WI - Cormorant Research Group Scientific meetings Last updated on 20-01-2002

Waterbird Conservation and Management

Waterbird Society
(formerly, Colonial Waterbird Society)

23° Annual Meeting and Workshops
8 - 12 November 1999
Palazzo Congressi, Grado, Italy

organised by
Dipartimento Biologia Animale, Universitŕ di Pavia

convened by
Regione Friuli-Venezia Giulia - Azienda dei Parchi e Foreste Regionali,
Osservatorio Faunistico - Comitato Provinciale Caccia – Udine
Riserva Naturale Regionale Foce Isonzo

Conference Chair: Mauro Fasola
Chair of the Scientific Program: Rob Butler

Organisation: Fabio Perco

Staff: Maria Grazia Bellio, Eleonora Boncompagni, Laura Dami, Marcello Giorda, Marilena Lorini, Carlo Pascoli


Workshop

Cormorants: Perceived Problems
and Proposed Solutions

Convenors: Chip Weseloh and Jeremy Hatch

The workshop will be a mix of contributed papers, informal presentations, and discussion with a goal to facilitate sharing new results and insights from cormorant biology, to evaluate basis for conflicts with fishing industry, and to identify information needed to make sound evaluations.

Pigmy Cormorant Session

& The wintering and breeding population changes of the Pygmy Cormorant in Greece, 1997-1998. Panayotopoulou M. Hellenic Ornithological Society, Thessaloniki Office, Kastritsiu 8, GR-54623, Thessaloniki, Greece.

& BEHAVIOURAL AND ECO-PHYSIOLOGICAL ASPECTS OF THE PYGMY CORMORANT'S BIOLOGY. Nathan M1, Izhaki I2, Zorovski Y1, Arad Z3, Katzir G 2. 1Faculty of Life Sciences, Bar Ilan University, Ramat Gan 52900 Israel; 2Department of Biology, University of Haifa at Oranim, Qiryat Tivon 36006, Israel; 3Department of Biology, Technion-Israeli Institute of Technology, Haifa 32000, Israel

& COMPARATIVE ONTOGENESIS OF PYGMY (PHALACROCORAX PYGMEUS) AND GREAT (P. CARBO) CORMORANTS: MORPHOMETRY AND ENERGETICS. Shmueli M1, Katzir G2, Izhaki I2, Arad Z1 1Department of Biology, Technion-Israeli Institute of Technology, Haifa 32000, Israel, 2Department of Biology, University of Haifa at Oranim, Qiryat Tivon 36006, Israel

Great Cormorant Session

& PREY DETECTION AND PREY PREFERENCE IN DIVING CORMORANTS. Strod T1, Izhaki I2, Arad Z 1, Katzir G 2. 1Department of Biology, Technion-Israeli Institute of Technology, Haifa 32000, Israel, 2Department of Biology, University of Haifa at Oranim, Qiryat Tivon 36006, Israel

& The predation of Great Cormorant in lakes geneva, Annecy and Bourget. Mathieu L, Gerdeaux D, Station d’Hydrobiologie Lacustre, INRA, BP 511, F-74203 Thonon cedex, France

& GREAT CORMORANT IN THE CZECH REPUBLIC: POPULATIONS STATUS AND ACTION PLAN. Musil P1,2, Cepák J 2, Martincová M 1. 1Department of Zoology, Faculty of Sciences, Charles University, Vinicná 7, Praha 2, CZ-128 44, Czech Republic; 2 Institute of Applied Ecology, Kostelec nad Cernými lesy, CZ-281 63, Czech Republic

& A population model for European Great Cormorant: preliminary results and applications to management. Frederiksen M, Lebreton J-D, Brengballe T. CEFE/CNRS, 1919 Route de Mende, F-34293 Montpellier Cedex 5, France

Double-crested Cormorant Session

& THE Status of THE Double-crested Cormorant in eastern and central North America (PART 1): DISTRIBUTION, DIET AND IMPACTS TO BIODIVERSITY. Wires LR, Cuthbert FJ, Trexel D. Department of Fish and Wildlife, University of Minnesota, St. Paul, Mn 55108 USA

& The Status of THE Double-crested Cormorant in eastern and central North America (PART 2): REVIEW OF MANAGEMENT STRATEGIES. Wires LR. Department of Fish and Wildlife, University of Minnesota, St. Paul, Mn 55108 USA

& STRATEGIC PLAN TO MANAGE DOUBLE-CRESTED CORMORANT DAMAGE TO SOUTHERN AQUACULTURE. Glahn JK, Tobin ME, Blackwell BF, Werner SJ. U.S. Department of Agriculture, Animal Plant Health Inspection Service, National Wildlife Research Center, P.O. Drawer 6099, Mississippi State, Mississippi 39762, USA


Summaries of Posters and Oral Contributions
(in alphabetical order)

CORMORANT COLONIES ATTRACT BREEDING AUKS
[POSTER BOARD # 31]

Andersson Ĺ
Swedish Association for Hunting and Wildlife Management, Bäcklösav. 8, S-756 51 Uppsala, Sweden

In the archipelagos of the Baltic Sea the great cormorant (Phalacrocorax carbo sinensis) nests in dense colonies on flat islands. Recently the guillemot (Uria aalge) and the razorbill (Alca torda) have started to breed on the same islands. While the guillemots prefer to lay their eggs in the centre of cormorant colonies the razorbills put their eggs in the periphery directly on the ground usually without any protection. I interpret this choice of breeding sites as an adaptation to minimize egg and chick losses to avian predators like carrion crow (Corvus corone) and herring gull (Larus argentatus). Preliminary observations indicate that the guillemot produce many young while the razorbill suffer from high predation rate.

 

CHANGES IN NUMBERS AND DIET OF CORMORANTS PHALACROCORAX CARBO
IN THE GULF OF GDANSK

[POSTER BOAD # 32]

Bzoma S, Stempniewicz L
University of Gdansk, Dept. of Vertebrate Ecology and Zoology, Al. Legionow 9, 80-441 Gdansk, Poland

Number of Cormorants staying in the Gulf of Gdansk has increased for over ten times during last 15 years. In 1998, from 500 (winter) to over 10 000 (summer) non-breeding birds were observed in the area. The food composition was determined by the analysis of over 1200 pellets collected twice a month between March 1998 and February 1999, at five roost occupied by 50 - 2500 non-breeding Cormorants and in the breeding colony at Katy Rybackie (6000 pairs). The most important prey was Round Goby Neogobius melanostomus (new to Baltic Sea) constituting on average 61%, Stickleback Gasterosteus aculeatus - 18% and Eelpout Zoarces viviparus - 7% of fish number found in pellets collected during the whole year at the main roost. Between April and September Round Goby constituted 70 - 95% of prey in all feeding areas. In late October and November, the Cormorant food consisted mainly of Stickleback (90%). During winter (December - March) the diet consisted of lower number of prey items and higher number of prey species.

 

INTRA-COLONY DIFFERENTIATION IN DIET OF CORMORANTS
PHALACROCORAX CARBO AT KATY RYBACKIE
AS A RESULT OF USING DIFFERENT FEEDING AREAS
[POSTER BOARD # 33]

Bzoma S, Stempniewicz L
University of Gdansk, Dept. of Vertebrate Ecology and Zoology, Al. Legionow 9, 80-441 Gdansk, Poland

Between March and August 1999 in the large colony of Cormorant (>7000 pairs) at Katy Rybackie (NE Poland), localised at a narrow peninsula - the Vistula Spit which divides two main feeding areas (the Vistula Lagoon and the Gulf of Gdansk), pellets were collected and analysed. It was assumed that the differences in the composition of ichtyofauna between the two bays allow for defining the feeding area of each particular bird. The results of pellets analysis confirmed known phenomenon (Goc et al. 1997) of the increase of the Gulf of Gdansk importance as a foraging area in subsequent months (from 0% in March to over 70% in July). The intra-colony differentiation in the level of using the main Cormorants’ feeding areas was stated. In three parts of the colony - western (1762 pairs, localised in the largest distance from the Vistula Lagoon), central (4019 pairs) and eastern (1313 pairs, localised closest to the Lagoon) pellets with fish from the Vistula Lagoon constituted gradually larger percent of their total number, respectively.

 

PRELIMINARY OBSERVATIONS ON DAILY AND SEASONAL ACTIVITY
OF THE SHAG AND THE CORMORANT POPULATION IN THE GULF OF TRIESTE

[POSTER BOARD # 34]
Chittaro S, Kravos K, Utmar P, Verginella L, Spoto M, Ferrero EE
Centro di Eco-Etologia, Riserva Naturale Marina di Miramare - WWF,
V.le Miramare 349, I-34136 Trieste, Italy

One of the main roosts of Phalacrocorax species in the Gulf of Trieste (N. Adriatic) is located on the floating buoys of the suspended mussel cultures at Punta Sottile (Muggia, Trieste). Monthly censuses on this roost carried out at dawn or at sunset revealed a maximum number of 170 Phalacrocorax carbo sinensis in December, and 653 Phalacrocorax aristotelis in August. After having checked that the Cormorants visiting the Natural Marine Reserve of Miramare at dawn come from Muggia, we made some observations on the feeding behaviour of this species in the Reserve, and we compared the census results for Miramare with the numbers at the Muggia roost. We found that more than half of the population at Muggia feed in the Miramare Marine Reserve. From data on diurnal activity at Miramare, we identified one peak of activity in the morning and one in the afternoon, with a resting period at noon. Social fishing in winter was probably correlated to the presence of schools of Lithognathus mormyrus. Summer censuses of Phalacrocorax aristotelis at Muggia were complemented by a simultaneous census of the two other roosts on the Gulf, located at the Trieste northern coastal reef and at the Isonzo river mouth. We found a total of 1014 individuals in July and 1095 in August. Preliminary information on the feeding behaviour of this species resulted from cursory data registered during monthly marine transects (from April 1998 to September 1999) and from observation made at dawn at Punta Sottile. Cormorants use to feed in open water and along the Trieste northern coastal reef.

 

THE STATUS OF THE DOUBLE-CRESTED CORMORANT IN EASTERN AND CENTRAL NORTH AMERICA (PART 2): REVIEW OF MANAGEMENT STRATEGIES

Cuthbert FJ, Trexel D, Wires LR
Dept. Fisheries and Wildlife, Univ. of Minnesota, 1980 Folwell Ave, St. Paul, MN 55108. USA.

Double-crested Cormorant numbers have significantly increased in North America since the 1970's. A variety of problems, both real and perceived, have been associated with these increases, including impacts to aquaculture, sport and commercial fisheries, terrestrial habitats and other avian species. The U. S. Fish and Wildlife Service contracted us to assess the status of the Double-crested Cormorant (DCCO) in eastern and central North America. Our report will be used to develop a management plan for the species in the U.S. This paper reviews management strategies used for DCCOs in North America and evaluates management impacts. Historically, management for population reduction has occurred to reduce DCCO impacts to (1) sport and commercial fisheries, (2) aquaculture and (3) biodiversity (e.g. other colonial nesting waterbirds, habitat). The general conclusion from our review is that population control is possible but must be large-scale, intense, long-term and well-monitored to have effect.

 

LONG-TERM EFFECTS OF CORMORANT PREDATION ON FISH COMMUNITIES
AND FISHERY IN A FRESHWATER LAKE (Ymsen) of south-central sweden
[POSTER BOARD # 1]

Engström HD
Dept. of Population Biology, Evolutionary Biology Centre, Uppsala University,
Norbyvägen 18D, SE-752 36 Uppsala, Sweden. e-mail: henri.engstrom@zoologi.uu.se

Cormorant impact upon natural fish populations has long been debated but little studied because of the requirements of sound data that are often hard to fill. In this study, I have monitored fish community composition/abundance both before and after cormorant colony establishment in a highly productive lake (Ymsen) of South-central Sweden. Data on fish abundance before cormorant establishment enabled to control for posible pre-establishment low fish densities. To control for possible changes in fish populations caused by factors other than cormorant predation (i.e. large-scale regional changes due to climate) data was compared with a control lake (Garnsviken). Since Lake Ymsen also harbor an important commercial fishery, cormorant impact upon fishery yields was evaluated. Most important foraging species of the cormorant was ruffe Gymnocephalus cernua (75% by number), roach Rutilus rutilus (11%) and perch Perca fluviatilis (10%). Except for perch, commercially important fish made up a very small fraction of cormorant diet. Eel Anguilla anguilla, the most important fish for the fishery, was absent in the cormorant diet, zander Ztizostedion lucioperca constituted 0.2% and pike Esox lucius 1.5%. Estimated fish outake by cormorants was 15 kg/year compared to 8.6 kg/ha/year for the fishery. Despite considerable fish withdrawal by the cormorants, fish populations seemed to withstand cormorant foraging pressure. This study indicates that cormorant impact upon fish populations in Lake Yimsen was small and probably in no case has led to decline of commercial/non commercial fish species. Furthermore, the number of cormorants in Lake Yimsen, in relation to the foraging area, is among the highest represented for Swedish lakes.

 

STRATEGIC PLAN TO MANAGE DOUBLE-CRESTED CORMORANT DAMAGE TO SOUTHERN AQUACULTURE

Glahn JK, Tobin ME, Blackwell B, Werner SJ
U.S. Department of Agriculture, Animal Plant Health Inspection Service, National Wildlife Research Center, P.O. Drawer 6099, Mississippi State, Mississippi 39762, USA

Aquaculture in the southern United States involves the extensive use of large shallow ponds that are highly susceptible to cormorant predation. Corresponding with increasing breeding populations and associated problems in the Great Lakes region, wintering Double-crested Cormorant populations in intensive catfish production areas of Mississippi have doubled in recent years, exacerbating predation problems on catfish. Current damage abatement measures, primarily involving harassment and shooting of birds at catfish farms and harassment of roosts have only limited effectiveness or are becoming increasingly difficult to effectively implement. Although further research is proposed for resolving cormorant predation problems on a localized basis, mitigation of cormorant conflicts with aquaculture and resources in the Great Lakes region requires consideration of cormorant population management on a flyway basis. To this end we outline proposed research for investigating the feasibility of managing cormorants that will both insure the future well being of the species and address the needs of other competing interests.

 

FORAGING FLIGHT PATTERN OF THE CORMORANT (PHALACROCORAX CARBO SINENSIS) STUDIED DURING A BREEDING SEASON BY TELEMETRY
AND VISUAL COUNTS
[POSTER BOARD # 35]

Goc M, Iliszko L, Brylski T
University of Gdansk, Dept. of Vertebrate Ecology and Zoology, Legionow 9, 80-441 Gdansk, Poland

Foraging activity of cormorants was studied during the 1999 breeding season at Katy Rybackie, the biggest (>7000 pairs) Polish colony. The colony is located on the Vistula Split separating Baltic Sea and Vistula Lagoon, cormorant's main two feeding areas. Two methods were used. 1) telemetry: from May to August bird's activity was recorded automatically by two antenna scanning receiver. The presence in the colony and foraging flights of eight birds equipped with radio-transmitters were continuously monitored. 2) visual counts: From March to August flights to the feeding grounds and back to the colony were counted during the whole day every week. Two observation posts were situated on the ways between colony and the feeding grounds. The role of Vistula Lagoon as a feeding ground decreased gradually from >90% of foraging flights in March to about 50% in May and June. The diurnal activity pattern generally showed two peaks and changed seasonally. The limitations of the two methods are discussed.

COMPARATIVE STUDIES IN FOOD COMPOSITION OF GREAT CORMORANT (PHALACROCORAX CARBO-SINENSIS) IN THREE DIFFERENT COLONIES
FROM THE DANUBE DELTA RESERVE

[POSTER BOARD # 36]

Gogu-Bogdan M.1, D. Hanganu 2
1Romanian Ornithological Center, Romanian Academy for Agricultural and Forestry Sciences,
8 Ion Ionescu de la Brad Av., 71592 Bucharest 1, Romania
2Danube Delta Biosphere Reserve Administration, Sf. Gheorghe, Tulcea District, Romania

The relationship between Cormorants during the breeding season and the places where they use to get their food is a important factor in the evolution of a colony. This paper analyses comparatively the Cormorant diet during the breeding season from two different biogeographical areas: fluvial colony (Belciug-Tarata), respectively fluvio-maritime colony (Prundu cu Pasari and Ceaplace). Through of analysis of the samples collected from colonies area we established the fish species and their frequency in the Cormorant diet during the breeding season.

 

FOREIGN RECOVERIES OF CORMORANT PHALACROCORAX CARBO SINENSIS
FROM AND TO HUNGARY
[POSTER BOARD # 37]

Halmos G, Csörgő T
Departure of General Zoology, Eötvös Loránd University, Puskin u.3., Budapest, H-1088, Hungary

The Cormorants breeding inside the Carpathian basin belong to Phalacrocorax carbo sinensis subspecies. It is the most migratory subspecies of this species. The cormorant is a expansive species everywhere in Europe. In Hungary both number of colonies and the size of colonies have increased since the seventies of this century. The observed increase was too fast to be based on reproduction rate of the original local population only. We have 32 recovery data of 689 (4.64 %) cormorant ringed in breeding time in Hungary and 173 recovery data of this species ringed in other countries of Europe. Most of the Hungarian birds have been recovered in Poland, Czech Republic and inland of Yugoslavia in summer and autumn, but the winter data originated from the coastline of Yugoslavia and Greece. The most of the recoveries from abroad originated from Yugoslavia in summer and from Scandinavia and the Baltic region at winter.

 

BREEDING AND FORAGING BEHAVIOUR OF MASS STOCKS
OF THE NEOTROPICLA CORMORANT (
PHALACROCORAX B. BRASILIANUS)
AS AN INDICATOR OF THE ENVIRONMENTAL STATUS
OF THE MANGROVE AREA CIÉNAGA GRANDE DE SANTA MARTA (COLOMBIA)
[POSTER BOARD # 38]

Hennig VCh
University of Hamburg. Department of Ecology and Conservation, D-20146 Hamburg, Germany

I investigated the breeding and foraging behaviour of the Neotropical Cormorant (Phalacrocorax b. brasilianus) which occur in mass stocks in the delta of the Rio Magdalena (Caribbean, Colombia) called Ciénaga Grande de Santa Marta. The cormorants feed exclusively on juvenile fish and their breeding success depends above all on their prey populations. Spatial and temporal distribution of fish shoals is changing in annual and interannual cycles of salinity and is indicated by the foraging areas of the cormorants. Social fishing flocks could be composed of up to 30,000 individuals. Different duration and form of hunting behaviour are linked to different prey species and their availability.

 

EXCREMENT PRODUCTION AND SOIL FERTILIZATION IN THE CORMORANT (PHALACROCORAX CARBO) BREEDING COLONY
AT KATY RYBACKIE, N POLAND
[POSTER BOARD # 39]

Iliszko L
University of Gdansk, Dept. of Vertebrate Ecology and Zoology, Legionow 9, 80-441 Gdansk, Poland

The delivery of Cormorant and Grey Heron (Ardea cinerea) excrement to the breeding colony (>7000 pairs) was studied during the entire 1998 season. Spatial and temporal changes in excrement production and its effect on the soil chemistry were monitored on six study plots every two weeks. Soil samples from the organic horizon and samples of dissolved excrement were collected and then analysed in the laboratory (in total, >1000 samples). Daily excrement input to the soil locally exceeded 8 g/m2 (dry mass). It has been estimated that up to 50 tons of dry mass excrement fertilized soil in the colony during one season. Concentration of P, K, NH4, NO3, Mg and Ca in the soil samples collected from the colony parts densely inhabited by cormorants were up to 200% higher than in those parts of the colony characterising with low nest density, and about 1000% higher than in the non-occupied parts.

 

CORMORANT MANAGEMENT IN BAVARIA, SOUTHERN GERMANY – SHOOTING AS A PROPER MANAGEMENT TOOL?
[POSTER BOARD # 40]

Keller TM
Technische Universität München, Angewandte Zoologie, Germany

Since autumn 1995 it has been legal to shoot Cormorants (Phalacrocorax carbo sinensis) in Bavaria to prevent anticipated economic damage and to protect native fish species. In the following winter of 1995/96 a number of 657 Cormorants was shot. This figure increased to 6,259 birds in 1996/97 and then decreased to 3,285 in 1997/98 and 3,577 in 1998/99. When comparing these numbers to the mean winter population of Cormorants in Bavaria, it can be seen that numbers equal to 50 - 100% of the winter population were shot, each year. But, mean winter numbers of Cormorants did not decrease, substantially. Thus, it could be argued that shooting Cormorants has not been an appropriate management tool to reduce overall depredation.

 

DAILY ENERGY EXPENDITURE OF GREAT CORMORANTS PHALACROCORAX CARBO SINENSIS WINTERING AT LAKE CHIEMSEE, SOUTHERN GERMANY
[POSTER BOARD # 41]

Keller TM, Visser GH
Technische Universität München, Angewandte Zoologie, Germany and University of Groningen, Centre of Isotope Research, The Netherlands

In the winters of 1993/94 and 1994/95 the daily energy expenditure (DEE) of Great Cormorants (Phalacrocorax carbo sinensis) was measured using the doubly labeled water technique (DLW). For the first time this method has been used on a species of the cormorant family (Phalacrocoracidae). DLW trials were carried out on 5 caged birds and on 5 free- ranging wild birds at Lake Chiemsee. Estimated DEE averaged 1,325 kJ×d-1 (SD = 130 kJ×d-1, n = 5) in the caged birds and 2,094 ± 174 kJ×d-1 (n = 5) in the free-ranging ones. To match their DEE, the Cormorants had to consume 341 g of fish per day under aviary conditions, while they needed 539 g in the wild.

 

BREEDING SUCCESS OF CORMORANTS PHALACROCORAX CARBO SINENSIS
IN THE COLONY AT KATY RYBACKIE (N POLAND), 1995-1999
[POSTER BOARD # 42]

Kopciewicz P, Nitecki C, Bzoma S, Stempniewicz L
Department of Vertebrate Ecology and Zoology, University of Gdansk, Legionow 9, 80-441 Gdansk, Poland

Data were collected from March to August during 5 breeding seasons in the biggest Polish colony of Cormorants (>7000 pairs). Clutch size was estimated on the basis of observations from helicopter and by climbing the trees in the sample plots. Mean clutch size varied from 3,5 (N=299) in 1996 to 3,9 (N=97) in 1998. Most frequently clutches were composed of four eggs in nests controlled in April and 3 eggs in May (range 2-6 eggs). Mean hatching success was 80%. Number of young birds leaving the nests fluctuated from 1 to 5. Mean number of fledglings per one nest varied from 2,1 (N=280) in 1997 to 2,5 (N=229) in 1995. The same values calculated for successful nests were 2,3 (N=252) in 1997 to 2,7 (N=144) in 1996. The breeding success of Cormorants at Katy Rybackie seems to be stable in the years of our study. Only strong winds may cause considerable increase in egg and chick mortality.

 

CLOSE OVERLAP BETWEEN FEEDING AREAS FOR GREAT CORMORANTS
AND KELP FORESTS
[POSTER BOARD # 43]

Lorentsen S-H, Rřv N
Norwegian Institute for Nature Research, Tungasletta 2, N-7485 Trondheim, Norway

Feeding areas of Great Cormorants Phalacrocorax carbo were studied outside Central Norway by visually following flights from the breeding colonies during a three-day period in mid July 1990. That year there were four colonies with a total of 735 pairs (mean 184 pairs) in the study area. In most of the nests there were large chicks so the study period represents the time of the breeding cycle with the highest energy consumption by the Cormorants. Their feeding areas were on average located 2.9 km from the colonies (SD 1.05, n = 10, range 1.5-5 km) and showed a close spatial overlap with the distribution of kelp (Laminaria hyperborea) forests. The kelp forests are important for juvenile fish and the Cormorants were observed to take both cod (Gadus morhua) and saithe (Pollachius virens) of up to 150-200 mm length from these foraging areas.

 

GREAT CORMORANT IN THE CZECH REPUBLIC: POPULATIONS STATUS
AND ACTION PLAN

Musil P1,2, Cepák J 2, Martincová M1
1Department of Zoology, Faculty of Sciences, Charles University, Vinicná 7, Praha 2,
CZ-128 44, Czech Republic
2 Institute of Applied Ecology, Kostelec nad Cernými lesy, CZ-281 63, Czech Republic

Regular breeding of the Great Cormorant has been documented in the Czech Republic since 1992. Until 1990, an increase in breeding population size has been recorded. Afterwards, a remarkable decline and stabilisation in numbers have been recorded. This decline was caused by the artificial regulation of numbers (shooting) and, also, by the reduction of available breeding sites. Recent population size has been estimated at 150-200 breeding pairs in 3-4 colonies. On the other hand, thousands of birds migrate through the territory of the Czech Republic during both autumn and spring migrations. These birds cause regularly a great damage to fish stocks in the ponds. The full protection of breeding population and the allowed flushing and/or shooting of the Cormorants during the non-breeding season will be included in the proposed action plan.

 

BEHAVIOURAL AND ECO-PHYSIOLOGICAL ASPECTS
OF THE PYGMY CORMORANT'S BIOLOGY
&

Nathan M. 1, Izhaki I 2, Zorovski Y 1, Arad Z 3, Katzir G 2
1Faculty of Life Sciences, Bar Ilan University, Ramat Gan 52900 Israel
2Department of Biology, University of Haifa at Oranim, Qiryat Tivon 36006, Israel
3Department of Biology, Technion-Israeli Institute of Technology, Haifa 32000, Israel

The Pygmy cormorant (Phalacrocorax pygmeus) is amongst the smallest of the Pelecaniformes and is associated with freshwater bodies where it feeds on small fish. Its restricted distribution includes Greece, Turkey, Iraq and Israel. Until 1997 it was classified as "Globally Threatened" and knowledge of the species' biology is meagre. In Israel, it was exterminated during the drainage of the Huleh swamps in the 1950's and only in the 1980's was it re-sighted. Breeding attempts have been recorded recently near Lake Kinneret and the Beit Sheean area. Our research objectives were to elucidate specific behavioural and eco-physiological aspects of the Pygmy cormorant's biology. Field observations were performed near the Sea of Galilee and the Bet Sheean valley. Focusing was on nesting, parent-offspring relationships, foraging and thermo-regulation. Peak foraging activity was 20-60 min after first light, immediately after the arrival of the cormorants at the foraging sites, and lasted 30-60 min. Foraging comprised a series of dives (mean dive duration 8.54 s, n=397) with a 3.54 s mean inter-dive interval (n=326). In 24.4% of the dives, a successful capture was observed. In the seven min. post-dive, the cormorants spent ca. 6% of the time in a wing - spread position. Pygmy cormorants bred in mixed colonies, with night herons, little egrets, cattle egrets and squacco herons. In all colonies, herons' nesting preceded that of the cormorants'. Colonies were established in reed beds (nest height 3.5-5.0 m), on Eucalyptus trees (nest height 8-15 m) or on Euphrates poplars (nest height 4.5-10 m). Parental change at incubation was performed either 2-3.5 hrs. after first light or 2.5-4 hrs. before darkness. A video film (ca. 15 min.) depicting feeding patterns, incubation and parent-offspring interactions will be presented. Filmed evidence will be provided of watering of nestlings by parents and of feeding on water-plants (Ceratophyllum sp.).

 

COMPARATIVE ONTOGENESIS OF PYGMY (PHALACROCORAX PYGMEUS) AND GREAT (P. CARBO) CORMORANTS: MORPHOMETRY AND ENERGETICS &

Shmueli M1, Katzir G2, Izhaki I2, Arad Z1
1
Department of Biology, Technion-Israeli Institute of Technology, Haifa 32000, Israel, 2Department of Biology, University of Haifa at Oranim, Qiryat Tivon 36006, Israel

The Great Cormorant (Phalacrocorax carbo sinensis) overwinters in Israel. The Pygmy Cormorant (P. pygmeus) is a resident bird on the verge of extinction. The natural feeding sites for both species in Israel have diminished during recent decades and intensive aquaculture became their favorite feeding sites. This study aims to compare the energy demands and growth of the two species as a basis for a future solution of the conflict. Eleven chicks of both species were hand-reared in captivity. Growth and morphometry were followed until the age of 5 month and energetics to adulthood. Chicks reached 90% of the stable juvenile mass in 28 and 34d, Pygmy and Great Cormorant, respectively. Most noticeable was the faster growing of the feet than the wing in both species. The BMR of both species did not change with age and were about 50% higher than expected from body mass. The metabolized energy was 426-563 and 970-1330 kJ/day per bird, respectively, at all ages. The food consumption of the Pygmy (20%-29% of body mass) was twice the measured consumption in Great Cormorants (9%-17% of body mass). The results of the present study will enable the estimation of the damages caused by cormorants of both species to the fish industry in Israel and the establishment of a biological basis for future solutions of this conflict, while protecting these valuable species.

 

PREY DETECTION AND PREY PREFERENCE IN DIVING CORMORANTS &

Strod T1, Izhaki I 2, Arad Z 1, Katzir G 2
1Department of Biology, Technion-Israeli Institute of Technology, Haifa 32000, Israel, 2Department of Biology, University of Haifa at Oranim, Qiryat Tivon 36006, Israel

Great Cormorants (Phalacrocorax carbo sinensis) forage underwater for fish by pursuit diving and are considered as a major pest to fisheries. Some 20,000 Great Cormorants over-winter in Israel. Our research aims at elucidating preference of prey variables (species, size, motion) and the role of vision in prey detection in Great Cormorants. Six cormorants were hand-reared in an aviary with a water tank and fed on dead/live Carp (Cyprinus carpio) and St. Peter's fish (Tylapia spp.). The birds could dive in a Y-shaped mesh tunnel, with a prey box at either end. Prey size was chosen significantly more often than non-prey size (P<0.001), at distances of both 0.8m and 1.4m. Detection of prey is thus possible at a distance of at least 1.4m and our data show that detection is visual. Dead fish were chosen significantly more than live fish and Tylapia were chosen significantly more often than carp (P<0.001). Preliminary results of choice experiments in which the birds could select one of six different sized prey (carp, 50 to 350gr) indicate a preference for larger fish on first choices and for medium sized fish on consecutive choices. Further studies are required on underwater foraging and visual capacities of Great Cormorants in order to formulate reasonable solutions to the fisheries - cormorant conflict. Supported by the Israeli Ministry of Science.

 

POPULATION DEVELOPMENT OF WINTERING AND BREEDING GREAT CORMORANTS IN THE NORTHERN ADRIATIC, ITALY
[POSTER BOARD # 44]

Volponi S, Cherubini G, Utmar P
Department of Biology, University of Ferrara, Via Borsari 46, I-44100 Ferrara
Provincia di Venezia, Ufficio gestione faunistica, Rampa Cavalcavia 31,
I-30170 Mestre, Venezia;
Osservatorio Faunistico, Regione Friuli-Venezia Giulia, Via A. Diaz 60, I-33100 Udine, Italy

In Italy, wetlands along the coastal belt of the Northern Adriatic Sea are a major area for wintering and breeding Great Cormorants (Phalacrocorax carbo). Counts at roosts located between the towns of Trieste and Cervia indicated that: (i) six sub-populations may be recognised by the use of distinct foraging areas; (ii) overall numbers of wintering cormorants increased exponentially between the early 1980s and mid 1990s, then showed the tendency to level out; (iii) in last winters distribution at local level changed as new satellite roosts were established inland or closest to the foraging grounds in the lagoon areas. First breeding occurred in the southern Po Delta in 1993 and since then four new colonies established in the Po Delta and the Lagoon of Venice. In 1999, more than 400 pairs (about fifty percent of the Italian population) nested in the Northern Adriatic area. Considering the extent of suitable nesting habitats available along the Northern Adriatic coast, there exists a potential for a substantial increase of the cormorant breeding population. Further growth of the breeding population, coupled with a high numbers of wintering birds, will certainly exasperate the conflict with aquaculture producers who may have to contend with cormorant predation as a year-round issue.

 

DIET AND PREDATION OF GREAT CORMORANTS WINTERING IN TWO AREAS ALONG THE NORTHERN ADRIATIC SEA COAST
[POSTER BOARD # 45]

Volponi S, Privileggi N
Department of Biology, University of Ferrara, Via Borsari 46, I-44100 Ferrara
and Department of Biology, University of Trieste, Via Weiss 2, I-34100 Trieste, Italy

The increase in numbers of Great Cormorants (Phalacrocorax carbo sinensis) has led to growing conflicts with fishermen and resulted in the request to manage the Great Cormorant population. Data on diet composition and prey characteristics are essential to evaluate the impact of cormorants on fish production. In this study, we analysed and compared the diet of Great Cormorants wintering in the Lagoon of Grado and in the southern Po Delta, two important areas for extensive fish exploitation. We also assessed monthly and seasonal predation as biomass of fish removed and compared these estimated with available data on fish yield. Results are based on the analysis of 1,206 regurgitated pellets collected at the roosts in Valle Cavanata (October 1997 - April 1998) and Valle Bertuzzi (October - March 1992-93, 1993-94 and 1996-97). Remains of 12,000 preys belonging to 24 fish taxa were identified. Diet composition was rather different between the two areas (index of percentage similarity = 46-49%) and showed evident variations during the winter due to prey distribution shift among habitats and change in cormorant foraging grounds. Potential impact on aquaculture production resulted heavier in the Po Delta where numbers of wintering cormorants and the proportion of valuable fishes in the diet are higher than in the Lagoon of Grado.

 

THE STATUS OF THE DOUBLE-CRESTED CORMORANT (Phalacrocorax auritus )
ON LAKE ONATRIO IN 1999: AT THE BEGINNING OF MANAGEMENT ACTIVITIES
[POSTER BOARD # 46]

Weseloh DVC1, Miller RL2
1. Canadian Wildlife Service, 4905 Dufferin St., Downsview, Ontario, CANADA M3H 5T4
2New York Department of Environmental Conservation, Wildlife Research Center,
108 Game Farm Rd. Delmar, NY, USA 12054

Double-crested Cormorants bred at 17 colony sites in Lake Ontario in 1999 when the total breeding population was censused as 20,053 pairs (nests). This represents a 63-fold increase since 1979 and a sustained average annual rate of increase of 23.1% per annum.. In recent years, this rate has slowed, e.g. 1996-1999 = 5.5% p.a.. The centre of the population has shifted from Little Galloo Island in the US Eastern Basin to High Bluff Island in the Canadian Central Basin. Since 1996 the number of cormorant nests in the Eastern Basin and Little Galloo Island have declined by 24.6% and 46.0%, respectively. At the same time, they have increased by 89.6% and 72.0%, respectively, in the Central and Western Basins of the Lake. There has been substantial disturbance at some of the colonies in the Eastern Basin, e.g. weekly research activity and illegal shooting, but no authorized control programs except egg oiling in 1999 and nest destruction at three small sites. These activities may have contributed to the substantial decline in the adult population in the Eastern Basin, prior to any major sanctioned management activities directed at breeding birds.