Mikael Kilpi

Habitat-specific clutch size and cost of incubation in common eiders, Somateria mollissima

Abstract Common eiders, Somateria mollissima, breed on two types of island in the Northern Baltic: open, sparsely vegetated islands and wooded islands with dense mixed forests. On open islands 79.8% of the nests were on open cliffs, exposed to wind and rain whereas on wooded islands 91.7% of the nests were sheltered inside dense spruce and pine thickets. We found that clutch size on open islands was significantly smaller than on wooded islands. Females started breeding simultaneously in the two habitats and they were similar in body size as measured by the length of the radio-ulna. During incubation females on open islands lost weight at a faster rate than females on wooded islands (34 g/day and 19 g/day, respectively). Heat loss is faster on open than wooded islands and therefore we suggest that the faster weight loss of females on open islands result from thermodynamically adverse incubation conditions. Because the eider is an extreme capital breeder, energy used for egg production cannot be used for incubation. To sustain a higher incubation cost on open islands, the optimal clutch size is therefore lower than on wooded islands.

Use of Serum Biochemistry to Evaluate Nutritional Status and Health of Incubating Common Eiders (Somateria mollissima) in Finland

During 1997–1999, we collected serum samples from 156 common eider (Somateria mollissima) females incubating eggs in the Finnish archipelago of the Baltic Sea. We used serum chemistry profiles to evaluate metabolic changes in eiders during incubation and to compare the health and nutritional status of birds nesting at a breeding area where the eider population has declined by over 50% during the past decade, with birds nesting at two areas with stable populations. Several changes in serum chemistries were observed during incubation, including (1) decreases in serum glucose, total protein, albumin, β‐globulin, and γ‐globulin concentrations and (2) increases in serum uric acid, creatine kinase, and β‐hydroxybutyrate concentrations. However, these changes were not consistent throughout the 3‐yr period, suggesting differences among years in the rate of carbohydrate, lipid, and protein utilization during incubation. The mean serum concentrations of free fatty acids, glycerol, and albumin were lowest and the serum α‐ and γ‐globulin levels were highest in the area where the eider population has declined, suggesting a role for nutrition and diseases in the population dynamics of Baltic eiders.

Social and maternal factors affecting duckling survival in eiders Somateria mollissima

1. With the aid of a novel survivorship model, an 8-year field study of social and maternal factors affecting duckling survival in eiders (Somateria mollissima) revealed that duckling survival probability varies in accordance with maternal brood-rearing strategy. This variability in survival provides compelling evidence of different annual fitness consequences between females that share brood-rearing and those that tend their broods alone. Consequently, as prebreeding survival is often a major source of individual variation in lifetime reproductive success, a females annual, state-dependent (e.g. condition) choice of a brood-rearing strategy can be a critical fitness decision. 2. Variance in duckling survival among lone tender broods was best explained by a model with significant interannual variability in survival, and survivorship tending to increase with increasing clutch size at hatch. Clutch size was correlated positively with female condition. Hatch date and female body condition together affected duckling survival, but their contributions are confounded. We were unable to identify a relationship between female age or experience and duckling survival. 3. Variance in duckling survival among multifemale brood-rearing coalitions was best explained by a model that included the number of tenders, the number of ducklings and interannual variation in how their ratio affected survivorship. Hatch date did not significantly influence survival. 4. Expected duckling survival is higher in early life for lone tenders when compared with multifemale brood-rearing coalitions. However, as ducklings approach 2-3 weeks of age, two or three females was the optimal number of tenders to maximize daily duckling survival. The survivorship advantage of multifemale brood-rearing coalitions was most evident in years of average survival. 5. The observed frequency distribution of female group sizes corresponds with the distribution of offspring survival probabilities for these groups. Evidence for optimal group sizes in nature is rare, but the most likely candidates may be groups of unrelated animals where entry is controlled by the group members, such as for female eiders. 6. Our study demonstrates that differences in social factors can lead to different predictions of lifetime reproductive success in species with shared parental care of self-feeding young.

Female characteristics and parental care mode in the creching system of eiders, Somateria mollissima

Eider females may abandon their young, care alone, or join in multifemale creches. We studied the characteristics of female eiders adopting these strategies in 1996-1999. Female condition at hatching varied significantly between years. Over all years, 31% of all females abandoned, 23% tended alone and 46% creched. In the year when average female condition at hatching was lowest, abandonment rate peaked (67%). Creching birds were further identified as true crechers staying more than 2 weeks with the original creche, and transient crechers leaving the creche. The condition of females shortly before hatching showed a decreasing trend, with lone tenders being in best condition, followed by true crechers, transient crechers and abandoners. Clutch size, date of hatching relative to the population median, and female body size did not differ between groups. Individual females switched between care modes between years. Females weighed significantly less when abandoning than when tending, with no significant weight difference when the females remained as tenders between 2 years. This is consistent with the energetic salvage strategy hypothesis, which states that females in poor body condition should be more prone to abandon their brood. Our results support an adaptive approach to offspring care behaviour in eiders, driven by female condition.  2001 The Association for the Study of Animal Behaviour

Isolation and Characterization of a Reovirus from Common Eiders (Somateria mollissima) from Finland

SUMMARY. Samples of brain, intestine, liver, lung, spleen, and bursa of Fabricius were collected from five common eider (Somateria mollissima) duckling carcasses during a die-off in the western Gulf of Finland (59°50′N, 23°15′E) in June 1996. No viral activity was observed in specific-pathogen-free chicken embryos inoculated with tissue suspensions, but samples of bursa of Fabricius from three birds were positive when inoculated into Muscovy duck (Cairina moschata) embryo fibroblasts. The isolates were characterized as nonenveloped RNA viruses and possessed several characteristics of the genus Orthoreovirus. Virus particles were icosahedral with a mean diameter of 72 nm and were stable at pH 3.0; their genome was separated into 10 segments by polyacrylamide gel electrophoresis. Mallard (Anas platyrhynchos) ducklings experimentally infected with the eider reovirus showed elevated serum activities of aspartate aminotransferase, creatine kinase, and lactate dehydrogenase enzymes and focal hemorrhages in the liver, spleen, and bursa of Fabricius. During 1997–99, the prevalence of neutralizing antibodies to the isolated virus ranged from 0 to 86% in 302 serum samples collected from incubating eider hens at three nesting areas along coastal Finland. The highest seroprevalence was found in Hanko in 1999, just weeks before reports of an uninvestigated mortality event resulting in the death of an estimated 98% of ducklings at that location. These findings raise the question of potential involvement of the virus in poor duckling survival and eider population declines observed in several breeding areas along coastal Finland since the mid-1980s.

Causes and consequences of fine-scale breeding dispersal in a female-philopatric species

The potentially confounded effects of factors affecting breeding dispersal have rarely been simultaneously examined. The consequences of breeding dispersal are even less studied, presenting a paradox: breeding dispersal seldom seems to improve breeding success, despite its presumed adaptiveness. We studied the causes and consequences of breeding dispersal in female-philopatric eiders (Somateria mollissima) in relation to the spatiotemporal predictability of nest success. Previous nest fate, breeding experience, and breeding density simultaneously affected breeding dispersal. Dispersal distances were longer among inexperienced breeders and after failed breeding. Individual dispersal distances decreased with increasing nest-site-specific breeding density, whereas island-specific nesting success peaked at intermediate densities. The fate of neighbouring nests (‘public information’) did not influence dispersal. Breeding dispersal was unrelated to subsequent hatching success, controlling for individual quality (body condition, breeding experience, previous nest fate), while it delayed hatch date, which is likely to impair reproductive success. This delay may result from the loss of acquired information of local breeding conditions, prolonging nest prospecting and establishment, also helping explain why breeding dispersal did not increase at high breeding densities, despite a potential reduction in nesting success. In long-lived species, however, dispersal-induced reductions in reproductive output in one season could be offset by improved parental survival prospects. Careful nest prospecting may be profitable, because overall nest success had a strong island-specific component but showed weak temporal variation, and successive individual nest fates were predictable between years. Once a safe nest site is found, females may breed at the same place successfully for many years.

Analysis of nodularin-R in eider (Somateria mollissima), roach (Rutilus rutilus L.), and flounder (Platichthys flesus L.) liver and muscle samples from the western Gulf of Finland, northern Baltic Sea

Nodularin (NODLN) is a cyanobacterial hepatotoxin that may cause toxic effects at very low exposure levels. The NODLN-producing cyanobacterium Nodularia spumigena forms massive blooms in the northern Baltic Sea, especially during the summer. We analyzed liver and muscle (edible meat) samples from common eider (Somateria mollissima), roach (Rutilus rutilus L.), and flounder (Platichthys flesus L.) for NODLN-R by liquid chromatography/mass spectrometry (LC-MS) and enzyme-linked immunosorbent assay (ELISA). Thirty eiders, 11 roach, and 15 flounders were caught from the western Gulf of Finland between September 2002 and October 2004. Eiders from April to June 2003 were found dead. The majority of samples were analyzed by LC-MS and ELISA from the same sample extracts (water:methanol:n-butanol, 75:20:5, v:v:v). Nodularin was detected in 27 eiders, nine roach, and eight flounders. Eider liver samples contained NODLN up to approximately 200 microg/kg dry weight and muscle samples at approximately 20 microg/kg dry weight, roach liver samples 20 to 900 microg NODLN/kg dry weight and muscle samples 2 to 200 microg NODLN/kg dry weight, and flounder liver samples approximately 5 to 1,100 microg NODLN/kg dry weight and muscle samples up to 100 microg NODLN/kg dry weight. The NODLN concentrations found in individual muscle samples of flounders, eiders, and roach (1-200 microg NODLN/kg dry wt) indicate that screening and risk assessment of NODLN in Baltic Sea edible fish and wildlife are required for the protection of consumers health.

Large-scale change in the sex ratio of a declining eider Somateria mollissima population

Abstract The breeding potential of a monogamous animal population should be maximal during equal operational sex ratio, and empirical evidence suggests that the population-wide sex ratio may be linked to population density. We studied the sex ratio of eiders Somateria mollissima migrating into the Gulf of Finland, the Baltic Sea, in nine years during 1979–2005 (1979–1980, 1982–1983 and 2001–2005), and the sex ratio of birds collected by Danish hunters during 1982–2004. In two decades, the sex ratio during peak migration has reversed from female bias to male bias, and hunting statistics have shown a significantly increasing adult male bias. Also the proportion of juvenile males has shown a significant increase (Danish hunting statistics 1982–2004), which indicates either that the primary sex ratio of ducklings is exceedingly male biased, or that the mortality of female ducklings has increased. This shift in sex ratio is paralleled by a dramatic decrease in the Baltic eider population which started in the early 1990s. The proportion of juveniles in the hunting bag, an indicator of breeding success in the Baltic, significantly decreased during our study period. The sex ratio of migrating eiders showed seasonal fluctuations, the pattern of which has changed during the study period. Particularly the proportion of late-migrating females has decreased dramatically since the early 1980s, suggesting a declining influx of subadult females. Both the increased male bias and the decreased breeding success are likely to be linked with the population decline. A primary contributor to the shift in sex ratio and the declining trend in breeding success and population size is possibly differential mortality of the sexes during breeding, as the mortality of breeding females has increased sharply in the western Gulf of Finland, mainly due to predation by white-tailed sea eagles Haliaeetus albicilla and American minks Mustela vison, the former of which has recently increased in numbers. It is unlikely that differential winter mortality of the sexes can explain our results, as the wintering area of eiders from the Gulf of Finland has remained the same, and the Danish hunting bag reflects the existing sex ratio. Our study highlights the need for future empirical and theoretical work on the relationship between population sex ratio and population density.

Eider females form non‐kin brood‐rearing coalitions

Kin selection is a powerful tool for understanding cooperation among individuals, yet its role as the sole explanation of cooperative societies has recently been challenged on empirical grounds. These studies suggest that direct benefits of cooperation are often overlooked, and that partner choice may be a widespread mechanism of cooperation. Female eider ducks (Somateria mollissima) may rear broods alone, or they may pool their broods and share brood‐rearing. Females are philopatric, and it has been suggested that colonies may largely consist of related females, which could promote interactions among relatives. Alternatively, shared brood care could be random with respect to relatedness, either because brood amalgamations are accidental and nonadaptive, or through group augmentation, assuming that the fitness of all group members increases with group size. We tested these alternatives by measuring the relatedness of co‐tending eider females in enduring coalitions with microsatellite markers. Females formed enduring brood‐rearing coalitions with each other at random with respect to relatedness. However, based on previous data, partner choice is nonrandom and dependent on female body condition. We discuss potential mechanisms underlying eider communal brood‐rearing decisions, which may be driven by the specific ecological conditions under which sociality has evolved in this species.

Shared care provides time-budgeting advantages for female eiders

Abstract Shared parental care resulting from brood amalgamation is often considered beneficial to parents. However, the benefit of grouping (a decline in individual vigilance despite an increase in collective vigilance, with a concomitant increase in individual feeding time) has not been evoked as a factor promoting shared care. Eider females, Somateria mollissima , are subject to substantial energetic costs during breeding, and sometimes share brood-rearing duties. We compared the activity budgets and feeding behaviour of lone tenders and multifemale tenders. We also measured the collective vigilance of multifemale tenders and examined whether the coordination of feeding activity among females changes with time. As expected, the proportion of time spent feeding increased, and the proportion of time spent vigilant decreased, as the number of females attending the brood increased. None the less, the collective vigilance of multifemale tenders was at least 20% higher than the vigilance of lone tenders. Furthermore, multifemale tending allowed females to feed more optimally, as dive duration increased with the number of females tending the brood. The level of parental investment by individual females after hatching of the eggs is therefore related to the number of tending females and, based on previous work, a females body condition when the eggs hatch is also logically connected with the number of tending females. Whether females sharing brood care on a permanent basis coordinate their feeding activity, so as to increase the potential protection of ducklings against predation, remains equivocal. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .