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.     

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.     

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 underlying age‐related avian malaria infection in a long‐lived host: the mute swan Cygnus olor

Quantifying the factors that predict parasite outbreak and persistence is a major challenge for both applied and fundamental biology. Key to understanding parasite prevalence and disease outbreaks is determining at what age individuals show signs of infection, and whether or not they recover. Age‐dependent patterns of the infection of a host population by parasites can indicate among‐individual heterogeneities in their susceptibility to, or rate of recovery from, parasite infections. Here, we present a cross‐sectional study of avian malaria in a long‐lived bird species, the mute swan Cygnus olor, examining age‐related patterns of parasite prevalence and modelling patterns of infection and recovery. One‐hundred and fifteen swans, ranging from one to nineteen years old, were screened for infection with Plasmodium, Haemoproteus and Leucocytozoon parasites. Infections with three cytochrome‐b lineages of Haemoproteus were found (pooled prevalence 67%), namely WW1 (26%), which is common in passerine birds, and two new lineages closely related to WW1: MUTSW1 (25%) and MUTSW2 (16%). We found evidence for age‐related infection in one lineage, MUTSW1. Catalytic models examining patterns of infection and recovery in the population suggested that infections in this population were not life‐long – recovery of individuals was included in the best fitting models. These findings support the results of recent studies that suggest hosts can clear infections, although patterns of infection‐related mortality in older birds remain to be studied in more detail.     

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.     

Density-dependent decline of breeding success in an introduced, increasing mute swan Cygus olor population

An increasing population of the mute swan Cygnus olor , was studied from its very establishment in 1976 until 1998. As the number of pairs increased, there was a decline in all production parameters, including the average number of clutches per pair, the average number of broods per clutch, and the average number of fledged young per brood. In a multiple regression analysis covering the whole breeding season, the number of pairs and the average number of clutches per pair explained 71% of the variation in the average number of fledglings per pair. During the brood season, the average number of fledglings per brood was an additionally important parameter in explaining fledgling production. Habitat quality seemed to affect breeding: in places occupied earlier more cygnets fledged from a clutch than in habitats inhabited later. The decreased production of young very likely reflects density-dependent effects on reproduction. This density dependence seems to operate on the breeding grounds, since winter harshness did not affect breeding success. Density-dependent processes started acting already when pairs were beginning to nest, and continued during the brood period. Density dependence has apparently not been detected at the pair stage in earlier studies of bird populations.     

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.     

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.     

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.     

Evolutionary response to selection on clutch size in a long-term study of the mute swan

Life-history traits in wild populations are often regarded as being subject to directional selection, and the existence of substantial variation and microevolutionary stasis of these characters is therefore a problem in need of explanation. Avian clutch size is an archetypal life-history trait in this context, and many studies have sought to test explanations for stasis in clutch size. Surprisingly, there are many fewer studies that used long-term data to ask how selection acts on clutch size, particularly in a multivariate framework. In this article, we report selection, inheritance, and evolution of clutch size over 25 years in a colony of mute swans using a multivariate quantitative genetic framework to control for correlations with breeding time. We show that clutch size is influenced by both additive genetic and permanent environmental effects and that selection acts on clutch size in combination with breeding time. Natural selection on clutch size is strongly directional, favoring larger clutches, and we observe an increase in clutch size of 0.35 standard deviations, consistent with the expected response based on selection and inheritance of clutch size. We hypothesize that these changes result from recent relaxation of food constraints and predation risks experienced by this colony.     

Intracellular localization of lead in tissues of the mute swan

The aim of this study was to examine the ultrastructure of kidney, liver, blood and intestine of a lead-poisoned bird and compare these with tissues of a healthy bird. From these results it was hoped to reveal that any abnormalities observed were due to lead poisoning and consequently suitable sections were also selected for X-ray analysis. Renal intranuclear inclusions were present in the lead-poisoned swan. X-ray analysis clearly demonstrated that these granules consist of an amorphous mass of lead probably as lead phosphate. Large numbers of electron dense granules were observed in the liver of the lead-poisoned bird and occasionally in the healthy swans liver. X-ray analysis demonstrated that these granules contain iron. Some of the red blood cells of the lead-poisoned swan have opaque granules associated with the plasma membrane, these were not observed in the healthy swan.     

Age-dependent genetic variance in a life-history trait in the mute swan

Genetic variance in characters under natural selection in natural populations determines the way those populations respond to that selection. Whether populations show temporal and/or spatial constancy in patterns of genetic variance and covariance is regularly considered, as this will determine whether selection responses are constant over space and time. Much less often considered is whether characters show differing amounts of genetic variance over the life-history of individuals. Such age-specific variation, if present, has important potential consequences for the force of natural selection and for understanding the causes of variation in quantitative characters. Using data from a long-term study of the mute swan Cygnus olor, we report the partitioning of phenotypic variance in timing of breeding (subject to strong natural selection) into component parts over 12 different age classes. We show that the additive genetic variance and heritability of this trait are strongly age-dependent, with higher additive genetic variance present in young and, particularly, old birds, but little evidence of any genetic variance for birds of intermediate ages. These results demonstrate that age can have a very important influence on the components of variation of characters in natural populations, and consequently that separate age classes cannot be assumed to be equivalent, either with respect to their evolutionary potential or response.     

Coexistence and population genetic structure of the whooper swan <Emphasis Type="Italic">Cygnus cygnus</Emphasis> and mute swan <Emphasis Type="Italic">Cygnus olor</Emphasis> in Lithuania and Latvia

Two closely related swan species, the mute swan Cygnus olor and the whooper swan Cygnus cygnus, were formerly allopatric throughout their breeding ranges, but during the last decades a sympatric distribution has become characteristic of these species in the Baltic Sea region. The whooper swan has gradually replaced the mute swan in many suitable habitats in Lithuania and Latvia. Marked differences in the genetic population structure of both species may partially explain the dominance of the whooper swan, as genetic population divergence can be a major factor affecting inter-specific competition. A homogenous genetic population structure was defined for mute swans breeding in Lithuania, Latvia, Poland and Belarus. Breeding mute swans in this region are mostly of naturalised origin. A diverse population genetic structure characterizes whooper swans breeding in Lithuania and Latvia.     

Seasonal changes in female size and its relation to reproduction in the parasitoid Asobara tabida

The relation between female size and fitness was studied in female Asobara tabida throughout the field season. The size of A. tabida females varied considerably, with average size being smallest in the middle of the season. There was a positive correlation of realized fecundity with size, and the fitness advantage of larger females increased later in the season. A possible explanation for this can be found in the energy expenditure during the season. Regression analysis showed that fat use increases with size of the female, but also with temperature. Temperature was low early and late in the season, but high in the middle. We argue that the high temperatures may constrain fitness advantages of large females because of their increased metabolic needs. Variation in the form of the fitness function within the season may moderate directional selection for larger females.     

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.     

Prefledging survival of Mute Swan Cygnus olor cygnets in the Lothians,UK

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% fledged. 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.     

Observations on a hybrid between the whooper swan (<Emphasis Type="Italic">Cygnus cygnus</Emphasis>) and the mute swan (<Emphasis Type="Italic">Cygnus olor</Emphasis>)

The swan obtained by hybridization between Cygnus cygnus and C.olor was delivered to the Moscow Zoo from the Leningrad Zoo in 1989. Between 2002 and 2004, it permanently remained with a female whooper swan in a large pond. The two swans behaved as a breeding pair, although the sex of the hybrid bird remained unknown. We observed no courtship displays addressed by the hybrid swan either to the female whooper swan or to other swans living in the pond. The hybrid swan was exteriorly closer to C. cygnus rather than to C. olor and showed increased aggressiveness. Its threatening behavior was intermediate between parental species in terms of threat displays and motor activity, although behavioral patterns characteristic of C.olor prevailed. The most frequent sounds in the vocal repertoire of the hybrid swan were close to the vibrant throbbing call of C.olor in terms of duration and frequency range. In contrast to these sounds, the call of the hybrid swan was noiselike, with distinct harmonic structure (as in the whooper swan except for extremely narrow interharmonic intervals). These vocal signals of the hybrid swan were shown to be intermediate between those of the parental species. In addition, the acoustic repertoire of the hybrid swan included rarely emitted sounds closely resembling elements of vocalizations of both C. cygnus and C. olor.