July 1981]
Short Communications
615
response.Although this possibilityhas not been disproven, there is no evidenceto date that one Swamp
Sparrowsyllableis more powerfulthan another.
It is alwayseasierto fail to rejectthe null hypothesisof no discriminationthan to supportthe alternative
that discriminationoccurs.Usingthe sameexperimentaldesignand with smallersamplesizes,however,
Peterset al. (1980)were able to showdiscriminationby male Swamp Sparrowson the basisof syllable
type (i.e. Swamp Sparrow syllablesversusSongSparrow syllables).Furthermore, they were able to show
discriminationby SongSparrowson the basisof temporalpattern, again with smallersamplesizesthan
used here. Thus, we are probably safe in concludingthat (a) male Swamp Sparrowsare much less
sensitiveto temporal pattern than they are to syllable type, and (b) male Swamp Sparrows are less
sensitivethan are male Song Sparrowsto temporal pattern.
Our resultsalso contrastto thoseof Searcyet al. (in press,Anita. Behav.) on songdiscriminationin
adult, female Swamp Sparrows.Theseauthorsexaminedthe responseof captive, femaleSwamp Sparrows to the sametest songsusedhere. The number and intensityof copulationsolicitationdisplayswere
usedto measureresponse.FemaleSwampSparrowsshowedsignificantlyweakerresponse
to the Complex
songthan to the SwampSyntheticsong.We have shownherethat male Swamp Sparrowsdo not respond
differentiallytowardsthesetwo songs.Thus, we can alsoconcludethat male Swamp Sparrowsare less
sensitiveto temporal pattern than are female Swamp Sparrows.
Financial supportwas providedby NIMH grantsPHS MH1525 and MH14651. We thank Peter Marler
and Dorothy Cheneyfor readingand commentingon a draft of the manuscriptand the Cary Arboretum
of the New York Botanic Garden for permissionto usethe studysites.
Received 6 October, 1980, accepted16 March 1981.
The Development of Effective Endothermy and
Homeothermy by Nestling Pition Jays
C. CLARK 1 AND RUSSELL P. BALDA 2
Leidy Laboratory,Departmentof Biology, Universityof Pennsylvania,
Philadelphia, Pennsyvania19104 USA and
Departmentof BiologicalSciences,NorthernArizonaUniversity,
Flagstaff,Arizona 86011 USA
Hatchling altricial birds beginlife as obligateectothermsbut developinto endothermswithin a few
days. The literature characterizingthe developmentof endothermyby individual chicks has grown
considerablyover the past two decades,yet the relevanceof such characterizationsto broodsin nature
has been questioned(Dunn 1975).
Individual endothermyis the ability of an isolatedchick to maintain its metabolismwithin its thertooneutralzone (TNZ) and to raiseits metabolismin responseto ambient temperatures(Ta) outsideits
TNZ. This may not coincidewith the developmentof effectiveendothermy,i.e. the ability of an individual within a brood and nest to maintain its metabolism within its TNZ
and to raise its metabolism
at Ta's beyondits TNZ. Furthermore,the degreeto which chicksare able to maintain a constantbody
temperature(Tb), i.e. homeothermy,may differ betweenisolatedindividualsand broods.This studywas
designedto determine the degreeof these discrepancies.The reasonssuch discrepanciesexist and the
potentialecologicalimportanceof effectiveendothermyand homeothermywill be addressedelsewhere
(Clark in prep.).
The Pition Jay (Gymnorhinuscyanocephalus)
nestsearly in the year (as early as Februaryin the
Flagstaff,Arizonaarea), when Ta is characteristically
low (Balda and Bateman 1972).Diurnal Ta during
incubationand the nestlingperiodis often at or below 0øC. Femalejays incubatethe eggsand broodthe
youngcontinuously.
Duringthistime thefemaleand the youngarefed entirelyby the male. Whenchicks
are capableof thermoregulation,the femalesleave the nestto foragewith the males,leavingthe young
jays unattendedfor a period of 60-70 rain (Bateman and Balda 1973). Thus, youngjays exist under
conditions that can be consideredharsh for a passedfiebird.
Pition Jays commonly raise broodsof 4 and 5. The modal clutch size in 1976 and 1977 was four.
Chicks were removed from their natural nests and taken to the lab for metabolic tests. In all cases one
616
Short Communications
INDIVIDUALS
BROOD
= 2
[Auk, Vol. 98
BROOD
= .3
6
5
12
4
$
4
I0
$
--
(,0
rr'
>"
%
0
$
2
6
I
$
I
0
10
z0
50
AMBIENT
0
10 20
30
TEMPERATURE
0
10
20
30
(ø C)
Fig. 1. Metabolic rates of nestlingPition Jays as a function of Ta. Each point representsthe O2
consumption
per gramof chick after 1 h. In the caseof broodsof 2 and 3, eachpointrepresents
the O2
consumptionof the entire brood divided by the brood weight.
chick was left in the nestto preventthe parent from deserting.Due to severepredationby the Common
Raven (Corax corax) and the asynochronyof hatching, it was not possibleto constructlarger broods
artificially. Thus, broods of three were the largest brood size tested.
Chicks were removed from the nest between 0830 and 0900 and transported to the laboratory, a trip
lasting20 min, in a wool cap enclosedwithin a cardboardbox to preventexcessivecooling.Three-dayold chickswere kept in the breast pocketof a flannel shirt during transport.
The metabolicapparatusconsistedof a clear acrylic metabolicchamberconstructedwith angledbaffles
at each end to ensure complete mixing of the air. The metabolic chambers were placed in constant
temperaturecabinets,and air was drawn through each chamberat a flow rate of 0.9-1.0 1/min by a
vacuum pump. The outlet air was passedthrough a desiccant(drierite), a COs absorbant(ascarite),and
a flowmeter before an aliquot of air was passedthrough a Beckman E-2 parmagnetic oxygenanalyzer.
Oxygenconsumption,correctedto STP, was calculatedusingthe equationfor a flow-throughsystemof
Depocas and Hart (1957).
Oncein the laboratory,chickswere weighedand warmed at a Ta of 34øCand fed until replete.Initial
Tb was measuredby insertinga YSI telethermometerprobe approximately0.75-1.0 cm into the cloaca.
Chicks tested as isolated individuals were set upon an elevated screenplaced in the metabolic chamber.
Broods were testedin natural Pition Jay nests.Trials were conductedat Ta's of 30ø, 20ø, 10ø, and 0øC
for 1-1.2 h duration. If the Os fraction in the sample fell close to zero, the trial was discontinued,
July 1981]
Short Communications
INDIVIDUALS
BROOD
= 2
617
BROOD
40
.30
12
40
•
.30
•
4.0
n,-
.30
I0
I.-
,•
D..
•
20
>'
Z
40
-
b•
.30
r•
o
20
rn
4O
.30
20
0
I0
20
.30
0
AMBIENT
I0
20
.30
TEMPERATURE
0
I0
20
.30
(ø C)
Fig. 2. NestlingTb as a functionof Ta. Each point represents
the Tb of a chickat the end of a
metabolictrial. Each trial lasted1 h for a given Ta. The soliddiagonalline represents
the theoretical
relationship
betweenTb and Ta for a nonregulating
object.The dashedregression
lineswerefitted to
the data usingthe SAS generallinear model program.
resulting
in missing
trialsat low Ta'sfor youngchicks.Because
theobjectivewasto lookfor an endothermicresponse
ratherthan to kill the chicks,we feel thesemissingtrialsare acceptable.
Oxygen
consumption
in acceptable
trialsremainedconstant
afterapproximately
40 rain,but valuesreportedhere
are basedon the last readingobtainedbeforechickswereremovedfrom the chamber.Final Tb and
weightwererecorded
aftereachtrial. Chickswerethenfeduntilreplete.WhenTb wasbelowtheinitial
Tb, the chickswere warmedbeforebeingtestedat the nextlowestTa. Up to four metabolictrials per
chickper day were performed.Chickswere not usedagainat olderages.
Within a nest,elevatedmetabolicresponses
to low Ta (0øCfor at least1 h) werefirstseenat 8 days
of agefor broodsof 3, and 10daysfor broodsof 2. Isolatedindividuals
showedan endothermic
response
at 12days(Fig. 1). In general,thelargerbroodexhibitedan endothermic
response
to a givenTa earlier
thandid the smallerbrood,whileisolatedindividualsshowedan evenmoredelayedonsetof an endo-
thermicresponse.
Asindividuals
withinnestswerenottested,it is notpossible
to determine
therelative
contribution of a nest or sibling.
Tb is plottedagainstTa for broodsizeand agein Fig. 2. Analysisof covariance
showsthat larger
clutches
effectively
regulateTb at earlierages(Table 1). At 3 daysof age,no endothermic
response
is
seenin isolatedchicksor in chicksfrom broodsof 2 or 3. Broodsof 2 are better able to keep Tb above
Ta thanareisolated
individuals,
andbroods
of 2 and3 donotdifferin theirabilityto maintainTb above
Ta. Similartrendsare seenfor chicksat 6 daysof age.At 8 daysbroodsof 3 are betterableto maintain
Tb above Ta than are broodsof 2. This is concurrentwith the ability of broodsof three to exhibit an
endothermic
response
of 0øCfor at least1 h. At thisagebroods
of two arenobetterat maintaining
Tb
aboveTa than are isolatedindividuals.When chicksare 10 daysof age, broodsof 2 and 3 do not differ
618
Short Communications
[Auk, Vol. 98
TABLE 1. Analysis of covariance for a test of significancebetween slopesof Tb vs. Ta for isolated
individuals (1), broods of 2 within a nest (2), and broods of 3 within a nest (3). F values contained in
the table are basedon the SAS generallinear model for analysisof covariance. Significancelevels are
indicated by *'0.01 and **'0.001.
Age
1 vs. 2
3
6
8
10
12
2 vs. 3
11.56'*
56.09***
3.99
79.77***
463.14'**
0.62
0.15
19.77'**
0.45
152.60'**
in their ability to keep Tb above Ta. This occurswhen both brood sizescan maintain an endothermic
responseat 0øC for a least 1 h. Isolated individuals do not yet demonstratethis capability and are not
able to maintain
Tb above Ta as well as a brood of two.
Table 1 indicates that broods of 2 maintain Tb above Ta better than a brood of 3 at 12 days. This is
principallydue, however,to unusuallyhigh Tb's recordedfor chickswithin broodsof 3 at the end of the
metabolictestsat 30øC.If theseTb's areomitted,the slopesbetweenbroodsof 2 and 3 are not significantly
different.Althoughisolatedindividualsdemonstratean endothermicresponse
to 0øCat 12 days,broods
of two still maintain Tb above Ta more effectively.
PitionJaysbeginto shivervisiblyat 5 daysof age,thusdemonstrating
an earlyendothermic
response.
The reasonthis responsewas not observedin broodsof two or isolatedindividualsis mostlikely due to
the time when the O2 fraction was recorded.Young jays may not be able to maintain an endothermic
responsefor an hour during testingat a low Ta, i.e. 0øC. Reductionin heat lossrelative to the chick's
capacityto produceheat is the most likely reasonfor the observeddifferencesin the ontogenyof the
endothermicresponsebetweenbrood sizesat a given Ta. Marsh (1979) has shown that an increased
thermal inertia is importantin reducingheat flow by individualnestlingBank Swallows(Riparia riparia)
prior to the maturation of muscletissuefor shiveringthermogenesis.
Our data confirmthoseof earlier
studies(O'Connor1975, Dunn 1976),which showedthat the weight of individualchicksat the age of
effectivehomeothermyis lower with increasingbrood size. This suggests
that a lower surface-volume
ratio compensatesto somedegreefor a lack of maturation of heat-producingtissues.
This study should serve as a cautionary notice in extrapolating data on the timing of individual
homeothermyand endothermyto ecologicalproblemsinvolving entire broods.Our criterionof an endothermicresponsemaintainedfor an hour at 0øCfor completeendothermyin PitionJaysis ecologically
relevant, as given parentsare often absentfrom the nest for similar lengthsof time at similary low Ta's.
BecausePition Jay broodsof 3 and 2 differ by 2 days in their ability to withstand0øCTa for an hour,
female jays may have to attend smaller broodslonger. This possibilitywas suggestedby Dunn (1976),
but no data have been publishedto date. There is someevidence,however, to show that this is the case
in Starlings(Sturnus vulgaris) (Clark unpubl.). Further study should be aimed at examiningthe implicationsfor adult birds of varying age of effectivehomeothermyand endothermyaccordingto brood size.
This study was partially supportedby a grant from the Frank M. Chapman Fund provided to Clark.
We would like to expressour appreciationto E. H. Dunn, A. Gilbert, J. F. Quinn, and severalanonymous
reviewersfor offering constructivecommentson earlier drafts of this paper.
LITERATURE
CITED
BALDA,R. P., & G. C. BATEMAN.1972. The breedingbiologyof the PitionJay. Living Bird 11:5-42.
BATEMAN,G. C., & R. P. BALDA. 1973. Growth, development,and food habitsof youngPitionJays.
Auk 90: 39-61.
DEPOCA$,F., & J. S. HART. 1957. Use of the Paulingoxygenanalyzerfor measurement
of oxygen
consumptionof animalsin open-circuitsystemsand in a short-lag,closed-circuitapparatus.J. Appl.
Physiol. 10: 388-392.
DUNN, E. H. 1975. The timing of endothermyin the developmentof altricial birds. Condor 77: 288293.
ß 1976. The relationshipbetweenbroodsizeand ageof effectivehomeothermyin nestlingHouse
Wrens.
Wilson
Bull.
88: 478•[82.
O'CONNOR,R. J. 1975. The influenceof brood size upon metabolicrate and body temperaturein
July 1981]
Short Communications
619
nestlingBlue Tits (Parus caeruleus)and HouseSparrows(Passerdomesticus).J. Zool. London i 75:
391-403.
MARSH,R. L. 1979. Developmentof endothermyin nestlingBank Swallows(Riparia riparia). Physiol.
Zool. 52: 340-353.
Geographic Variation in the Juvenal Plumage of the Lesser
Nighthawk ( Chordeiles acutlpennis)
ROBERT
W.
DICKERMAN
Department of Microbiology, Cornell University Medical College,
New York, New York 10021 USA
In attemptingto identify a seriesof LesserNighthawks (Chordeilesacutipennis)collectedon the Pacific
lowlands of Guatemala, and to ascertainthe applicable trinomial to use, I encountereda striking degree
of variation amongjuveniles in the collectionof the American Museum of Natural History (AMNH). To
evaluate the taxonomic usefulnessof the juvenal plumage in the species,additional juveniles were
borrowedfrom the University of Michigan Museum of Zoology(UMMZ), the U.S. National Museum of
Natural History (USNM), the CarnegieMuseum of Natural History (CM), the Field Museum of Natural
History (FMNH), and the Moore Laboratory of Zoology(MLZ). A total of 32 juveniles was available for
study. Sevenplumagegroupingsarrangednorth to southcan be recognizedamongthesejuveniles(Fig.
1).
C. a. texensis(includinginferior).--The juvenal plumageof texensisis the palestgray with pale, more
cinnamon,lessochraceoustippingson the feathersof the crown, interscapulars,and wing coverts.Dorsal
feathershave extremelyfine vermiculations,i.e. they are much less"blotchy"than in other races.Two
juvenilesfrom Lower California("inferior")are inseparablefrom 10 of comparableagefrom Texas, New
Mexico, and Arizona. Color phasesare not evident in this seriesof juveniles. Specimensexamined(13):
Baja California, AMNH 87446, 43850; Arizona, AMNH 51993, USNM 268828, 235064, 130577;New
Mexico, USNM 365443, 204515; Texas, AMNH 81618-81620, USNM 14013, 18491.
C. a. micromeris.--Thedorsaldark markingsof the singlejuvenilespecimenseenfrom the YucatAn
Peninsulaare coarserthan thoseof the juvenal plumageof texensis,contrastmore with the paler feather
edges than in littoralis, and thus differ from both. Dorsally, including the tail, it is grayer, less buffy
than littoralis but darker than texensis.The feather edgingsare slightly more buffy, lesscinnamonthan
in texensisbut lessdeeply coloredthan in littoralis. Specimenexamined (1): Yucatan, USNM 130206.
C. a. littoralis.--The four specimens
availableare uniform and differ from texensisin beinga darker
gray with a generally browner overall cast. The darker barring of dorsal feathers is heavier, more
"blotchy," and edgingsof dorsal feathersand covertsare darker, more ochraceous.Specimensexamined
(4): Michoacan, La Placita, UMMZ 130530; Guerrero, Ajuchitlan, MLZ 43446; Oaxaca, Tehuantepec,
UMMZ 137450;Chiapas,Arriaga, UMMZ 102227.
C. a. acutipennis.--The nine juveniles from within the range currently assignedto C. a. acutipennis,
but alsoincludingPanama, includetwo distinctivelydifferentforms:
A. These young are most similar to the young of littoralis but are yet darker, having a near sooty
appearance,with more extensiveand darker, richer, ochraceous-cinnamon
feather edgingsand tippings,
thus giving the appearance of having a deep ochraceous-cinnamonwash over the dorsum. The black
blotchingis more pronounced,especiallyon the crown. The crown, mantle, and lessercovertscontrast
rather sharply with the paler terials (Fig. 1). Specimensexamined (4): Panama, San Carlos, USNM
448729; Colombia, Turbaco, Choco (north coast near Cartegena), AMNH 123261;Venezuela, San Antonio del Golfo, Sucre, AMNH 706096, San Felix, Bolivar, CM 34356.
B. Five juvenilesfrom Colombia, Guyana, and Brazil are much grayer. The ochraceoustipping of
dorsal feathers and coverts is reduced, being restricted to the feather tips; it is most pronouncedon the
crown. The tail barring is dark and light, clear gray lacking a warm cast. The ventral colorationis paler.
These specimensdiffer from juvenile littoralis in being darker gray dorsallywith far lessbrown overcast.
Specimensexamined (5): Colombia, Riohacha (base of Guajira Peninsula), CM 78710, 78711; Guyana
(BritishGuiana),La Penetiance
(nearGeorgetown),FMNH 97795;Brazil, Santarlm, CM 78612,78644.
It is not unexpectedfor specimensfrom Choco and Panama to be similar, but the similarity of those