An analysis of weight changes in the Mute Swan Cygnus olor

The weights of Mute Swans contain useful information on individuals' prospects for survival and breeding but to interpret them one needs to know what 'typical' weights would be. This paper uses multiple linear regression to predict such 'typical' weights: 1968 zveighings of 957 Mute Swans, from south Staffordshire, England, are analysed with respect to sex, age, moultstage, month of capture and breeding status. Because of marked sexual dimorphism, knowing a swan's sex is fundamental to interpreting its weight; age from hatching and stage of primary feather growth affect cygnets' weights near fledging; weights of young swans change with age during their first years of life; primary feather moult significantly depresses the weights of first year males but not, in this study area, of older males or females; monthly, seasonal changes are generally small; breeding adults are significantly heavier. The results and their biological implications agree well with other, less comprehensive, analyses. The method described could facilitate both the identification of other factors that should be investigated and comparisons between different study areas.     

Winter territoriality of Mute Swans Cygnus olor

There was considerable variation in winter territoriality among Mute Swan pairs around Oxford, though most pairs maintained their territories for at least half the winter. Variation was associated with temperature and with territory quality pairs left their territories most commonly during the coldest months of the winter, and pairs on good territories, with abundant vegetation and accessible pasture. stayed longer on territory than those on poor territories with sparse vegetation and little pasture. As in other species, exclusive territorial defence was maintained at intermediate levels of resource availability, and flocks were able to settle on a few particularly good territories. Circumstantial evidence suggested that winter territories may be maintained not only to provide an adequate food supply for the owners but also to ensure access to a brerding site by preventing other individuals from taking over the area.     

Colonial breeding in Mute swans (Cygnus olor) associated with an allozyme of lactate dehydrogenase

The Mute swan ( Cygnus olor Gmelin (Anatidae)) is a common water bird of lowland freshwaters and coastal shallows. Its typical breeding system involves lifelong monogamous pairs which vigorously defend large breeding territories, sometimes killing intruding swans that are unable to escape. However, in some unusual circumstances (superabundant food coupled with limited nesting sites) Mute swans may nest colonially. At the only two colonies in southern England a rare allele for lactate dehydrogenase (LDH) was found to be unusually common and colony swans carrying this allele were shown to breed more successfully. This isolated finding could, however, have originated either from a chance 'founder' effect or from human management of the main colony. We now show that this allele is also significantly commoner at two recently formed colonies in Denmark, implying that the association between the allele and colonial breeding may be widespread and longstanding.     

Resources and reproductive performance in Mute swans Cygnus olor

Around Oxford, breeding pairs of mute swans maintained territories throughout most of the year and these territories varied considerably in potential food availability in the form of aquatic vegetation, bread supplied by the public and pasture for grazing. On territories with abundant aquatic vegetation females laid earlier larger clutches than on those with little aquatic vegetation. Clutches were also larger on territories with a high potential bread supply. In addition, adult females were heavier on territories with a high diversity of aquatic vegetation. However, contrary to expectation, there were no direct relationships between territory quality measures and other aspects of reproductive performance including number of young fledged, egg volume, cygnet weight or size, or adult male weight. Instead, the number of young fledged was related to clutch size; egg volume was related to laying date; and cygnet weight was related to age and egg volume. Adult male weight was positively related to age.     

Lead levels in the blood of Mute swans Cygnus olor on the River thames

In this paper blood lead levels in three categories of Mute swan are examined, (i) flock birds (ii) breeding birds and (iii) cygnets. From these regional, seasonal and sex variation for both 1980 and 1981 was examined. In addition a portable haematofluorometer was assessed to determine its possible use as an alternative to atomic absorption and spectrophotometry for determining a measure of lead exposure.
Very few swans on the River Thames had blood lead levels below the maximum acceptable level of 40 mgg/100 ml. In general lead levels increased with proximity to London and the swans on the tributaries consistently had the lowest levels which were always below the maximum acceptable level. Blood lead levels in flock birds were shown to be highest during the coarse fishing season and it was only during the close season that levels dropped to around 40 g/1OO ml. Breeding females had significantly higher lead levels than males and females with lead levels in excess of 200 g/1OO ml seemed to have a poor chance of producing cygnets or surviving to the next breeding season. Cygnet mortality was significantly higher on the lower Thames where blood lead levels were also known to be at their highest.     

Causes of mortality in the Mute swan Cygnus olor on the River Thames

Over the last 20 years there has been an unprecedented decline of the Mute swan on the River Thames. Between August 1979 and October 1981 a systematic attempt was made to collect as many swan corpses as possible. Of 94 swan corpses examined at post-mortem 57% died from lead poisoning due to ingestion of anglers' weights. Birds dying from lead poisoning had significantly higher liver and kidney lead levels. Kidney proved to be the most useful indicator tissue, the median lead level in birds with lead weights in their gizzard was 908 μg/g DM compared to 8 μg/g DM in birds without weights. More immature birds die from lead poisoning than other factors and significantly more corpses were found between the months of July-October.
Ultra-structure examinations revealed electron dense intra-nuclear inclusions in the cells of proximal convulated tubules of the kidney and X-ray analysis confirmed that these structures consisted of lead.     

The epidemiology of the highly pathogenic H5N1 avian influenza in Mute Swan (Cygnus olor) and other Anatidae in the Dombes region (France), 2006

In February 2006, a highly pathogenic avian influenza (HPAI) H5N1 virus was isolated from Common Pochards (Aythia ferina) in the Dombes region of France, an important migrating and wintering waterfowl area. Thereafter, HPAI H5N1 virus was isolated from 39 swab pools collected from dead waterfowl found in the Dombes, but only from three pooled samples collected outside of this area but located on the same migration flyway. A single turkey farm was infected in the Dombes. The epizootic lasted 2 mo and was restricted to the Dombes area. Virus-positive pools were detected in 20 of 1,200 ponds and infected Mute Swans (Cygnus olor) represented 82% of the virus-positive pools. Other infected species included Common Pochard (n=4), Grey Heron (Ardea cinerea, n=1), Eurasian Buzzard (Buteo buteo, n=1), and Greylag Goose (Anser anser, n=1). Despite intensive monitoring during and after the outbreak, HPAI H5N1 virus was not isolated from healthy wild birds. Our results are consistent with an HPAI H5N1-virus introduction into the Dombes via migrating ducks. These birds could have been pushed west by a severe cold spell in central Europe where the virus had already been detected. The Mute Swan served as an excellent epidemiologic sentinel during this outbreak; swans appear to be highly sensitive to infection with these viruses and swan mortality was easy to detect. During the outbreak, the mortality rates for wild birds remained moderate and the virus affected a limited number of species.     

The mitochondrial genome of Cygnus columbianus, the Whistling Swan.

The nucleotide sequence of the mitochondrial genome of the Whistling Swan, Cygnus columbianus, is reported. Many of the features common to avian mitochondrial genomes are present in C. columbianus and are described here. The gene order is the same as in Gallus gallus. The sequence of this mitochondrial genome allows relationships within the family Anatidae (swans, geese and ducks) to be reconsidered in the light of a large suite of mitochondrial characters. Protein-coding gene sequences of C. columbianus were concatenated to form a supergene, which was analyzed phylogenetically with similar constructs from previously published avian genomes. Relationships within Anatidae and between the Anatidae and the galliform birds were addressed. Three independent phylogenetic methods confirmed traditional classifications and the existence of the Galloanseres clade.     

Macrophages,a normal component in seasonally involuting testes of the swan,Cygnus olor

Summary In the swan, Cygnus olor, spermatogenesis shows a pronounced seasonal cycle. During the long involution phase a transient invasion of macrophages into the seminiferous tubules regularly takes place at the height of regression prior to total rest. These macrophages are involved in the additional disposal of supernumerary and degenerating premature germ cells, at a time when the Sertoli cells are already filled with phagolysosomes.     

Some sub-lethal effects of lead on mute swan Cygnus olor

Tissue and blood lead levels in mute swans Cygnus olor (Gmelin) were used to investigate sublethal effects of lead. Three categories of swan mortality were defined: (1) acute lead poisoning; (2) collisions; and (3) other reasons. In most tissues, lead concentrations were highest according to the cause of death in order: lead poisoning < collisions < other causes. Elevated blood levels and haematological disorders were detected in swans which had collided with objects. The possible role of elevated lead in causing collisions in mute swans is discussed.     

Seasonal changes in male and female bill knob size in the mute swan Cygnus olor

Sexual selection theory predicts that sexually selected ornaments are costly to maintain and, as condition-dependent signals, are likely to vary in attractiveness with season and age. Mute swans Cygnus olor possess a black, fleshy knob at the base of the bill, which is present in both sexes. Using measures calculated from digital photographs taken over two years we monitored changes in the size of the bill knob in individual swans throughout the breeding season. Our longitudinal data show that bill knob size is highly dynamic. Relative bill knob size was larger in males than females and was consistently greater for breeding males than for non-breeders. For males, relative bill knob size peaked during cygnet hatching, when male protection of the brood is most important, and was smallest during moult. In females, breeders had larger bill knobs than non-breeders at all times apart from immediately after egg-laying and incubation, when the reverse was true, presumably reflecting the costs of reproduction. Body mass was a highly significant predictor of relative bill knob size in both sexes, as was age, with an initial increase and then later a decline in relative ornament size across the lifetime of male birds. The bill knob ornament in mute swans thus appears to be a condition-dependent, highly malleable trait. It accurately reflects the differing pressures experienced by individual birds as they progress through the breeding season, suggesting selection by both intra- and inter-sexual forces.     

Male Incubation and its Effect on Reproductive Success in the Black Swan,Cygnus atratus

Male incubation is very unusual among Anatidae. In the black swan, males spend more time incubating the clutch than females do. We investigated the incubation patterns of males and females in a breeding colony in Vienna over a one-year period. Breeding occurred year round, with a peak in winter. Inattentive periods during incubation were shorter in winter than at other times of the year, probably because the heat loss of eggs is then higher. We tested the importance of the costs of incubation by prolonging the breeding period experimentally. Eggs were exchanged for dummies, which were readily accepted and incubated for up to 342 days. The higher the incubation effort of females, measured as the product of their proportion of incubation and the total length of the incubation phase, the longer was the interval between the end of incubation and laying of a subsequent clutch. This suggests that the incubation effort of females is limiting the reproductive output of a pair. By taking charge of the greater part of incubation, males may increase the productivity of their female partners and thereby their own reproductive success. This amplification of female fecundity is a factor favouring a high share in male incubation which is discussed in polyandrous species (e.g. Jenni 1974) but generally overlooked in monogamous systems. The ultimate cause for male incubation in black swans may lie in the combination of a monogamous mating system and the capability of this species to breed whenever the environmental conditions turn favourable, at any time of the year.     

Assessment of body condition in live birds; measurements of protein and fat reserves in the mute swan, Cygnus olor

Condition in animals is often measured in relation to various demands, such as reproduction, migration and cold weather. Usually, indices of protein and fat reserves have to be measured on dead animals. Measurements on live animals enable variations in the condition of individuals to be monitored over time, and can be related to their life histories.
In birds, the size of the breast muscle is the most commonly used measure of protein reserves. A technique for measuring breast muscle thickness was developed, using ultrasound, and was tested on mute swans. The measurements were accurate and highly repeatable. Breast muscle thickness was positively related to the lean dry weight of the breast muscle, and is likely to be a good indicator of total protein reserves.
A system of fat scoring by colour was developed to assess the size of the subcutaneous fat layer. Although the method relies on subjective judgements, the results were highly correlated with the percentage of fat in the subcutaneous layer, and with other measures of fat reserves.
Measurements were made on live, non-breeding swans to monitor seasonal variations in reserves. The seasonal pattern of fat reserves was similar to the normal cycle of weight changes; high in winter and low in summer. There was no change in relation to the moult. No distinct seasonal variation in muscle thickness was found.
There is an unusual pattern of change in the relative size of reserves during emaciation in swans. Muscle reserves appear to be depleted to a greater extent than fat reserves. This is possibly due to the effects of lead poisoning, causing protein necrosis and preventing muscle regeneration.     

Effects of seasonality,isolation and patch quality for habitat selection processes by mute swans Cygnus olor in a fishpond landscape

Foragers in patchy environments do not only select sites for single patch characteristics, but also have to consider the local environment of such patches. We studied habitat selection by mute swans Cygnus olor in a wide and heterogeneous fishpond region (the Dombes, eastern France). In this study, we considered fishpond isolation, resource quality within fishponds and breeding status of mute swans during both summer and winter. Mute swans did not select aquatic habitat randomly within the landscape. During summer, the population spread preferentially on medium to large fishponds, in subregions with numerous or closely related waterbodies, without generating a clumped distribution of birds. In addition to a positive effect of local fishpond number (2 km radius), breeding birds also responded positively to fishpond size. Non‐breeders selected fishponds mainly according to their size. Intraspecific territoriality did not appear to limit the presence of non‐breeders (i.e. moulting flocks), since both breeders and non‐breeders could coexist on the larger fishponds. During winter, mute swans used medium to large reflooded fishponds after summer drainage. The surrounding aquatic environment of fishponds played a minor role in determining flocking, compared to actual patch quality. Flocking occurred on large fishponds that had reflooded after having dried the summer before, whatever the agricultural cultivation practiced in the summer following drainage. The results suggest that geographical aspects should be taken into account when considering the potential impact of this expanding species within such ecosystems, and also in more general management policies dealing with aquatic habitats for waterbird populations.