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Environmental Contaminants in Tissues of Bald Eagles
Sampled in Southwestern Montana, 2006–2008
Author(s): Alan R. Harmata
Source: Journal of Raptor Research, 45(2):119-135.
Published By: The Raptor Research Foundation
https://doi.org/10.3356/JRR-10-37.1
URL: http://www.bioone.org/doi/full/10.3356/JRR-10-37.1
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ENVIRONMENTAL CONTAMINANTS IN TISSUES OF BALD EAGLES
SAMPLED IN SOUTHWESTERN MONTANA, 2006–2008
ALAN R. HARMATA1
Ecology Department, Montana State University, Bozeman, MT 59717 U.S.A.
ABSTRACT.—Blood and feathers of Bald Eagles (Haliaeetus leucocephalus) banded as nestlings (n 5 17),
captured as free-flying (n5 91), or submitted for rehabilitation (n5 29) in southwestern Montana between
December 2005 and April 2008 were sampled for mercury (Hg), selenium (Se), lead (Pb), seven other trace
elements, and organochlorines. Hg concentrations in blood (hereafter ‘‘HgB’’) did not differ between
captured eagles and those submitted for rehabilitation, and HgB in both were higher than concentrations
in nestlings (P , 0.01). Se concentrations in blood (‘‘SeB’’) were similar among groups. Pb concentrations
in blood (‘‘PbB’’) were higher in captured eagles than in those submitted for rehabilitation (P 5 0.05). No
bird submitted for rehabilitation exhibited toxic levels of PbB, but 9% of captured eagles did. HgB and PbB
in captured eagles declined as date of capture advanced from autumn to spring. Hg and Se concentrations
in feathers (‘‘HgF’’; ‘‘SeF’’) tended to increase with age-class. HgB and SeB, and HgB and HgF were
correlated in nestlings and captured eagles (P , 0.05) but not in birds submitted for rehabilitation. Birds
captured in autumn during this study had higher HgB (P , 0.05) than birds captured in autumn in the
early 1990s, but SeB did not differ. HgB and SeB in birds captured in spring during this study were similar
to those of birds captured in spring in the early 1990s, but PbB was lower. Five eagles were recaptured and
resampled for contaminants up to 18 yr after initial banding and sampling but no time-trends were
detected in contaminant concentrations due to small sample size. Other trace elements and organochlo-
rines if detected in blood were at very low concentrations.
KEY WORDS: Bald Eagle; Haliaeetus leucocephalus; capture; DDE; lead; mercury; nestling; rehabilitation; seleni-
um.
CONTAMINANTES AMBIENTALES EN TEJIDOS DE HALIAEETUS LEUCOCEPHALUS MUESTREADOS
EN EL SUROESTE DE MONTANA, 2006–2008
RESUMEN.—Muestreamos sangre y plumas de a´guilas Haliaeetus leucocephalus anilladas como pichones (n 5
17), capturadas en su ambiente (n 5 91) o de individuos enviados para rehabilitacio´n (n 5 29) en el
suroeste de Montana entre diciembre de 2005 y abril de 2008 para determinar las concentraciones de
mercurio (Hg), selenio (Se), plomo (Pb), restos de otros siete elementos y compuestos o´rganoclorados. Las
concentraciones de Hg en la sangre (HgB) no difirieron entre las a´guilas capturadas y aquellas enviadas a
rehabilitacio´n, y la HgB en ambos grupos fue ma´s alta que las concentraciones en los pichones (P , 0.01).
Las concentraciones sanguineas de Se (SeB) fueron similares entre los grupos. Las concentraciones san-
guineas de Pb (PbB) fueron ma´s altas en las a´guilas capturadas que en aquellas enviadas a rehabilitacio´n (P
5 0.05). Ningu´n ave enviada a rehabilitacio´n mostro´ niveles to´xicos de PbB, pero el 9% de las a´guilas
capturadas sı´ mostro´. HgB y PbB en las a´guilas capturadas disminuyeron a medida que progreso´ el dı´a de
captura desde el oton˜o hacia la primavera. Las concentraciones de Hg y Se en las plumas (HgF; SeF)
tendieron a incrementar con las clases de edad. HgB y SeB, y HgB y HgF estuvieron correlacionadas en los
pichones y en las a´guilas capturadas (P , 0.05), pero no en las aves enviadas a rehabilitacio´n. Las aves
capturadas en oton˜o durante este estudio tuvieron HgB ma´s altas (P , 0.05) que las aves capturadas en
oton˜o a principios de los 1990, pero SeB no difirio´. En las aves capturadas durante este estudio en
primavera, HgB y SeB fueron similares a las concentraciones de las aves capturadas en primavera a princi-
pios de los 1990, pero PbB fue ma´s baja. Cinco a´guilas fueron recapturadas y muestreadas nuevamente en
busca de contaminantes hasta 18 an˜os despue´s del anillado y muestreo inicial, pero no se detectaron
tendencias temporales en las concentraciones de contaminantes debido a un taman˜o de muestra pequen˜o.
En aquellos casos en que se detectaron restos de otros elementos y de compuestos o´rganoclorados en la
sangre, e´stos ocurrieron a concentraciones muy bajas.
[Traduccio´n del equipo editorial]
1 Email address: ubijt@montana.edu
J. Raptor Res. 45(2):119–135
E 2011 The Raptor Research Foundation, Inc.
119
During winter 2005–06, debilitated Bald Eagles
(Haliaeetus leucocephalus) submitted to Montana
Raptor Conservation Center (MRCC), a raptor re-
habilitation organization in Bozeman, Montana,
were found to contain mercury (Hg) concentrations
in blood considered above background levels for
some piscivorous species ($0.4 ppm wet weight;
Burgess et al. 2005). Most were recovered within
30 km of the Upper Missouri River watershed in
southwestern Montana. Staff at MRCC indicated
that the number and morbidity of Bald Eagles sub-
mitted during this period was unusual and ques-
tioned whether there may be an emerging or chron-
ic problem with Hg concentrations in the local
environment. To address this concern, a pilot pro-
gram was launched in May 2006 to monitor Hg con-
centrations in tissues of Bald Eagles submitted for
rehabilitation (hereafter referred to as ‘‘rehabs’’)
and wild nestling Bald Eagles in southwestern Mon-
tana. Scope of study expanded to include migrant
and wintering eagles captured in southwestern
Montana between autumn 2006 and spring 2008.
Study methods permitted collection of tissues for
analysis of other chemical elements and organo-
chlorine compounds, in addition to Hg.
Study objectives were to determine the amount
and extent of Hg, selenium (Se), lead (Pb), and
organochlorines in tissues of nestling, rehab, mi-
grant, and wintering Bald Eagles in southwestern
Montana. Hg and Pb were emphasized because they
are nonessential and toxic and have documented
effects on avian health and reproduction (Eisler
1987, Boening 2000, Haruka et al. 2009). Hg is of
primary concern in aquatic environments studied
(e.g., Sorensen et al. 1990, Scheuhammer and Gra-
ham 1999) and Pb is of recent concern in upland
habitats (Watson et al. 2009), both of which are
frequented seasonally by Bald Eagles. Selenium
was included because of its reported detoxification
properties for Hg (Yoneda and Suzuki 1997, Odsjo¨
et al. 2004, Yang et al. 2007, Berry and Ralston
2008). Methods also permitted screening for other
potentially toxic chemical elements not typically re-
ported (Burger and Gochfeld 2009).
STUDY AREA AND SAMPLE POPULATIONS
Nestling eagles were sampled along the Madison
and Missouri rivers in southwestern Montana from
the inlet to Ennis Lake near McAllister, Montana, to
Holter Reservoir, northeast of Helena, Montana.
Some nestlings from nests on the Gallatin and Jef-
ferson rivers within 25 km of their confluence with
the Missouri River and the Yellowstone River near
Big Timber, Montana, were also included. Free-fly-
ing eagles were captured between November and
April 2006–07 and 2007–08 within the same geo-
graphical area where nestlings were sampled, but
capture efforts were focused within 25 km of the
headwaters of the Missouri River. Some eagles were
captured in March near Ringling, Meagher County,
Montana. Bald eagles classified in ‘‘rehab’’ group
consisted of Bald Eagles submitted for rehabilita-
tion to MRCC from throughout Montana, but most
originated in the southwestern part of the state.
Most captured eagles were likely migrants origi-
nating in the boreal forests of western Canada be-
cause (1) many juvenile and other nonadult age
classes of Bald Eagles produced in southwestern
Montana leave in autumn to winter in coastal west-
ern states (Harmata et al. 1999) and (2) large num-
bers of migrant Bald Eagles move through Montana
seasonally (Nijssen et al. 1985, McClelland et al.
1994, Miller et al. 1998, Harmata 2002). Further,
over 300 Bald Eagles have been observed along
the Madison–Missouri River system in southwestern
Montana (Restani et al. 2000) in late autumn and
winter and .200 in one 2-km2 pasture within the
study area in January 2008 (A. Harmata unpubl.
data) and (3) only approximately 20 pairs of breed-
ing Bald Eagles occur within the study area (Mon-
tana Fish, Wildlife, and Parks unpubl. data) with an
estimated resident autumn/winter population of
40–50. Accordingly, the probability that a significant
proportion of the captured eagles were produced or
breeding in southwestern Montana was low.
METHODS
Montana Bald Eagle Working Group members
and APEX Environmental, LLC, surveyed nesting
activity of Bald Eagle breeding pairs in April and
May. Nestling eagles were sampled when .6 wk of
age. Sex was not assigned to nestling eagles because
of uncertainty of hatching date and thus, stage in
morphological development. Nestlings were consid-
ered a plumage class and a seasonal group for some
comparative analyses.
Free-flying eagles were captured with a command-
detonated, Coda net launcher (Coda Enterprises,
Mesa, Arizona, U.S.A.). Road-killed ungulate car-
casses, mostly white-tailed deer (Odocoileus virgini-
anus), were used as bait, as were wild lagomorph
and domestic bovine carcasses when available. The
net launcher was usually not detonated when fewer
than three eagles were within net range.
120 HARMATA VOL. 45, NO. 2
Date of capture was the sole criteria for classifying
seasonal groups of captured eagles. Although a few
captured eagles may have been associated with local
nest sites, identification of local breeders was not
possible. Eagles captured between 1 and 22 Decem-
ber were classified as autumn migrants; those cap-
tured between 23 December and 29 February classi-
fied as wintering; and those captured between 1
March and 15 April classified as vernal migrants.
Both migrant classes and wintering eagles are re-
ferred to collectively as ‘‘captured’’ to distinguish
them from nestlings and rehabs. Sex was assigned
to captured and rehab eagles using the methods
described by Bortolotti (1984) and Garcelon et al.
(1985). Captured and rehab eagles were categorized
in juvenile, immature, subadult, and adult plumage
classes, which were related to advancing age
(McCullough 1989). Nestling and captured eagles
are also referred to collectively as wild.
Contaminant samples were collected only from
eagles submitted live to MRCC for rehabilitation.
Samples were collected at time of submission before
any other palliative or rehabilitative care was admin-
istered.
One to 3 cc of whole blood and 250–500 mg of
lower breast and/or abdominal feathers were col-
lected from most eagles. MRCC staff collected, re-
corded, and shipped blood samples from rehab ea-
gles. Blood is an appropriate medium for evaluating
metal levels in birds (Kahle and Becker 1999) and
half-life of Hg in avian blood is 1–3 mo (Stickel et al.
1977, Evers et al. 2005), permitting evaluation of
seasonal differences in contamination (Tsao et al.
2009). Harvesting feathers is a noninvasive method
for assessing metal contamination in birds (Burger
and Gochfeld 2009) and breast feathers are the best
indicator of whole-body burdens (Furness et al.
1986, Burger 1993). Metals ingested in food or wa-
ter are excreted into feathers during a 2-wk to 1-mo
period of development and are a profile of expo-
sure during that time (Burger 1993, Burger and
Gochfeld 2009). Heaviest molt in Montana Bald Ea-
gles occurs during late summer (A. Harmata un-
publ. data), thus breast feathers are an indicator
of contaminant exposure in summer/nesting areas.
Feathers were clipped near the skin surface with
surgical scissors and deposited in plastic sandwich
bags. All feathers were fully developed when harvest-
ed. Whole blood samples were divided on site; O
for organochlorine analysis and M for analysis of
Hg, Pb, Se and other toxic elements. Blood for or-
ganochlorine analysis was cooled for 24 hr, centri-
fuged, and sera withdrawn. Blood and serum sam-
ples were refrigerated and shipped with feather
samples at season end.
Blood and feather samples were shipped for anal-
ysis to Michigan State University, College of Veteri-
nary Medicine, Diagnostic Center for Population and
Animal Health, Toxicology Section, Lansing, Michi-
gan, U.S.A. (DCPAH). Whole blood was analyzed for
the following chlorinated hydrocarbons with a detec-
tion limit of 1.0 part per billion (ppb): aldrin, alpha-
benzene hexachloride (BHC), beta-BHC, delta-BHC,
gamma-BHC, alpha-chlordane, gamma-chlordane,
dichlorodiphenyldichloroethane (DDD), dichloro-
diphenyldichloroethylene (DDE), dichlorodiphenyl-
trichloroethane (DDT), dieldrin, endosulfan I, en-
dosulfan sulfate, endrin, heptachlor, heptachlor
epoxide, trans-nonachlor, and oxychlordane. Refer-
ence standard chlorinated pesticides came as 2000 mg
each in toluene/hexane (50:50) from Supelco, Inc.,
Bellefonte, Pennsylvania, U.S.A. Chlorinated pesti-
cide analysis followed Price et al. (1986). Concentra-
tions were reported in ppm (mg/ml). Two ml of
whole blood were extracted (three times) with 6 ml
hexane/acetone (9:1) by vortexing for 30 sec, centri-
fuging at 1430 3 g for 10 min, and transferring the
hexane layer. Combined hexane fractions were evap-
orated under nitrogen and redissolved in 1 ml hex-
ane for silica gel clean-up. Silica gel clean-up was
accomplished using 9 mm chromaflex columns fitted
with silanized glass wool that was prepared by pour-
ing through 20 ml of hexane containing 5 g silica gel
60 followed by 2.54 cm of anhydrous sodium sulfate.
The prepared column was layered with sample, in-
cluding 1-ml hexane rinses as needed. Three frac-
tions were collected: FI, from 10-ml hexane elution,
FII from next 25-ml hexane elution, and FIII from
the next 20 ml of benzene elution. Fractions FII and
FIII were evaporated under nitrogen and resus-
pended in 2 ml ethanol/iso-octane, 20:80; aldrin
elute in FII, whereas DDE and heptachlor elute in
both FII and FIII, and the remaining chlorinated
pesticides elute in FIII. One ml each of fractions FII
and FIII were run on a Varian (Varian, Inc.) Gas
Chromatograph (GC)—Electron Capture Detector
(ECD; Varian Inc., Palo Alto, California, U.S.A.) on
an initial screening set-up followed by a confirmatory
set-up. Initial run utilized a DB-1701 15 m 3 0.30 mm
3 0.25 u film thickness column with the injector
temperature at 250uC and the detector at 300uC.
The program was initially 150uC for 0.5 min, followed
by a linear increase at 5uC /min to 280uC, then held
at 280uC for 15 min. Confirmatory run used a DB-608
JUNE 2011 CONTAMINANTS IN MONTANA BALD EAGLES 121
30 m 3 0.32 mm 3 0.5 m film thickness column, with
the injector temp at 250uC and the detector at 300uC.
The program was initially held at 150uC, then in-
creased linearly at 12uC/min to 280uC, then held at
280uC for 20 min. Blank solvent injections were run
through the analyzer between samples. Sample ex-
traction efficiency was judged on determination of
recovery of compound standards from spiked blanks
to verify that all recoveries exceeded a minimum of
60%. Blanks, spikes, standards, and specimens in sin-
glicate were run together in the same sequence and
GC peak identities were considered verified if peak
retention times varied by no more than 0.1 min from
those of standards.
Metals in blood and feathers were analyzed by
inductively coupled plasma mass spectrometry
(ICPMS; Agilent 7500ce ICP-MS, Santa Clara, Cali-
fornia, U.S.A.) also at the DCPAH (Goulle et al.
2005, Wahlen et al. 2005). Reportable quantization
limits for metals were as follows: Pb, 1 ppb; Hg,
5 ppb; Se, 1 ppb; antimony (Sb), 1 pp; arsenic
(As), 1 ppb; beryllium (Be), 5 ppb; cadmium
(Cd), 5 ppb; chromium (Cr), 5 ppb; nickel (Ni),
1 ppb; thallium (Tl), 1 ppb; and vanadium (V),
1 ppb. Samples (0.2 ml each) were diluted with
5 ml of 0.05% EDTA, 1% NH4OH, 0.05% Triton-
X 100 and 2% n-butanol. Internal standards includ-
ed 10–15 ppb scandium, germanium, rhodium and
indium, each of which was associated with its near-
est analyte by atomic weight. ICPMS was calibrated
with 0, 1, 10, and 100 ppb standards, and sample
concentrations were measured against standard ref-
erence solutions arranged in a linear relationship.
Diluent blanks and Quality control (QC) materials
were run with each sample sequence. QC was main-
tained by monitoring results obtained with Bio-Rad
(Hercules, California, U.S.A.) Lypochek Whole
Blood Metals Controls Levels 1 and 2. Calibrations
were also cross-checked against nitric acid-digested
Standard Reference Materials obtained from the
National Institute of Standards and Technology
(NIST, Gaithersburg, Maryland, U.S.A.), for exam-
ple NIST Bovine Liver for various elements and
NIST SRM 2976 mussel for mercury. Feathers were
analyzed by ICPMS only for Hg and Se.
Organochlorine concentrations were not ana-
lyzed in eagles submitted for rehabilitation. Nestling
eagles were included for organochlorine analysis
because no historical data were available for south-
western Montana. Because origins of most captured
eagles were presumed to be in Canada, and Henny
et al. (1979) found low organochlorine concentra-
tions in migrant eagles as early as 4 yr after use of
DDT was banned, only a few wintering/migrant
Bald Eagles were tested for organochlorines. Organ-
ochlorines were measured only in adult females.
Contaminant concentrations were reported as
parts per million wet weight (ppm) from DCPAH
and units are retained here. Terms concentra-
tion(s), load(s), and level(s) are used interchange-
ably throughout. Geometric means are presented to
promote comparison with other contaminant stud-
ies but geometric mean was not calculated if ,50%
of samples had concentrations below detection lim-
it. When $50% of samples contained detectable
levels of a contaminant, those with no detectable
levels were assigned a concentration of half the de-
tection limit of respective analytes for calculation of
geometric mean. Arithmetic means are presented
and compared for groups that had ,50% of sam-
ples with no detectable levels and are so noted.
Contaminant data were transformed to common
logarithms for parametric statistical tests. Pearson
Product-Moment tests were used to test correlations
(r values) between categories. Tukey’s honestly sig-
nificant difference tests for unequal n were used to
detect differences among groups if ANOVA/MAN-
OVA tests indicated differences. Multiple compari-
sons (Student’s t-tests, ANOVA) with Bonferroni ad-
justments (i.e., 0.05/n tests) were conducted if all
cells for MANOVA tests could not be filled. If log-
transformations were inappropriate and raw data
plots revealed curvilinear relationships or outliers,
or Kolmogorov-Smirnov tests indicated nonnormal
distribution, nonparametric tests were employed
and Bonferroni adjusted for appropriate P value.
P values #0.05 were considered significant. Season
was excluded from any analyses involving feather
contaminants because all eagles most likely devel-
oped their feathers in the summer. All statistical tests
were performed and graphics produced in various
modules of STATISTICA ver. 6.0 (StatSoft 2003).
Based on data presented by Kramer and Redig
(1997) and Neumann (2009), Pb concentrations
in blood of ,0.2 ppm were considered background,
0.2 to 0.6 ppm were considered elevated (‘‘sub-clin-
ical’’ in Kramer and Redig 1997); .0.6 to 1.0 ppm
as acute (‘‘clinical’’ in Kramer and Redig 1997) and
.1.0 ppm considered toxic (‘‘fatal’’ in Kramer and
Redig 1997). Similar exposure levels of Hg and Se
in blood that potentially may affect health and re-
production in Bald Eagles have not been estab-
lished (Burger and Gochfeld 1997, Spallholz and
Hoffman 2002, Scheuhammer et al. 2008).
122 HARMATA VOL. 45, NO. 2
RESULTS
Blood and feather samples were obtained from 17
nestling Bald Eagles in southwestern Montana, 12 in
2006 and 5 in 2007. Most samples (78%) were ob-
tained from nests associated with free-flowing rivers
(Gallatin, Jefferson, Madison, Yellowstone, Mis-
souri). Four nestlings in nests associated with two
reservoirs of the Missouri River (Canyon Ferry and
Holter reservoirs) were also sampled.
Ninety-one Bald Eagles were captured, 30 in
2006–07 and 61 in 2007–08. Blood samples were
obtained from 88 eagles; samples were not collected
from three birds because ambient air temperature
was ,223uC. Feather samples were collected from
90 captured eagles and one juvenile eagle found
recently (,2 d) expired under a power line. More
males (51) than females (40) were captured but sex
distribution did not differ (x2 5 1.35, P . 0.24).
The most numerous plumage class represented
among captured eagles was adult at 42%, followed
by 32% juveniles, 20% immature, and 7% subadults.
Blood and feather samples were collected from 29
rehab eagles submitted to MRCC for rehabilitation
between 10 December 2005 and 15 April 2008. Hg,
Se, and Pb were analyzed in blood of most rehab
eagles (early submissions) but a few also were tested
for additional elements plus Hg and Se in feathers.
Rehabs included one subadult male eagle captured
and sampled during this study, and recaptured alive
30 d later due to electrocution. Most rehabs (72%)
were found in southwest Montana, including the
Upper Missouri River watershed, and most (62%)
rehabs were males. The most numerous plumage
class represented was subadult (52%); 17% were
adults, 17% immatures, and 14% juveniles. Most
(75%) died or were euthanized. Two eagles banded
as nestlings in Montana were among the rehab sam-
ple. No others were known to have bred or hatched
in Montana.
Mercury, Selenium, and Lead in Tissues. Hg, Se,
and Pb were detected in the blood of all Bald Eagles
sampled (Table 1). Concentrations of Hg, Se, and
Pb in blood (hereafter HgB, SeB, and PbB, respec-
tively) of nestlings did not differ between 2006 and
2007 (P . 0.37) nor between 2006–07 and 2007–08
(P . 0.22) in captured eagles and no trends were
detected in HgB, SeB, or PbB relative to date of
admittance for rehab eagles. Thus, years were
pooled for further analysis. HgB was lowest in nest-
ling eagles (P , 0.01) but did not differ between
captured and rehab eagles (P 5 0.79). SeB did not
differ among all groups (P . 0.78). PbB was lower
in nestling eagles than in captured and rehab eagles
(P , 0.01) and PbB of captured eagles was higher
than that of rehab eagles (P 5 0.05; Fig. 1). HgB
and PbB were lower in nestlings than all other
plumage classes of wild eagles (P , 0.01), but no
differences in HgB, SeB, or PbB associated with
plumage class were detected in captured eagles (P
5 0.71; Fig. 2, top). In rehab eagles, PbB of imma-
tures was lower than that of juveniles (P 5 0.04) but
not subadults or adults and no differences in HgB
or SeB among rehab plumage classes were detected
(P . 0.21; Fig. 2, bottom). Both HgB and PbB de-
clined as capture date progressed (Fig. 3), but SeB
remained stable across all seasons. PbB of captured
eagles was higher in males (geometric mean 5
0.34 ppm) than in females (geometric mean 5
0.21 ppm; P 5 , 0.007) but no difference between
sexes was detected for HgB, SeB, or PbB in rehab
eagles (P 5 0.411).
Proportion of eagles with PbB .0.2 ppm (above
background; Fig. 4) differed among groups (x2 5
Table 1. Geometric mean concentrations (ppm wet wt.) of mercury (Hg), selenium (Se), and lead (Pb) in whole blood
and feathers of Bald Eagles sampled in southwestern Montana, May 2006–April 2008.
GROUP
Hg (n) Se (n) Pb (n)
BLOOD FEATHERS BLOOD FEATHERS BLOOD
Nestlings 0.100 (17) 3.04 (16) 0.795 (17) 1.927 (16)a 0.037 (17)
Captured 0.709 (88) 13.038 (91) 0.736 (88) 1.538 (91) 0.272 (88)
Autumn 0.877 (23) 13.769 (25) 0.706 (23) 1.524 (25) 0.414 (23)
Winter 0.728 (46) 11.074 (47) 0.823 (46) 1.461 (47) 0.264 (46)
Vernal 0.514 (19) 18.176 (19) 0.592 (19) 1.767 (19) 0.177 (19)
Rehab 0.670 (26) 9.72 (11) 0.835 (19) 1.435 (11) 0.132 (23)
All 0.544 (131) 10.415 (118) 0.759 (124) 1.427 (118) 0.183 (128)
a Se concentrations in 2006 (geometric mean 5 1.97 ppm), 2007 (geometric mean 5 0.26 ppm).
JUNE 2011 CONTAMINANTS IN MONTANA BALD EAGLES 123
26.5, P, 0.001). No nestling or rehab eagle, but 9%
of captured eagles had PbB above toxic threshold,
although none appeared sick, debilitated, or in-
jured. Mild-to-severe symptoms that might have
been attributable to heavy metal poisoning (Gilslei-
der and Oehme 1982) especially from Pb (Locke
and Thomas 1996), were recorded for 60% of re-
habs, but the severity of symptoms was not correlat-
ed to HgB, SeB, or PbB (R. Key pers. comm.). Symp-
toms included most or some of a suite of symptoms
including drooping wings and head, inability to
stand, clenched toes, tremors, discolored (green)
excreta, unresponsiveness, half-closed eyelids, de-
pression, foul-smelling breath, nonregenerative
anemia, vomiting, diarrhea, ataxia, blindness, and
epileptiform seizures (Kramer and Redig 1997).
HgB, SeB, or PbB of rehab eagles that died or were
euthanized (n5 17) did not differ (P. 0.132) from
those of birds that were eventually released (n 5 6).
HgB and SeB were positively correlated in nest-
lings and captured eagles (Fig. 5), but not in rehabs
(n 5 19, r 5 0.34, P 5 0.157). SeB was negatively
correlated with PbB in captured eagles (n 5 88, r 5
20.26, P 5 0.016) but not in nestlings (n 5 17, r 5
20.05, P 5 0.851) or rehab eagles (n 5 17, r 5
0.178, P 5 0.494).
Hg concentrations in feathers (‘‘HgF’’) and Se
concentrations in feathers (‘‘SeF’’) were detectable
in all eagles tested (Table 1). HgF and SeF in nest-
lings were both higher in 2006 than in 2007 (P ,
0.03). Eagles captured in 2006–07 may have had
lower (P 5 0.054) HgF (geometric mean 5
10.0 ppm) than eagles captured in 2007–08 (geo-
metric mean 5 14.9 ppm) but SeF did not differ
between years (geometric means 5 1.44, 1.58 ppm,
P 5 0.06). HgF and SeF in younger plumage classes
of wild eagles were different than older plumage
classes (P , 0.01) and concentrations tended to
increase with age (Fig. 6). No difference in HgF
and SeF among plumage classes of rehab eagles
were evident, nor were there differences in HgF
and SeF between sexes for captured eagles (P .
0.150) or rehab eagles (P . 0.541).
HgB was positively correlated with HgF in nest-
lings and captured eagles (r . 0.45, P , 0.001)
but not in rehabs (r 5 0.29, P 5 0.454). SeB and
SeF were correlated for captured eagles (r 5 0.25, P
5 0.02) but not for nestlings or rehabs (r 5 0.23, P
5 0.55).
Historical Comparisons. HgB and PbB of eagles
captured in autumn of 2006 and 2007 in southwest-
ern Montana (Table 1) were higher (P # 0.05) than
Figure 1. Mean (point) and 95% confidence interval (whisker) of mercury (Hg), selenium (Se), and lead (Pb) con-
centrations (wet wt.) in blood of nestling, captured, and rehabilitated (rehab) Bald Eagles in southwestern
Montana, 2006–08.
124 HARMATA VOL. 45, NO. 2
Figure 2. Mean (point) and 95% confidence interval (whisker) of mercury (Hg), selenium (Se), and lead (Pb) con-
centrations (wet wt.) in blood of wild (top) and rehabilitated (bottom) Bald Eagle plumage classes sampled in south-
western Montana, 2006–08. Unequal sample sizes for respective Hg, Se, and Pb in rehabs follow plumage class labels.
Figure 3. Concentrations (ppm wet wt.) of mercury (Hg) and lead (Pb) in blood of Bald Eagles captured in south-
western Montana by advancing date of capture. Data were pooled for both December–April 2006–07 and 2007–08.
Capture Day 1 was December 1 for both years.
JUNE 2011 CONTAMINANTS IN MONTANA BALD EAGLES 125
those of autumn migrants captured at Hauser
Lake in Montana in the early 1990s (Hauser Lake
HgB geometric mean 5 0.50 ppm; PbB geometric
mean 5 0.256; M. Restani and A. Harmata unpubl.
data; Fig. 7). SeB did not differ (Hauser Lake: geo-
metric mean 5 0.609 ppm). Geometric mean and
maximum concentration of HgB in vernal migrants
captured in southwestern Montana from 2006–08
(Table 1) were virtually identical to those of vernal
migrants captured in central Montana between
1987 and 1995 (0.54, 1.7 ppm, respectively; Har-
mata and Restani 1995) and detection rates
were not different (100% vs. 94%; P5 0.52). Vernal
migrants captured in southwestern Montana
between 2006–08 had similar geometric mean
SeB (0.59 ppm), detection rate (100%), and maxi-
mum detected concentration (3.17 ppm) as vernal
migrants captured by Harmata and Restani (1995)
between 1987 and 1995 (0.55 ppm, 94%, 2.8 ppm,
respectively). Geometric mean PbB of vernal mi-
grants captured in southwestern Montana in the
late 2000s (Table 1) was lower than that reported
for vernal migrants captured in central Montana
between 1987 and 1995 (0.32 ppm; Harmata and
Restani 1995), but detection rate was similar (97%).
HgB and SeB of five Bald Eagles were measured
both at the time of the original banding and at a
subsequent encounter (Table 2). Time between
samplings ranged from 5 mo to 18 yr and all en-
counters occurred within 57 km of original cap-
ture sites. No trends in contamination were evi-
dent among eagles that were encountered after
banding.
Other Blood Contaminants. Other chemical ele-
ments if detected in blood of Bald Eagles were at
low concentrations (Table 3). No captured eagle
exhibited signs of toxicity or teratogenic or muta-
genic effects. Only one nestling exhibited signs of
morbidity, but no blood was drawn from this bird
due to its debilitated condition. Symptoms of toxic-
ity manifest in rehabs were attributed to heavy met-
als and were likely not influenced by other elements
detected. No differences in blood concentrations of
other chemical elements (Table 3) among groups
were detected (P . 0.05).
DDE residues in blood were detected in 36% of
nestlings and nearly 60% of captured eagles tested
(Table 3). No differences were found in DDE con-
centrations or detection rates among seasonal
groups of captured birds.
DISCUSSION
Mercury. The primary impetus for initiation of
this study was concern that Bald Eagles in southwest-
ern Montana may have been exposed to Hg at levels
that would affect survival and reproduction of the
local population. Reproduction is the most sensitive
endpoint of Hg toxicity in birds (e.g., Toschik et al.
Figure 4. Exposure levels of lead (Pb) in blood of Bald Eagle sample groups in southwestern Montana, 2005–08.
Background 5 ,0.2 ppm wet wt., elevated 5 .0.2 # 0.6 ppm, acute 5 .0.6 # 1.0 ppm, toxic 5 .1.0 ppm.
126 HARMATA VOL. 45, NO. 2
2005, Sheuhammer et al. 2007, Burgess and Meyer
2008). Concentrations of Hg in blood of nestlings in
Montana were similar to those in nestlings in Flor-
ida (geometric mean 5 0.13, n 5 48) that Wood et
al. (1996) considered to be ‘‘baseline’’ and lower
than those in Maine (0.53), where DeSorbo and
Evers (2005) felt Hg did not have a major impact
on reproduction.
Deposition of Hg in developing feathers is impor-
tant in excretion of total body burdens (Furness et
al. 1986, Braune and Gaskin 1987, Wolfe et al.
1998). Feather concentrations may be more repre-
sentative of Hg in the local environment in summer,
where all feather development occurred in a local-
ized area (i.e., nest site) over an extended period.
Bowerman et al. (1994) considered HgF in Bald
Eagles of the Great Lakes (geometric mean 5
21.1 ppm, range: 3.6–48) as merely ‘‘elevated.’’
Odsjo¨ et al. (2004) found geometric mean concen-
tration of HgF in juvenile Osprey (Pandion haliaetus)
in Sweden was 5.25 ppm dry weight, which they
considered low. Wood et al. (1996) considered geo-
metric mean HgF of 3.23 (ppm wet wt; n 5 61) in
Florida Bald Eagle nestlings as ‘‘background.’’ HgF
in Montana nestlings were well below concentra-
tions found in these studies and although nestlings
displayed 30-fold more HgF than HgB, this differ-
ence was intermediate among several studies in the
continental U.S. where Bald Eagle production has
not been affected (Weech et al. 2006). Hg is clearly
not limiting reproduction of Bald Eagles in Mon-
tana. The Bald Eagle nesting population in Mon-
tana has grown from 19 nesting pairs in 1980 (Flath
et al. 1991) to nearly 500 pairs in 2009 and contin-
ues to grow at about 10% annually (Hammond
2010).
Montana nestlings and captured juveniles were
essentially the same plumage/year class but HgB
of nestlings were much lower than those of juve-
niles. However, HgF of nestlings and juveniles were
not different (Fig. 7), suggesting similar contamina-
tion profiles. Differences in contaminant concentra-
tions in blood between these age classes may be
more a reflection of time-trend in bioaccumulation
rather than geographical origin, as juveniles were
sampled 5 to 6 mo later in life than nestlings. Breast
feathers of most eagles were probably developed in
summer/nesting grounds. Higher HgB in juveniles
than nestlings may be indicative of Hg accumulated
in juvenile natal areas during summer and seques-
tered in other tissues (liver, kidney), then mobilized
in migrant eagles under food or physiological stress
as a result of rigors of migration. Declining HgB
from autumn to spring in captured eagles (Fig. 4)
suggested that food items were more contaminated
with Hg farther north, or at least earlier in late sum-
mer/early fall than in spring.
Atmospheric aerosols now are considered to be
the primary mechanism by which Hg contaminates
aquatic environments on which Bald Eagles depend
Figure 5. Relationship of selenium (Se ppm wet wt.) and mercury (Hg ppm wet wt.) in blood of nestling (left) and
captured (right) Bald Eagles in southwestern Montana, 2006–08.
JUNE 2011 CONTAMINANTS IN MONTANA BALD EAGLES 127
(Engstrom et al. 1994, Fitzgerald et al. 1998, 2005,
Hammerschmidt and Fitzgerald 2006, Lamborg et
al. 2002, Wiener et al. 2006). Although anthropo-
genic sources such as mine effluents, burning of
fossil fuels, and cement production contribute to
atmospheric loads (Pacyna et al. 2010), recent focus
has been on the role of natural and human-caused
wildfires in deposition of Hg in aquatic systems
(Friedli et al. 2001, 2003, Turetsky et al. 2006).
Large, intense forest fires in the continental U.S.
(e.g., Yellowstone fires of 1988) and Canadian bo-
real forest (Witt et al. 2009) release Hg into the
atmosphere not only from trees consumed, but es-
pecially peat that absorbed disproportionate
amounts of atmospheric Hg emitted during the in-
dustrial age (Grigal 2003, Friedli et al. 2003, Tur-
etsky et al. 2006). Higher HgB of eagles captured
in southwestern Montana early in the 21st century
as compared to those captured late in the 20th cen-
tury (Fig. 7) suggest environmental Hg may be in-
creasing. Advancing global climate change and as-
sociated desiccation and ignition of temperate and
boreal forests (Sigler et al. 2003), exacerbated by
extensive clear-cutting (Garcia and Carignan 1999,
2000) and projected increases of industrial effluents
(Pacyna et al. 2010), may intensify poisoning of
aquatic ecosystems with Hg, hence the need for
continued, periodic monitoring.
Selenium. Se-induced mortality has been docu-
mented in waterfowl, but effects are primarily tera-
togenic or manifested in reduced natality or pro-
ductivity (Eisler 1985, Ohlendorf et al. 1986,
Spallholz and Hoffman 2002). No nestling, cap-
tured, or rehab Bald Eagle exhibited any physical
symptom of Se poisoning. Se concentrations in tis-
sues were similar for all groups of eagles (Fig. 1, 2,
Figure 6. Mean (point) and 95% confidence interval (whisker) of mercury (Hg) and selenium (Se) concentrations in
feathers of plumage classes of wild (top) and rehabilitated (bottom) Bald Eagles sampled in southwestern
Montana, 2006–08.
128 HARMATA VOL. 45, NO. 2
5, 6) and it was unlikely that these concentrations
represent anything more than benign background
or even beneficial levels. Se is considered efficacious
for detoxifying Hg (Yoneda and Suzuki 1997, Odsjo¨
et al. 2004) in organisms and Hg toxicity in birds
may be highly dependent upon the availability of
dietary Se (Weech et al. 2003). Strong correlations
of HgB and SeB of nestling and captured eagles
(Fig. 5) may indicate an active, antagonistic meta-
bolic process with Hg, as additional Se is absorbed
to mitigate the effect of Hg (Rudd et al. 1980, Eisler
1985, Chen et al. 2006). Lack of correlation of HgB
and SeB in rehabs and dissimilar trends in HgF with
ostensibly healthy eagles (nestlings and captured)
may indicate a malfunction of the detoxification
mechanism or lack of Se in food or water available
to rehabs.
Se is present at high concentrations in some arid
areas of the western U.S. (Crampton and Harris
1969). Dissolution of Se from soils and accumula-
Figure 7. Mean and 95% confidence interval (whiskers) of mercury, selenium, and lead in blood of Bald Eagles
captured in autumn at Hauser Lake, Montana, in the early 1990s (dot; M. Restani and A. Harmata unpubl. data) and
in autumn in southwestern Montana in the late 2000s (box).
Table 2. Mercury (Hg), selenium (Se), and lead (Pb) concentrations (ppm wet wt.) in blood (B) and feathers (F) of
Bald Eagles at initial banding and subsequent encounter in southwestern Montana.
BANDING ENCOUNTER
BAND AGE1 DATE
Hg Se Pb
DATE TIME2 WHY
Hg Se Pb
B F B F B B F B F B
23653 Nest 6/07 0.07 1.40 0.74 0.21 0.12 6/08 1.2 yr Impact 0.49 13.7 0.75 1.70 0.30
23655 Nest 6/07 0.17 5.69 0.91 0.29 0.02 10/07 5 mo Impact 1.32 4.75 0.88 1.53 0.01
32087 Juv 3/91 0.80 ND 0.20 2/08 18 yr Capture 0.62 41.7 0.52 1.82 0.70
37359 Juv 11/92 0.57 0.32 0.12 3/07 16 yr Capture 0.86 32.8 0.42 1.74 0.31
00030 Ad 1/08 1.40 32.2 0.66 2.2 0.75 3/08 2 mo Electro 0.92 0.35 0.20
1 By plumage.
2 Time from banding to encounter.
JUNE 2011 CONTAMINANTS IN MONTANA BALD EAGLES 129
tion in ecosystems is accelerated by irrigation (Eisler
1985). Southwestern Montana is a mosaic of irrigat-
ed and dry cropland interspersed with native habi-
tats. The region is most likely high in Se, as demon-
strated by relatively common occurrence of milk
vetch (Astragalus spp.), most species of which are
indicators of Se-rich soils (Beath et al. 1939). Geo-
graphic regions with low soil Se have higher Hg-
bioaccumulation, e.g., northern Canada (Ralston
2005), where at least some eagles in this study prob-
ably originated. Seasonal residence in southwestern
Montana for Bald Eagles therefore may have thera-
peutic value because of high concentrations of en-
vironmental Se, which may help neutralize effects of
Hg acquired in other areas of the continental U.S.
or Canada.
Lead. Lead concentrations in Montana eagles
were low, surprisingly even for those submitted for
rehabilitation (Table 2). Low PbB in nestlings prob-
ably reflects the seasonal diet of local Bald Eagles,
which mainly feed on fish during the nesting season
in southwestern Montana (Swenson et al. 1986).
Fish are unlikely to contain sinkers or shot, and less
likely than ungulates, waterfowl, or sciurids to con-
tain Pb fragments from rifle or shotgun pellets. Au-
tumn migrants and wintering eagles had geometric
mean PbB above background concentrations (Ta-
ble 1). Autumn concentrations most likely reflect
seasonal contamination or residency in areas far-
ther north (see Miller et al. 1998). Eagles captured
in autumn likely have more recently arrived from
northern latitudes than eagles captured in winter
or spring. Lower winter levels suggest elimination
or at least less ingestion of Pb in southwestern Mon-
tana. Declining detection rates and blood concen-
trations of toxic elements with season of capture
suggest that residency in southwestern Montana
may provide food and water less contaminated with
Hg and Pb than areas where captured eagles origi-
nated. Concentrations of Pb considered toxic ac-
cording to Kramer and Redig (1997) were found
in 9% of captured eagles. Theoretically, they should
have been dead, or at least moribund (P. Redig
pers. comm., Kramer and Redig 1997), but all ap-
peared healthy and unaffected and plumage was in
good condition. However, these apparently healthy
eagles may become sick later in the year and simply
not be found. No rehab birds exhibited toxic con-
centrations of Pb (Fig. 4). These metals may be
purged from the system prior to recovery, whereas
indirect effects or symptoms may linger. Perhaps
other preemptive causes of morbidity such as for-T
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130 HARMATA VOL. 45, NO. 2
aging ineptness, disease, or injury predispose eagles
to suffer toxic effects of metals, or metal presence
may be merely an identifiable proximate rather
than the ultimate cause of debilitation in rehabs.
Historically, etiology of Pb poisoning in eagles
focused on effects of residual Pb shotgun pellets in
waterfowl (Pattee and Hennes 1983). As a result, the
U.S. and Canada imposed bans on Pb shot for water-
fowl hunting by the 1990s in response to large-scale
poisonings of eagles. However, concentrations of Pb
in blood of Bald Eagles in Montana apparently did
not decline. Detection rate (100%) and PbB of au-
tumn migrants (Table 1) captured in southwestern
Montana during this study were higher than those of
autumn migrants tested in northern Montana before
the Pb ban (1980, 1981; ,50% and 0.072 ppm; Wie-
meyer et al. 1989) and seemingly higher than those
of Bald Eagles captured at Hauser Lake in Montana
in the early 1990s (Fig. 7). Like HgB, PbB declined in
samples from autumn through spring (Fig. 3), indi-
cating eagles were feeding on a less-contaminated
food base as seasons progressed.
Recent attention on the etiology of Pb poisoning
in eagles has been focused on effects of residual
fragments from Pb-core center-fire rifle bullets in
big game carcasses (Hunt et al. 2006, Watson et al.
2009). Higher PbB in captured juveniles may reflect
this phenomenon. Increased scavenging by inexpe-
rienced young birds might expose them to more Pb
in carcasses than that available to older eagles more
adept at catching live, uncontaminated prey (water-
fowl, fish). Perhaps the source of much Pb in Mon-
tana eagles always has been residual fragments from
rifle bullets (including small caliber rim fire ammu-
nition; Harmata and Restani 1995) in terrestrial
nongame such as lagomorphs, ground squirrels
(Spermophilus spp.), prairie dogs (Cynomys spp.),
and big game carcasses rather than from shotgun
pellets in waterfowl or upland game birds. Contin-
ued monitoring of both Pb in eagles and degree of
hunter compliance with voluntary Pb-free ammuni-
tion campaigns may confirm relationships of Pb
contamination and use of Pb-core projectiles.
Organochlorines. DDE (a metabolite of DDT) was
the primary contaminant reducing reproductive suc-
cess of Bald Eagles in North America, with the ma-
jority of exposure apparently derived from the avian
portion of the diet (Wiemeyer 1991). Low concentra-
tions found in this study reflect the 1972 ban on DDT
and subsequent decline in use. Despite low levels of
contamination, detection in nestlings, wintering
birds, and vernal migrants reflects long-term persis-
tence of the compound. Lowest concentration was
detected in a nestling sampled farthest upstream in
the Upper Missouri River watershed, and the highest
concentration was found in a nestling sampled far-
thest downstream. A continual decrease in DDE res-
idues can be expected barring unforeseen changes in
legalization and use.
Other Trace Elements. Low concentrations and de-
tection rates of trace elements other than Hg, Se, and
Pb (Table 3) in eagles during this study indicated that
these elements are currently of little concern in popu-
lation management of Bald Eagles in western North
America. However, expense and effort to continue
monitoring is minimal, especially when samples for oth-
er blood-borne contaminants are obtained. Likewise,
once birds are in hand, the collection of feather sam-
ples from eagles is minimally invasive, as well as infor-
mative, and if the feathers are not immediately ana-
lyzed, they can be easily archived for future inspection.
Detection rates of contaminants suggested that
Bald Eagles residing in southwestern Montana, re-
gardless of origin, were exposed to a variety of po-
tentially toxic substances. However, low contami-
nant concentrations in nestling blood and feathers
indicated that Bald Eagles in southwestern Montana
lived and reproduced in a relatively clean environ-
ment. Seasonally resident eagles in Montana have
been shown to originate in Canada, the greater Yel-
lowstone ecosystem, Arizona (Hunt et al. 2009), and
southern California (Harmata 1992). Analysis of
blood and feathers of captured eagles outside the
nesting season suggested that nonresident eagles
arrived in southwestern Montana more contaminat-
ed than resident breeders. Further, declining detec-
tion rates and contaminant concentrations in eagles
captured as autumn progressed through spring sug-
gested that local environments in southwestern
Montana provided clean foods that assisted in re-
ducing overall body burdens of deleterious chemi-
cals and compounds. Although contaminants cur-
rently may not be of major concern in the health
of local Montana Bald Eagle populations, numbers
and mortality rates of rehabs may indicate that oth-
er anthropogenic mortality or morbidity pressures,
exacerbated by contaminants, may be.
ACKNOWLEDGMENTS
Funding and support was provided by: U.S. Fish and
Wildlife Service, Migratory Birds Section (Stephanie
Jones); PPL-Montana (Jon Jourdannaise, Rob Hazlewood);
Montana Fish, Wildlife and Parks (FWP; Kristi DuBois);
and Montana Dept. Natural Resources and Conservation
(DNRC; Ross Baty). Landowners and managers providing
JUNE 2011 CONTAMINANTS IN MONTANA BALD EAGLES 131
access and cooperation were: Mike Actkinson, Channels
Ranch, Ennis, MT; Page Anderson, CA Ranch, Three
Forks, MT; Jim Higgins, Higgins Bros. Ranch, Ringling,
MT; Greg Strohecker and KG Ranch, Willow Creek, MT;
Danny Johnson, Mark Kossler, Flying D Ranch, Gallatin
Gateway, MT; Tom Milesnick, MZ Bar Ranch, Belgrade,
MT; Gary Paulson, Hammer Ranch, Manhattan, MT; Bu-
reau of Land Management, Dillon Resource Area (Susan
Janis); and Craig Campbell, DNRC. Nestling banding was
performed by: George Montopoli, Arizona Western Univ. /
National Park Service (NPS); Hank Harlow, Univ. Wyo-
ming / NPS Research Center; Kurt Alt, FWP, and Pete
Harmata, Volkswagen North America. Capture specialists
included Radell Key, MRCC; Jeremiah Smith and Rose
Jaffe, FWP, Marco Restani, St. Cloud St. Univ., and Greg
Doney. Dennis Flath, Apex Environmental, conducted ae-
rial nest surveys. Additional logistics and support were
provided by Kevin Frey and Sam Shepard (FWP), Brooks
Gehring, United Parcel Service, and Melody Harmata.
Marco Restani graciously permitted use of contaminant
data obtained at Hauser Lake, Montana, for comparison
here. Stan Wiemeyer assisted with chemical methods pre-
sentation. He, Cheryl Dykstra, and two anonymous review-
ers vastly improved earlier drafts of the manuscript.
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