Comparative study of the breeding success of Whooper Swans Cygnus cygnus nesting in upland and lowland regions of Iceland

The study assessed the reproductive success at different stages of the breeding season of Whooper Swans Cygnus cygnus from two geographically distinct areas of Iceland, one an upland and the other a lowland region. Censuses made at both sites indicated that the majority of the birds did not attempt to breed and that annual recruitment came from 30 to 40% of the population. Individual females tended to lay more eggs in the lowlands, with a mean clutch-size of 4.7 eggs, compared with 3.8 eggs per clutch in the highlands. A mean brood-size of 3.1 cygnets was obtained at both the highland and the lowland sites in August but the highland cygnets were significantly smaller and lighter. The difference in cygnet size could be attributable to one or a combination of factors including age differences and habitat variables. Lowland adults were significantly heavier than those from the highlands, which reinforced the view that habitat quality was superior at the lowland site. There was no difference in the feather length recorded for adult swans moulting in the two study areas, indicating that the moult occurred concurrently in the highlands and lowlands. The number of cygnets lost per brood between ringing and resighting in the wintering range was significantly higher for the highland swans, although the number of highland families relocated was small. The results indicate that birds from different breeding areas may contribute disproportionately to the percentage of juveniles reared annually in the population.     

Extra-pair paternity does not result in differential sexual selection in the mutually ornamented black swan (Cygnus atratus)

We studied patterns of parentage in 85 broods (332 cygnets) of black swans during three breeding seasons, using a set of eight polymorphic microsatellite markers. We detected both intraspecific brood parasitism (IBP; < 5% of cygnets per year) and extra-pair paternity (EPP). In these years, 10-17% (mean = 15.1%) of cygnets resulted from EPP, and 27-40% (mean 37.6%) of broods contained at least one extra-pair cygnet. Compared with levels of EPP in closely related species with similar life histories, these values are unexpectedly high. EPP in black swans appears unrelated to ecological factors (breeding density and synchrony) or genetic factors (genetic similarity between pair members or genetic quality of the offspring). We found no evidence that a mutual sexual feather ornament known to play a role in social mate choice in black swans (curled wing feathers) is involved in extra-pair mate choice. EPP does not lead to greater variance in reproductive success in males, relative to females in this species. We therefore suggest that EPP does not result in differential sexual selection on males and females, explaining why they are ornamented to the same degree.     

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.     

Blood lead levels in wintering and moulting Icelandic whooper swans over two decades

Lead poisoning of waterfowl through the ingestion of spent gunshot and discarded anglers' weights continues to be a problem worldwide. We took blood samples from 363 whooper swans Cygnus cygnus at wintering sites in Britain and Ireland and at moulting sites in Iceland during 2001–2005, and analysed them for total blood lead. Lead levels were generally low in swans in Iceland; 6% of samples exceeded 1.21  μ mol L⁻¹, the level indicative of elevated lead and above background levels. The proportion of swans with elevated lead was much higher in the wintering range, varying between 43 and 70% at three sites monitored over the winters 2003/2004–2005/2006, and with blood lead levels ranging up to 19.6  μ mol L⁻¹. The highest levels were in samples taken from swans in Scotland, with a mean value of 3.0  μ mol L⁻¹, but nevertheless they indicated a marked decrease compared with blood lead levels measured for whooper swans at the same site 20 years ago. There also appeared to be a significant long-term decrease in the proportion of swans with elevated blood lead in Iceland, from 60% of birds in 1984 to 8% in 2005, although this may be due to the birds being caught in different parts of Iceland. The most likely source of elevated lead in whooper swans is spent gunshot. Management measures to reduce the impact of lead in the environment on the birds are discussed.     

Costs and Benefits of Subadult Plumage in Mute Swans: Testing Hypotheses for the Evolution of Delayed Plumage Maturation

In some avian species, young birds capable of reproducing diminish their prospects of doing so by molting into a subadult plumage that accurately signals their subadult status. Several hypotheses have been proposed to explain the evolution of delayed plumage maturation, but testing them usually has involved interspecific comparisons that are hard to interpret. Mute swans (Cygnus olor) exhibit two phenotypes that differ in whether the birds have a gray subadult plumage (SAP phenotype) or molt immediately into an all white adult plumage (AP phenotype). The AP phenotype results from a recessive allele on the X chromosome; both phenotypes occur in the same population and even in the same brood. We compared costs and benefits of both phenotypes in mute swans on the Chesapeake Bay in 1972-1980 and on Long Island Sound in 1982-1989. Swans with the SAP phenotype had higher survival rates from hatching to fledging than AP swans. In the fall, when AP cygnets began to molt into their white plumage, their parents often attacked and drove them off while allowing SAP cygnets from the same brood to remain on their territories for several more months. SAP males had higher survival rates during their first 2 yr of life than AP males, but AP swans bred at a younger age than SAP swans. The only proposed hypothesis for the evolution of delayed plumage maturation that can explain its occurrence in mute swans is the status-signaling hypothesis. This hypothesis argues that males with subadult plumage honestly advertise their age and subordinate status while AP swans are cheaters and engaging in dishonest communication. SAP males acquire a longer period of parental care, suffer less aggression from older birds, and increase their survival but forgo the opportunity to breed at an early age. This is a unique example of how a single gene resulted in either honest or dishonest communication, changed a bird's relationship with its parents and potential mates, and altered the bird's chances to survive and to reproduce.     

Functional aspects of prolonged parental care in Bewick's swans

In Bewick's swans prolonged parental care is important in protecting offspring from feeding competition with other individuals in winter flocks. When separated from their parents, cygnets were less successful in aggressive encounters, were frequently displaced and spent less time feeding than when close to their parents. parents protected their offspring by intervening in encounters on their behalf. They were able to do so because of their high dominance rank within the flock. Differences in dominance rank among families were correlated with differences in dominance of cygnets both with and away from their parents, and preliminary evidence suggested that cygnets may assume their parents' dominance, the effect continuing into the second winter. Parental care involved measurable costs to both parents at the beginning of the winter.     

Lead poisoning in swans and sources of contamination in Ireland

A study of blood levels in mute swans Cygnus olor in Ireland has revealed that ingested lead pellets are responsible for acute lead poisoning. Forty-two percent of blood samples from 890 live birds at one site showed elevated lead levels. X-ray examination of live birds revealed the source of contamination to be ingested lead pellets. Urban birds were shown to have higher ( P 0001) lead levels than rural birds, the blood lead levels of which were presumed to reflect natural background levels. Urban grass was shown to have elevated lead but this did not cause lead poisoning in Canada geese Branta canadensis . Post-mortem examination has shown that 68% ( n = 101) of all mute swans examined from a number of sites died from lead poisoning. Two sources of poisoning were identified; spent gunshot from a claypigeon shooting site at Lough Neagh, Northern Ireland, and lost or discarded anglers' weights at Cork Lough and at a fishing pond in Belfast, N.I. The first known case of lead poisoning in whooper swans Cygnus cygnus in Ireland is recorded which resulted from the ingestion of gunshot used almost two decades earlier. Aspects of the pathology of lead poisoned swans is discussed.     

Molecular Detection of Hematozoa Infections in Tundra Swans Relative to Migration Patterns and Ecological Conditions at Breeding Grounds

Tundra swans (Cygnus columbianus) are broadly distributed in North America, use a wide variety of habitats, and exhibit diverse migration strategies. We investigated patterns of hematozoa infection in three populations of tundra swans that breed in Alaska using satellite tracking to infer host movement and molecular techniques to assess the prevalence and genetic diversity of parasites. We evaluated whether migratory patterns and environmental conditions at breeding areas explain the prevalence of blood parasites in migratory birds by contrasting the fit of competing models formulated in an occupancy modeling framework and calculating the detection probability of the top model using Akaike Information Criterion (AIC). We described genetic diversity of blood parasites in each population of swans by calculating the number of unique parasite haplotypes observed. Blood parasite infection was significantly different between populations of Alaska tundra swans, with the highest estimated prevalence occurring among birds occupying breeding areas with lower mean daily wind speeds and higher daily summer temperatures. Models including covariates of wind speed and temperature during summer months at breeding grounds better predicted hematozoa prevalence than those that included annual migration distance or duration. Genetic diversity of blood parasites in populations of tundra swans appeared to be relative to hematozoa prevalence. Our results suggest ecological conditions at breeding grounds may explain differences of hematozoa infection among populations of tundra swans that breed in Alaska.     

Managing the social environments of flamingos for reproductive success

Recent research has shown that large flamingo flocks are more likely to experience reproductive success than small flocks and that there is a positive relationship between behavioral stimulation from group displays and reproductive success. This study compares the group displays and reproductive success in a captive flock of Caribbean flamingos over 6 years at the National Zoological Park. Birds were added to the flock in two different years. In each case, the flock produced fertile eggs during the breeding season following the addition of new birds. Furthermore, the addition of new birds in 1988, and then again in 1991, significantly increased group display activity over the previous year when the flock size was lower. That the addition of birds stimulated group display activity suggests an alternative management strategy for promoting reproduction in captivity: separate birds in a flock and then reunite them prior to the breeding season. © 1994 Wiley-Liss, Inc.     

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.     

Patterns of Haemoproteus beckeri parasitism in the gray catbird (Dumatella carolinensis) during the breeding season

We determined the prevalence and intensity of blood parasites in breeding gray catbirds (Dumatella carolinensis) at Killbuck Wildlife Area in Wayne and Holmes Counties, Ohio (USA) from June through August 2000. Of 98 catbirds sampled, 40 (40.8%) had detectable infections of Haemoproteus beckeri. Overall prevalence of H. beckeri in this population is high relative to that reported in earlier blood parasite surveys of both breeding and migrant catbirds. Mean intensity of H. beckeri infection did not vary significantly between young and old birds or among sampling periods. We found no effect of age on prevalence or intensity of H. beckeri infection. Older birds were not more likely to be infected than younger birds, despite longer exposure to arthropod vectors. Prevalence varied significantly with season and was highest in June and lowest in August. This pattern also was observed in older birds sampled repeatedly. This seasonal variation may reflect both newly acquired infections and chronic infections relapsing in response to hormonal changes associated with breeding. Evidence of transmission was observed in the single hatching year bird that lacked detectable infection in early summer, but demonstrated a very high intensity infection in late summer. These observations provide supportive evidence that hematozoa infections are acquired on the breeding grounds during the first year of life and relapse during the breeding season in subsequent years.     

Gender effects on aggression, dominance rank, and affiliative behaviors in a flock of captive adult cockatiels (Nymphicus hollandicus)

Agonistic and affiliative behaviors and spatial positioning were studied in a small psittacine species, Nymphicus hollandicus. Subjects studied were flock-housed breeders including five hens and seven cocks. Fifteen-minute focal animal samples were collected for the entire flock in a randomly distributed order during mate selection and the onset of the breeding season. All agonistic behaviors were recorded, including the winner and loser of each interaction, along with allopreening and copulation behavior. Point samples were recorded every 60s to determine social spacing. Rates of aggression were significantly higher for male cockatiels than female cockatiels. Results based on dyadic agonistic interactions showed males to rank significantly higher in the social hierarchy than females. Associations within the flock were not random. Individual birds associated more with specific birds than would be predicted by chance. Analysis of spatial data revealed that there were both same-sex and opposite-sex preferred associations within the flock. Male cockatiels engaged in allopreening behavior with females significantly more than with other males. Observations of breeding and nesting behaviors revealed pairs, a triad, and extra-pair mating.     

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.     

Age-specific variation in reproduction is largely explained by the timing of territory establishment in the New Zealand stitchbird Notiomystis cincta

1. Using data from 327 nests over a consecutive 8-year period we examined age-specific variation in reproduction in a population of stitchbirds (or hihi) Notiomystis cincta and related how differences in reproductive performance were linked to the timing of territory establishment and breeding. 2. Across the population all reproductive parameters showed a quadratic relationship with an increase mainly between the first and second breeding season and a decline after the fourth year. A longitudinal analysis showed evidence of senescence by the sixth year in the numbers of chicks fledged and recruited. 3. Reproductive increases between years 1 and 2 were the result of poor-quality females dying after their first breeding season (differential selection hypothesis) in combination with surviving females showing improvements in reproduction in their second year (individual improvement/constraint hypothesis). 4. There was no effect of mate experience or territory quality on improvements in breeding between years. 5. The key variable influencing reproductive output was the timing of breeding. Birds that started laying earlier were more likely to lay multiple clutches in any given season. This was the main difference between first-year and older birds; generally first-year birds initiated egg laying later and consequently laid fewer clutches. 6. Approximately half of all first-year birds did not establish their territory until after the breeding season had begun. This delay in territory establishment resulted in these birds delaying breeding, which resulted in them having a lower reproductive output relative to all other birds. First-year birds that managed to establish their territory before breeding commenced, had similar rates of reproduction as older birds. 7. There was a positive relationship between the timing of territory establishment during a female's first year and her hatching date in the previous breeding season. We hypothesize that this was because late-hatched females were less able to effectively compete for territories against earlier-hatched members of their cohort, and this delayed their establishment and breeding in their first year. Thus, this social constraint is likely to be a major factor driving age-specific reproductive variation in this population.     

卧龙自然保护区血雉的社群组织

１９９４年１１月至１９９５年９月在四川卧龙自然保护区五一棚地区,采用无线电追踪技术并结合野外观察,对血雉的社群组织进行了研究。血雉冬季集群活动,相邻群体相遇,有驱逐行为发生。分群配对时,雌鸟长距离迁移。血雉为单配偶制,配偶关系联结紧密,可维持整个繁殖季节。孵卵由雌鸟承担,取食时由雄鸟相伴,雌雄鸟共同育雏。繁殖季节不参加繁殖的亚成体雄鸟、参加繁殖的成体雄鸟或配偶对往往也有集群活动的倾向。在繁殖季节,     

Temperature and egg-laying experience influence breeding performance of captive female houbara bustards

The influence of climate, age and egg-laying experience on reproductive performance (propensity, fecundity, timing) of a flock of captive houbara bustards was determined. The flock, established in Saudi Arabia for reintroduction purposes, was housed in outdoor pens, and fed food and water ad libitum. Birds were artificially inseminated when they came into breeding condition and eggs were removed soon after laying. Winter temperatures, rather than rainfall, synchronized reproduction in the captive flock. Cooler winter temperatures led to higher proportions of females laying, an earlier start to laying, and greater numbers of eggs laid per season. The first significant rainfall of the season stimulated some females to lay their last egg. Age per se had little effect on breeding performance independent of egg-laying experience. Females with no previous egg-laying experience laid fewer eggs than similarly aged females with previous experience. This difference, in combination with a pattern of increasing recruitment into the breeding population between 1 and 5 years of age, led to improved breeding performance in the population with age. The inferior performance of first-time egg-layers, despite ad libitum food, indicates restraint in the onset of breeding, which may be an adaptation for optimizing life-time fitness.     

Plasma levels of luteinizing hormone and steroid hormones in free-living winter groups of willow tits (Parus montanus)

Plasma levels of LH, DHT, testosterone, and corticosterone were measured for all members in free-living winter flocks of willow tits, Parus montanus. Hormonal data were related to (1) flock size and (2) age/sex differences. The winter flock defends a large winter territory and shows a well-established social hierarchy in which adults consistently dominate first-year birds. One winter group normally consists of four individuals, two adults and two juveniles. In flocks containing four or five members juvenile willow tits had significantly higher corticosterone values than adults. In small-sized groups, containing three members, all individuals had high plasma levels of corticosterone. No other effects of flock size was found. When data were treated on an age/sex basis, i.e., flock size was not considered, juvenile females were found to have significantly higher plasma levels of testosterone than adult birds, and also significantly higher levels of DHT than juvenile males and adult females. Also, juvenile willow tits had significantly higher plasma levels of corticosterone than adult birds.     

Corticosterone responses of grey-faced petrels (Pterodroma macroptera gouldi) are higher during incubation than during other breeding stages

We report the results of the first field study examining seasonal changes in corticosterone responses of typically long-lived birds of the order Procellariiformes. In particular, we examined whether grey-faced petrels Pterodroma macroptera gouldi showed changes in circulating baseline corticosterone concentrations and corticosterone responses to a standardized handling protocol across the breeding season. Such changes have been associated with changes in body condition and variations in energy demands on adult birds through the breeding season. During early incubation, males were in significantly better condition than females that had just completed laying, whereas during late incubation, males were in significantly poorer condition than females. In spite of these differences, there was no significant difference in baseline corticosterone concentrations between sexes or among birds at different reproductive stages. However, we detected significant differences in corticosterone responses associated with a standardized handling protocol at different stages through the breeding season. Responses were significantly greater during incubation compared with the prelay period and late chick rearing. Body condition was weakly and negatively correlated with maximum and total integrated corticosterone level, indicating that some of the individual variability in stress corticosterone responses could be explained by variation in body condition. However, the largest stress response occurred during late incubation and was independent of sex, although males were in relatively poor condition and females in relatively good condition. This period coincided with the breeding stage in which energy constraints on individual adults were higher than at other periods of the reproductive cycle and birds may be physiologically primed for extended fasts.     

Lead poisoning in whooper and tundra swans

Six weak whooper swans (Cygnus cygnus) and two weak tundra swans (Cygnus columbianus) were found at Swamp Miyajima (Hokkaido, Japan) in May 1998. Anorexia, depression, green watery feces, pale conjunctiva, and anemia were observed. Radiographs showed from six to 38 suspected lead pellets in the gizzard. Blood lead concentrations were 2.5-6.7 microg/g (mean+/-SD=4.6+/-1.14 microg/g) on day 1. After blood collection, the birds were treated with calcium disodium ethylenediaminetetraacetate (CaEDTA) given intravenously and force fed. Despite treatment, seven birds died the next day. Green, bile-stained livers and pale or green kidneys were observed on necropsy. Microscopically, bile pigment was widespread in the liver and acid-fast intranuclear inclusion bodies were observed in renal tubular epithelium. Lead concentrations in livers and kidneys were 14.0-30.4 microg/g and 30.2-122 microg/g wet weight, respectively. Only one bird survived and this whooper swan continued to be treated with CaEDTA and activated charcoal. No lead shot was observed in the proventriculus and gizzard by radiography on day 64 and the blood lead concentration decreased from 2.9 microg/g to 0.09 microg/g during that same period. After 4 mo of rehabilitation, the whooper swan was returned to the wild. Lead intoxication continues to be a problem at Swamp Miyajima.     

Effects of male courtship and gonadal steroids on pair formation, egg-laying, and serum LH in Canvasback ducks (Aythya valisineria)

The effects of social stimuli on the reproductive physiology of female birds have been widely studied. This study examined the endocrine and behavioural responses of female Canvasbacks ( Aythya valisineria ) to changes in the behavioural and endocrine states of the male, as signalled by his courtship displays. Male Canvasbacks exposed to female conspecifics exhibited a variety of courtship displays which increased significantly with testosterone administration. However, the testosterone-increased courtship displays of males did not increase female receptivity or serum LH, or stimulate reproductive development or egg-laying in unpaired females placed with them. Females confined in cubicles within a pen that held breeding pairs and a free-swimming flock had higher serum LH levels and laid more eggs than did females in cubicles in another pen without breeding pairs or a free-swimming flock. This suggests that social factors, such as vocalizations from a flock and breeding pairs, may increase serum LH and egg-laying in unpaired females. Oestradiol implants in female Canvasbacks did not elevate receptivity to courting drakes, nor did they stimulate pair formation, nesting activity, or egg-laying behaviour. Testosterone implants in drakes and oestradiol implants in females decreased serum LH in each group. These results show that increasing the amount of courtship is not adequate to stimulate pairing behaviour or increases in reproductive hormones. Thus, our results suggest that female receptivity to male courtship may be a key determinant of pair formation and consequent synchronization of the behaviour patterns between members of a pair of wild birds. Our results may further suggest a dissociation between effects of courtship and pair formation in wild Canvasbacks.