Predatory bird health - white-tailed sea eagle

 

	Authors: Björn Helander & Anders Bignert, Department of Contaminant Research, Swedish Museum of Natural History, Stockholm, Sweden Christof Herrmann, Agency for Environment, Nature Conservation & Geology of Mecklenburg-Western Pomerania, Germany Torsten Stjernberg, Zoological Museum, Finnish Museum of Natural History, Helsinki, Finland

 

Key message

Strong relationships have been found between white-tailed sea eagle reproductive ability and concentrations of DDTs and PCBs in their eggs (Helander et al. 2003a). Reproduction in the Baltic eagle population in the 1970s was reduced by 80%, to one-fifth of the pre-1950 background level. Following bans of DDT and PCB in the Baltic region during the 1970s, eagle productivity began to recover in the 1980s, and since the mid-1990s is largely back to pre-1950 levels (Hauff & Wölfell 2002,, Helander 2003a, Stjernberg et al 2003). The population on the Swedish Baltic coast has increased by an average of 7.5% per year between 1990 - 2010 (Herrmann et al. 2011). On the Swedish coast of the Bothnian Sea, nestling brood size remains below the pre-1950 level and the occurrence of dead eggs is significantly higher than in the Baltic Proper and Bothnian Bay, indicating a possible impact from other contaminants (Helander et al 2008).

This fact sheet includes data from two coastal populations in Sweden, two coastal populations in Finland and from a sample of coastal and inland populations in Germany (Federal States of Mecklenburg and Western Pomerania).

Results and assessments

Relevance of the indicator for describing developments in the environment

The white-tailed sea eagle was the first species that indicated there were deleterious effects from environmental pollutants in the Baltic Sea. If white-tailed sea eagle reproduction had been monitored in the Baltic Sea earlier during the 20th century, the negative impact of DDT may have been noticed as early as the 1950s. The sea eagle is the ultimate top predator of the Baltic ecosystem, feeding on fish, sea birds, and seals, and is thus strongly exposed to persistent chemicals that magnify in the food web.

Currently, eagles are breeding along the coasts of the whole of the Baltic Sea, as well as in inland freshwater systems, and are monitored in a network of national projects that use the same methodology. Monitoring of sea eagle reproduction in Sweden has been included in the National Environment Monitoring Programme since 1989, as an indicator of effects from chemical pollutants. Pre-1954 background data on breeding success and pre-1950 background data on nestling brood size are available from the Swedish Baltic coastline (Helander 1994a, 2003a). This data is used as reference levels for evaluation of observations within the programme

 

 

Figure 1. Mean brood size (number of nestlings per successfully breeding pair) of white-tailed sea eagle on the Swedish Baltic coast since 1858. Sample size for each time period is given in brackets. A reference level (solid black line) with 95% confidence limits (shaded grey) is based on data between 1858-1950 (blue bars) according to (Helander 2003a ).

 

Policy relevance and policy references

An improvement in Baltic white-tailed sea eagle reproduction occurred about 10 years after most countries around the Baltic had implemented bans of DDT and PCB. This serves as a clear reminder of the long-term effects of persistent pollutants. The subsequent recovery, from an 80% reduction in reproductive ability in the 1970s, is nevertheless important evidence of successful results from wise political decisions.

The maintenance of viable populations of species is one important objective of the HELCOM Baltic Sea Action Plan. The EU Birds Directive (Directive 2009/147/EC of the European Parliament and of the Council of 30 November 2009 on the conservation of wild birds; this is the codified version of Directive 79/409/EEC) lists the white-tailed sea eagle in Annex I, binding member states to establish protected areas for the species in order to secure reproduction and survival of the species. White-tailed sea eagles are listed in the following international conventions:

Bern Convention Annex II (strictly protected species);

Bonn Convention Annex I and II (conservation of migratory species);

Washington Convention (CITES) Annex I (regulating trade).

The maintenance of healthy populations of white-tailed sea eagles is in accordance with the following four Environmental Quality Objectives defined for Sweden:

• a non-toxic environment;

• a balanced marine environment,

• flourishing coastal areas and archipelagos;

• a rich diversity of plant and animal life.

Monitoring of sea eagle population health as an environmental indicator, as well as monitoring of contaminants in eagles and their prey, is recommended in an international Species Action Plan, adopted under the Bern Convention in 2002 (Helander & Stjernberg 2003).

Conservation targets

The reproduction of white-tailed sea eagles should not be affected by chemical contaminants. Breeding success should be >60%, and the productivity >1.0 nestling/checked territorial pair (both values measured as an average for the last 5 years). These thresholds are based at the lower end of the 95% confidence limits for estimated background brood size and breeding success on the Swedish Baltic coast (Helander 2003a) and thus refer to coastal populations. (NB: it has not yet been validated whether these threshold values are fully relevant for all coastal regions of the Baltic Sea. Future regional specification may be necessary).

 

Assessment

Measurements and biological samples

Trees containing nests are climbed for assessment of reproductive parameters (see the following paragraphs). In connection with these nest visits, measurements and biological samples are taken. Nestlings are measured: wing chord (for estimation of age in days), tarsus width and depth (for estimation of sex, see Helander 1981, Helander et al.2007), and are weighed (for nutritional status), and sampled (feather and blood, for chemical analyses and genetic studies), and ringed (using an international colour ringing programme for identification, according to Helander (2003b). Dead eggs and shell pieces are collected for measurements, investigation of contents and chemical analyses, for studies on relationships with reproduction (cf. fig. 6). Feathers shed from adults are collected at all sites. All samples are archived in the Swedish National Specimen Data Bank.

White-tailed sea eagle population health status is assessed by monitoring the following indicators:

¤ Reproduction

¤ Contaminant burdens

¤ Nutritional condition of nestlings

¤ Cause of death of deceased individuals

 

Reproduction

White-tailed sea eagle reproductive ability is monitored annually by assessing the frequency distribution of occupied eagle nests containing [0], [1], [2] and [3] nestlings (3 being the maximum observedin this species). Survey techniques and sampling methods are presented in (Helander 1985, 2003a, Helander et al. 2008). Three indicators of reproductive ability are calculated from these data:

Breeding success – the proportion of nests containing at least one nestling of at least three weeks of age, out of all occupied nests ([n1] + [n2] + [n3] / [n0] + [n1] + [n2] + [n3]).

Trends in breeding success of sea eagles on the northern, central and southern Baltic coast over time are presented in fig. 2. As breeding success of sea eagles on the northern, central and southern Baltic coast improved over time, populations around the Baltic Sea grew over the study period (Herrmann et al. 2011). The number of annually checked pairs in Sweden increased: in the Baltic Proper, from between 20 – 30 pairs prior to 1975 to  217 pairs in 2010, and in the Gulf of Bothnia from approximately 10 pairs prior to 1975 (all in the Bothnian Sea) to 109 pairs in 2010 (including a re-occupation of the Bothnian Bay). Similarly, the total number of annually checked pairs in Finland grew from about 10 - 20 pairs in the early 1970s, to 300 pairs in 2010. In the sample from Mecklenburg-Western Pomerania, Germany, numbers of checked pairs increased from around 75 to 230 between 1973 - 2010.

Retrospective studies have shown that breeding success along the whole Swedish Baltic coast decreased from an average of 72% up to the early 1950s, down to 47% between 1954 – 1963, and 22% between 1964 - 1982 (Helander 1985). Breeding success increased significantly in the Baltic Proper as well as in the Gulf of Bothnia from the early 1980s (fig. 2). By the mid to late 1990s, breeding success in both areas was no longer significantly different from background levels. The development in the southern Baltic (Germany) is similar to that in the central Baltic (Sweden, Baltic Proper, fig. 2). Impacts of intraspecific competition in areas with a high density of breeding pairs in Mecklenburg-Western Pomerania have been discussed as a possible reason for lower breeding success (Hauff 2009). In densely populated areas in Sweden and Finland, fatal territorial fights have been recorded more frequently in recent years. It may be that intraspecific competition in densely populated areas could explain why breeding success appears to have stabilized at levels slightly below the mean value for the estimated reference level in fig 2. The reference level was based on data from a more sparse population during the first half of the 20^th century.

Nestling brood size – the mean number of nestlings of at least three weeks of age in nests containing young ([n1] + [n2x2] + [n3x3] / ([n1] + [n2] + [n3].

Based on data from nests inspected by climbing the nest tree, and excluding nests checked only from the ground, nestling brood size is a precise standard. Nestling brood size began to increase from the 1980s, at roughly the same time as the increase in breeding success was observed (fig. 3). This synchronous development is inherent with an improvement in egg hatching success, affecting both of these indicators in parallel. In the Baltic Proper (Sweden and Germany), brood size had reached pre-1950 reference levels in the late 1990s. However, in the Gulf of Bothnia, brood size remains below this reference level regionally. Mainly in the southern part of the Bothnian Sea coast of Sweden, and in the Åland archipelago, Finland (fig. 4).

Productivity - the mean number of nestlings of at least three weeks of age, out of all occupied nests ([n1] + [n2x2] + [n3x3] / [n0] + [n1] + [n2] + [n3]).

This indicator combines the breeding success and nestling brood size into one indicator, and assesses the reproductive output of the population. It is a most useful indicator in studies on relationships between reproduction and contaminants (fig. 6). It is also a vital parameter in assessments of population status from a management perspective.

The time trends in productivity naturally follow those of breeding success and brood size. From being as low as 0.2 in the 1970s, productivity increased significantly and reached the 95% confidence interval for the estimated background (reference) level in all sub-populations in the 1990s (fig. 5).

Contaminant burdens

Tissue and egg samples of white-tailed sea eagles have contained among the highest residue concentrations of persistent organochlorine contaminants and heavy metals in the Baltic and the world (Henriksson et al. 1966, Jensen 1966, Jensen et al. 1972, Koivusaari et al. 1980, Helander 1994b, Helander et al. 1982, 2002, Olsson et al. 2000, Nordlöf et al. 2010). Predatory birds are highly exposed to persistent chemicals and are useful in detecting the presence of “new” pollutants that are potentially harmful, as illustrated by the discovery of PCBs in 1966 in a Baltic white-tailed sea eagle (Jensen 1966), and the discovery of the flame retardant congener PBD-209 in peregrine falcon eggs in 2004 (Lindberg et al. 2006).

Chemical analyses of samples of the contents from collected dead eggs provide possibilities to study relationships between the concentrations of contaminants and reproduction. In free-ranging birds, this is usually done on a population level, but more detailed studies can also be made when individual breeding pairs are followed over time periods. In addition to being highly exposed to persistent chemicals, the white-tailed sea eagle has other features that are favourable from a monitoring perspective. Territorial adults on the Baltic Sea coast are mainly sedentary and thus reflect the regional contaminant situation. Mating pairs generally pair for life, and remain at the same breeding site, with sites commonly used over many generations of eagles, providing good opportunities for long-term studies. A large portion of breeders in the Baltic region are currently ringed, improving possibilities for study of individual birds over time.

Studies of sea eagles in the Baltic Sea have revealed strong correlations between residue concentrations of DDTs and PCBs and reproduction (Koivusaari et al. 1980, Helander 1994b, Helander et al. 1982, 2002, 2008). Studies of individual eagles over time showed that females that were exposed to high concentrations of contaminants during the 1960s and 1970s remained unproductive after residue concentrations in their eggs had declined, indicating persistent affects from previous exposure (Helander et al. 2002). Trends in productivity and residue concentrations of DDE and PCBs show that residue concentrations of DDE have now declined below an estimated critical threshold level for affecting reproduction (fig. 5). Residue concentrations of brominated flame retardants have been investigated in eagle egg samples from four regions in Sweden – the Baltic Proper, Bothnian Sea, and inland freshwaters in southern Sweden and northern Sweden Lapland (Nordlöf et al. 2010). No significant difference was found between the samples from the Baltic coast. Concentrations in the Baltic samples were three and six times higher than from inland samples from southern Sweden and Lapland, respectively. Investigations on other contaminants are in progress, to search for an explanation for the smaller brood size in the Bothnian Sea.

Nutritional condition of nestlings

Body mass can be indicative of food stress and health, and such information is usually easily obtained when handling nestlings. An age-dependant increment in body mass naturally takes place in growing nestlings, and comparison of weights between nestlings must therefore be based on specimens of the same age. Wing length is strongly correlated to age in sea eagle nestlings (Helander 1981) and can be used as a proxy for age. A sub-sample (all nestlings available from 1977 - 1982) illustrates a considerable difference in weight between nestlings from the Swedish Baltic coast and from an inland population in Swedish Lapland (fig. 7). In this case the difference was a result of food shortage. Age-specific body mass data from nestlings can also be used to monitor trends in condition and health within a population. Since sea eagles are sexually dimorphic (females are usually bigger than males), body mass records should ideally be assigned to either sex and treated separately. Tarsus width is a good indicator of sex in sea eagle nestlings (Helander et al. 2007). But mixed samples may be useful as well in the monitoring of trends, or to study differences between areas as shown in figure 7. When sex can be verified, a higher resolution in the studies can be achieved (Helander et al. 2007).

Cause of death of deceased individuals

Eagles found dead in nature belong to the state in all countries around the Baltic Sea, except Germany. This provides good opportunities for investigations of the cause of death. In Sweden, state game is normally sent to the Swedish Museum of Natural History for registration, measurements, examination and preparation for the museum collections. Before being opened, all white-tailed sea eagles are inspected macroscopically for body condition and signs of trauma, and x-rayed to assess the presence of lead shot, fractures etc. Distributions of cause of death of sea eagles from Germany, Finland and Sweden are presented in Herrmann et al. (2011). In Sweden, organ samples are saved in the museum’s Specimen Data Bank from all reasonably fresh specimens. Analyses of heavy metals in archived samples of sea eagle liver and kidney tissue have been carried out recently. The results for lead contamination revealed no decrease in lead concentrations over the period 1981 - 2004, and indicated that a minimum of 14% of investigated specimens were lethally poisoned from ingestion of lead ammunition (Helander et al. 2009). A follow-up study of lead in sea eagles from 2005 - 2010 will be undertaken in 2011 - 2012. Analyses of sea eagles found dead in Finland up till 2011 (death reasons, body condition, heavy metals, pesticides, parasitology, virology) will be conducted in a near future.

Data

 

(a). Baltic Proper, Sweden 1964 - 2010  

           

 

(b). Gulf of Bothnia, Sweden 1964 - 2010

 

(c). Mecklenburg-Western Pomerania, Germany 1973 - 2010

 

Figure 2. Breeding success (%, number of successfully reproducing out of all checked territorial pairs) of coastal white-tailed sea eagle subpopulations in Sweden, and of costal and freshwater populations in Mecklenburg-Western Pomerania, Germany. The blue line in graph (a) and (c) represents a locally weighted scatterplot smoothing (LOESS) that explains significantly more than the linear regression line. A pre-1950 reference level (black line) with 95% confidence limits (shaded grey) according to Helander (2003a) is given in each graph. Whether the reference level, estimated from data from the Swedish Baltic coast, is fully relevant for other populations has not been validated.

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(a). Baltic Proper, Sweden 1964 - 2010   

          

(b). Gulf of Bothnia, Sweden 1964 - 2010

 

(c). Åland, Finland 1970 - 2010

 

 

 (d). Gulf of Bothnia, Finland 1970 - 2010 (nests checked only from the ground in 1976 - 1979)                      

 

 

(e). Mecklenburg-Wester Pomerania, Germany 1973 - 2010 (nests checked only from the ground in 1973 - 1980)

 

Figure 3. Mean brood size (number of nestlings per successfully breeding pair) of coastal white-tailed sea eagle subpopulations in Sweden and Finland, and of costal and freshwater populations in Mecklenburg-Western Pomerania, Germany. The blue line in graph (a) represents a locally weighted scatterplot smoothing (LOESS) that explains significantly more than the linear regression line. A pre-1950 reference level (black line) with 95% confidence limits (shaded grey) according to Helander (2003a) is given in each graph. Whether the reference level, estimated from data from the Swedish Baltic coast, is fully relevant for other populations has not been validated. Five-year mean values from Finland for 1965 – 1999 are from Stjernberg et al. (2003), and completed for 2000 - 2010

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Figure 4. Mean white-tailed sea eagle nestling brood size around the Baltic Sea in 2000 - 2010. Sample sizes given in brackets. The reference level up to 1950 based on data from the Swedish coast was 1.84, with 95% confidence limits 1.64 - 2.04 (Helander 2003a). Nestling brood sizes below 1.60 are highlighted (red) in the map. Data from Finland 1965 - 1999 are from Stjernberg et al. (2003), and completed for 2000 – 2010.

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(a). Baltic Proper, Sweden 1964 - 2010

             

 (b). Gulf of Bothnia, Sweden 1964 - 2010

 

(c). Åland, SW Finland 1970 - 2010      

                        

(d). Gulf of Bothnia, Finland 1970 - 2010

 

 

(e). Mecklenburg-Western Pomerania, Germany 1973 - 2010

 

Figure 5. Mean annual productivity (number of nestlings per checked occupied territory) of coastal subpopulations of white-tailed sea eagles in Sweden and Finland, and of costal and freshwater populations in Mecklenburg-Western Pomerania, Germany. The blue line in graph (a) and (c) represents a locally weighted scatterplot smoothing (LOESS) that explains significantly more than the linear regression line in those graphs. The data set from Germany includes nests that were inspected only from the ground in 1973 - 1980. A pre-1950 reference level (black line)  given with a range (shaded grey)  based on confidence limits for breeding success and brood size according to Helander (2003a) is given in each graph. Whether the reference level, estimated from data from the Swedish Baltic coast, is fully relevant for other populations has not been validated.

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(a)

 

 

(b)

 

 

(c)

 

 

(d)

 

 

Figure 6. Mean annual productivity (number of nestlings per checked occupied territory) and residue concentrations of DDE (a, c) and total-PCB (µg/g, lipid.weight) (b,d) in white-tailed sea eagle eggs from the Swedish Baltic coast 1965 - 2010 (a, b) and from a reference population in Swedish Lapland 1976 - 2010 (c, d). Shaded grey areas in graph (a) and (c) indicate a range of concentrations below a previously estimated lowest-observable-effect-level (LOEL) for DDE according to Helander et al. (2002). Large dots = annual geometric means; small dots = individual clutches; vertical lines = 95% confidence limits (for sample sizes > 3). Regression lines for DDE and PCB in the eggs decreased significantly during the study periods (p<0.001). Productivity of the coastal population increased significantly (p<0.001).There was no statistically significant change in productivity over the study period in the reference population in Lapland. From Helander et al. (2008).

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Figure 7. Ratio between weights of nestlings of the same age from two white-tailed sea eagle populations in Sweden, based on 56 nestlings from Lapland and 53 from the Baltic Sea coast (from Helander et al. 2008). Wing length in cm is used as a proxy for age according to Helander (1981). Winglength data in the graph was grouped into 19 intervals, and ratios are for Lapland/Baltic nestlings (the blue reference line at 1.0 reflects equal weight of nestlings of the same age in the two populations). The much thinner nestlings in Lapland within the winglength interval 16 – 28 cm (corresponding to approximately 3.5 – 5 weeks of age) was obviously a result of food stress that also lead to emaciation and death in many nestlings (Helander 1985).

 

Metadata

Technical information

Data source

The National Swedish Monitoring Programme of Seas and Coastal Areas/National Environment Protection Agency; Swedish Museum of Natural History; Swedish Society for Nature Conservation (Project Sea Eagle).

Finland: WWF Finland, Project Sea Eagle; Finnish Museum of Natural History.

German Data: Agency for Environment, Nature Conservation, and Geology of Mecklenburg-Western Pomerania

Description of data

Surveys of breeding populations and reproduction, sampling, sample preparation, storage in specimen bank and evaluation of results are carried out by the Department of Contaminant Research at the Swedish Museum of Natural History, Stockholm. Surveys of breeding populations and reproduction of reference freshwater populations are carried out by the Swedish Society for Nature Conservation (Project Sea Eagle), Stockholm. Chemical Analysis is carried out at the Institute of Applied Environmental Research at Stockholm University.

In Finland surveys of breeding populations and reproduction, ringing of nestlings, sampling, are carried out by voluntary members of WWF Finland’s White-tailed Sea Eagle working group. Data are stored in a competent data base. Specimens found dead, DNA-samples from nestlings as well as addled eggs are stored in the Finnish Museum of Natural History, University of Helsinki.

In Germany, Mecklenburg-Western Pomerania, data are collected by voluntary ornithologists, co-ordinated by the “Project group for large bird species” under the auspices of the Agency for Environment, Nature Conservation and Geology. The data are compiled by Peter Hauff, who submits the annual reports to the mentioned governmental agency.  

Geographical coverage

Baltic coast and archipelagos between latitude 56 and 66 in Sweden, Baltic coast and archipelagos between latitude 62 and 64 and Åland archipelago in Finland, Baltic coast and inland of Mecklenburg-Western Pomerania in Germany.

Temporal coverage

Sweden 1964 - 2010, Finland 1965 – 2010, Germany 1973 - 2010. Reference levels derived from older data from Sweden. For details see figs.

Methodology and frequency of data collection

see 1-3 above.

Methodology of data processing

Simple log-linear regression analysis has been carried out to investigate average changes over time. To check for significant nonlinear trend components, a locally weighted scatterplot smoothing (LOESS) was applied according to Cleveland (1979) and Nicholson et al. (1995) and an analysis of variance (ANOVA) was used to check whether the smoother explained significantly more than the regression line. Statistical power analyses were used to estimate the minimum annual trend likely to be detected at a statistical power of 80% during a monitoring period of 10 years. To investigate the possible effect of a future reduced sampling scheme, repeated random sampling (5000 times) from 1991 - 2006 in the current database was carried out, simulating a maximum of 50, 25, 20, 15, and 10 records each year. Contingency analysis, using the G-test with William´s correction, a log-likelihood ratio test, was applied for comparisons between geographical regions and time periods. For references see Helander et al. (2008).

 

Quality of information

Minimum detectable yearly trend (%) for a 10-year monitoring period at a statistical power of 80% has been estimated for Swedish data for different sample sizes, based on random sampling from data collected during 1991 - 2006 Helander et al. (2008). Minimum detectable trends based on the raw data set between 1991 - 2006 (with a varying annual n of observations) was 1.3% for brood size (Baltic Proper), 2.0% for breeding success (Gulf of Bothnia) and 3.0% for productivity (Gulf of Bothnia).

 

References

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Hauff, P. & L. Wölfel (2002). Seeadler (Haliaeetus albicilla) in Mecklenburg-Vorpommern im 20. Jahrhundert. Corax, Special Issue 1, 15-22

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Helander, B., J. Axelsson, H. Borg, K. Holm.& A. Bignert (2009). Ingestion of lead from ammunition and lead concentrations in white-tailed sea eagles (Haliaeetus albicilla) in Sweden. Sci. Tot. Environ. 407:5555–5563.

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Helander, B., M. Olsson & L. Reutergårdh (1982). Residue levels of organochlorine and mercury compounds in unhatched eggs and the relationships to breeding success in white-tailed sea eagles Haliaeetus albicilla in Sweden.  Holarct. Ecol. 5(4):349-366.

Helander, B. & T. Stjernberg (eds.) (2003). Action Plan for the conservation of White-tailed Eagle (Haliaeetus albicilla). Recommendation 92/2002, adopted by the Standing Committee of the Bern Convention in Dec., 2002. BirdLife International. 51 pp.

Henriksson, K., E. Karppanen & M. Helminen (1966). High residue levels of mercury i Finnish white-tailed eagles. Orn. Fenn. 43:38-45.

Herrmann, C., O. Krone, T. Stjernberg & B. Helander (2011). Population Development of Baltic Bird Species: White-tailed Sea Eagle (Haliaeetus albicilla). HELCOM Baltic Sea Environment Fact Sheets 2011. Online. http://www.helcom.fi/BSAP assessment/ifs/ifs2011/en GB/White-tailedSeaEagle/

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Jensen, S., A.G. Johnels, M. Olsson & T. Westermark (1972). The avifauna of Sweden as indicators of environmental contamination with mercury and organochlorine hydrocarbons. Proc. Int. Orn. Congr. 15:455-465.

Koivusaari, J., I. Nuuja, R. Palokangas & M. Finnlund (1980). Relationships between productivity, eggshell thickness and pollutant contents of addled eggs in the population of white-tailed eagles Haliaeetus albicilla L. in Finland during 1969–1978. Environ. Pollut. (Ser. A) 23:41–52.

Lindberg, P., U. Sellström, L. Häggberg & C.A. De Wit (2004). Higher brominated diphenyl ethers and hexabromocyclododecane found in eggs of peregrine falcons (Falco peregrinus) breeding in Sweden. Environ. Sci. Technol. 38:93–96.

Nicholson, M.D., Fryer, R. & Larsen, J.R. 1995. A robust method for analysing contaminant trend monitoring data. Tech. Mar. Environ. Sci. ICES.

Nordlöf, U., B. Helander, A. Bignert & L. Asplund (2010).Levels of brominated flame retardants and methoxylated polybrominated diphenyl ethers in eggs of white-tailed sea eagles breeding in different regions of Sweden. Science of the Total Environment 409: 238–246. doi:10.1016/j.scitotenv.2010.09.042

Olsson, A., Ceder, K., Bergman, Å. & Helander, B. 2000. Nestling blood of the White-tailed   Sea Eagle (Haliaeetus albicilla) as an indicator of territorial exposure to organohalogen compounds - an evaluation. Environ. Sci. Technol. 34:2733-2740.

Stjernberg, T., Koivusaari, J. & Högmander, J. 2003: Population trends and breeding success of the White-tailed Sea Eagle in Finland, 1970–2000. In: SEA EAGLE 2000. Helander, B., Marquiss, M. and Bowerman, B. (eds). Åtta.45 Tryckeri AB, Stockholm, pp. 103–112.

 

For reference purposes, please cite this Baltic Sea Environment Fact Sheets as follows:
[Author’s name(s)], [Year]. [Baltic Sea Environment Fact Sheets title]. HELCOM Baltic Sea Environment Fact Sheets 2011. Online. [Date Viewed],

 

Last updated: 23 September 2011