T H E VALUE OF C H I C K FEATHERS TO ASSESS SPATIAL AND I N T E R S P E C I F I C VARIATION IN THE MERCURY CONTAMINATION OF SEABIRDS PETER H. BECKER 1, ROBERT W. FURNESS2 and DIANA HENNING 1 1 Institutfiir Vogelforschung, An der Vogelwarte 21, 1)-26386 Wilhelmshaven, Germany. 2 Applied Ornithology Unit, Zoology Department, Glasgow University, Glasgow G12 8QQ, U.K. (Received: December 1992; revised manuscript received: April 1993)
Abstract. In 1991 we compared eggs, down and body feathers of chicks of Common Terns, Herring Gulls and Black-headed Gulls in their utility to assess contaminationwith mercury. Like eggs feathers distinctly show interspecific and intersite differences in contamination. Highest levels were found in Common Terns, lowest in Black-headed Gulls. Chicks hatched at the Elbe had much higher mercury levels than those in other areas of the German North Sea coast. Conversion ratios between tissues have to be used with caution.
1. Introduction Seabirds have been found to be effective bioindicators of mercury in the marine environment: Feathers were used to demonstrate historical changes in contamination with mercury (e.g. Appelquist et al., 1985; Thompson et al., 1992, 1993), interspecific differences (Lock et al., 1992; Monteiro et al., in press) and large scale spatial trends (Thompson et al., 1992; Furness et al., in press). Besides assessing interspecific and year to year variation, eggs are a matrix especially suitable to monitor intersite differences (Becker et al., 1985; Becker, 1989, 1991). In this paper we investigate the usefulness of taking samples of body feathers of chicks in order to study spatial and interspecific trends in contamination with mercury. As almost all egg mercury passes over into the chick (Becker and Sperveslage, 1989; Becker et al., 1993), and as feathers contain 38-65% of the total mercury body burden of larid chicks (Lewis and Furness, 1991; Becker et al., 1993), we can expect that chick feathers, like eggs, should indicate clear geographical and interspecific variation in mercury contamination of seabird species breeding on the highly polluted German Wadden Sea coast (see Section 4). In addition to mercury derived from the egg concentrations of mercury in feathers should reflect uptake of mercury during chick growth. 2. Materials and Methods
In 1991 we collected eggs, feathers of chicks not fledged and some freshly dead chicks at six breeding sites on the German North Sea coast or at the river Elbe (Figure 1) under licence from the Bezirksregierungen Oldenburg and Ltineburg or the Landesamt fiir den Nationalpark Schleswig-Holsteinisches Wattenmeer. SamEnvironmental Monitoring and Assessment 28: 255-262, 1993. (~) 1993 Kluwer Academic Publishers. Printed in the Netherlands.
256
PETER H. BECKER ET AL.
r
~= ~
~
~-~ M e l l u m L(Jhesand
ilhelmsha
)~
Fig. 1. Location of the sampling sites on the German Wadden Sea coast and at the Elbe river.
pies of Herring Gulls (Larus argentatus) originated from Mellum, Trischen and Ltihesand, Black-headed Gulls (Larus ridibundus) from Augustgroden, Trischen and Hullen, and Common Terns (Sterna hirundo) from Wilhelmshaven, Augustgroden and Hullen (Figure 1). One egg per clutch was collected at random soon after clutch completion (see Becker, 1989). Eggs as well as dead chicks were frozen at - 18°C prior to further treatment. The feathers - down and body feathers growing with advancing age, from side (or shoulder in case of Herring Gulls from Mellum) or b a c k - were stored in polythene bags. We collected about 0.1 g feathers per type and chick (10 - 20 feathers each). In some chicks we were able to sample all three feather types. In Common Terns down was taken from dead chicks only. The livers of chicks were dissected out after thawing. Egg contents were homogenized. After weighing (+ 1 rag) all samples were dried to constant mass in an oven at 50°C. The samples were digested in a 1 : 4 mixture of concentrated nitric and sulfuric acid. Total mercury concentrations were determined in Glasgow by a cold vapour technique using a Data Acquisition Ltd DA 1500-DP6 Mercury Vapour Detector (Furness et al., 1986; detection level about 0.01 #g g-1 fresh mass). The ratio between fresh and dry masses being known for each sample, mercury concentrations are presented here on a fresh mass basis. The eight Common Tern eggs from Hullen were analysed according to Becket et al. (1985) at the Chemis-
USING CHICK FEATHERS TO MONITOR MERCURY IN SEABIRDS
257
ches Institut der Tier~irztlichen Hochschule Hannover. An intercalibration exercise involving the analysis of the same eggs by both laboratories produced identical mean mercury levels in the calibration set. We used two-tailed, non-parametric statistics to test for the significance of intersite or interspecific differences (three groups: Kruskal-Wallis test ( K - W); two groups: Mann-Whitney U-test ( M - W)). If the K - W test indicated significance of differences between three groups (p < 0.05), we compared two sites or species, respectively, by subsequent M - W tests.
3. Results 3.1. INTERSITEDIFFERENCES In Herring Gull eggs and in each of the different chick feathers, the intersite differences were highly significant (io < 0.001 between each site, Figure 2). Highest values were found at Liahesand, Elbe, intermediate levels on Trischen, inner German Bight, and lowest concentrations on Mellum, at the Jade Bay. In the Common Tern, too, the mercury concentrations in eggs and chicks of the colonies at the Jade were much lower than those at Hullen, Elbe estuary (Figure 3). Differences between the two Jade colonies, Wilhelmshaven and Augustgroden, were small and significant only in case of the liver values (p < 0.05). In Black-headed Gulls only side feathers were available to study the intersite variability in mercury contamination of chicks (Figure 4). We found higher mercury concentrations at Hullen, Elbe, and Trischen, inner German Bight, than at Augustgroden, Jade (p _< 0.001), whereas no significant difference was found between samples from Hullen and Trischen (Figure 4). 3.2.
INTERSPECIFIC DIFFERENCES
As intersite differences in mercury contamination within the Jade were low (Figure 3, see also Becker et aL, 1985; Becker, 1989, 1991), we compared mercury concentration in eggs and chick feathers between the three species with data pooled for all breeding sites at the Jade. Highly significant interspecific differences were found in all tissues: in eggs, down, side/shoulder and back feathers (cf. Figures 2--4, p < 0.001). Comparing pairs of species, only the egg concentrations between Common Terns and Herring Gulls were not significantly different. The Common Tern tissues were most highly contaminated, intermediate concentrations were found in the Herring Gull, and lowest concentrations in the Black-headed Gull. This pattern is confirmed by the data from Trischen and from the Elbe. At Trischen, concentrations of mercury in side feathers were higher in Herring Gull chicks than in Black-headed Gull chicks (p _< 0.01; cf. Figures 3,4). Common Terns from the Elbe (Hullen) were more contaminated than Herring Gulls from the Elbe (Ltihesand; eggs, down: p < 0.05; cf. Figures 2,3).
258
PETER H. BECKER ET AL.
Pletlum
4.0
Tri~l~n LLit~n~
egg
3.0 2.0 1.0
17
10
10
15.0
10.01 ~
5.0
160- si,~/~,,12.0-
8.O" ~.0"
12.0-
39
10
back
9.0 6.0 3.0 39
6
Fig. 2. Mercury concentrations in eggs, liver and down of chicks of Common Terns from two sites at the Jade Bay and from Hullen, Elbe estuary (Fig. 1). Presentation as in Fig. 2. p-Values of intersite differences are given ( K - W test).
USING CHICK FEATHERS TO MONITOR MERCURY IN SEABIRDS
259
Wilhelm.s- August- Hullen hdven groden
3.0
egg p- .05
2.0 1.0
12 A ~.0
6
B
7
5
liv~ p-.05
3.o 2.0 E 1.0
19 60.0" ao~n p-. 001
/.,5.0-
.,
30.01.5.0
19
7
5
Fig. 3. Mercury concentrations in eggs and chick feathers of Herring Gulls from the German North Sea coast and from the Elbe river (Fig. 1). Arithmetic means (columns), 2 standard deviations (hatched bars) and ranges (lines) are as well as sample sizes (n, below the columns) presented. All intersite differences are significant with p < 0.001 (U-test).
260
PETER H. BECKER ET AL.
August- Trischen Hullen groden
8.0 6.0
~
,.O 2.0 46
12
10
Fig. 4. Mercury concentrations in feathers from the side of Black-headed Gull chicks from the German North Sea coast and from Hullen, Elbe estuary (Fig. 1). Intersite differences are significant with p < 0.001 (/< - W test).
4. Discussion
The results show that feathers of chicks are as useful as eggs to assess intersite and interspecific variability in mercury contamination of seabirds. This was expected, as chicks accumulate the mercury in the egg, 90% of which is methylmercury (Umweltprobenbank, 1989). They also eliminate most of their body burden of mercury accumulated in soft tissues into their growing feathers (Lewis and Furness, 1991; Becker et aL, 1993). Accordingly mercury concentrations in the down of Common Tern young were positively correlated with whole body mercury concentrations and amounts (Becker et al., 1993). In small live Common Tern chicks it would be difficult to remove a sample of down sufficient for mercury analysis without harm to the bird. Sampling of 0.1 g of body feathers from the side, shoulder or back of older chicks is a very small operation without any noticeable effect on plumage integrity of the chicks, and can be strongly recommended for biomonitoring of mercury, and possibly of other heavy metals (see Burger and Gochfeld, 1992). Taking eggs for biomonitoring has a comparatively greater impact on the population. However, the advantage of egg matrix is that other chemicals such as organochlorines can be monitored in addition to heavy metals, should this be desirable or necessary. Conversion ratios allow estimation of the concentration of a chemical in a specific tissue from the known concentrations in another tissue. At the Jade, the
USING CHICK FEATHERS TO MONITOR MERCURY IN SEABIRDS
261
down/egg ratio was 14.4 (= 14.4/1) for Common Terns and 14.7 for Herring Gulls. At the sampling sites on the Elbe, however, the conversion ratios were different from those at the Jade: Common Tem (Hullen) 17.3, Herring Gull (Ltihesand) 7.4. Conversion ratios appear to vary geographically and from species to species, presumably depending on the site specific contamination level and chick growth characteristics. Thompson et al. (1990) also recommend caution with conversion ratios forcomparisons between studies as ratios involving feathers are influenced by species, type of feather and by sampling date relative to the stage of moult. The analyses of mercury in chick feathers confirm interspecific differences found in seabirds in the Wadden Sea (Becker et al., 1985; Becker, 1991): The fish-eating terns (Becker et al., 1987) are contaminated more than gulls which feed also at lower trophic levels and in terrestrial habitats (Gorke, 1990; Ncordhuis and Spaans, 1992). The distinct spatial differences in pollution by mercury on the Wadden Sea coast shown by environmental sampling of Blue Mussels (Mytilus eduIis, Loz~in et aL, 1991; Common Wadden Sea Secretariat, 1991), Flounder (Platichthysflesus, Luckas and Harms, 1987; Unweltbundesamt, 1989) and birds eggs (Becker et al., 1985; Becker, 1991) is also obvious from the feather analyses. The mercury concentrations found in birds on the Wadden Sea coast and especially at the Elbe are extremely high compared to those reported from other areas of the world. For example, feathers of Herring Gull chicks from the Shetlands contained 2.2 #g g-1 (cf. Figure 2), and of Common Tern chicks from the Azores 1.7 #g g-1 (Monteiro et al., in press) or from Cedar Beach, New York 2.6 #g g-1 (Burger and Gochfeld, 1992), cf. Figure 3. The mercury levels in Common Terns at the Elbe are much higher than concentrations at which toxic effects become evident in terrestrial or freshwater birds (Scheuhammer, 1987). However, it is not known if chick development or survival is affected by these high mercury levels.
Acknowledgements Our studies were supported by grants from the DAAD and the British Council to P.H. Becker and R.W. Furness (Anglo-German Foundation ARC). For their help in sampling we thank H. Bietz, E Btising, P. Hunck, H. Krethe, P. Todt, M. Wagener and S. Wolff. The Chemisches Institut of the Tierfirztliche Hochschule Hannover kindly analysed some Common Tern eggs.
References Appelquist, H., Drabaek,I., and Asbirk, S.: 1985, 'Variationin MercuryContentof GuillemotFeathers over 150 years', Mar. Pollut. Bull 16, 244-248. Booker, EH.: 1989, 'Seabirds as MonitorOrganismsof Contaminants along the German North Sea Coast', Helgoliinder Meeresunters. 43, 395--403, Becker,EH.: 1991, 'Populationand ContaminationStudiesin CoastalBirds withSpecialReferenceto the CommonTern (Sterna hirundo)', in Pert'ins,C.M., Lebreton,J.D., and Hirons, G.J.M. (eds.), Bird Population Studies: Relevance to Conservation and Management, pp. 433--460. Oxford UniversityPress.
262
PETER H. BECKER ET AL.
Becker, EH., Frank, D., and Walter, U.: 1987, 'Geographische und j~ihrliche Variation der Ern~ihrung der FluBseeschwalbe (Sterna hirundo) an der Nordseek0ste', J. Orn. 128, 457-475. Becker, P.H., Fumess, R.W., and Henning, D.: 1993, 'Mercury Dynamics in Young Common Tern (Sterna hirundo) Chicks from a Polluted Environment', Ecotoxicol. 2, 33-40. Becker, P.H. and Sperveslage, H.: 1989, 'Organochlorines and Heavy Metals in Herring Gull, Larus argentatus, Eggs and Chicks from the Same Clutch', Bull. Environ. Contam. Toxicol. 42, 721727. Becker, P.H., Ternes, W., and ROssel, H.A.: 1985, 'Schadstoffe in Gelegen von Brutv0geln der deutschen Nordseektiste. II. Quecksilber', J. Orn. 126, 253-262. Burger, J. and Gochfeld, M.: 1992, 'Trace Element Distribution in Growing Feathers: Additional Excretion in Feather Sheaths', Arch. Environ. Contam. ToxicoL, in press. Common Wadden Sea Secretariat: 1991, 'The Wadden Sea-Status and Developments in an International Perspective', Report Sixth. Trilateral Governmental Conf. on the Protection of the Wadden Sea. Esbjerg. Furness, R.W., Muirhead, S.J., and Woodburn, M.: 1986, 'Using Bird Feathers to Measure Mercury in the Environment: Relationships between Mercury Content and Moult', Mar. Pollut. Bull 17, 27-30. Furness, R.W., Thompson, D.R., and Becker, P.H.: 'Spatial and Temporal Variation in Mercury Contamination of Seabirds in the North Sea', Helgoliinder Meeresunters., in press. Gorke, M.: 1990, 'Die Lachm/~we (Larus ridibundus) in Wattenmeer und Binnenland', SeevOgeI 11 (Sonderheft), 1-48. Lewis, S.A. and Furness, R.W.: 1991, 'Mercury Accumulation and Excretion in Laboratory Reared Black-headed Gull, Larus ridibundus, Chicks', Arch. Environ. Contam. ToxicoL 21, 316-320. Lock, J.W., Thompson, D.R., and Furness, R.W.: 1992, 'Metal Concentrations in Seabirds of the New Zealand Region', Environ. PoIlut. 75, 289-300. Luckas, B. and Harms, U.: 1987, 'Characteristic Levels of Chlorinated Hydrocarbons and Trace Metals in Fish from Coastal Waters of North and Baltic Sea', Intern. J. Environ. Anal. Chem. 29, 215-225. Monteiro, L.R., del Novo, A.J., Furness, R.W., and Granadeiro, J.P.: 'Total Mercury Levels in Feathers of Seabirds from the Azores Archipelago', in: Mercury as Global Pollutant- Toward Integration and Synthesis (Int. Conf. Monterey, 1992), in press. Noordhuis, R. and Spaans, A.L.: 1992, 'Interspecific Competition for Food between Herring, Larus argentatus, and Lesser Black-backed gulls, L. fuscus, in the Dutch Wadden Sea Area', Ardea 80, 115-132. Scheuhammer, A.M.: 1987, 'The Chronic Toxicity of Aluminum, Cadmium, Mercury, and Lead in Birds: A Review', Environ. Pollut. 46, 263-295. Thompson, D.R., Becker, P.H., and Furness, R.W.: 'Long-term Changes in Mercury Concentrations in Herring Gulls Larus argentatus and Common Terns Sterna hirundo from the German North Sea Coast', J. Appl. Ecol. 30, 316-320. Thompson, D.R., Furness, R.W., and Walsh, EM.: 1992, 'Historical Changes in Mercury Concentrations in the Marine Ecosystem of the North and North-east Atlantic Ocean as Indicated by Seabird Feathers', J. Appl. Ecol. 29, 79-84. Thompson, D.R., Stewart, EM., and Furness, R.W.: 1990, 'Using Seabirds to Monitor Mercury in Marine Environments: The Validity of Conversion Ratios for Tissue Comparisons', Mar. Pollut. Bull 21, 339-342. Unweltbundesamt: 1989, 'Daten zur Umwelt 1988/89', Erich Schmidt, 1-613. Umweltprobenbank: 1989, 'Umweltprobenbank der Bundesrepublik Deutschland', Report Umweltprobenbank, JUlich.
Abstract. In 1991 we compared eggs, down and body feathers of chicks of Common Terns, Herring Gulls and Black-headed Gulls in their utility to assess contaminationwith mercury. Like eggs feathers distinctly show interspecific and intersite differences in contamination. Highest levels were found in Common Terns, lowest in Black-headed Gulls. Chicks hatched at the Elbe had much higher mercury levels than those in other areas of the German North Sea coast. Conversion ratios between tissues have to be used with caution.
1. Introduction Seabirds have been found to be effective bioindicators of mercury in the marine environment: Feathers were used to demonstrate historical changes in contamination with mercury (e.g. Appelquist et al., 1985; Thompson et al., 1992, 1993), interspecific differences (Lock et al., 1992; Monteiro et al., in press) and large scale spatial trends (Thompson et al., 1992; Furness et al., in press). Besides assessing interspecific and year to year variation, eggs are a matrix especially suitable to monitor intersite differences (Becker et al., 1985; Becker, 1989, 1991). In this paper we investigate the usefulness of taking samples of body feathers of chicks in order to study spatial and interspecific trends in contamination with mercury. As almost all egg mercury passes over into the chick (Becker and Sperveslage, 1989; Becker et al., 1993), and as feathers contain 38-65% of the total mercury body burden of larid chicks (Lewis and Furness, 1991; Becker et al., 1993), we can expect that chick feathers, like eggs, should indicate clear geographical and interspecific variation in mercury contamination of seabird species breeding on the highly polluted German Wadden Sea coast (see Section 4). In addition to mercury derived from the egg concentrations of mercury in feathers should reflect uptake of mercury during chick growth. 2. Materials and Methods
In 1991 we collected eggs, feathers of chicks not fledged and some freshly dead chicks at six breeding sites on the German North Sea coast or at the river Elbe (Figure 1) under licence from the Bezirksregierungen Oldenburg and Ltineburg or the Landesamt fiir den Nationalpark Schleswig-Holsteinisches Wattenmeer. SamEnvironmental Monitoring and Assessment 28: 255-262, 1993. (~) 1993 Kluwer Academic Publishers. Printed in the Netherlands.
256
PETER H. BECKER ET AL.
r
~= ~
~
~-~ M e l l u m L(Jhesand
ilhelmsha
)~
Fig. 1. Location of the sampling sites on the German Wadden Sea coast and at the Elbe river.
pies of Herring Gulls (Larus argentatus) originated from Mellum, Trischen and Ltihesand, Black-headed Gulls (Larus ridibundus) from Augustgroden, Trischen and Hullen, and Common Terns (Sterna hirundo) from Wilhelmshaven, Augustgroden and Hullen (Figure 1). One egg per clutch was collected at random soon after clutch completion (see Becker, 1989). Eggs as well as dead chicks were frozen at - 18°C prior to further treatment. The feathers - down and body feathers growing with advancing age, from side (or shoulder in case of Herring Gulls from Mellum) or b a c k - were stored in polythene bags. We collected about 0.1 g feathers per type and chick (10 - 20 feathers each). In some chicks we were able to sample all three feather types. In Common Terns down was taken from dead chicks only. The livers of chicks were dissected out after thawing. Egg contents were homogenized. After weighing (+ 1 rag) all samples were dried to constant mass in an oven at 50°C. The samples were digested in a 1 : 4 mixture of concentrated nitric and sulfuric acid. Total mercury concentrations were determined in Glasgow by a cold vapour technique using a Data Acquisition Ltd DA 1500-DP6 Mercury Vapour Detector (Furness et al., 1986; detection level about 0.01 #g g-1 fresh mass). The ratio between fresh and dry masses being known for each sample, mercury concentrations are presented here on a fresh mass basis. The eight Common Tern eggs from Hullen were analysed according to Becket et al. (1985) at the Chemis-
USING CHICK FEATHERS TO MONITOR MERCURY IN SEABIRDS
257
ches Institut der Tier~irztlichen Hochschule Hannover. An intercalibration exercise involving the analysis of the same eggs by both laboratories produced identical mean mercury levels in the calibration set. We used two-tailed, non-parametric statistics to test for the significance of intersite or interspecific differences (three groups: Kruskal-Wallis test ( K - W); two groups: Mann-Whitney U-test ( M - W)). If the K - W test indicated significance of differences between three groups (p < 0.05), we compared two sites or species, respectively, by subsequent M - W tests.
3. Results 3.1. INTERSITEDIFFERENCES In Herring Gull eggs and in each of the different chick feathers, the intersite differences were highly significant (io < 0.001 between each site, Figure 2). Highest values were found at Liahesand, Elbe, intermediate levels on Trischen, inner German Bight, and lowest concentrations on Mellum, at the Jade Bay. In the Common Tern, too, the mercury concentrations in eggs and chicks of the colonies at the Jade were much lower than those at Hullen, Elbe estuary (Figure 3). Differences between the two Jade colonies, Wilhelmshaven and Augustgroden, were small and significant only in case of the liver values (p < 0.05). In Black-headed Gulls only side feathers were available to study the intersite variability in mercury contamination of chicks (Figure 4). We found higher mercury concentrations at Hullen, Elbe, and Trischen, inner German Bight, than at Augustgroden, Jade (p _< 0.001), whereas no significant difference was found between samples from Hullen and Trischen (Figure 4). 3.2.
INTERSPECIFIC DIFFERENCES
As intersite differences in mercury contamination within the Jade were low (Figure 3, see also Becker et aL, 1985; Becker, 1989, 1991), we compared mercury concentration in eggs and chick feathers between the three species with data pooled for all breeding sites at the Jade. Highly significant interspecific differences were found in all tissues: in eggs, down, side/shoulder and back feathers (cf. Figures 2--4, p < 0.001). Comparing pairs of species, only the egg concentrations between Common Terns and Herring Gulls were not significantly different. The Common Tern tissues were most highly contaminated, intermediate concentrations were found in the Herring Gull, and lowest concentrations in the Black-headed Gull. This pattern is confirmed by the data from Trischen and from the Elbe. At Trischen, concentrations of mercury in side feathers were higher in Herring Gull chicks than in Black-headed Gull chicks (p _< 0.01; cf. Figures 3,4). Common Terns from the Elbe (Hullen) were more contaminated than Herring Gulls from the Elbe (Ltihesand; eggs, down: p < 0.05; cf. Figures 2,3).
258
PETER H. BECKER ET AL.
Pletlum
4.0
Tri~l~n LLit~n~
egg
3.0 2.0 1.0
17
10
10
15.0
10.01 ~
5.0
160- si,~/~,,12.0-
8.O" ~.0"
12.0-
39
10
back
9.0 6.0 3.0 39
6
Fig. 2. Mercury concentrations in eggs, liver and down of chicks of Common Terns from two sites at the Jade Bay and from Hullen, Elbe estuary (Fig. 1). Presentation as in Fig. 2. p-Values of intersite differences are given ( K - W test).
USING CHICK FEATHERS TO MONITOR MERCURY IN SEABIRDS
259
Wilhelm.s- August- Hullen hdven groden
3.0
egg p- .05
2.0 1.0
12 A ~.0
6
B
7
5
liv~ p-.05
3.o 2.0 E 1.0
19 60.0" ao~n p-. 001
/.,5.0-
.,
30.01.5.0
19
7
5
Fig. 3. Mercury concentrations in eggs and chick feathers of Herring Gulls from the German North Sea coast and from the Elbe river (Fig. 1). Arithmetic means (columns), 2 standard deviations (hatched bars) and ranges (lines) are as well as sample sizes (n, below the columns) presented. All intersite differences are significant with p < 0.001 (U-test).
260
PETER H. BECKER ET AL.
August- Trischen Hullen groden
8.0 6.0
~
,.O 2.0 46
12
10
Fig. 4. Mercury concentrations in feathers from the side of Black-headed Gull chicks from the German North Sea coast and from Hullen, Elbe estuary (Fig. 1). Intersite differences are significant with p < 0.001 (/< - W test).
4. Discussion
The results show that feathers of chicks are as useful as eggs to assess intersite and interspecific variability in mercury contamination of seabirds. This was expected, as chicks accumulate the mercury in the egg, 90% of which is methylmercury (Umweltprobenbank, 1989). They also eliminate most of their body burden of mercury accumulated in soft tissues into their growing feathers (Lewis and Furness, 1991; Becker et aL, 1993). Accordingly mercury concentrations in the down of Common Tern young were positively correlated with whole body mercury concentrations and amounts (Becker et al., 1993). In small live Common Tern chicks it would be difficult to remove a sample of down sufficient for mercury analysis without harm to the bird. Sampling of 0.1 g of body feathers from the side, shoulder or back of older chicks is a very small operation without any noticeable effect on plumage integrity of the chicks, and can be strongly recommended for biomonitoring of mercury, and possibly of other heavy metals (see Burger and Gochfeld, 1992). Taking eggs for biomonitoring has a comparatively greater impact on the population. However, the advantage of egg matrix is that other chemicals such as organochlorines can be monitored in addition to heavy metals, should this be desirable or necessary. Conversion ratios allow estimation of the concentration of a chemical in a specific tissue from the known concentrations in another tissue. At the Jade, the
USING CHICK FEATHERS TO MONITOR MERCURY IN SEABIRDS
261
down/egg ratio was 14.4 (= 14.4/1) for Common Terns and 14.7 for Herring Gulls. At the sampling sites on the Elbe, however, the conversion ratios were different from those at the Jade: Common Tem (Hullen) 17.3, Herring Gull (Ltihesand) 7.4. Conversion ratios appear to vary geographically and from species to species, presumably depending on the site specific contamination level and chick growth characteristics. Thompson et al. (1990) also recommend caution with conversion ratios forcomparisons between studies as ratios involving feathers are influenced by species, type of feather and by sampling date relative to the stage of moult. The analyses of mercury in chick feathers confirm interspecific differences found in seabirds in the Wadden Sea (Becker et al., 1985; Becker, 1991): The fish-eating terns (Becker et al., 1987) are contaminated more than gulls which feed also at lower trophic levels and in terrestrial habitats (Gorke, 1990; Ncordhuis and Spaans, 1992). The distinct spatial differences in pollution by mercury on the Wadden Sea coast shown by environmental sampling of Blue Mussels (Mytilus eduIis, Loz~in et aL, 1991; Common Wadden Sea Secretariat, 1991), Flounder (Platichthysflesus, Luckas and Harms, 1987; Unweltbundesamt, 1989) and birds eggs (Becker et al., 1985; Becker, 1991) is also obvious from the feather analyses. The mercury concentrations found in birds on the Wadden Sea coast and especially at the Elbe are extremely high compared to those reported from other areas of the world. For example, feathers of Herring Gull chicks from the Shetlands contained 2.2 #g g-1 (cf. Figure 2), and of Common Tern chicks from the Azores 1.7 #g g-1 (Monteiro et al., in press) or from Cedar Beach, New York 2.6 #g g-1 (Burger and Gochfeld, 1992), cf. Figure 3. The mercury levels in Common Terns at the Elbe are much higher than concentrations at which toxic effects become evident in terrestrial or freshwater birds (Scheuhammer, 1987). However, it is not known if chick development or survival is affected by these high mercury levels.
Acknowledgements Our studies were supported by grants from the DAAD and the British Council to P.H. Becker and R.W. Furness (Anglo-German Foundation ARC). For their help in sampling we thank H. Bietz, E Btising, P. Hunck, H. Krethe, P. Todt, M. Wagener and S. Wolff. The Chemisches Institut of the Tierfirztliche Hochschule Hannover kindly analysed some Common Tern eggs.
References Appelquist, H., Drabaek,I., and Asbirk, S.: 1985, 'Variationin MercuryContentof GuillemotFeathers over 150 years', Mar. Pollut. Bull 16, 244-248. Booker, EH.: 1989, 'Seabirds as MonitorOrganismsof Contaminants along the German North Sea Coast', Helgoliinder Meeresunters. 43, 395--403, Becker,EH.: 1991, 'Populationand ContaminationStudiesin CoastalBirds withSpecialReferenceto the CommonTern (Sterna hirundo)', in Pert'ins,C.M., Lebreton,J.D., and Hirons, G.J.M. (eds.), Bird Population Studies: Relevance to Conservation and Management, pp. 433--460. Oxford UniversityPress.
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