Eggshell Quality of Black-Billed Magpies Nesting in Idaho
Author(s): Scott L. Findholt and Charles H. Trost
Reviewed work(s):
Source: The Murrelet, Vol. 64, No. 3 (Winter, 1983), pp. 91-93
Published by: Society for Northwestern Vertebrate Biology
Stable URL: http://www.jstor.org/stable/3535268 .
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GENERALNOTES
WINTER 1983
91
HOFFMAN, W., J.A. WIENS, AND J.M. SCOTT. 1978. Hybridizationbetween gulls (Larusglaucescens
and L. occidentalis)
in the PacificNorthwest.Auk 95:441-458.
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of nest spacing. Auk 92:270-279.
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BRIGGS.1981. Summaryof marine mammal and seabird surveyson the southernCalifornia
bight areas, 1975-1978. Vol. III. Invest. Rep. Part III. Seabirds. Book II. Final Reportto BLM.
Univ. Cal., Irvine.
MCLANNAHAN, H. M. C. 1973. Some aspects of the ontogeny of cliffnesting behavior in the
and the Herring Gull (Larus argentatus).
Kittiwake(Rissa tridactyla)
Behaviour 44:36-86.
PIEROTTI, R. 1981. Male and female parental roles in the WesternGull under differentenvironmental conditions. Auk 98:532-549.
1975. Effectsof human disturbanceon the breeding success of
ROBERT, H. C. AND C. J. RALPH.
gulls. Condor 77:495-499.
on San Nicolas Island,
SCHREIBER, R. W. 1970. Breedingbiology of WesternGulls (Larusoccidentalis)
California,1968. Condor 72:133-140.
SCOTT, J. M. 1973. Resource allocation in four syntopic species of marine diving birds. Ph.D.
thesis,Oregon State Univ., Corvallis.
VAROUJEAN, D. H. AND R. L. PITMAN. 1980. Oregon seabird colony survey, 1979, U.S. Fish and
Wildlife Service Report,Portland,Oregon.
WINNETT, K. A. 1979. The influenceof cover on the breeding biology of WesternGulls on Santa
BarbaraIsland, California.M.S. thesis,CaliforniaState Univ., Northridge.
P.O. Box 1467,Newport,OR 97365. Received5 September
1982,accepted2 May 1983.
EGGSHELL
QUALITY OF BLACK-BILLED
NESTING IN IDAHO
MAGPIES
SCOTT L. FINDHOLT AND CHARLES H. TROST
The problem of eggshell thinning associated with organochlorineexposure, particularlyDDE,
in raptorialand fish-eatingbirds has been well documented (Anderson and Hickey 1972, Cooke
1973, Ohlendorf et al. 1978).
The American Falls Reservoir,located in the upper Snake River ecosystem,is contaminatedwith
organochlorine insecticides and PCB's (Johnsonet al. 1977). Levels of chlorinated hydrocarbons
increased in the upper Snake River ecosystemwhen the Teton Dam collapsed on 5 June 1976 and
released 2.96 x 1010m3 (24 million acre-feet)of water into the upper Snake River Valley. The
resultingflood inundated an extensive agriculturalarea in the upper Snake River Valley. At least
three commercialfacilitiesstoringpesticides were damaged, and an undisclosed amount of pesticides in privatestorage were lost. Unknown quantities of DDT and PCB's were among the organochlorines dispersed when the Teton Dam collapsed (Perry 1979).
We were interestedin understandingwhetherbirds nestingin the upper Snake River ecosystem
were experiencingeggshell changes induced by organochlorineexposure compared to other geographicareas in Idaho and to pre-1947eggshell quality data. Black-billedMagpies (Pica pica) nesting
in the upper Snake River ecosystemand in areas of southeasternIdaho unaffectedby the Teton
flood were chosen for the following reasons: 1) abundance in Idaho, 2) reasonable accessibilityof
nests, 3) residentstatus with little or no annual movement,unlike most raptorsand ardeids, and
4) potentialsensitivityto organochlorinesbecause of a diet thatincludes dead fishand othercarrion
(Linsdale 1937; Bent 1946; C. H. Trost,unpubl. data).
METHODS
Between 3 March and 27 April 1978, 39 complete, fresh clutches of Black-billed Magpie eggs
were collected in Idaho. Twenty-fourclutches were taken fromthe upper Snake River ecosystem
92
THE MURRELET
64(3)
TABLE 1. Comparison of pre-1947and recenteggshell data forBlack-billedMagpies.
Location
Upper Snake River-1978
(experimental)
SoutheasternIdaho-1978
(control)
Pre-1947Idaho
Pre-1947Wyoming
Pre-1947 Colorado
No. clutches
measured (eggs)
24 (167)
Mean clutch
size + SE
Mean thickness
index ? SE'
7.0 ? 0.19
0.711 ? 0.003
15 (105)
7.0 ? 0.19
0.700 + 0.004
4 (26)
4 (30)
12 (79)
6.5 ? 0.87
7.5 ? 0.65
6.6 + 0.23
0.683 ? 0.006
0.721 ? 0.005
0.729 + 0.005
'Thickness index of pre-1947 Idaho, Wyoming,and Colorado eggshells significantlydifferent(ANOVA, p < 0.001); thickness
index of upper Snake River and southeasternIdaho eggshells significantlydifferent(ANOVA, Student-Newman-Keulsmultiple
range test,p < 0.05); thicknessindex of upper Snake River and pre-1947Idaho eggshells significantlydifferent(ANOVA, StudentNewman-Keuls multiple range test,p < 0.01).
fromnests adjacent to the Snake River or its reservoirs.The remaining15 clutcheswere taken from
areas in southeasternIdaho unaffectedby the Teton flood. All eggs were blown, air dried until no
additional weight loss could be measured, then used to calculate Ratcliffethicknessindices (Ratcliffe1967). Lengths and greatestbreadths of eggs were measured to the nearest 0.1 mm using a
Helios vernierdial caliper. Weights,including membranes,were determinedto the nearest0.01 g
using a Mettlertop-loading pan balance. Comparable measurementsof eggshells collected before
1947 in Idaho, Wyoming,and Colorado were taken at the WesternFoundation of VertebrateZoology, Los Angeles.
RESULTS
Numbers of clutches, mean clutch sizes, and mean Ratcliffethickness indices of Black-billed
Magpie eggs measured are in Table 1. Highly significantdifferenceswere detected between pre1947 thicknessindex data of Black-billed Magpie eggs fromColorado, Wyoming,and Idaho (ANOVA, p < 0.001). Therefore,recenteggshell qualitydata of magpies were only comparedto archival
eggshell data fromIdaho. The mean thicknessindex of Black-billed Magpie eggs collected from
the upper Snake River ecosystemwas 3.9% + 2.9% (95% C.L.) higher thalt the mean thickness
index of magpie eggs collected before 1947 in Idaho and 1.5% + 1.4% (95% C.L.) higher than
the mean thicknessindex of magpie eggs fromareas in southeasternIdaho unaffectedby the Teton
flood (ANOVA, Student-Newman-Keulsmultiple range test,p < 0.01 and p < 0.05, respectively).
There was no significantdifferencebetween the mean thicknessindex of Black-billedMagpie eggs
fromareas of southeasternIdaho not flooded when the Teton Dam collapsed and pre-1947eggshell
thicknessdata (ANOVA, Student-Newman-Keulsmultiple range test,p > 0.05).
DIScuSSION
Althoughmembersof the Corvidae appear to be less sensitiveto organochlorinesthanare raptors
and ardeids, eggshell changes have been observed in some corvids including the Rook (Corvus
and Carrion Crow (C. corone).Recent mean eggshell thicknessindex decreased by 5.0%
frugilegus)
in the Rook and 4.8% in the Carrion Crow compared to the thicknessindex of archival eggshells
(Ratcliffe1970). Also, the severe decline of magpie populations in eastern England was probably
caused by dieldrin and other organochlorines(Cooke 1979).
Small sample sizes may explain the geographical variationdetectedin mean thicknessindices of
pre-1947 magpie eggs fromIdaho, Wyoming,and Colorado (Klaas et al. 1974). The pre-1947eggs
fromIdaho are also a small sample forcomparisonwith our 1978 data; thismay explain the apparent
increase we found in mean thicknessindex. However, our resultssuggestthatBlack-billedMagpies
nesting in Idaho are not experiencingorganochlorine-inducedeggshell thinning.
The only comparativedata available fromthe United States on organochlorineresidues in egg
contentsand shell thinningof magpie eggs are fromOregon (C. J.Henny, U.S. Fish and Wildlife
Service,pers. comm.). Of nine eggs analyzed fororganochlorines(one egg fromeach of nine nests),
DDE was presentat low concentrations(range 0.12 ppm to 1.4 ppm, freshwet weight) in six eggs.
Also, shell thicknessof eggs analyzed for organochlorineswas identical to that of pre-1947 eggs
fromOregon and Washington.
WINTER 1983
GENERALNOTES
93
In Idaho, Black-billed Magpies may not have been very susceptible to organochlorine-induced
eggshell thinningbecause of diet. Although our observationsindicate thatmagpies consume large
quantities of dead fish and other carrion,a proportion of their diet also consists of insects and
vegetable matter(Bent 1946). Thus, Black-billed Magpies would be feeding at a much lower level
on the food chain and consequentlywould be exposed to lower concentrationsof organochlorines.
In Britain,Black-billed Magpies accumulated less total organochlorineresidues in eggs than four
other species of corvids and five species of raptorsbecause of a diet of seed oats (Ratcliffe1965).
Also, eggshell thinningmay not have been evident in Black-billedMagpies because the levels of
to cause
organochlorinesthatmagpies were exposed to in theirdiet of dead fishwere insufficient
eggshell thinning.The mean concentrationsof total DDT (0.28 ppm wet weight,whole fishbasis)
and PCB's (0.17 ppm) in 27 fishfromthe upper Snake River in 1978 and 1979 (A. E. Murrey,Idaho
Departmentof Health and Welfare,pers. comm.) were not particularlyhigh. The susceptibilityof
Black-billedMagpies to organochlorinesrequires furtherinvestigation.
personnel including L. Kiff,S. Sumida, R. Cobb, and M. Morrison
Acknowledgements.-Curatorial
of the WesternFoundation of VertebrateZoology, provided pre-1947oological data on Black-billed
Magpies. We thankL. Epperson forinvaluable assistancein the laboratoryand L. Farleyforhelping
with fieldwork. We also thankJ.E. Anderson, C. J.Henny, D. W. Anderson,and H. M. Ohlendorf
forcriticalreview of the manuscript.The primarysource of fundingwas the Idaho Departmentof
Health and Welfare. Financial support also came from the Department of Biology, Idaho State
Universityand a Grant-in-Aidof Research fromSigma Xi.
LITERATURE
CITED
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fromAmerican Falls Reservoirsediments to forageand predaceous fishes.Idaho Water Resource Institute,Univ. Idaho, Moscow.
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sampling. Wilson Bull. 86:156-164.
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Idaho, following the collapse of the Teton Dam in 1976. Arch. Environ. Contam. Toxicol. 8:
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State
Pocatello,ID 83209. Presentaddress (SLF): Wyoming
Department
ofBiology,IdahoStateUniversity,
7
20
1983.
WY
82520.
Received
School,
Lander,
1982,
September
July
accepted
Training