Bull. Environ. Contam. Toxicol. (1984) 32:453-459 �9 1984 Springer-Verlag New York Inc.

E n v i r o n m e n t a l C o n t a m i n a t i o n

~and Tox ico logy

Mercury in Feathers of Swedish Gyrfalcons, Falco rusticolus, in Relation to Diet

Peter Lindberg

Department of Zoology, University of G6teborg, Box 25059, S-400 31, G6teborg, Sweden

The gyrfalcon (Falco rust&olus) is mainly a resident bird breeding in mountain areas in Fennoscandia. The population (estimated to 300-500 pairs) probably fluctuates according to the presence of willow grouse (Lagopus lagopus) and ptarmigan (Lago- pus mutus) (Bengtson 1971, Swartz et al. 1975). From later decades there are no reli- able reports on population decline, as noted among many other European bird-eating raptors (Bijleveld 1974, Newton 1979). The species breeds in areas with little human interference and takes up a low trophic level, feeding on herbivorous grouse (Cade 1960, Hagen 1952, Langvatn & Moksnes 1979).

Cade et al. (1971) demonstrated the difference in exposure to organochlorines for Alaskan gyrfalcons and the highly migratory peregrine falcon (Falco peregrinus) breeding in the same area. The peregrine feeds mainly on insectivorous and omnivo- rous species that have higher pollutant levels than herbivorous species. Walker (1977) analyzed addled eggs and biopsy fat samples from adult gyrfalcons, and found DDE and PCB in all samples. He assumed that pollutants entered the arctic ecosystem via fallout, after aerial transport from sources of contamination. He also stressed that migrant birds are a direct pathway for contaminents into the Arctic from more pol- luted areas, and that these birds were the main source of contamination of gyrfal- cons. However, levels of organochlorine in Alaskan gyrfalcons were low and proba- bly insignificant for reproduction.

Little is known about pollutant levels in Fennoscandian gyrfalconS. Holt et al. (1979) found low levels of DDE, PCB and mercury in organs from six Norwegian gyrfal- cons. In this paper I have included additional information on mercury levels, based on feather analyses from a few nests in northern Sweden. The use of feathers is a simple method to monitor mercury levels without sacrificing the birds (Berg et al. 1966).

M A T E R I A L A N D M E T H O D S

Moulted feathers were collected in 1972-77 at four nests in the national park of Stora Sj6fallet (67~ 17~ and Sjaunja Bird Preservation area (67~ 19~ in northern Sweden. Samples of 16 feathers (9 primaries, 4 rectrices, 2 secondaries, 1 wingcovert) from adult birds were analysed for mercury content. Of ten feathers, that could be sex determined, eight belonged to females. The mercury levels are assumed to reflect intake during June-July, one year before collection date.

453

From one young (age 28-35 days) at three different nests, the distal parts of a secon- dary and a rectrix were cut in 1975-77. Young birds in the same clutch can be sup- posed to exhibit comparable levels as they are all fed with the same type of food (Odsj6 & Olsson 1975, H/ikkinen & H~s~inen 1980). Levels in nestling feathers reflect intake during May-June in the years of collection.

Analyses of mercury were performed by the Isotopes Techniques Laboratory, Stock- holm, using the neutron activation method (Sj6strand 1964, Christell et al. 1965). Analyses of moulted feathers were made on the proximal part i.e. the calamus. Mer- cury levels are given in ppm dry weight.

Food habits were checked by analysing food remains, pluckings and pellets at and near the nests. A total of 1409 prey from nine nests were identified.

For studies of accumulation effect in a gyrfalcon food web, I used information on mercury levels in the pectoral muscle (ppm wet weight) from certain prey species shot in the vicinity of Sjaunja Bird Preservation area in 1976-77 (Lindberg & Odsj6 1983).

RESULTS AND DISCUSSION

Mercury levels in adult birds varied both within and between the pairs (table 1). This difference can be ascribed to different amounts of mercury in the blood during feather formation. Low levels and variance were noted at nest A, a breeding locality consistently occupied during the 1970's by a pair which feed mainly on grouse. The highest levels were noted for a female at an occasionally occupied nest (D) in 1972. I have no information on either food choice or dwelling place for the female when the feathers were formed.

Mercury levels in feathers of nestlings can be better correlated with levels in the actual food choice than levels based on adult feathers. Nestlings fed partly with aquatic bird species (Anatidae, Charadriidae, Scolopacidae, Laridae) had higher levels of mercury (table 3).

Table 1. Mercury levels ppm (dry weight) in feathers from adult gyrfalcons breeding in Sweden.

Nest Formation year Number of Number of Hg ppm of feathers falcons feathers x + S.D.

A 1972-76 1-2 9 0.24 + 0.10 B 1971 2 2 1.03 + 1.11 C 1973 1-2 2 1.70 + 1.98 D 1972 2 3 6.65 + 5.89

TOTAL 16 1.72 + 3.35

454

Tab

le 2

. M

ercu

ry l

evel

s p

pm

(w

et w

eigh

t) i

n th

e pe

ctor

al m

uscl

e o

f ce

rtai

n pr

ey s

peci

es o

f th

e gy

rfal

con.

T

he d

iet

of

the

falc

on,

by b

iom

ass,

is

base

d on

140

9 pr

ey s

peci

es,

coll

ecte

d at

nin

e ne

sts

in t

he

inve

stig

atio

n ar

ea.

Spe

cies

N

um

ber

A

vera

ge

Hg

pp

m

% B

iom

ass

in

wei

ght,

g

~ +

S.D

.

Ana

s cr

ecca

6

300

0.09

+

0.04

0.

31

Ayt

hya

fuli

gula

3

750

0.09

+

0.02

0.

38

Lag

opus

lag

opus

/mut

us

21

500

0.00

•

0.00

82

.88

Plu

vial

is a

pric

aria

5

170

0.11

+

0.03

0.

06

Phi

lom

achu

spug

nax

10

155

0.23

+

0.07

0.

02

Num

eniu

spha

eopu

s 4

375

0.12

+

0.03

0.

32

Trin

ga n

ebul

aria

5

175

0.44

+

0.08

0.

03

Turd

us p

ilari

s 5

105

0.07

+

0.03

0.

02

Tab

le 3

M

ercu

ry l

evel

s p

pm

(dr

y w

eigh

t) i

n fe

athe

rs f

rom

yo

un

g g

yrfa

lcon

s in

rel

atio

n to

the

fra

ctio

n o

f te

rres

tria

l (T

etra

onid

ae)

and

aqu

atic

pre

y sp

ecie

s (A

nati

dae,

Cha

radr

iidae

, Sc

olop

acid

ae,

Lari

dae)

fo

un

d a

t th

e ne

sts

in t

he y

ear

feat

her

sam

plin

g w

as d

one.

Cal

cula

tion

of

biom

ass

is b

ased

on

the

fo

llow

ing

wei

ghts

: A

nati

dae

725

g,

Tetr

anoi

dae

500

g, C

hara

driid

ae-S

colo

paci

dae

210

g, L

arid

ae

450

g.

Nes

tlin

gs

Pre

y s

peci

es i

n fa

lcon

die

t

t~

G',

Nes

t F

orm

atio

n

Nu

mb

er

Nu

mb

er

Hg

pp

m

Tetr

aoni

dae

Ana

tida

e, C

hara

driid

ae

To

tal

year

of

of

nest

- o

f Sc

olop

acid

ae,

Lar

idae

n

um

ber

of

feat

hers

lin

gs

feat

hers

B

io-

Nu

mb

er

Bio

- N

um

ber

pr

ey i

tem

s m

ass

~ ~

mas

s ~

~ co

llec

ted

A

B

C

1977

1

2 0.

035

98.3

90

.0

0 0

50

0.03

6

1975

1

3 0.

485

91.8

88

.7

4.8

3.2

62

0.75

0.

75

1977

1

2 1.

14

88.3

75

.4

10.6

8.

2 61

1.

29

In an area occupied by both gyrfalcons and peregrine falcons, samples of the most common prey species were shot in 1976-77. Mercury levels in the pectoral muscle were highest in waders and ducks, whereas very low levels were noted in the ptarmigan and the willow grouse (table 2). No industrial contamination of mercury is known in the actual investigation area, so most of the mercury in the migrating waders and ducks is probably picked up during passage through and during winter stay in coastal areas in north-western and southern Europe. Aquatic migratory birds are thus probably the main source of mercury contamination for Fennoscandian gyrfalcons and peregrines.

The food choice for the gyrfalcon depends both on the bird community within hunt- ing range, and on individual specialization. Low mercury levels were found at nest A (table 3), situated on the border between the mountain birch forest and the alpine heath (500-900 m. above sea-level), which is a good grouse habitat. Nest C was situ- ated in a lowland area (460-600 m. above sea-level) with a large proportion of bogs which is a good water fowl habitat (27% of the area within a radius of 5 km from the nest was bogs). Depending on food choice, certain pairs are thus more exposed to mercury than others. During years with a low abundance of grouse, the falcons will probably shift to another diet and can then be more exposed to mercury. Juvenile birds migrating during their first winter may be more exposed than adults staying in their breeding areas all year round.

Levels in adult and young gyrfalcons were significantly lower than in peregrine fal- cons breeding in northern Sweden. A mean + S.D. of 1.72 + 3.35 ppm based on all feathers from adult gyrfalcons (no significant difference between nests, p<0.05, Kruskall-Wallis' one-way analysis of variance, two-tailed) was lower than a mean of 17.60 + 6.99 ppm (n =41) for peregrine feathers formed during the breeding season (p<0.0~, Mann-Whitney U-test, two-tailed)(Lindberg & Odsj6 1983). A mean of 8.31 + 2.59 ppm (n = 12) for peregrine nestlings also exceeded the highest level noted for a young gyrfalcon (table 3).

The food choice of the peregrine falcon mainly consists of migrating waders resulting in the falcons being exposed to higher mercury levels. In figure 1 the relation among mercury in feathers ( a mean based on all feathers from adult birds), mercury in the food and proportion aquatic prey in the diet are given for gyrfalcons and peregrines breeding in different areas in Sweden 1971-77 (Lindberg & Odsj0 1983). The mercury level in the food was estimated by multiplying the level in the pectoral muscle of prey species with average proportion biomass of various prey species in the falcon's diet. As only a sample of the prey species has been analysed for mercury, I assume that levels in prey species not analysed are the same as in the analysed sample. By biomass the analysed sample of prey represents 84% of the gyrfalcon's diet whereas the cor- responding figures for the peregrine are 47% in northern and 66~ in southern Swe- den.

The mercury levels in the gyrfalcons can be considered as low, and in some adult birds (nest A, mean 0.24 ppm) even markedly lower than for peregrines (mean 0.59 + 0.21, n = 10) kept in captivity and given a low contaminated captive-produced food (p<0.002, Mann-Whitney U-test, two-tailed).

The gyrfalcons diet of mainly resident prey are thus much better from the contami- nation point of view than the migrating bird species forming the main food of the peregrine.

457

Hg ppm 20 in feofhers

15

10

S

,t "P

~oe,," / /i <~ ~e,7 ~/~___~/n:39

0.0 0.1

"PN

0.0 0.2 Hg ppm

in food

Figure 1 The relations among mercury in feathers (ppm, dry weight), in food (ppm, wet weight) and proportion aquatic prey in the diet of adult gyrfalcons and peregrines in Sweden. G --- gyrfalcon, northern Swe- den, PS = peregrine, southern Sweden, PN = peregrine, northern Sweden.

458

Acknowledgements

I would like to thank T. Odsj0 at the Swedish Museum of Natural History, Stock- holm, who prepared samples for analyses. I also thank A. Johnels, B. Broo and R.,~. Norberg for critical comments on the manuscript. This study was supported by the Swedish Society for the Conservation of Nature, Swedish Environment Protection Board and World Wildlife Fund/Sweden.

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Received August 25, 1983; accepted September 22, 1983

459