INTERNATIONAL
WADER
White-wingedScoters,(Melanitta
perspicillata),preliminaryanalysis
of Carbon- 13 indicates considerable
variation between individuals
in the
relative contribution of terrestrial
preyto overalldiet.Individual
valuesrangefromhighlymarine
signatures
to highly terrestrialones,
andthe populationaveragevaried
significantlybetweenyears,
suggesting
thatuseof field varies
both within populationsand over
time.No significant
differences
in
foodoriginwerefoundbetween
sexesand age classes.Sincethe use
STUDY
GROUP
requiredup to 18 daysto achieve
sustainedflight. Among 12 and 19
broodsobservedin 1999 and 2000,
respectively,
malestendedbroodsa
meanof 11.75 daysand 13.2 days
after hatch,while mean female
attendancewas 8 and6.4 daysin
thosetwo years. Males and females
didnotdiffersignificantlyin the
lengthof attendance
in 1999,but
BreedingEcologyofWestern
Sandpipersonthe centra!YukonKuskokwim Delta, ALASKA.
Dan Ruthrauff
2000. Males demonstrated
bandedin 1998,only5 (23.8%)were
resighted
in 1999,only 1 (4.7%) of
which was subsequently
resighted
againin 2000. Of 31 malesbandedin
1998,23 (74.2%) wereresighted
in
1999,and20 (64.5%)wereagain
resightedin 2000. Despitefindinga
Males were observed
0700- 1900h (ADT) whilefemales
incubated
from2000- 0600h (ADT).
Thiswithin-daypatternof
incubation between the sexes did
not changeduringthe threeweek
incubationperiod. Duringthebrood
careperiod,mostmalesremained
with theirbrooduntil fledging.
Femalesdesertedtheirbroodpriorto
theirmates(22 of 24, 91.6%). The
numberof daysthat a female
remained with her brood was
negativelycorrelatedwith hatchdate
(r = - 0.66,P < 0.001). Theseresults
suggestthat male Western
Sandpipers
contributesignificantly
moreduringthe incubationand
35 ha. areasurroundingour core
studyplotin 1999and2000, we
broodcareperiods,providingstrong
observed no additional banded
parentalcare.
AK 99559. email:
brian_mccaffery•fws.gov.
2000 than unsuccessful females. We
We studiedthe breedingecologyof
the WesternSandpiper(Calidris
mauri) from 1998through2000 at a
permanentYukonDelta National
WildlifeRefugefield sitein western
Alaska. The densityof nestingpairs
1999. Therewasa cleartemporal
divisionof parentalrolesduring
incubating
moreoften(57 % of time)
thanfemales(43%). Maleswere
morelikely to be incubating
between
females.Further,femaleswhobred
successfully
in 1998werelesslikely
to be resightedin both 1999 and
WildlifeRefuge,POBox346,Bethel,
remained with the brood in 1998 and
incubation.
combined 99 nests on an additional
HumboldtStateUniversity,PO Box
4212, Arcata,CA 95518,
drr6•humboldt.edu,andBrian
McCaffreyYukonDeltaNational
(Holmes1973, Erckmann1981).To
determineparentalrolesof Western
Sandpipers
on theirbreeding
groundsnearNome, Alaska,I
repeatedlydocumentedwhichmate
was presentat the nestduringthe
incubationperiod,andwhichmate
significantlylongerthanfemalesin
from other studies. Of 21 females
BIOLOGY
TIN
males remained with broods
significantseasonaldeclinesin
durationof attendancein both years,
of fields to at least some extent is
whilefemalesexhibitedsignificant
widespreadthroughoutthe
seasonal
declinesonly in 2000.
Finally,survivalestimatesbasedon
population,I proposethat land
stewardshipprogramsare necessary resightingsof bandedadultswere
to ensure the future conservation of
extremelylow for femalesrelativeto
this importantandpreviously
malesat our studysite,aswell asto
undervalued shorebird habitat.
breedingfemalesurvivalestimates
BREEDING
BULLE
thereforesuspectthat the low
survivalestimateisprimarilythe
restfitof mortalityratherthan
emigration.
Divisionof parental rolesin
breedingwesternsandpipers.
evidence that the sexes differ in
Age-specificvariation in the
reproductiveperformanceof
westernsandpipers.
Brett K. Sandercock
Dept.of ForestSciences,
University
of BritishColumbia,VancouverBC,
Canada. email:
bsanderc•interchange.ubc.ca.
in 1999 and 2000 was 2.95/ha. and
3.01/ha.,respectively,
amongthe
highestdensitiesrecordedfor this
species.Mayfield nest successon a
16ha.plotfrom 1998to 2000 was
0.56,0.24 and0.35,respectively.
Fledgingsuccess,
definedas a nest
fledgingoneor moreyoung,was
75% (12 of 16hatchednests)in 1999
and68% (19 of 28 hatchednests)in
2000. Chicks were observed to
38
fledgeas soonas day 13, but often
Julie A. Neville
Researchin the pastdecadehas
shownthat juvenile Western
Department
of Biology& Wildlife,
Sandpipers
(Calidrismauri)face
Universityof Alaska-Fairbanks,
manyecologicalandphysiological
Fairbanks,AK 99775. e-mail:
challenges
duringtheirfirstyearof
ftjan•uaf. edu
life. Comparedto adults,juveniles
departbreedingareasat laterdates
Previous observations of Western
andwith lower fat reserves,maintain
Sandpipers
(Calidris mauri), a
a largergutduringfall migration,and
monogamousshorebird,suggested havelargerhomerangesat more
differencesin parentalcaremay exist northerlywinteringsites.If these
Bulletin
93
December
2000
INTERNATIONAL
eventshavelong-termeffects,
WesternSandpipers
and other
migratoryshorebirds
mightbe
expectedto exhibitage-specific
variationin theirvital rates(i.e.,
breedingpropensity,
fecundityand
survivorship.Indeed,some
yearlingsoversummer
at equatorial
latitudesin theirfirst spring,whereas
othersmigrateto arcticareasto
breed. The objectiveof this study
wasto investigateage-specific
variationin the reproductive
performance
of femaleWestern
Sandpipers.Birdswereclassifiedas
yearlings,newlybandedadultsor
old returningadultson thebasisof
plumagecolorationandprevious
bandinginformation.A subsetof
known-agebirdsshowedthat
WADER
STUDY
GROUP
difficult to age. The resultsof this
studysuggestthat the potential
effectsof ageshouldreceivegreater
attention in future studies of
shorebirdbiology.
FeedingandPhysiology
The Role of Corticosterone
in the
Orchestrationof Long- Distance
ShorebirdMigration.
BULLETIN
conditions.
To furtherexploretheregulatoryrole
of corticosterone
duringmigration,I
experimentally
manipulated
corticosterone
levelsduringthe
migratoryperiodandmonitored
resultingbehavioraldifferencesin
captiveRed Knots Calidris canutus,
alsoa long-distance
migratory
shorebird. Red Knots were chosen
Meta M. Landys
as the modelspeciesbecausethey
performwell in captiveconditions,
andbecausethey displayan
Dept.of Zoology,Univ.of Washing-
association between corticosterone
ton, SeattleWA 98195, USA. email:
andmigratorysub-stage
that is
similarto thatseenin godwits.Only
probingbehaviordifferedbetween
groups;RedKnotswith artificially
meta•u.washington.edu
Avianspeciesmigratelong
distances
betweensummerbreeding
coloration of the inner tertials and
localitiesanddistantwinteringsites
upperwing covertswasa reliable
to take advantageof seasonalcycles
characterfor agingWestern
in foodabundance.
Many of the
Sandpipers.In newlyformedpairs,
behavioralandphysiological
yearlingandadultfemalesmated
processes
expressed
during
assortatively
with birdsof the same migrationincludethosethat
age-class.Yearlingfemalesnested
glucocorticosteroid
hormones
significantly
later(by 6 d), andlaid
regulate,e.g.,metabolism,
feeding
eggsthatwere5% smallerthan
and activity.Corticosterone,
the
those of old adults. Clutch size did
glucocorticosteroid
foundin bird
notvary with age-class;
a majorityof species,
maythereforeplaya primary
clutchescontained4 eggs.Yearlings role in theorchestration
of migration.
lowered corticosterone titers tended
to investigate
the mudflat andcage
floor less than did control birds. In
addition,birdswithartificiallylow
corticosterone
titerssignificantly
decreased
in mass,eventhough
feedingbehaviorswerenot affected.
Theseresultssuggestthat
corticosterone
assists birds in
perceivingtheenvironment
during
flight, andalsoallowsbirdsto
maintainthe heavymasstypicalof
departure- perhapsthrough
bad lower ratesof nest success,
In fact, levels of this hormone
lowered metabolic rate or increased
higherratesof partialclutchfailure,
andlowerratesof renestingthanold
adults. In all components
of
reproduction,new adultshad
performancethatwasintermediateto
yearlingsandold adults.Overall,
themeannumberof nestlings
leavingthenestwas2.07 per
yearlingfemale,2.93 pernewadult,
and3.66 perold adult. For the same
population,minimumestimatesof
survivalforadultfemalesrangefrom
0.55 to 0.59. Preliminarypopulation
modelingwith an age-structured
increasespecificallyduringthe
migratoryperiodin manybird
species.
digestiveefficiency.On-going
matrix model indicated that the
observedlevelsof productivity
would be adequateto maintain
stablepopulationnumbers,but only
if survivalof juvenilesisrelatively
high(ca.70% of adults).
Comparativedatafor other
populationsof shorebirds
are few
becausemost specieshave strong
nataldispersal
andareotherwise
To investigate
whichparticular
processes
of migration
corticosterone
mayregulate,I
examinedthepatternof
corticosterone
secretion across
studies will determine whether
corticosterone
alsoplaysan energymobilizingroleduringmigration,and
whether measured effects are
specificto themigratorystage.
Foragingecologyofjuvenile
WESAs in southwestern
BC during
their first fall migration.
differentmigratorysub-stages
in a
long-distance
shorebirdmigrant,the
Bar-tailedGodwitLimosalapponica. Nicholas Wolf
Elevated levels of corticosterone
werefoundonlyimmediatelypriorto
andduringmigratoryflight.
Corticosterone
may therefore
regulateprocesses
expressed
specificallyduringthe flight stage,
whichmayincludeenergy
mobilization,organreconstruction,
Zugunruhe,andexploratory
movement - a behavior that would
adaptivelyincreaseawarenessof
rapidlychangingenvironmental
BehavioralEcologyResearch
Group,
SimonFraserUniversity,Burnaby,
BC, V5A 1S6, Canada.email:
nwolf•sfu.ca.
The goalof thisprojectwasto
determine(1.) whatjuvenileWestern
Sandpipers
are eatingwhenthey
forageon two mudflatsnearthe
FraserRiver estuaryin British
Columbia,and(2.) whethertherate
Bulletin
93 December 2000
39