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DEMOGRAPHY STATUS, DYNAMICS AND LOW REPRODUCTIVE PERFORMANCE IN AN ITALIAN MUTE SWAN POPULATION

Authors:
Nicola Ventolini
Nicola Ventolini
Nicola Ventolini
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Stefano Sponza at University of Trieste
Stefano Sponza
Fabio Perco at Stazione Biologica Isola Cona
Fabio Perco
  • Stazione Biologica Isola Cona
Kajetan Kravos
Kajetan Kravos
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DEMOGRAPHY STATUS, DYNAMICS
AND LOW REPRODUCTIVE
PERFORMANCE IN AN ITALIAN
MUTE SWAN POPULATION
Nicola Ventolini, Stefano Sponza, Fabio Perco,
Kajetan Kravos, Paolo Utmar, Silvano Candotto and Enrico Ferrero.
DISTRIBUTION
Distribution map of the two metapopulations of Mute Swan in western Eurasia (Scott et al., 1996). Northern
Adriatic area is marked by the red dot.
WINTERING POPULATION:
•1991-1995 885 individuals (29 sites).
•1995-2000 1798 individuals (67 sites). (Baccetti et al. 2002).
ITALY
FRIULI VENEZIA GIULIA
•Originally irregularly migrant, mainly wintering.
•1981: species introduction (Parodi et al., 1992).
•1984: first successfull reproduction (Utmar,1999).
Wintering individuals (1981-2006 data FVG Region; 2004 Astore-FVG, Guzzon et al. 2006) and mating pairs
(Faunistic observatory FVG 1998-1999 data) from 1981 to 2007. Data of mating pairs from 2000 to 2004 are not
available.
0
10
20
30
40
50
60
70
80
0
100
200
300
400
500
600
700
800
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
NESTING PAIRS
WINTERING INDIVIDUALS
WINTERING INDIVIDUALS
NESTING PAIRS
AIM OF THE STUDY
•MONITORING OF THE POPULATION
•MOVEMENTS ANALYSIS
•BREEDING STATUS
STUDY AREA
•FVG coastal wetlands grouped in 5 areas: Lisert, coastline between
Timavo river mouth and Mula di Muggia mudflats, Valle Cavanata
Natural Reservation, Grado and Marano lagoons.
MARANO LAGOON
GRADO LAGOON
VALLE
CAVANATA
ISONZO RIVER
MOUTH
LISERT
POPULATION MONITORING
386
215
66 RESIDENT
ERRATIC
FLEDGEDYOUNG
2007
METHODS
•Monthly censuses by two boats.
•Aerial survey during censuses of ANSER project (Adriatic
Cross Border Interreg IIIA Programme), coordinated by the Regional
Faunistic Study Office.
342
243
106
RESIDENT
ERRATIC
FLEDGEDYOUNG
2006
AREAS SEASONALLY FREQUENTED BY THE SPECIE
SECCADI
MUZZANA
SACCA
VENCHERE
SACCA
ALBERO
PANTANIFISH
FARM
MARINETTA
NOGHERAFISH
FARM
MULADI
MUGGIA
CAVANATA
FISHFARM
PANZANOBAY
CONAISLAND
LISERT
LIGNANO
SABBIADORO
GRADO
MARANO
LAGUNARE
MONFALCONE
ISONZORIVER
MOUTH
1a. CAPTURE. 1b. CAPTURE.
2. BIOMETRY AND MARKING BY
COLLAR AND RING 3. RELEASE.
MARKING CAMPAIGN
MARKING CAMPAIGN 2005-2008
ADULTS IMMATURES JUVENILES
CAPTURE
SITE 2005 2006 2007 2008 2005 2006 2007 2008 2005 2006 2007 2008 TOTAL
ISONZO
RIVER MOUTH 34 85 56 22 5 13 20 0 1 13 7 0 256
MARANO
LAGOON 1460061031090 40
VALLE
CAVANATA 000000000500 5
TOTAL 35 89 62 22 5 19 21 0 4 28 16 0 301
32,49
24,55
17,69
9,03 16,61
SEDENTARY
REGIONAL
NORTHERN
ADRIATIC
FOREIGN
OTHER
MOVEMENTS WITHIN THE REGION
•32,49% (N=90) of the marked sample, mainly
breeding territorial adults (N=22) and yearlings
(N=21) revealed sedentary.
•24,55% (N=68) were individuals wintering (november
to february) in Marano Lagoon and moulting
(summer) at Isonzo river mouth.
MOVEMENTS TO VENETO
•17.32% (N=30) individuals were observed in Veneto
•Westbound movements happen wintertime
•Summertime they tend to rejoin moulting flocks in FVG
• RECOVERIES IN VENETO
MOVEMENTS TO AND FROM CENTRAL-EASTERN
EUROPE
•CAPTURE AREA
•FOREIGN RECOVERIES
ETA' SEX DEPARTURE FIRST RECOVERY
COUNTRY RETURN
AD M 27 feb 07 SLOVENIA 18 lug 07
AD M 22 gen 07 CROATIA 25 ott 07
IMM F 30 gen 07 CROATIA 25 ott 07
AD F 26 gen 08 AUSTRIA -
AD M 27 feb 07 AUSTRIA -
IMM M 26 Gen 08 AUSTRIA -
IMM F 7 feb 08 AUSTRIA -
AD M 14 feb 08 AUSTRIA -
IMM F 14 feb 08 GERMANY -
AD F 06 feb 07 HUNGARY -
AD M 25 feb 07 SLOVAKIA 25 ott 07
IMM M 18 gen 07 SLOVAKIA -
AD M 13 feb 07 CZECH REPUBLIC 18 dic 07
AD M 6 feb 07 CZECH REPUBLIC -
AD M 3 mar 06 CZECH REPUBLIC -
AD F 3 mar 06 CZECH REPUBLIC -
IMM M 27 feb 07 POLAND 12 nov 07
AD M 13 feb 07 POLAND 6 dic 07
AD F 24 feb 07 POLAND 10 dic 07
AD F 21 feb 06 POLAND -
JV M 13 feb 07 POLAND 18 dic 08
AD M 06 giu 07 POLAND 26 gen 08
AD F 6 feb 08 POLAND -
AD M 28 feb 06 POLAND 14 nov 06
IMM M 16 Gen 08 POLAND -
ERRATIC AND SEDENTARY INDIVIDUALS
•Adult (N=83, Chi-square=5.31, P<0.02) and immature males
(N=16, Chi-square=9.00, P<0.005) are more dispersive
compared to females and juveniles.
•An Irish study showed that females made longer movements
than males (Collins, 2002).
NESTING IN THE MAIN BREEDING SITES
Nesting pairs during 2005-2007 in the five study areas.
2
8
19
88
3
17
21
6
16
3
11
17
12
18
0
5
10
15
20
25
LISERT
ISONZO
RIVER
MOUTH
VALLE
CAVANATA
GRADO
LAGOON
MARANO
LAGOON
N. NESTS
2005
2006
2007
BREEDING AREAS
•Nests are usually built by material taken from reeds
Phragmites australis, Thypha latifolia (45.25%).
•Fish farms are the predilect nesting environments
(51.4%) (Valle Cavanata and Grado Lagoon), followed
by river mouths (18.44%) (Marano Lagoon e Foce
Isonzo).
•91% of the nests are in no-draining areas and 75% in
no-tidal areas.
•Breeding pairs significatively select fresh water or lighly
salted sites (N=179, Chi-square=23.79, df=1, P<0.0001).
BREEDING SUCCESS
Fig. 1 - Mean percentage of failure and minimum/maximum of breeding
success in the 5 study areas between 2005-2007.
SITE NESTS BORN
CYGNETS
FAILED
NESTS
FAILED
BROODS
FLEDGED
YOUNG
AVERAGE FLEDGED
YOUNG PER PAIR
LISERT 2-3 9-17 22,22% 50% 0-9 2
ISONZO RIVER
MOUTH 11-18 17-57 31,52% 13,4% 9-47 1,67
VALLE
CAVANATA 17-21 37-67 32,95% 84,87% 4-8 0,31
GRADO
LAGOON 6-12 24-30 18,06% 49,21% 7-11 1,19
MARANO
LAGOON 8-18 19-66 21,53% 41,36% 15-31 1,5
AVERAGE 25,26% 47,77% 1,11
2007-2008 BREEDING SEASONS
METHODS
•MAP OF NESTS AND
TERRITORIES OF BREEDING
PAIRS.
•CONSTANT MONITORING
(SUNRISE TO SUNSET) OF
THE MOVEMENTS OF FAMILY
GROUPS.
•DATA COLLECTION ABOUT
CYGNET’S DEATH CAUSES.
BREEDING FAILURE IN VALLE
CAVANATA NATURAL RESERVATION
NESTS 2007
NESTS 2008
SITE FIDELITY 2007-2008
CYGNET’S BIRTH IN THE FISH FARM WATER SHEET
CYGNET’S DIRECT PREDATION BY YELLOW-LEGGED GULL
AGGRESSIVE ENCONTERS AGAINST
TERRITORIAL NESTING PAIRS
CYGNET’S PREDATION BY YELLOW-
LEGGED GULL
MOVEMENTS LOOKING FOR
FOOD AND FRESH WATER MOVEMENTS TO THE AVERTO
CHANNEL
(ABUNDANT WIDGEONGRASS)
DURING
ENCOUNTERS
BETWEEN ADULTS
BECAUSE OF THE ABANDON OF
CYGNETS BY PARENTS
CAUSES OF PULLI’S DEATH
•PREDATION BY YELLOW-LEGGED GULLS
•PREDATION BY YELLOW-LEGGED GULLS
DURING PAIRS AGGRESSIVE ENCOUNTERS
•YOUNG FLEDGED
•OTHER DEATH CAUSES
•YELLOW-LEGGED GULLS PRAYED 80% OF CYGNETS.
•AVERAGE CYGNETS LIFESPAN: 6 DAYS (2007), 7 DAYS (2008).
•4/37 PAIRS RAISED CHICKS TO FLEDGING ADOPTING DIFFERENT
STRATEGIES.
•LAYING EGGS LATER IS MORE CONVENIENT.
2007 2008
2
3
1
SUCCESSFULL PAIRS
NESTS
Fresh water areas
Fresh water pond
exclusively used by one pair
Fighting and consequent
predation areas 2007
Fighting and consequent
predation areas 2008
DISTRIBUTION OF AGGRESSIVE ENCOUNTERS
AND CONSEQUENT PULLI PREDATION.
CAUSES OF BREEDING FAILURE
COMBINATION OF VARIOUS CAUSES:
•SCARCE FRESH WATER AND TROPHYC RESOURCE
CONCENTRATED IN A FEW ZONES.
•HIGH AGGRESSIVENESS AND TERRIRIALITY OF
BREEDING PAIRS.
•PREDATORY PRESSURE OF YELLOW-LEGGED GULL.
VALLE CAVANATA NESTING HISTORICAL SERIES
FISHFARM
TROPHYC
RESOURSE
QUANTITY
PRESENCEOF
YELLOW‐LEGGES
GULLS
BREEDINGPAIRSFROM
2005TO2007 BORNPULLI AVER AGEBORN
PULLIPERPAIR
FLEDGED
YOUNG AVER AGE
VALLE
CAVANATA LOW HIGH 56(COLONIAL) 169 3,02 19 0,3
NOGHERA
FISHFARM LOW LOW 6(TERRITORIAL) 18 312 2
COMPARISON TO VALLE NOGHERA FISH FARM
BREEDING SUCCESS
COMPARISON TO OTHER NORTH AMERICAN AND
EUROPEAN BREEDING AREAS
AREA AVERAGE
LAID
EGGS
AVERAGE
BORN
PULLI
AVERAGE
FLEDGED
YOUNG
DIFFERENCES
WITH FVG
FRIULI VENEZIA GIULIA 5,6 3,21 1,11 -
AISHIRE 1983-1986 (GREAT BRITAIN) (Leach, 1988) / 2,3 1,6 0,49
STAFFORDSHIRE 1969-1978 (GREAT BRITAIN) (Coleman et
al. 1980). / 2,57 1,97 0,78
CHESAPEAKE BAY 1968-1974 (USA) (Reese, 1975). 6,2 3,90 2,20 1,01
OXFORD (GREAT BRITAIN) (Bacon, 1980). 6,45 / 2,50 1,31
LOTHIANS ISLANDS (SCOTHLAND) (Brown et al. 2002). / / 2,60 1,41
IRELAND (Collins, 1989). 6,07 4,20 2,70 1,51
POLAND (Czapulack et al. 1991). 5,8-6,2 / 2,80 - 3,30 1,61-2,11
CHESAPEAKE BAY 1969-1979 (USA) (Reese, 1980). 4,30 3,10 1,91
SOUTHEAST CORK (IRELAND) (Smiddy et al. 1991). 5,50 / 3,80 2,61
STAFFORDSHIRE 1961-1985 (GREAT BRITAIN) (Coleman et
al. 1991). / 4,51 4,40 3,21
LAKE ERIE (CANADA) (Knapton, 1993). / 4,90 3,10 1,91
DELTA VOLGA (RUSSIA) (Krivonosov, 1989). 6 5,20 4,50 3,31
ARCHIPELAGO SEA (FINLAND) (Hästbacka et al., 1987). 4,9-6,2 / 5,85 4,66
CAUSES OF THE LOW BREEDING SUCCESS:
- SCARCE TROPHIC RESOURCE IN FISH FARMS (DEFECATIONS
AND ARTIFICIAL GRAIN FEEDING CAUSE WATER BED ANOXY).
-FISH FARM BREEDING PAIRS MOVE TO MOULT TO ISONZO
RIVER MOUTH.
-PREDATORY PRESSURE BY YELLOW-LEGGED GULLS.
-SCARCE FRESH WATER (OSMOREGULATION).
-SCOTHLAND: LESS FLEDGED YOUNG IN SALT LAKES
(Spray, 1980).
-POPULATION DECREASE DURING BREEDING SEASON
(SPRING).
-TEMPERATURE GROWTH IN SPRING AND CONSEQUENT
EVAPORATION AND RAISE OF SALINITY LEVELS.
SITO AVERAGE
EGGS
AVERAGE
BORN
PULLI
AVERAGE
FLEDGED
YOUNG DIFFERENCE
COLONIAL (Roskilde) DENMARK (Bacon et
al. 1989). 4,9-5,9 / 1,90 1,6
TERRITORIAL (Kobenhavn) DENMARK
(Bacon et al. 1989). 5,80 / 3,50
COLONIAL NORTH SJIAELLAND
(DENMARK) (Bacon et al. 1989). / / 1,10 1,4
TERRITORIAL NORTH SJIAELLAND
(DANIMARCA) (Bacon et al. 1989). / / 2,50
COLONIAL (VALLE CAVANATA) / 2,88 0,31 1,22
TERRITORIAL FRIULI VENEZIA GIULIA / 3,19 1,53
COLONIAL vs TERRITORIAL BREEDING
•COLONIAL BREEDING GENETICALLY DETERMINED (Bacon et al.,1989).
•INERTIA TO GO BACK TO AN INPRODUCTIVE SITE (HIGH ENERGY
RATE, SURVIVAL DANGER); PAIRS RENESTED IN THE SAME PLACE (2007: N=6;
2008 N=5) NEVERTHELESS THE PREVIOUS INSUCCESSFUL BREEDING SEASON.
•COLONIALITY PROTECTION? AGGRESSIVE RATE THRESHOLD DOES NOT
DECREASE.
•BIRTH SITE IMPRINTING.
•DINSTANCE FROM SEAGRASS PRAIRIES.
•Mute swan cygnets might born grey-brown or in a white
leucistic form commonly defined polish.
•Grey-brown cygnets would be advantaged by their
subadult plumage that would inhibit aggressions by their
parents and other swans.
•Polish cygnets, having the same cromatism of adult at
birth would receive more aggressions and sometimes be
victims of infanticide (Norman, 1977, Reese, 1980).
GREY AND POLISH PULLI
•POLISH CYGNETS WERE 27.54% (N=152) OF TOTAL BORN
CYGNETS (N=552), AS MUCH AS MARKED MOULTING
INDIVIDUALS.
•CHESAPEAKE BAY (U.S.A.): GREY-BROWN CYGNETS HAD A
14% HIGHER SURVIVAL RATE THAN POLISH CYGNETS
(Reese, 1980).
•POLISH CYGNETS HAVE A 22,88% HIGHER SURVIVAL RATE
THAN GREY-BROWN CYGNETS.
STUDYAREA %OFBORNPOLISHCYGNETS
Poland(Wieloch etal.,1991) 2‐9%
Yellowstone,U.S.A(Mccoy,1967) 13%
RhodeIsland,U.S.A(Munro etal.,1968) 17%
ChesapeakeBay,U.S.A.(Reese,1980) 27%
FriuliVeneziaGiulia 28%
Groningen,Olanda(Latzer etal.,1985a,1985b) 50%
Gettingen,Olanda(VanDjik et al.,1985) 76%
•FOR A GREY-BROWN CYGNET IT’S MORE CONVENIENT TO
BORN IN A MIXED BROOD.
•HIGHER SURVIVAL RATE OF GREY-BROWN CYGNETS IN
MIXED BROODS DOES NOT CORRESPOND TO A LOWER
SURVIVAL RATE OF POLISH CYGNETS.
•PROTECTION EFFECT OF POLISH CIGNETS ON THEIR
GREY-BROWN BROTHERS AND SISTERS?
GREY AND POLISH CYGNETS DEATH RATE
ACKNOWLEDGEMENTENTS
A. Rocco, A. Grimaldi, G. Vicario, M. De Luca, D. Mattellone, N.
Perco, P. Vacilotto, L. Boscain, M. Cosolo, F. Roppa, M. Tofful, C.
Trani, B. Cimador, M. Skodler, D. Ota, M. Zucchi, A. Piazza, M.
Wieloch, R. Wlodarkzyk, M. Zenatello, A.st.o.r.e.-FVG, Grado and
Marano councils, National Institute for Wild Fauna, management
and personnel of Grado and Marano fish farms, Faunistic Studies
Office - Friuli Venezia Giulia region and all those who helped in
the field and by their recoveries.
NICOLA VENTOLINI
nicvento@psico.univ.trieste.it
THANKS FOR
YOUR
ATTENTION
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... Mute Swans have been present for so long in Europe, with coordinated counts not being organized until the mid-1960s (Fouque et al. 2007), that examples of this type of trend from there are limited. However, this pattern played out in Finland, France, and northern Italy for more recently introduced populations (Nummi and Saari 2003, Fouque et al. 2007, Ventolini et al. 2008. In modern times, most European breeding populations underwent modest increases between 1970-1990, but overall underwent a large increase during 1990-2000 (Burfield and von Bommel 2004). ...
... In Europe, Mute Swans are known to use Phragmites for nesting (Ventolini et al. 2008) and there are indications that they favor it in North America as well ). There are both native and non-native genotypes of Phragmites australis present in North America (Saltonstall 2002). ...
... Typical causes of mortality of Mute Swans during the breeding season have been mostly attributed to wave action or flooding destroying nests or chilling eggs; exposure of young cygnets to cold or storms; and predation of cygnets by snapping or marine turtles, fox, raccoons, and other animals (Reese 1980, Gelston andWood 1982). In a population studied over two years in Italy, 80% of cygnets were preyed upon by Yellow-legged Gulls (Larus michahellis) (Ventolini et al. 2008). For post-fledging cygnets and adults in Michigan, starvation and disease have been cited as the primary causes of mortality in Michigan Wood 1982, Ciaranca et al. 1997). ...
View
... Mute Swans have been present for so long in Europe, with coordinated counts not being organized until the mid-1960s (Fouque et al. 2007), that examples of this type of trend from there are limited. However, this pattern played out in Finland, France, and northern Italy for more recently introduced populations (Nummi and Saari 2003, Fouque et al. 2007, Ventolini et al. 2008. In modern times, most European breeding populations underwent modest increases between 1970-1990, but overall underwent a large increase during 1990-2000 (Burfield and von Bommel 2004). ...
... In Europe, Mute Swans are known to use Phragmites for nesting (Ventolini et al. 2008) and there are indications that they favor it in North America as well ). There are both native and non-native genotypes of Phragmites australis present in North America (Saltonstall 2002). ...
... Typical causes of mortality of Mute Swans during the breeding season have been mostly attributed to wave action or flooding destroying nests or chilling eggs; exposure of young cygnets to cold or storms; and predation of cygnets by snapping or marine turtles, fox, raccoons, and other animals (Reese 1980, Gelston andWood 1982). In a population studied over two years in Italy, 80% of cygnets were preyed upon by Yellow-legged Gulls (Larus michahellis) (Ventolini et al. 2008). For post-fledging cygnets and adults in Michigan, starvation and disease have been cited as the primary causes of mortality in Michigan Wood 1982, Ciaranca et al. 1997). ...
View
... For example, incorporating more local measures of the amount of emergent vegetation may be important in more narrowly defining the range of suitable habitat. Habitat restoration efforts that include eradication of a mute swan preferred nesting material, Phragmites australis (Ventolini et al., 2008), may reduce breeding habitat. However, restoration of native waterfowl habitat may provide significant food resources for large congregations of mute swans wintering in coastal wetlands (Craves and Susko, 2010). ...
Great Lakes coastal wetlands as suitable habitat for invasive mute swans in Michigan
Article
  • Apr 2020
  • J GREAT LAKES RES
Great Lakes coastal wetlands provide critical habitat and food resources for more species than any other Great Lakes ecosystem. Due to past and current anthropogenic disturbances, coastal wetland area has been reduced by >50% while remaining habitat is frequently degraded. Invasive mute swans have contributed to the degradation of coastal wetlands by removing submergent vegetation and competitively excluding native species from breeding areas and food resources. Despite current control practices, mute swan population estimates in Michigan are ~8,000, comparable to population estimates in the entire Atlantic Flyway of North America. We collected local abiotic data and adjacent land cover data at 3 scales from 51 sites during 2010 and 2011 and conducted 2 mute swan detection surveys each year during the summer and fall. We developed a single-species, single-season occupancy-based habitat suitability model to determine current and potential mute swan habitat among Great Lakes coastal wetlands. We found mute swans occupied heterotrophic coastal wetlands adjacent to urban areas, which were high in ammonium and oxidation-reduction potential and low in nitrates, dissolved oxygen, and turbidity. Our model provides managers with a valuable tool for rapidly identifying mute swan habitat areas for control efforts, particularly the need for targeting mute swan populations in or near urbanized areas. Our model will also aid managers in monitoring areas that mute swans may invade and prioritizing coastal wetland areas for restoration efforts.
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Factors affecting the number of pairs and breeding success of mute swans Cygnus olor in an area of south Staffordshire, England between 1961 and 1985
Article
  • Jan 1991
Considerable fluctuation in the number of swan pairs and their breeding success has been noted. The decline within the Birmingham/Wolverhampton conurbation has been a case for concern, human influence being a major factor. Most pairs retained the same mate from the previous season; 87% of this segment of the paired population laid eggs. Overall clutch failure was 45%, humans being the chief cause; failure in the industrial conurbation was 22% more than in the rural area. Number of cygnets fledged per breeding pair was significantly less in the conurbation. Rearing success was uniform and tended to decrease with brood size. Over 50% of the broods were reared without loss. Highest mortality after fledging occurred during the first year with peak periods in October and March. Overhead wires were the commonest cause of known death. An average maximum mortality rate of 21% was calculated for breeding birds and 31% for non-breeding paired birds with deaths due to vandalism highest in the breeding birds. A low immmigration of breeding birds was recorded. -from Authors
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The breeding ecology of the mute swan Cygnus olor in Poland - preliminary report
Article
  • Jan 1991
Data were collected from the Gdansk area, the reserve "Przemkow Ponds' and Milicz fish ponds. Mute swans from N Poland (Gdansk) nested later than those in the SW (Silesia). The difference in the occurrence of the peak of first egg laying was c20 days though after mild winters it was c10 days. Mean clutch size was similar in all three areas, viz 5.8-6.2, but swans from Gdansk laid larger eggs than those from Silesia. Mean number of fledged cygnets per successful pair (which raised at least one cygnet) varied between 4.1-4.3. Production of young per breeding pair was 2.8-3.3. Pairs which started to breed before 20 April had larger clutches, laid bigger eggs, and produced more cygnets than those breeding late. -from Authors
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Mute swan (Cygnus olor) impact on submerged aquatic vegetation and macroinvertebrates in a Rhode Island coastal pond
Article
  • Jan 2003
  • NORTHEAST NAT
We followed the annual use of a shallow coastal pond by molting Mute Swans to examine their potential impacts on waterfowl habitat. Effects of Mute Swan herbivory on submerged aquatic vegetation (SAV) and macroinvertebrates were measured by comparing control vs. exclosure plots in varying water depths from 1990 to 1994. Mute Swans fed in all water depths, but appeared to prefer feeding in shallow sites (< 0.5 m) where they were capable of reducing SAV biomass by up to 95%. The impact of Mute Swans on macroinvertebrates could not be demonstrated. Only three species of macroinvertebrates (Grammarus spp., Hydrobia spp., Limnephilus spp.) showed reduced densities on some grazed plots.
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Productivity and Management of Feral Mute Swans in Chesapeake Bay
Article
  • Apr 1975
One or two mated pairs of pinioned mute swans (Cygnus olor) escaped from impoundments along tributaries of east central Chesapeake Bay in 1962. These feral swans and their offspring have bred successfully in the wild each year since and increased their numbers to about 151 during the last decade. In the past 7 years, the breeding pairs hatched 54 percent of their eggs, fledged 86 percent of their young, and achieved 80 percent nesting success. This has caused a rapid population increase which presents waterfowl biologists with new problems in management. Ecological implications for the Chesapeake Bay are discussed.
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Prefledging survival of Mute Swan Cygnus olor cygnets in the Lothians, UK: Survival rates 1981-98 were quantified between four growth stages, and related to habitat type and altitude
Article
  • Jul 2002
Capsule: Survival rates 1981-98 were quantified between four growth stages, and related to habitat type and altitude. Aims: To investigate variability in Mute Swan productivity in relation to habitat type and altitude. Methods: Cygnets were studied and categorized as they developed from small size through medium and large to fledged. Natal territory was classed as river, canal or still water, and altitude of each site established. Results: Of 2576 cygnets studied, 69% fedged. Fledging rate varied from 57% on low altitude still waters to 78% on mid-altitude still waters, and from 72% on rivers to 82% on canals. Survival was lower between the early growth stages. Of the pairs that bred, 72% produced at least one small cygnet and 61% fledged at least one cygnet. Pairs that nested on rivers suffered the greatest loss of complete clutches or broods of newly hatched cygnets and 41% failed to raise at least one small cygnet. The breeding population increased annually by 7% from 15 pairs to 69 pairs between 1978 and 1998 and consequently the number of cygnets fledged increased annually by 7%. Productivity was higher than in other populations at 2.6 cygnets fledged per breeding pair; ranging from 2.1 on rivers to 3.6 on mid-altitude still waters. Conclusions: Cygnet survival was lower during the early growth stages across all habitats. Survival was consistently poorer on low altitude still waters, probably due to inadequate diet. Although survival in the Lothians varied with habitat type and altitude, productivity was higher than in other areas of Britain.
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A Role for Plumage Color in Mute Swan (Cygnus Olor) Parent-Offspring Interactions
Article
  • Jan 1977
  • BEHAVIOUR
Mute Swan (Cygnus olor) cygnets usually hatch out covered with a brownish gray colored down. Less frequently the cygnets will hatch out white. According to reports in the literature, white Mute Swan cygnets receive disproportionately more parental aggression than their brownish gray coloured siblings. To test whether this aggression is the result of plumage colouration, brown and white swan models were presented to four territorial pairs of adult Mute Swans in a series of two sets of experiments. The first set of experiments consisted of presenting each model separately to the swans on their respective territories. The second set of experiments consisted of presenting both models to the territory holders at the same time. The models were accorded significantly different treatments by the territorial adults. The white model received more threats and attacks than did the brown model. The experimental results together with anecdotal evidence suggest the use of
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Mate fidelity in swans: an interspecific comparison
Chapter
  • May 1996
Reproductive success improved with pair duration in three swan species after controlling for the effects of other variables. The effect of pair duration was more pronounced in some years than in others for the migratory Bewick’s and Whooper Swans, which breed at high latitudes. Fighting ability of pairs (i.e. dominance rank) did not appear to be the mechanism behind the reproductive improvement. The combination of male and female age, and of male and female size, also influenced reproductive success in Bewick’s and Whooper Swans, indicating that the compatibility of individual characteristics may determine the quality of the pair. Mate replacement resulted in higher short-term costs for Bewick’s Swans than for Whooper or Mute Swans. Interspecific differences in the benefits of long-term monogamy, measured in terms of increased reproductive success, were attributed to variation in limitations imposed on the swans’ breeding programmes by the migratory distances undertaken and shortness of the arctic summer. Mate change did not appear to affect an individual’s lifetime reproductive success.
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