FOODS
OF NESTING
BALD
EAGLES
IN
LOUISIANA
JOSEPHA. DUGONI,PHILLIPJ. ZWANK,ANDGARYC. FURMAN
ABSTRACT
-- During the summerof 1979,remainsof 243 vertebratescomprising31 species
werecollectedfrom 10nests
thathad fledgedyoungduringthe pr&vious
springto determinethe foodhabitsof nestingBaldEagles(Haliaeetus
leucocephalus)
in Louisiana.American Coots(Fulicaamericana)and freshwatercatfish(Ictalurusspp.) were the most
abundantspecies,
but fishprobablyconstituted
a greaterportionof the dietthanresultsindicate,dueto morecomplete
digestibilityof piscianskeltons.
The Bald Eagle(Haliaeetus
leucocephalus)
nestsin
swamps of southcentral and southeastern
Louisiana.Portionsof this habitatare being lostor
altereddue to drainage,channelizationconversion
of land to agriculture,and industrialdevelopment
(Yancey 1970). Lossof swamphabitatmay harm
nestingeaglesby reducingthe availabilityor abundanceof prey. Supportfor this hypothesisis provided by McEwan (1977) who found that Bald
Eaglesin Floridarely primarilyon fishandwetland
birds for food. Foodsof nesting Bald Eaglesin
Louisianahave not been previouslydocumented.
STUDY AREA AND METHODS
Fieldwork
was conducted
in coastal southeastern
and south-
birds, while freshwatercatfish(Ictalurussup.) accounted for 53 (52%) of 101 fish. Muskrat (Ondatra
zibethicus)
and Nutria( (Myocastor
coypus)
combined
comprised82.2% of mammals,and the reptile remains were those of a Mud Turtle (Kinosternon
subrubrum).
DISCUSSION
Remainsof 31 vertebrateprey speciesmay support claimsthat Bald Eaglesare opportunisticfeeders (Retfalvi 1970; Todd et. al. 1982; fielder 1982).
However, American Coots and catfish made up
nearly 42% of prey animals,indicatingthat a preferencefor thesespeciesmay exist.Our findings
agreewith thoseof McEwan(1977),whofound that
American Cootsand catfishcomprisedthe major
portionsof the diet of Bald Eaglesin Florida. Fielder (1982) reported that American Cootswere the
major prey animalof Bald Eaglesat a studysitein
Washington,but concludedthat availabilityof prey
dictated usage. Haywood and Ohmart (1986)
centralLouisiana,includingTerrebone,Jefferson,St. Charles,St.
Tammany, and AssumptionParishes.Climate is subtropical
maritime.Wetlandsof 0-2 m elevationpredominate;relief isprovided by leveesand spoilbanks.
Much of the region consists
of
permanentlyor annuallyfloodedbaldcypress
(Taxodium
distichum)
- tupelogum(Nyssa
aquatica)
forests.Dominantland usesinclude
gas and oil productionand industrialdevelopment,as well as
hunting,fishingand trapping.Area vegetationand othercharacteristicsare further describedby Bahr et. al. (1983) and Chabreck found in Arizona that, while catfish and other
and Condrey(1979).
benthic-feedingfish comprisedthe majority of
Bald Eaglenestlocationsweredeterminedin 1977and 1978by
prey,AmericanCootswerethe majoravianpreyof
interviewswithprivatecitizensandbyusinghelicoptersurveys.
In
JuneandJuly 1979,immediatelyfollowingfledgingof youngand Bald Eagles.Benthicfishare commonprey probaseasonal
departureof parents,preyremainswerecollected
from 9
bly becauseof their high vulnerabilityto aerial prenests.Additionalremainswerecollectedin Julyfrom a nestafter it
dators(Todd et. al. 1982). Bald Eagleconsumption
wasdownedby a hurricane.To ensureasmuchaspossiblethat
of benthic fish, American Coots, and dabbling
prey remainswere thoseleft by 1979nesters,we collectedonly
thoseremainson or near the nestsurfaceimmediatelyafter eagles waterfowlmakesobviousthe importanceof shallow
wetlandswithin foraging distanceof nestsites.Bevacatedthe nest,prior to possiblenestuseby other species.
RESULTS
Prey speciesof nestingBald Eagleswere determined from remainsfound in 10 nestsduring the
summer of 1979. We collected remains of 243 ver-
tebrates,including 4 classesand 31 species(Table
causeof this importance, proposalsto alter such
wetlandsshouldbe carefullystudied.
A bias toward nonfish prey speciesprobably
existsin our study,becausefishskeletalpartscanbe
more completelydigestedthan thoseof other vertebrates(Todd et. al. 1982). For instance,although
1). Birdscomprisedthe highestpercentage
of prey we observed over 20 Gizzard Shad (Dorosoma
brought to nestsand consumed,the
animals(42.4%), followedby fish (41.5%), mam- cepedianum)
mals(15.7%), and a reptile (0.4%). American Coots remainsof only 2 were recovered.
(Fulicaamericana)
comprised40 (47.6%), of the 103
124
RAPTORRESEARCH
VOL. 20 (3/4): 124-127
FALL/WINTER 1986
FOODSOF BALD EAGLES
125
126
DUGONI
ET.AL.
VOL.20, No.3/4
F^LL/WINTER
1986
FOODS
OVB^LD
E^gLES
ACKNOWLEDGMENTS
Contribution
of the Louisiana
Cooperative
Fishand Wildlife
Research
Unit; Louisiana
StateUniversity,
U.S.FishandWildlife
Service,Louisiana
Departmentof Wildlifeand Fisheries,
and
127
FIELDER,
P.C. 1982. Foodhabitsof Bald Eaglesalongthe
mid-ColumbiaRiver,Washington.
Murrelet63:46-50.
HAYWOOD,
D.D., ANDR.O. OHMART.1986. Utilizationof
benthic-feeding
fishby inlandbreedingBaldEagles.
Condor 88:35-42.
WildlifeManagement
Institute,
cooperating.
WewishtothankDr.
JohnV. Conner,
Professor,
Louisiana
StateUniversity,
andDr. McEwAN,L.C. 1977. Nest siteselectionand the producRoyal
B.Suttkus,
Director,
TulaneUniversity
Museum
ofNatural
tivityoftheSouthern
BaldEagle.
M:S.Thesis,
Univ.of
History,
for helpin identification
of specimens.
We thankMr.
Florida, Gainesville.63pp.
JohnD. Newsom,
Leader,Louisiana
Cooperative
WildlifeUnit, RETFALVI,
L.I. 1970. Foodof nestingBaldEagleson San
retired,for guidance
duringtheearlystages
of thisstudy,and
JuanIsland,Washington.
Condor
72:358-361.
Todd,
thanktheU.S.ArmyCorpsof Engineers
for financial
support.
C.S.,
L.S.Young,
R.B.Todd,
C.S.,
L.S.•oung,
R.B.
LITERATURE CITED
BAHR,
L.M.JR.,R. COSTANZA,
J.W.DAYJR.,S.E.BAILEY,
Owen,J.R., andF.J.Gramlich.1982.
YANCEY,
R.K. 1970. Our vanishing
deltahardwoods.
La.
Consew. 22:30-36.
C. NEILL, S. G. LEIBOWITZANDJ. FRUCI. 1983.
Ecologic
characterization
of the Mississippi
Deltaic
Addressof first and secondauthors: Louisiana Cooperative
Plain region; a narrativewith managementrecom- Wildlife Research Unit, Louisiana State University, Baton
Rouge,Louisiana
70803.Address
of thirdauthor:School
of
mendations,FWS/OBS-82/69. 189pp.
Forstry,WildlifeandFisheries,
Louisiana
StateUniversity,
BatCHABRECK,
R.H., ANDR.E. CONDREY.1979. Common ron Route, Louisiana 70803.
vascular
plantsof theLouisiana
marsh.La.StateUniv.
Centerfor WetlandRes.SeaGrant publ.LSU-T-79003. 116pp.
Received1 February1986;Accepted31 October1986.