

Naito, W., Murata, M. & K. Yoshida (2004): Evaluation of population-level ecological risks of fish-eating birds to dioxinlike PCBs exposure. Organohalogen Compounds 66: 3350 - 3355. Internet version of this report.

Naturvårdsverket (2000): Förvaltningsplan för mellanskarv och storskarv. Rapport 5261. Stockholm 2002. Internet version of this report.

Newson, S. E., Hughes, B., Hearn, R. & T. Bregnballe (2005): Breeding performance and timing of breeding of inland and coastal breeding Cormorants Phalacrocorax carbo in England and Wales. Bird Study 52: 10 - 17.

Aims To compare breeding performance of inland and coastal breeding Cormorants in England and Wales and to provide breeding performance data for Cormorants for future demographic studies.
Methods Breeding performance and timing of breeding was monitored at six inland and four coastal colonies during 1997 and 1998. We compare clutch and brood size and egg and nestling survival.
Results Breeding performance was higher at inland colonies because of higher nestling survival during the later stages of nestling development, from 15-56 days.
Conclusions Greater and earlier food availability at inland colonies, resulting in earlier and more protracted breeding is the most probable explanation for differences in breeding performance. A more protracted breeding season would reduce competition for food and enhance breeding performance, which may be especially apparent during late chick development when energy demands are greatest.

Nienhuis, J. (2000): The use of chewing pads and otoliths of cyprinids for estimating food intake of Cormorants Phalacrocorax carbo. CRGB 4: 40 - 45.


Otel, & J. B. Kiss (2001): Data concerning the food components of the Cormorant (Phalacrocorax carbo) in the Danube delta, colony Martinca. Sc. Ann. Danube Delta Inst. 2001: 186 - 191. Internet version.

18 fish species have been identified in the Cormorant's chick regurgitations, belonging to the following families: Cyprinidae (49 %), Percidae (22 %), Gobiidae (10 %), Siluridae, Esocidae and Centrarchidae (by 6 %). The most frequent species were Carassius gibelio, Blicca bjoerkna, Rutilus rutilus and Alburnus alburnus (35,8 % - 21 %), while Cyprinus carpio, Gymnocephalus cernuus, Neogobius eurycephalus and Stizostedion lucioperca had the least frecquency value (1,2 %). The highest value of numerical relative abundance (26,2 % - 17,3 %) has been found to Carassius gibelio, Alburnus alburnus, Blicca bjoerkna and Rutilus rutilus, having proportion beetwen juvenils and adults about equal. Barbus barbus, Cyprinus carpio, Gymnocephalus cernuus and Neogobius eurycephalus have been recorded the least frequency value (0,4 %). Concerning the gravimetrical relative abundance, it may be remarked predominance of Carassius gibelio (47,2 %) and Blicca bjoerkna (30,8 %) generated by adult specimens, following Rutilus rutilus (8,4 %), while Gymnocephalus cernuus, Lepomis gibossus and Neogobius eurycephalus were situated at the last places (0,1 %). On base of ecological preferences of catching fishis, it was determined that main aquatic habitat types in which adult Cormorants fished to ensure its chick food were as follows: 46,9 % of prey belonged from lakes and channals, 6,3 % from Danube river and 46,8 % could be both from stagnant waters and Danube. The ray of catching area was approximately 15 km from nesting colony.


Paillisson, J.-M., Carpentier, A., Le Gentil, J. & L. Marion (2004): Space utilization by a cormorant (Phalacrocorax carbo L.) colony in a multi-wetland complex in relation to feeding strategies. Comptes Rendus Biologies 327: 493 - 500.

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.

Pajkert, Z. & W. Górski (1996): Breeding biology of Great Cormorant Phalacrocorax carbo sinensis in the Slowinski national park (northwestern Poland). CRGB 2: 6 - 10.

Platteeuw, M. & M. R. Van Eerden (1995): Time and energy constraints of fishing behaviour in breeding Cormorants Phalacrocorax carbo sinensis at lake IJsselmeer, The Netherlands. Ardea 83: 223 - 234.

Two Cormorant colonies in The Netherlands (Naardermeer and Oostvaardersplassen), exploiting the same water bodies but situated at different distances from them, were compared with respect to daily variations in exact fishing sites and corresponding variations in time budget and fish consumption. Mean flying distances between colony and fishing site were estimated at 22 and 15 km respectively. Birds from the Naardermeer colony carried out less trips but of a longer duration than birds from Oostvaardersplassen, most markedly so in the chick rearing period (2 trips per day of 185 min vs. 3 trips of 165 min). Daily fluctuations in time spent away from the colony were clearly dependent on daily shifts in main fishing sites. On days when fishing was concentrated at larger distances, individual foraging trips lasted longer, due to the increase in flying time. Neither net fishing time nor daily fish consumption, as estimated by pellet analyses, compensated for the increment in time and energy expenditure on those days. It was estimated that the average daily energy expenditure would amount to about 2.8xBMR (basal metabolic rate) in birds from Naardermeer and to about 2.7xBMR in birds from Oostvaardersplassen. Fish consumption estimates based on pellet analyses led to an estimated DME (daily metabolisable energy) of2xBMR for both colonies. Thus, an overall negative energy balance became apparent, resulting in estimated mass losses throughout the breeding season of on average 980 and 860 g for Naardermeer and Oostvaardersplassen birds, respectively. Mass losses are likely to be higher with increasing travelling distances, indicating that travelling distance may influence reproductive output. This could be one of the factors causing consistently lower reproductive outputs at the Naardermeer throughout the years.

Platteeuw, M., Koffijberg, K. & W. Dubbeldam (1995): Growth of Cormorant Phalacrocorax carbo sinensis chicks in relation to brood size, age ranking and parental fishing effort. Ardea 83: 235 - 245.

Growth parameters of Cormorant hatchlings are described in relation to brood size and age ranking of each chick within individual broods. Growth rates, expressed as body mass increment per day over the period of linear growth (5-30 days), ranged from 56.4-102.8 g/day and were found to be independent of brood size and age ranking. Asymptotic fledging mass, logistic growth rate coefficient and age at point of inflection were estimated for 14 chicks measured up to ages of over 30 days. Estimated body mass and age at fledging (twice the age at point of inflection) were further used to estimate the energetic needs. The fastest growing chicks would require peak energy needs of 3022 kJ/day, the slowest growing of about 2050 kJ/day. Total energy needs throughout the nestling period ranged from 46,000 to 69,000 kJ, implying average daily requirements of 1300-1800 kJ. Individual energy needs were on average 40 % higher in fast growing chicks than in slow growing ones. However, slower growth, as a means of energy saving, does not seem to be chosen for voluntarily by younger chicks in larger broods. Parental fishing effort (expressed as total amount of time spent on fishing trips) increased with brood size. Maintaining a foraging uptake of 3g/min of fresh fish, found in the field, and a flying distance of 20 km, a bottleneck is expected to occur at the period of maximum energy needs. In order to cover maximum needs a chick should be fed with an average of 632 g of fish per day. Such a food provisioning level can be achieved for three chicks at an uptake level of 3 g/min of fresh fish. A range of other flying distances and uptake levels is also presented to indicate the margins.


Quintana, F. & P. Yorio (1998): Kelp Gull Larus dominicanus predation on an Imperial Cormorant Phalacrocorax atriceps colony in Patagonia. Mar. Orn. 26: 84 - 85.


REDCAFE (2002): Report of a Concerted Action funded by the European Union. Study contract no. Q5CA-2000-31387: Reducing the conflict between cormorants and fisheries on a pan-European scale. Edited by D. N. Carss. The report on the Internet.

Reymond, A. & O. Zuchuat (1995): Axial migration routes in Cormorants Phalacrocorax carbo passing through or wintering in Switzerland. Ardea 83: 275 - 280.

Sightings of colour rings were used to study the origin of wintering and migrating Cormorants in Aswitzerland between 1977 and 1988. The recorded individuals originated from all parts of the breeding range of sinensis and included also two carbo birds from Norway. According to the recovery rate of each colony/colonies most birds present in Switzerland belong to the Danish population. Significant lower recovery rates were found for eastern Germany, Poland and Sweden, while that for The Netherlands was comparable to western Denmark. These data suggest a west-east axial migration pattern, in which Cormorants predominantly disperse SSW from their breeding areas.

Robards, M. D., Anthony, J. A., Rose, G. A. & J. F. Piatt (1999): Changes in proximate composition and somatic energy content for Pacific sand lance (Ammodytes hexapterus) from Kachemak Bay, Alaska relative to maturity and season. J. Exp. Mar. Biol. & Ec. 242: 245 - 258.

Mean dry weight energy values of adult Pacific sand lance peaked in spring and early summer (20.91 kJ/g for males, 21.08 kJ/g for females), then declined by about 25 % during late summer and fall (15.91 kJ/g for males, 15.74 kJ/g for females). Late summer declines in energy density paralleled gonadal development. Gender differences in energy density (males < females) were only apparent from August to October. Adult sand lance spawn in October, entering the winter with close to their minimum whole body energy content. Juvenile sand lance exhibited a relatively constant protein to lipid ratio until they reached 80 mm fork length. Thereafter, relative proportions of protein remained constant while lipid proportions increased significantly. Dry weight energy densities of juveniles increased from a minimum 16.67 kJ/g to a maximum of 19.68 kJ/g, and (per g) are higher than adults in late summer. The seasonal food value of adult sand lance to predators varies markedly, but maximum energetic value coincides with important feeding periods for marine mammals, fish and seabirds. Internet version of this paper.

Ross, R. M. & J. H. Johnson (1999): Fish Losses to Double-Crested Cormorant Predation in Eastern Lake Ontario, 1992 - 1997. Symposium on Double-Crested Cormorants, Technical Bulletin No. 1879, Dec. 1999.

We examined 4,848 regurgitated digestive pellets of double-crested cormorants (Phalacrocorax auritus) over a 6-year period (1992-97) to estimate annual predation on sport and other fishes in the eastern basin of Lake Ontario. We found more than 51,000 fish of 28 species. Using a model that incorporates annual colony nest counts; fledgling production rates; adult, immature, and young-of-year residence times (seasonal); estimates of mean number of fish per pellet and mean fish size; and a fecal pathway correction factor (4.0 percent), we estimate total annual number of fish consumed by cormorants in the eastern basin of Lake Ontario to range from 37 million to 128 million fish for 1993-97. This fish loss equates to an estimated 0.93 million to 3.21 million kg (mean 2.07 million kg) of fish consumed per year, principally alewife (Alosa pseudoharengus, 42.3 percent) and yellow perch (Perca flavescens, 18.4 percent). Forage fish (alewife, cyprinids, trout-perch {Percopsis omiscomaycus], and other minor components) accounted for 65 percent of the diet, and panfish contributed 34 percent of the diet for the 5-year-period.Gme fish were minor components of the diet, in view of an average estimated annual consumption of 900,000 smallmouth bass (Micropterus dolomieui, 1.1 percent) and 168,000 salmonines (mostly lake trout, Salvelinus namaycush, 0.2 percent). Cormorant predation on lake trout fingerlings stocked in May 1993 and June 1994 was estimated through the use of coded wire tag recoveries from pellets collected on Little Galloo Island 1 and 4 days after stocking events. We estimated losses of 13.6 percent and 8.8 percent. respectively, of the fish stocked for the two events, an average of 11.2 percent. Such losses may be reduced through alteration of existing stocking practices. Internet version of this paper.


Saulamo, K., Andersson, J. & G. Thoresson (2001): Skarv och fisk vid svenska Östersjökusten. Fiskeriverket informerar 2001:7 (1-21).

The abundance of the Great Cormorant (Phalacrocorax carbo sinensis) has increased rapidly in Europe during the last decade. In Sweden, the number of nesting pairs was 15 400 in 1998. The core-area of the Swedish cormorant population is in the Kalmar sound area, where the number of breeding pairs in the largest colony (Svartö) was about 3 000 in 1998. The increasing number of cormorants has led to conflicts between different usergroups, mainly fishermen and conservationists. Possible effects of cormorant predation on fish populations were studied with a model based on published data from studies of cormorant diet and fish monitoring performed in three different coastal areas, including Kalmar sound. Eurasian perch (Perca fluviatilis L.), which is an important prey object for cormorants in the area, was used as model species. It was shown that high mortality of 4-5 year old perch in the Kalmar sound area could be related to cormorant predation. With a total daily consumption of 600 grams of fish, constituting 20-30% of perch averaging 22.5 cm length, estimated mortalities from testfishing and from the model showed best fit. At such predation pressure mortality overrides the production of perch, and may result in a significant reduction of the perchstock. Also effects on eel (Anquilla anquilla L.) were studied using Catch Per Unit Effort and length data from five different areas. The CPUE's were lower in areas close the cormorant colonies. Pdf document on Internet.

Schifferli, L., Burkhardt, M. & M. Kestenholz (2005): Bestandsentwicklung des Kormorans Phalacrocorax carbo in der Schweiz 1967-2003. Orn. Beob. 102: 81 - 96.

Population of Great Cormorants Phalacrocorax carbo wintering in Switzerland, 1967-2003, and numbers during the breeding season. - Based on counts at roosts and on national waterbird counts in mid-January, 1967-2003 and mid-November, 1991-2002, we document the numbers wintering in Switzerland and adjacent waters (Fig. 1). Numbers in January increased exponentially, from 331 in 1967 to the maximum of 8415 in 1992, and in parallel to the growth of the breeding population in The Netherlands, Denmark and Germany (Fig. 3), the major sources of the Swiss wintering population. In subsequent winters, Cormorant numbers fluctuated at a lower level (mean 1993-2003 5686 ± 464), in spite of a continued growth of the breed­­ing population. On 15 large lakes (surface >10 km2), holding three quarters of the national total, fluctuations following the peak run in parallel to the yield of professional fisheries (Fig. 5), which was taken as an index of food supply (Perca fluviatilis, Rutilus rutilus and «other Cyprinid fish»). This confirms the predictions of Suter (1995a), suggesting that food would limit the population in the Swiss winter quarters earlier than on the breeding grounds. In November, 1991-2002, Cormorants were more numerous (mean 8623 ± 2256) than in January in each winter (Fig. 2). Until 1976, Cormorants were restricted to the Lakes of Constance, Geneva, Zurich and Neuchâtel (Fig. 7). Subsequently, other lakes were colonised. Cormorant numbers on lakes peaked in 1989. The final stage of increase was mainly the result of an expansion to rivers (free-running and dammed parts), which held a third of the Ja­nuary numbers in 1991 (Fig. 6). Coinciding with measures taken to scare Cormorants fishing and roosting on rivers holding important populations of threatened fish species (e.g. Thymallus thymallus), the proportions of Cormorants on these waters declined and stabilised (January mean, 1996-2000: 19.7 ± 5.1 %). Since the mid-1980s, the number of summer visitors has increased to some 200 individuals (Fig. 9). About half of them used Lake Geneva. However, first breeding was recorded on Lake Neuchâtel in 2001. The number of pairs has been increasing, and in 2004 100 young fledged from 53 broods (Fig. 10).

Schjørring, S., Gregersen, J. & T. Bregnballe (1999): Prospecting enhances breeding success of first-time breeders in the Great Cormorant, Phalacrocorax carbo sinensis. Animal Behaviour 57: 647 - 654.

In many species of colonial seabirds, young birds visit colonies in the years before they start breeding. This prospecting behaviour may allow them to obtain information that could enhance their future breeding success. We examined the reproductive consequences of prospecting behaviour in the colonial great cormorant, and found support for this idea. New breeders that had been prospecting actively in the previous year obtained breeding sites of higher quality (i.e. closer to sites where conspecifics had fledged young in the previous year) and had higher breeding success than those that had been less active. Prospecting occurred mostly late in the breeding season, and coincided with the time when the majority of the eggs had hatched but before the chicks started fledging, that is, when breeding success in the colony reflected habitat suitability. These results are thus consistent with the use of conspecific reproductive performance as a cue for the quality of a breeding habitat as expected from the 'performance-based conspecific attraction hypothesis'.

Schjørring, S., Gregersen, J. & T. Bregnballe T. (2000): Sex difference in criteria determining fidelity towards breeding sites in the great cormorant. J. An. Ecol. 69: 214 - 223.

1. Many animals choose to breed ìn sites where they have previously been successful. Such fidelity could arise from the predictability of high quality breeding sites in a temporally stable environment. The quality of a site may be indicated by factors other than an individual's own success, because it may fail as a result of a random event that is unrelated to the intrinsic quality of the site. In particular, prior experience (familiarity) with the breeding area and the performance of neighbours could give complementary information about the quality of the site.
2. We present results from a long-term study of colonial great cormorants (Phalacrocorax carbo sinensis), where movement and reproductive success of individually marked birds within a colony was known.
3. Individuals were more likely to return to the same breeding site if they had been successful the previous season.
4. Fidelity of both males and females increased with increasing level of familiarity with the breeding area. Males were more likely to breed again in the same area, and their fidelity was more dependent on familiarity with the area than female fidelity.
5. The success of breeding'sites within the colony was spatially autocorrelated, and cueing on neighbour performance should thus be advantageous. Female fidelity increased with increasing success of neighbouring birds, while male fidelity was unaffected by neighbour success.
6. We suggest that the difference between the sexes in the criteria determining fidelity arises because it is mainly the males that are involved in territorial disputes. They may therefore benefit more than females from knowing their neighbours, and this could override the importance of the intrinsic quality of the breeding area (i.e. reproductive success of neighbours).
7. The conflict over preferred breeding sites that arises within breeding pairs because of this sex difference may be an explanation for the high rate of mate change between years (92.5%) observed in this species.

Schjørring, S. (2001): Ecologically determined natal philopatry within a colony of great cormorants. Behavioural Ecology, 12: 287 - 294.

Sellers, R. M. (1995): Wing-spreading behaviour of the Cormorant Phalacrocorax carbo.. Ardea 83: 27 - 36.

This paper describes an investigation into the factors influencing the occurrence and duration of the wing-spreading behaviour of the Cormorant. It was found to occur only after a period in the water (that is, when the plumage was wet), and its duration to be inversely related to wind speed and the length of time spent in the water. In addition birds tended to face into the wind during wing-spreading and, at low wind speeds, away from the sun. The extent to which the wings were spread was also inversely related to wind speed. The results are discussed with respect to five proposed functions of wing-spreading (wing-drying, thermoregulation, balancing, intraspecific signalling and as an aid to swallow fish) and it is concluded that they support overwhelmingly the wing-drying (or more generally plumage-drying) explanation, with the ultimate goal of conserving metabolic energy.

Shieldcastle, M. C. & L. Martin (2000): Colonial Waterbird Nesting on West Sister Island National Wildlife Refuge and the Arrival of Double-Crested Cormorants. Symposium on Double-Crested Cormorants, Technical Bulletin No. 1879, Dec. 1999.

Recent survey data have shown the importance of West Sister Island National Wildlife Refuge, Lake Erie, to nesting waders. About 40 percent of all herons and egrets nesting in the U.S. Great Lakes are found here, including the Great Lakes' largest colonies of great blue heron (Ardea herodia), great egret (Ardea alba), and black-crowned night-heron (Nycticorax nycticorax), and the largest of two snowy egret (Egretta thula). West Sister Island's importance to Ohio has grown in recent decades with the loss of smaller mainland colonies of waders, especially the black-crowned night-heron. The double-crested cormorant (Phalacrocorax auritus) returned to Ohio as a successful nester in 1992 for the first time in more than a century. The effects of this species on wading bird colonies have been well documented in Canadian Lake Erie. Cormorants have successfully competed against great blue herons for nesting space and eliminated black-crowned night-herons through habitat destruction Nest estimates made at the island since 1991 indicate that the night-heron has fallen to 37 percent of its historic numbers on the island and is dropping dramatically in the region. That species has been affected negatively as canopy height has increased with vegetation succession. A second concern is the cormorant, whose nest counts have increased from 0 to c. 1,5000 in 5 years. This rate of increase mirrors that of East Sister Island, a few kilometers northeast in Canada. To date, competition has not been a significant problem, but habitat degradation has been documented, with major leaf loss noted in 1995 on trees having cormorant nests and along the perimeter of West Sister Island. The Ohio Division of Wildlife and the U.S. Fish and Wildlife Service are concerned, both biologically and esthetically, about the future status of the island's colonies in light of habitat succession and the addition of the cormorant. Internet version of this paper.

Shmoely, M. (2001): Comparative Ontogenesis of the Pygmy cormorant (Phalacrocorax pygmeus) and the Great Cormorant (Phalacrocorax carbo sinensis); Morphometry and Energetics. Dissertation, Technion, Haifa 2001. In Israel, there are two species of cormorants: The Great Cormorant (Phalacrocorax carbo sinensis) is a migrating bird that overwinters in Israel (16000 individuals) from November to March and returns to Europe for breeding. The smaller Pygmy Cormorant (P. pygmeus) is a resident bird that lives and breeds (400 individuals) in colonies along the Hula, Jordan and the Beit Shean Valleys. The natural sites for both species in Israel have diminished during recent decades due to human activity. As a consequence, intensive fishery and aquaculture sites became their favorite feeding sites and the fish industry reports huge damage to fish yield. This study compares the energy demands and growth rate in captivity of the two species, as a basis for a future solution of the conflict.
Age-related changes in morphometric parameters and in energy demands were measured in captivity throughout ontogenesis. Basal metabolism was measured in the laboratory in fasting, resting birds, Existence metabolism, daily food intake and digestibility were measured in outdoors cages. Morphometric measurements of wintering Great Cormorant corpses, enabled a discriminant analysis between sexes.
The growth rate of Pygmy Cormorants was higher than that of the Great Cormorant in all parameters. Growth rate constant (K) of both species was higher than predicted from the allometric equation, based on the asymptotic body mass of the chicks. In both species, the legs grew faster than any other body part (including body mass), whereas the wings grew at the lowest rate. Male and female Pygmy Cormorants differ in body mass and wing length only, whereas in the Great Cormorant they differ in all morphometric parameters. Bill length, body length and wing length are the most discriminant parameters of sex in the Great Cormorant. The mass specific energy requirements of the Pygmy cormorant are much higher than those of the Great Cormorant, as expected from the size difference. The highest basal metabolism in both species was measured in young chicks (2-3 weeks), and decreased there after, in juveniles and adults. Basal metabolism of adults of both species was higher than predicted from the allometric equation. However, the existence metabolism was lower than predicted for waterbirds and shorebirds. Daily food intake of the adult Pygmy Cormorant (115 g) is higher than predicted from allometric equation for piscivorous birds whereas that of the Great Cormorant (244 g) is lower than predicted.
Based on the above energetic demands, the potential damage to the fish industry by 400 Pygmy Cormorant and by 12000 Great Cormorant that feed in the fish ponds is estimated at 460 tons of fish annually, corresponding to 2.8% of the annual fish yield in Israel.
From this study, it is clear that the two species of cormorants differ in their growth rate and energy demands. Therefore, their ecological impact on waterbodies in Israel is different and thus, a different management policy is necessary. The Pygmy Cormorant, as an extremely vulnerable species, needs a complete protection at the breeding colonies. In some areas, various deterring measures might be combined to prevent the cormorants from fish ponds, while offering some alternative reservoirs for feeding. Although the Great Cormorant is no longer endangered, its treatment should combine advanced management that would take into consideration its specific demands.

Siegel-Causey, D. (2000): The Problems of being Successful: Managing Interactions Between Humans and Double-Crested Cormorants. Symposium on Double-Crested Cormorants, Technical Bulletin No. 1879, Dec. 1999.

The natural history, behavior, and ecology of double-crested cormorants (Phalacrocorax auritus) predispose this species for conflict with human sport and commercial fisheries. Cormorants breed early in life, have large broods, are efficient predators even in marginal conditions, seem to be able to adjust colony sizes quickly in response to local conditions, and have limited requirements for feeding and nesting habitats. A survey of the past history of successes and failures in managing cormorants reveals that economic impact is greatest with acquaculture and least in sport fisheries. Research during the past 5 years suggests that some control methods like culling and egg spraying are effective but must be balanced against the actual impacts on humans. Internet version of this paper.

Skov- og Naturstyrelsen (1992): Forvaltningsplan for skarven i Danmark. - Miljøministeriet, Skov- og Naturstyrelsen.

Internet version of this report

Skov- og Naturstyrelsen (2004): Midtvejsevaluering af forvaltningsplan for Skarv i Danmark. - Miljøministeriet, Skov- og Naturstyrelsen.

Internet version of this report

Stempniewicz, L., Goc, M., Bzoma, S., Nitecki, C. & L. Iliszko (2000): Can timing and synchronisation of breeding affect chick mortality in the Great Cormorant Phalacrocorax carbo? Acta Orn. 35: 33 - 39.

In 1996, following a relatively severe and prolonged winter, Great Cormorants Phalacrocorax carbo sinensis started to breed at the Katy Rybackie colony (NE Poland) one month later than in 1995 but breeding finished at the same time in both years. The estimated total food consumption of the Cormorants was lower during the shorter and more synchronised 1996 breeding season (737 tonnes) than in 1995 (805 tonnes) despite the larger population present in 1996 (5929 pairs) than in 1995 (4942). However, during the period of peak energy need in June the estimated total daily food consumption of Cormorants present in the colony was about 2 tonnes higher in 1996. In June 1996, after a couple of windy days, 24.3% of chicks died and the total fledging success was lower (2.19 fledglings/nest) than in 1995 (2.45). The observed mass chick mortality could be due to the combined effect of strong breeding synchronisation, decreased food availability, and increased costs of foraging due to strong winds. Large breeding colonies of Cormorants can only function successfully when the suitable breeding period is prolonged and breeding can start early. Long-term climate change due to global warming could have favoured the observed Cormorant population increase during the last decades and its expansion into NE Europe. Asynchrony could be adaptive towards alleviating the food requirements of both individual broods and the whole colony.

Suryan, R. M., Irons, D. B., Kaufman, M., Benson, J., Jodice, P. G. R., Roby, D. D. & E. D. Brown (2002): Short-term fluctuations in forage fish availability and the effect on prey selection and brood-rearing in the black-legged kittiwake Rissa tridactyla. MEPS 236: 273 - 287.

To better understand how fluctuations in prey abundance may impact seabird reproductive success, we studied short-term changes in prey populations and their effect on prey selection and brood-rearing in the black-legged kittiwake Rissa tridactyla, a predator of near-surface-schooling forage fishes. Our fine-scale approach involved a weekly assessment of forage fish abundance and brood-rearing conditions during 4 consecutive years (1996 to 1999) at the Shoup Bay kittiwake colony in Prince William Sound, Alaska. We conducted forage fish surveys from a fixed-wing aircraft to determine weekly prey abundance throughout the known foraging range of breeding kittiwakes. Our results provide clear evidence that short-term fluctuations in prey availability are responsible for dramatic, within-season changes in the breeding conditions of black-legged kittiwakes. Adult kittiwakes often showed immediate response to changes in the prey base by altering prey selection; however, there were instances when kittiwakes selected prey species disproportionate to their availability (typically selecting for Pacific herring Clupea pallasi and against Pacific sand lance Ammodytes hexapterus). Changes in prey selection often resulted in striking differences in the amount of time required to obtain a load of food. The cascading effects of longer foraging trips was translated into reduced nestling growth and survival. Of the 3 components of energy provisioning to nestlings (meal delivery rate, meal size, and energy density), meal delivery rate had the strongest and most consistent positive effect on nestling growth and survival. Overall, these results demonstrate that complex foraging conditions limit the reproductive success of a central place-foraging species relying on an ephemeral food source. Moreover, we demonstrated that feeding conditions during the first 2 wk of brood-rearing were most critical for survival of the brood. Given the potential for such marked within-season variation in breeding conditions, it is critical that investigators adequately sample throughout the brood-rearing period, or, alternatively, select that portion that is germane to their study. Internet version of this paper.

Suter, W. (1991): Der Einfluss fischfressender Wasservögel auf Süsswasserfischbestände. J. Orn. 132: 29 - 45.

Suter, W. (1995): Are Cormorants Phalacrocorax carbo wintering in Switzerland approaching carrying capacity? An analysis of increase patterns and habitat choice. Ardea 83: 255 - 266.

The increase rate of the number of Cormorants overwintering in Switzerland between 1970 and 1990 was the same as in the strongly growing breeding population. From 1930 to 1970, however, wintering Cormorants increased while the breeding population remained stable. The reasons are believed to be a better food supply as cyprinid and percid fish biomass increased due to the eutrophication of Swiss lakes. Conversely, the increased rate of overwintering birds in Switzerland recently began to slow down while numbers during autumn passage are still following the growth of the breeding population. The resulting sigmoid pattern suggests that Cormorant numbers in Switzerland in winter are approaching carrying capacity. Cormorant density on lakes is strongly correlated with density of Perch and cyprinid fish, especially Roach, which shows signs of decrease as the input rate of nutrients into lakes is being reduced. The stepwise process of filling up different types of water bodies partly supports the Fretwell-Lucas model of habitat occupancy although behavioural responses to reduced persecution may also be involved in habitat choice. Even if increased winter survival were partly responsible for the current strong population increase (the cause of which is in fact unknown), the inland waters of western and central Europe hold a too small part of the north-central European Cormorant population (estimated at 300,000 birds in spring 1992) compared to coastal areas, as to play an important role in such a process.

Suter, W. (1997): Spatial and temporal variation in the diet of Cormorants Phalacrocorax carbo sinensis overwintering in Switzerland. Ardea 85: -- --.

The spatial and temporal variation in the diet of Cormorants Phalacrocorax carbo visiting Switzerland in the non-breeding season was studied from 1985 to 1991, by means of regurgitated pellets and stomach contents. The results, combined with the data of most other dietary studies from Switzerland since 1974, rest on 4810 samples representing 24 122 fish from 10 lakes and 9 river stretches. Of 31 fish species occurring at the feeding sites, 23 were found in the diet, yet 5-7 accounted for 85-95% by numbers. Roach Rutilus rutilus was found in 58% of all samples and, together with Perch Perca fluviatilis, accounted for 65% by numbers. Diet was habitat-specific, and three main types could be discerned by canonical variate analysis: a) diet strongly dominated by Roach and Perch, typical for most eutrophic lakes and empounded rivers; b) diet containing a high percentage of whitefish Coregonus sp. and Tench Tinca tinca, on two lakes with extremely low Roach biomass; c) diet dominated by Grayling Thymallus thymallus, Trout Salmo trutta or riverine cyprinids, in free-running rivers. Seasonal variation was found to be small in Roach-dominated diets but strong at some other sites. Prey size ranged from small fry to adult fish of up to 800 g and was on average larger in rivers than in lakes. Small fish (<12 cm) were mainly taken in lakes and reservoirs. At a landscape scale, the high proportion of Roach in the diet was associated with a preference for eutrophic lakes that support high densities of Roach and Perch. Roach was estimated to provide >50% of the biomass ingested by Cormorants in Swiss waters. At a local scale, possible preferences were less conclusive, but Roach was apparently still overrepresented compared to abundance while whitefish was underrepresented. Roach and Perch are both shoaling species and are hunted by Cormorants which themselves congregate in large flocks. A similar preference for highly gregarious fish is apparent in most other studies from continental European inland sites.


Tierney, M, Hindell, M. & S. Goldsworthy (2002): Energy content of mesopelagic fish from Macquarie Island. Antarctic Science 14: 225 - 230.

(The water and calorific content of fifteen species of mesopelagic sub-Antarctic fish from Macquarie Island were determined. Mean percent water content was 69-82 %. Calorific content was highly variable between species, especially in theMyctophidae, where it ranged between 22.62-59.26 g/dry weight. The water and calorific content varied with size class within a species, with the smallest size classes generally having the lowest water content but highest calorific content. These values will be useful for future assessment of energy transfer between trophic levels and energetic modelling of Southern Ocean ecosystems. Internet version of this paper.

Trauttmansdorff, J. & G. Wassermann (1995): Number of pellets produced by immature Cormorants Phalacrocorax carbo sinensis. Ardea 83: 133 - 134.

(from text): young Cormorants digested their food completely without producing pellets.

Tyson, L. A., Belant, J. L., Cuthbert, F. J. & D. V. Weseloh (2000): Nesting Populations of Double-Crested Cormorants in the United States and Canada. Symposium on Double-Crested Cormorants, Technical Bulletin No. 1879, Dec. 1999.

Double-crested cormorants (Phalacrocorax auritus) are receiving increasing attention in North America because of depredations of acquaculture facilities and alleged impacts on sport and commercial fisheries. We obtained recent (most since 1994) estimates for the number of nesting double-crested cormorants in the United States and Canada from published references and by conducting telephone interviews with State and Provincial biologists. Using published data, we also determined annual rates of change in the number of cormorants since about 1990. The estimated minimum number of nesting pairs (colonies) of double.crested cormorants was 372,000 (852). Most cormorants nested in the Interior region (68 percent). Overall, double-crested cormorants increased about 2.6 percent annually during the early 1990's. The greates decline (-7.9 percent annual change) was in the West Coast-Alaska region. The greatest increase (6.0-percent annual change) was for the Interior region. THe increase there was primarily a consequence of a 22-percent annual increase in Ontario and U.S. States bordering the Great Lakes. These baseline population data are essential for monitoring trends in nesting populations and for developing informed management decisions. However, the completeness, quality and timing of surveys varied substantially among jurisdictions. Population estimates and rates of changes should, therefore, be used with caution. Methods and timin of future surveys should be coordinated among political jurisdictions (at least within regions) to improve accuracy of estimates and allow more meaningful comparisons of population status. Internet version of this paper.


Van Dobben, W. H. (1952): The food of the Cormorant in The Netherlands. Ardea 40: 1 - 63.

Van Eerden, M. R. & M. Zijlstra (1988): Aalscholvers Phalacrocorax carbo met kleurringen uit de Oostvaardersplassen. Limosa 61: 57 - 60.

Van Eerden, M. R., K. Koffijberg & M. Platteeuw (1995): Riding on the crest of the wave: possibilities and limitations for a thriving population of migratory Cormorants Phalacrocorax carbo in man-dominated wetlands. Ardea 83: 1 - 9.

This paper summarises the general findings of the scientific contributions to this special issue of Ardea (83: 1) on Cormorant biology in Europe. After a brief historical introduction setting the main traditional questions that arise whenever man and a species of a free-living animal compete for the same resources in the same habitat, an overview is given of how Cormorant populations have recovered after protective measures were taken over most of Europe. This recovery, particularly spectacular in the continental population, has brought the species once again into direct conflict with human interests. Research has been aimed at unravelling the principal natural factors limiting population growth. Surface area, productivity and accessibility of fishing grounds for breeding birds seem to set the extent to which the population may increase, but the end of the population growth seems not yet to be at hand. Because of their migratory behaviour birds spread all over western Europe outside the breeding season, showing often site tenacity to stop-over sites as well as predictable migration patterns. Factors influencing the non-breeding distribution include age, sex and probably individual experience of the birds concerned. Local conflicts between human interests and breeding as well as non-breeding Cormorants seem impossible to cope with satisfactorily on a local level, without consideration of the population as a whole. Not every possible impact of Cormorants on fish stocks is bound to be treated as negative: recent studies tentatively indicate that the birds may serve as an 'aid' to fisheries management, keeping eutrophic waters free from dense Bream stocks. Finally, the position of top-predator that Cormorants occupy in aquatic ecosystems, makes them vulnerable to the accumulation of micropollutants. These may hamper breding success in various ways and, in larger concentrations, may even cause death. Monitoring breeding success as well as pollutant contents in adult and juvenile Cormorants as well as in their eggs may serve as a means to check on trends in environmental quality of aquatic ecosystems.

Van Eerden, M. R. & J. Gregersen (1995): Long-term changes in the northwest European population of Cormorants Phalacrocorax carbo sinensis. Ardea 83: 61 - 79.

The current expansion (1978-1993) in the number of breeding Cormorants in NW Europe resulted in an annual increase rate of 16.3 %. Recently indications of a decline in growth rate have become apparent. With their large waterbodies Denmark and The Netherlands form the stronghold for the population (94 %). The expansion of numbers and range extension was faster in Denmark than in The Netherlands which correlated with a higher average young production. The density of breeding Cormorants in relation to the fishing grounds available was highest in the small scaled, eutrophicated, freshwater habitat of the Dutch provinces of Friesland and Overijssel (>25 pairs/km2). At large freshwater lakes as IJsselmeer and along the large rivers lower densities were recorded (7-15 pairs/km2). The Danish waters are considered to be to a large extent undersatiated with respect to the number of Cormorants (<5 pairs/km2): Several colonies located in trees counted over 2000 pairs (11 % of all colonies which harboured 65 % of all breeding pairs in 1992). Maximum colony size so far was recorded at Oostvaardersplassen (The Netherlands, Flevoland 1992, 8380 nests) and Brændegård (Denmark, Fyn 1992, 7087 nests). It is concluded that, although feedback mechanisms in the oldest colonies may cause a stabilisation and even a local decline in numbers, the overall population still continues to explore new, previously unoccupied habitat. Extrapolation of the number of breeding pairs into the future was made in relation to the area of feeding grounds available and provided a conservative estimate of 103,300 breeding pairs, compared tp 60,331 pairs in 1993.

Van Eerden, M. R. & B. Voslamber (1995): Mass fishing by Cormorants Phalacrocorax carbo sinensis at lake IJsselmeer, The Netherlands: a recent and successful adaptation to a turbid environment. Ardea 83: 199 - 212.

The habit of mass fishing by Cormorants at lake IJsselmeer, The Netherlands, is a recent phenomenon. During the first half of the 1970's the birds changed behaviour probably as a result of the deteriorating under water visibility in the lake (3-4 m water depth). The behavioural switch coincided with years of high numbers of Smelt Osmerus eperlanus and Ruffe Gymnocephalus cernuus present in thesotheastern part of lake Markermeer, the birds' main fishing area at that time. Social fishing by Cormorants is directed towards the catch of relatively small, pelagically dwelling fish. It is argued that for a large water system where social fishing is the rule, a minimum colony size of c. 1000 pairs is required. Typically each colony had one socially fishing group (4000 - 5000 birds) that slowly changed position during the course of the day. Depending on the direction of the wind the flock's position could greatly change between days. Hunting speed was measured and coincided with maximum swimming speed of medium sized fish prey (15-25 cm). Hunting speed increased during the season probably as a result of the greater swimming speeds of the fish at higher temperatures. Intake rate was closely linked to the birds' position within the flock indicating local depletion of the fished water layer. Mass fishing was especially rewarding at intermediate light intensities under water (50-80 cm Secchi depth, or 300-500 microE per square metre and second at 40 cm depth). The habit of pushing up the fish against the light background of the clear top water layer was only possible when wind caused no greater turbidity than 40 cm Secchi depth (100 microE per square metre and second) which is considered a breakpoint for this kind of behaviour. Adapting the habit of mass fishing effectively enabled the birds to exploit the turbid, rapidly changing environment which resulted in the extension of the foraging range thus maximising colony size relative to the resources available.

Van Eerden, M. R. & M. J. Munsterman (1995): Sex and age dependent distribution in wintering Cormorants Phalacrocorax carbo sinensis in western Europe. Ardea 83: 285 - 297.

The winter distribution of the Cormorant shows a clear example of partial migration, some birds staying close to the colonies whereas others migrate some 2500 km south. Counts on the wintering area gave an estimate of 165,000 - 210,000 birds compared to about 180,000 as derived from the breeding census and young production during summer (1990). Countries taking up many Cormorants were France (18 %), Spain (15 %) and Tunisia (15 %). The demographic pattern of the winter distribution of the Cormorant shows that adult males stay closest to the breeding grounds whereas juvenile females migrate furthest to the south in the Mediterranean. Scans on roosts throughout the wintering range in western Europe, combined with the numbers present indicate an overall male surplus, being most prominent in adults (1 male:0.66 female for adults and 1:0.86 for juveniles). All three currently available hypotheses (body size, social dominance and arrival time) apply to the system of differential migration as observed in this species. It is argued that the unequal sex ratio may reflect different mortality rates in relation to the cost of migration, being highest in females and juveniles.

Van Eerden M. & S. van Rijn (2003): Redistribution of the Cormorant population in the Ijsselmeer area. CRGB 5: 33 - 37.

Van Rijn, S., & M. Platteuw (1996): Remarkable fledgling mortality at the largest Great Cormorant Phalacrocorax carbo sinensis colony in The Netherlands. CRGB 2: 30 - 35.

Van Rijn, S. (1998): Unusually prolonged breeding in the Great Cormorant Phalacrocorax carbo sinensis in the Ijsselmeer area in the Netherlands in 1997. CRGB 3: 40 - 43.

Van Rijn, S. & M. Zijlstra (2000): Extension of colour ringing programme in Great Cormorants Phalacrocorax carbo sinensis in the Netherlands. CRGB 4: 36 - 39.

Van Rijn S. & M. van Eerden (2003): Cormorants in the Ijsselmeer area: competitor or indicator? CRGB 5: 31 - 32

Veldkamp, R. (2000): The use of chewing pads for estimating the consumption of cyprinids by Cormorants Palacrocorax carbo. Ardea 83: 135 - 138.

Veldkamp, R. (2000): Diet of Cormorants Palacrocorax carbo sinensis at Wanneperveen, The Netherlands, with special reference to Bream Abramis brama. Ardea 83: 143 - 155.

Recent diet studies in a Cormorant colony in NW Overijssel, The Netherlands, reveal that analysis of regurgitated stomach contents and pellets have several limitations. Nonetheless, the best results of year-round diet studies are to be expected from pellet analysis, especially if a correction for wear in the stomach is applied. Since pellet production of Cormorants rearing young seems to be irregular or even stops, pellets possibly do not give an accurate impression of food eaten by these birds. Regurgitated stomach contents collected during the breeding season are likely to provide a better idea of the food of Cormorants rearing young. Roach, Bream and Pikeperch are the most important prey species, as shown by analysis of both pellets and regurgitates. Total fish consumption of the colony in 1991 was estimated at 245 ton by pellet analysis. Cyprinids made up c. 74 % of that amount. The mass share of cyprinids in regurgitates in April-July 1991 was 86 %. It is shown that at the study area the consumption of relatively large Bream (up to 31 cm) is far more important than has been suggested by most studies elsewhere. Consumption figures derived from this study suggest that Cormorants at Wanneperveen consumed at least c. 5-16 % on mass basis from the available standing stock of Bream in the lakes surrounding the colony in 1991, emphasizing on the larger individuals (> 200 mm).

Volponi, S. (1999): Reproduction of a Newly-established Population of the Great Cormorant in Northeastern Italy. Waterbirds, 22(2): 263 - 273.

A study of the breeding biology of the Great Cormorant (Phalacrocorax carbo sinensis) was carried out during 1993-1998 in the Po River Delta, a major wintering area in northeastern Italy. The first of five colonies was founded in 1993, and breeders increased from 69 pairs in 1994 to 285 pairs in 1998. The period of egg-laying lasted from early March to late July, but 65% of all clutches were initiated between late March and the end of April. The average clutch size (± SD) was 3.83 ± 0.65 eggs (range two to six). The survival rate of entire nests, evaluated by the Mayfield method, was always higher during the nestling stage than during incubation. The majority of losses occurred during the egg stage due to predation by Hooded Crows (Corvus corone cornix). During the five years, hatching success was 72-91% and total nest success, 67-86%. The number of young fledged per successful nest ranged between 2.3 and 2.9. The reproductive parameters of Great Cormorants recorded in the Po Delta lay at the upper range reported for NW Europe populations and are close to the estimated values for newly-established colonies in Italy and for growing colonies in the traditional breeding areas. Unlike other Italian colonies, the availability of breeding sites and food presently do not limit expansion of the breeding population in the Po Delta. If no control measures are undertaken, it is likely that this southern population will continue to grow.


Warke, G. M. A. & K. R. Day (1995): Changes in abundance of cyprinid and percid prey affect rate of predation by Cormorants Phalacrocorax carbo carbo on Salmon Salmo salar smolt in northern Ireland. Ardea 83: 157 - 166.

Cormorant diet is described from the analysis of pellets, fledgling regurgitates and the stomach contents of adult birds. Non-breeding coastal birds consumed mostly marine fish while breeding birds were found to feed mostly on freshwater fish species. The long distances travelled to inland feeding sites while breeding suggested that the high energy investment in commuting could be traded against the rewards of greater, more varied or more predictably exploitable food supplies in certain freshwaters at certain times. In years when Roach and Perch were much less abundant in Lough Neagh, diet at the breeding colony reverted to an increased proportion of marine fish and even a high Salmon smolt run on an inland river was practically neglected. In recent years the impact of Cormorants on fish in this river close to the breeding colony has declined and a number of reasons for this are discussed. Nevertheless, Cormorants visit the river all the year round and their impact on older Salmon parr is likely to be particularly significant.

Weingartl, H. M., Riva, J. & P. Kumthekar (2003): Molecular Characterization of Avian Paramyxovirus 1 Isolates Collected from Cormorants in Canada from 1995 to 2000. J. Clin. Microbiology 41: 1280 - 1284.

Sequences encompassing cleavage sites of fusion protein genes were obtained for avian paramyxovirus 1 isolates from cormorants in Canada. All isolates have the virulent cleavage site SRGRRQKR*FVG. They form a distinct cluster within isolates obtained around the world and may represent a novel genotype closely related to genotype V.Internet version of this paper.

Weseloh, D. V., Teeple, S. M. & M. Gilbertson (1983): Double-crested Cormorants of the Great Lakes: Egg-laying Parameters, Reproductive Failure, and Contaminant Residues in Eggs, Lake Huron 1972-1973. Canadian Journal of Zoology 61: 427 - 436.

West, B., Cabot, D & M. Greer-Walkob (1975): The food of the Cormorant (Phalacrocorax carbo) at some breeding colonies in Ireland. Proc. R. Irish Acad. 75: 285 - 305.

Winney, B. J., Litton, C. D., Parkin, D. T. & C. J. Feare (2001): The subspecific origin of the inland breeding colonies of the cormorant Phalacrocorax carbo in Britain. Heredity 88: 45 - 53. pdf-dokument på Internet.

The establishment of cormorant breeding colonies inland within south-east Britain since 1981 is a matter of major conservation and pest management concern. This study was initiated to investigate the subspecific origin of two recently established breeding colonies. The analysis examined sequence variation of the control (D-loop) region of the mitochondrial genome. Samples of tissue were obtained from 334 individuals from across the species range in western Europe from both subspecies (Phalacrocorax carbo carbo and P. c. sinensis) and 84 birds from two inland breeding colonies in Britain. Single-strand conformation polymorphism (SSCP) was used to assess mitochondrial variation among samples, revealing four haplotypes. The samples from the traditional breeding colonies clustered into three distinct phylogeographic groupings: Norway-Scotland, Wales-England-Iles des Chausey and the rest of Continental Europe. These results only partly agree with the traditional subspecific taxonomic groupings and are slightly at variance with results using microsatellite DNA frequencies, and a hypothesis using results from both studies is advanced. The subspecific origin of the inland colonies was investigated using maximum likelihood and Bayesian models.


Yésou, P. (1995): Individual migration strategies in Cormorants Phalacrocorax carbo passing through or wintering in western France. Ardea 83: 267 - 274.


The attendance of individually recognisable Cormorants has been studied at a roost site in western France together with the overall use of this roost. Only first and second year birds arrived at the roost before mid-October and almost only 1st-year birds did so after February. In the meantime birds of any age arrived at any time, and the arrival dates of birds of different geographical origin did not vary significantly. A majority of stays (58 %) were less than 8 days, and 21 % of the stays lasted for more than three months (mean duration 139 days) but there are indications that the true proportion of birds performing long stays, probably elsewhere, must be higher. The mean duration of stays was 27 days, hence the number of birds using the roost during the season was 3.9 to 6.2 times higher than the highest mid-month count. Short-stayers did not tend to return to the area in consecutive years, although part of them remained faithful to their overall migration route. Long-stayers were markedly site-faithful: 48 % of the first year birds among them returned at the same wintering site in their second winter; the return rate thereafter was c. 76 %, i.e. close to the survival rate of these birds, indicating that site-fidelity was the rule for them. The presented data disagree with an earlier statement that Cormorants are 'nomadic' outside the breeding season. It is suggested that the strategy of long-staying and site-faithful individuals is of adaptive value.


Zijlstra, M. & M. R. Van Eerden (1995): Pellet production and the use of otoliths in determining the diet of Cormorants Phalacrocorax carbo sinensis - trials with captive birds. Ardea 83: 123 - 131.

In a feeding experiment with two separated captive Cormorants, production of pellets and otoliths and wear of otoliths was investigated. It was found that Cormorants produce one pellet a day, containing only undigested remains from the day before. With regard to fish species offered, a great variation in proportions of otoliths recovered was found. The recovery rate of otoliths (about 52 %) was highest for the larger size classes of Ruffe. Although the calculated mean wear of otoliths from small and large size classes did no differ significantly in absolute terms, the recalculated fish mass did. The results differ strongly from field experiences. It is hypothesized that experiment induced stress causes severe otolith wear in feeding trials with captive Cormorants, making this type of research unfit for calibration of the use of otoliths in diet studies.




Last addition (54 entries) 5.3.07.

  • Till artlistan för Vår Fågelvärld / To species list for Vår Fågelvärld
  • Till innehållsförteckning för Vår Fågelvärld 40:1 - 49:8 / To contents of Vår Fågelvärld 40:1 - 49:8
  • Till innehållsförteckning för Vår Fågelvärld 30:1 - 39:6 / To contents of Vår Fågelvärld 30:1 - 39:6
  • Till innehållsförteckning för Vår Fågelvärld 24:1 - 29:4 / To contents of Vår Fågelvärld 24:1 - 29:4
  • Till artlistan för DOFT / To species list for DOFT
  • Till innehållsförteckning för DOFT 63:1 - 80:4 / To contents of DOFT 63:1 - 80:4
  • Till artlistan för Ornis Svecica / To species list for Ornis Svecica
  • Till innehållsförteckning för Ornis Svecica 1:1 - 9:4 / To contents of Ornis Svecica 1:1 - 9:4
  • Till ruggningsuppsatser A - F / To moult papers A - F
  • Till ruggningsuppsatser G - M / To moult papers G - M
  • Till ruggningsuppsatser N - R / To moult papers N - R
  • Till ruggningsuppsatser S - Z / To moult papers S - Z
  • Skarvreferenser, författarnamn A - M. / Cormorant references, author's name A - M.
  • Till uppsatser om vikter, fett, energetik, A - K / To papers about fat, weights, energetics, A - K
  • Till uppsatser om vikter, fett, energetik, L - W / To papers about fat, weights, energetics, L - W