Download nest-monitoring plots: methods for locating nests and monitoring

J. Field Ornithol., 64(4):507-519
NEST-MONITORING
NESTS
AND
PLOTS:
METHODS
FOR LOCATING
MONITORING
SUCCESS
THOMnS
E. M^RTIN
•
U.S. Fish and WildlzfeService
ArkansasCooperativeFish and Wildlife ResearchUnzt
Unzversityof Arkansas
Fayetteville,Arkansas72707 USA
GEOFFREY
R. GEUPEL
Point ReyesBzrd Observatory
d990 ShorehneHighway
StinsonBeach, Califorma 9d92d USA
Abstract.--Attention to long-term declinesin populationsof Neotropical migratory birds
has generatedincreasedinterest in how to monitor and manage them. Measurementof
nestingsuccess
providesinformationon trendsin recruitment,andmeasurement
of vegetation
associated
with nestsmay identifyhabitatinfluenceson breedingproductivity.Examination
of nestsalso allows collectionof life history data (e.g., clutch size, numbersof broods,
numbersof nestingattempts,nestingsuccess),which provide important insight into vulnerability of speciesto decimationor perturbations.Comparisonsof nesting successand
habitat use acrossthe geographicrange of a speciescan determine local habitat effectson
population recruitment and historical constraintson habitat use and speciesdistributions.
In this paper, standardizedmethodsand cuesare describedthat aid in locatingand monitoring
neststo allow comparisonsacrossstudiesin spaceand time.
MgTODOS
PARA LOCALIZAR
NIDOS Y MONITOREAR
EL gXITO
DE ESTOS
Sinopsis.--E1decrecimiento
progresivode las poblaciones
de avesque migranal neotr6pico
ha generadogran interasen c6momonitoreary manejar a 6stos.E1 medir el 6xito de
anidamientoproveeinformaci6nen relaci6nalas tendencias
en el reclutamientopoblacional
y las medidasde la vegetaci6nasociadaa nidospuedeset importanteen identificaraspectos
de 6staque infiuyan en la productividad.E1 examende nidostambi6n permite recopilar
datossobreciclosde vida (ej. tamafiode la camada,nfimerode camadaspot afio, nfimero
de intentosde anidamiento,y axito de anidamiento)el cual proveeinformaci6nimportate
en referenciaa la vulnerabilidadde la especiea perturbaciones.
La comparaci6ndel 6xito
de anidamientode una especieen diferenteshabitatsa lo largo de extensiones
geogrfificas
puededeterminarel efectode habitatslocalesen el reclutamientopoblacionaly restricciones
hist6ricasen el uso de habitat y la distribuci6nde la especie.En estetrabajo, se describen
m6todosestandarizados
y pistasque puedenayudar a localizar y monitorearnidosde tal
manera que se puedanhacer comparaciones
entre estudiosy lapsosde espacioy/o tierepo.
Habitat featuresthat influencebreedingproductivityof birdsare poorly
known (Martin 1992). Measurement of nestingsuccessand associated
vegetationallowsidentificationof suchhabitatfeaturesand alsoprovides
greater insight into evolutionof habitat requirementsand speciescoexistencethan traditional metricssuchas presenceor abundance(Martin
1986, 1988a, 1992). Data on nest sites and mortality also improve understandingof ecologicaland evolutionaryinfluenceson life historytraits
• Currentaddress:
MontanaCooperatwe
WildlifeResearchUmt, Departmentof BiologicalSciences,Universityof Montana,Missoula,Montana59812 USA.
507
508]
T. E. MartinandG. R. Geupel
J.Field
Ornithol.
Autumn 1993
(Lack 1968; Martin 1988b, 1993a, b; Martin and Li 1992), which can
give insight into the abundanceand vulnerability of speciesto population
decimation(Martin 1993a, Pimm et al. 1988). Knowledgeof life history
traits taken togetherwith data on breedingproductivitycan alsoprovide
information on demographictrends and warn of population problems
beforedeclinesin densityactually occur(Martin 1992, 1993a; Pienkowski
1991; Temple and Wiens 1989). Many life history traits, however,are
unknown or poorly known for many speciesin North America;breeding
biology studiesare poorly representedamong speciesand geographic
locations(Martin 1992, 1993a; Ricklefs 1969). The paucity of studies
exists in part from a misconceptionthat nestsare too difficult to find.
Yet, cuesand techniquesfor finding nestscan be learned, as we describe
here, thereby providing the vital information neededto curb long-term
populationdeclinesof many species(seeRobbinset al. 1989).
Nestrecordprograms,wherevolunteersturn in recordsof nestattempts,
havebeenin existencefor yearsin both the United Kingdom (Ballie 1990)
and United States(Bart 1977). These programsobtain data for broad
geographicregionsfrom volunteerswho often locatenestsincidentalto
other activities.Sample sizesfor many geographicregionsand habitat
typesare minimal and consistency
in monitoringnestsoncethey are found
is poor. Thus, these programs suffer from severalpotential biasesand
require careful interpretation(Ballie 1990). In contrast,studiesthat focus
on nest monitoring on long-term plots can provide data on breeding
productivityfor entire collectionsof speciesto allow comparisons
within
and amongspeciesin spaceand time (e.g., Martin 1992, 1993a; Martin
and Li 1992; Sherry and Holmes 1992). Moreover, broad-scaledeterioration of environmentalconditionsfrom habitat degradationor global
warming can be detectedif suchstudiesare distributed acrosslocal microclimaticgradientsandbroadgeographicregions(Martin 1992, Temple
and Wiens 1989). Additionally, if vegetationis measured,habitat features
that influence nesting successcan be compared acrossthe geographic
rangesof speciesto provide insight into habitat requirementsand distribution of species(seeJames et al. 1984, Knopf et al. 1990). Effective
comparisonsamong speciesand locations,however,dependon standardization of samplingprotocols.
In this paper we describeaidsand standardizedtechniquesfor locating
and monitoring successof nests.These methodsare provided to standardize data collectionto allow comparisonsacrossinvestigatorsand in
the hopeof increasingboth samplesizesand numbersof studiesof breeding
biology.
NEST
LOCATION
Nest finding is labor intensive(DeSante and Geupel 1987), but most
observers
can improvetheir ability to locatenestsin a matter of dayswith
training and practice. The behavioral observationsand cluesdescribed
below work effectivelyfor a variety of species.Our experienceincludes
only a small subsetof speciesand habitatsavailablein North America,
Vol.64,No.4
FindingandMonitoring
Nests
[509
however, and is largely restrictedto wooded(scrub and forest) habitats.
Other methodsmay be more effectivein other habitats. For example,
cable-dragging(Higgins et al. 1969) and rope-dragging(Labisky 1957)
may be more effectivemethodsfor many grasslandspecies.The patience
and alertnessof observersand their familiarity with the habitat and
behaviorof speciesare the mostimportantinfluencesoneffectivelylocating
nests.
We have successfullyused thesetechniquesto train individualswho
even lack experienceat bird identification.For example, a crew of four
assistantsinitiated a study in Arkansasin 1991 where nestingbehaviors
of specieswere unstudied;this crew was providedonly the generalnestfindingguidelinesgivenbelow.The crew includedoneexperiencednestfinder,onepersonexperiencedat identifyingbirdsand two peoplewithout
experienceat either. These workersfoundover300 nestsof open-nesting
birds(Table 1). A crewof sevenassistants
that includedtwo experienced
nest-findersfound more than 800 open-cupand cavitynestson Arizona
sitesin the same year (Table 1). In general, about 20 nestsare needed
for an adequateestimateof nestingsuccess
(Hensler and Nichols 1981),
andsuchsamplesizeswere obtainedfor mostspecies(Table 1). Moreover,
specieswith small sample sizescan be compiledacrossyears.
We recommendthat two study plots be establishedfor each person
searchingfor nestsand he or she shouldwork on thesetwo plots for the
entire nestingseason.Nest-searchingshouldbe alternatedbetweenplots
betweendays.This scheduleallows consistentmonitoringand allowsthe
person to becomefamiliar with the plot and identify "hot spots." In
general, eight plots, each 40 ha in size, should be establishedin forest
habitat to find adequatenumbersof nestsfor most speciescoexistingin
any given forest,but smaller plotscan be establishedif studyinghabitats
with higher densities.This designfits in the national BreedingBiology
Researchand monitoring Database (BBIRD) administeredby Martin.
Nest finding should begin early, as soonas territories are established.
Non-migratory speciesgenerally are more variable than migrants and
may initiate breedingconsiderablyearlier in someyears (e.g., Geupel
and DeSante 1990). Visits prior to nestingare recommended
to ensure
early nestsare not missedin 'unusual'years.Oncegeneralchronologyof
nestinitiation is known (after the first year), a generaldescriptionof this
chronologyhelps assistantsto know specieson which to focusearly in
the season.
Nest locationduring nestconstruction.--Nestslocatedduring construction provide the best estimatesof nest success.Permanent residentsand
many ground-nestingspeciesoften begin the earliest. Only the female
constructsthe nest and incubatesfor most small terrestrial bird species
in North America (Kendeigh1952, Silveret al. 1985). Exceptionsinclude
woodpeckers(Picidae), vireos (Vireonidae), and wrens (Troglodytidae).
Thus, the mosteffectiveway of findingnestsis by locatingand following
females, although males may provide some cues (see later), and some
nestsin the shrub layer can be found by random search.Ground nests
510]
T. E. MartinandG. R. Geupel
J.Field
Ornithol.
Autumn
1993
TABLE1. List of speciesand numbersof nestsfound in a singlefield seasonin Arkansas
and Arizona using teamsof four and sevenfield assistants,respectively.
Arkansas
Yellow-billed Cuckoo
Acadian Flycatcher
Wood Thrush
Red-eyedVireo
Coccyzus
amerwanus
Emptdonaxwrescens
Hylocichlamustelina
Vtreoolwaceus
13
51
40
51
Black-and-white
Mnzotilta
Warbler
Ovenbird
Worm-eating Warbler
Hooded
Warbler
varza
19
Seiurusaurocapillus
Helmitherosvermivorus
14
16
Wzlson•a citrma
67
Passerinacyanea
30
Acorn Woodpecker
Red-napedSapsucker
Williamson's Sapsucker
Hairy Woodpecker
Downy Woodpecker
Northern Flicker
Cordilleran Flycatcher
Mountain Chickadee
Pygmy Nuthatch
Melanerpe6
formwworus
Sphyrapicus
varius
Sphyrapicus
thyroideus
Dendrocopus
vdlosus
Dendrocopos
pubescens
Colapresauratus
Emp•donaxdi•]Scdzs
Parusgainbell
&tta pygmaea
8
30
32
10
8
26
36
45
24
Red-breasted
Nuthatch
White-breasted
Nuthatch
Sztta canadensts
&tta carolinensis
26
14
Brown Creeper
Certhiafamiharis
22
House Wren
Hermit Thrush
American Robin
Ruby-crowned Kinglet
Warbling Vireo
Orange-crowned Warbler
Virginia's Warbler
Yellow-rumped Warbler
MacGillivray's Warbler
Red-faced Warbler
Western Tanager
Black-headedGrosbeak
Green-tailed Towhee
Dark-eyed Junco
Troglodytesaedon
Catharusguttatus
Y•rdus mzgratorzus
Reguluscalendula
Vireogilvus
Verrnworacelata
Verrnworavirginiae
Dendrozcacoronata
Oporornistolmiei
Cardellmarubrifrons
Pzrangaludov•ciana
Pheucticu,melanocephalus
Pzpilochlorurus
Juncohyemahs
83
74
24
14
58
71
34
45
9
21
39
7
24
46
Indigo Bunting
Arizona
in forestsare usuallythe mostdifficult to find and ground-nestingspecies
are poorly studied (Martin 1992, 1993a). Yet, this group is thought to
be particularly area-sensitiveand goodindicatorsof habitat disturbance
(Martin 1993a, Whitcombet al. 1981). Thus, specialeffortsshouldbe
made at locating and monitoring ground-nestingspecies.
Females tend to be extremely furtive during nest building. Mated
femalesmay be recognizedby copulationeventsduring latter stagesof
building or by observingthat they move about the territory unharassed
by the male. Any non-matedbird, especiallyan intruding male, is normally attackedimmediately.Any femaleobservedshouldbe checkedwith
Vol.64,No.4
Finding
andMonitoring
Nests
binoculars,especiallyafter long flights acrossthe territory, to determine
whether nesting material is being carried. Nest material may not be
obvious.For example, speciessuch as Yellow-rumped Warblers (Dendroicacoronata)and Wrentits (Charnaeafasciata) collectspider webbing,
which is only observableas a small white spotafter careful examination
of the bill (Martin and Geupel, pets. ohs.). Similarly, many birds carry
fine materials for lining nests,and thesematerials are not obviousupon
casualinspection.
Sitting near sourcesof nestingmaterial (i.e., failed nests,thistles)or
open areaswith a goodview of the territory can help detectionof nestbuilding females.Different pathsacrossplotsshouldbe usedon eachvisit
to increasethe probability of randomly encounteringfemalesnear undiscoverednests.Follow a bird carrying nestingmaterial from a distance
to avoiddisturbance.Do not interrupt a long flight. If the bird disappears,
beginto scanfor potentialnestsites.Be patient and wait for anothervisit,
beingcareful not to interferewith her behavior.If the femaledisappeared
near the nest, she will spendtime in the area. Remain aware, however,
that she may also move out of the back side of the patch to a different
patch that containsthe nest.
Some birds tolerate nearby observersand behave normally, but most
are very wary of observers.If the observeris too closeto the nest, the
bird often will sit on a perch and eventuallydrop the nestingmaterial if
the observerdoesnot moveaway. The observershouldmovequickly and
quietly in the oppositedirectionfrom which the bird came.Obtain a new
hiding position at least 15 m away and watch the female take nesting
material severaltimes and leave without it. Stay alert to the possibility
that the female may enter onepatch and then surreptitiouslymoveamong
patchesonly to return the sameway to give the appearanceof nestingin
the first patch.Somespeciessuchas MacGillivray'sWarblers (Oporornis
tolmiei), Hooded Warblers (Wilsoniacitrina) and Sage Sparrows(Amphispizabelli) will walk on the groundfor severalmetersto approachthe
nest secretly.Speciesthat nest off the ground can often be detectedas
they movethrough a thick patch of vegetationby watching the vegetation
move.Verify the neststatusand locationa few hourslater, being careful
to make sure the female is not present.Later visitationis recommended
becauseusually the female has becomeaware of observersduring their
nest-findingactivities.
Nest locationduring egg-laying.--the most difficult stagefor finding
nestsis during egg-layingbecausethe femalemay visit the nestonly when
shelaysan eggand mostsongbirdslay oneeggper day. In coldclimates,
the female will sometimessit on the nestduring egg-layingwhen weather
is particularly harsh. Also, nest visitation becomesmore frequent with
increasesin numbersof eggslaid (Kendeigh 1952, Zerba and Morton
1983). One means of finding nests during egg-laying is by carefully
observingfemale and male behavior.When either parent gets near the
nest, it will look at the nest. If an egg-layingfemale detectsa predator
in the area, suchas an observerfollowing her, shewill sometimescheck
512]
T. E. MartinandG. R. Geupel
J.Field
Ornithol.
Autumn
1993
the nestby lookingdown at it repeatedly.A goodcue is a femalestaying
in an area without activelyfeeding.
Finally, copulatory behavior can be used to detect nestsduring both
nest-buildingand egg-laying.Copulation often occursin the same tree
abovea nest,on the samebranch, or in the next tree. Carefully examine
the area immediatelyadjacentto any copulatoryactivity observed.
Nestlocationduringincubation.--Whenfemalessuddenly"vanish" and
malesincreasethe frequencyof singing,femaleshaveprobablyinitiated
incubation.An increasein femaleforagingspeedalsoindicatesthe onset
of incubation.Femalesforageat slowerspeedsprior to incubation(during
pre-construction,nest construction,and egg-laying) than during incubation and nestlingstages.Femalesthat are movingobviouslyfast (e.g.,
rapid hops,quick short flights, rapid wing flicks) shouldbe carefully
followed becausethey will return to the nest soon;on average,female
passetinesstay off the nestfor 6-10 min and on for 20-30 min at a time
acrossspecies(e.g., Nice 1937, Southern1958, Zerba and Morton 1983).
Detectionof incubatingfemalescanbe accomplished
in two ways.First,
femalescanbe encountered
by constantlymovingthroughthe studyplot,
but constantalertnessis imperative. Sometimes,sitting down in a spot
for 20-30 min is usefulbecauseincubatingfemaleswill leavethe nestin
that period. Second,femalescan be detectedby call notes.Femalesof
many taxa (e.g., Silviidae, Parulinae, Emberizinae) chip or call when
they are off the nest. The femalebeginschippingjust prior to leaving
the nest or as soon as she is off it. Some taxa such as emberizid
finches
and icterinesgive a unique nest departure call when leaving the nest
(McDonald and Greenberg 1991). If a vocalizingfemale is detectedand
then lost during the courseof following her, immediatelyreturn to the
point of original detectionbecauseit is often near the nestand the female
can often be relocatedbeforegettingback on the nest.
Males can also be of some help. First, males often will respondto
femaleswhen they leavethe nestand either quietly guard the nest (e.g.,
Gray Catbird, Dumetella carolinensis;Slack 1976), or the female. Detection of a quiet male may indicatepresenceof a foragingfemaleor a nest
somewherenear him. Second,males will feed incubatingfemalesfor a
great array of species,particularly cavity-nestingbirds, but for many
open-nestingbirds as well (Lyon and Montgomerie 1987, Silver et al.
1985, Martin and Geupel, unpubl. data). Any birds (male or female)
observedshouldbe checkedfor material in their bills becausethey potentiallycouldbebuildingnests,feedingfemalesor feedingyoung.Finally,
malesof somespecies(e.g., Chestnut-sidedWarbler, Dendroicapensylvanica) use favorite singing perchesthat are in direct view of the nest
(Martin, pers.obs.).The nestcanbe locatedby followinghis line of sight.
Femalesare fairly tolerantof peoplefollowingwhile they forage.The
femaleis morecautiousas shereturnsto the nest.A relativelylongflight
after foragingis probablya return to the nestand is oftenalongthe same
route. Quickly running in her directionfor about25 m may often allow
Vol.64,No.4
FindingandMonitoring
Nests
[5 ] 3
resightingbecausethe disturbancewill keep her from returning to the
nest. If she is near the nest, but cautiousabout approaching,she will
display nervousdisplacementbehavior.This "nest dance"involvesbouncing back and forth between a few trees or substrates,and in somecases
alsoincludesvery rapid foraging.Eventually,shewill start to movedown
toward the nest and then suddenlyfly back up. This behavior will be
repeated several times in the course of a few minutes. If the observer is
too close to the nest, the bird will continue to bounce back and forth
between substratesand will sometimesfly off for a short time, only to
return within a few minutes. The observer should back off and watch
her with binoculars and she will then return to the nest. If the work is
being conductedin cold conditions,do not keep her off the nestfor more
than 15 min becausethe eggscan chill to lethal levels.If the female has
beenfollowedfor more than 30 min and hasnot disappearedor exhibited
displacementbehavior,then sheprobablydoesnot havea nest.Of course
this "30-min rule" doesnot apply to specieswhere both sexesincubate.
If a female disappearsinto a tree or shrub, memorizethe area where
the female disappearedand choosepotential nesting sites before approaching. Moving quietly, begin tapping potential nest shrubs in this
area with
a stick. Listen
for the flush of the female
off the nest. Watch
for the female or the "nest dance." Note that spotting the female will
confirmthat the nest is nearby. If the nest is not found and the female
is not observedleaving, then there is no confirmationthat a nest is in the
area. Because the nest is in a fixed location, the site can be revisited for
careful
searches in the future.
In many species,nest site preferenceseemsto be an evolutionarily
conservative
trait (Martin 1988a, 1992, 1993c). Many birds prefer to
nest in or under certain plant speciesor patch types that differ among
bird species(Geupel 1993, Martin 1993c, Martin and Roper 1988).
Familiarity with nestsubstrateand patchpreferences
can help in finding
nests.Describe and visit nest locationsfrom previousyears to aid new
observersin finding nests.
Nest locationduring the nestlingstage.--Finding nestsduring the nest-
ling period is easiestbecauseboth males and femalescommonlybring
foodto the nestlingsand removefecalsacs.Males are normallythe easiest
to follow becausethey are generally less cautiousthan femalesin approachingnests.Nestscan usuallybe foundfrom a greaterdistanceusing
binocularsbecauseof the constantactivityof the parents.
Knowledgeof the nestingcycleallows an observerto anticipatewhen
to start lookingfor a new nest.Most specieswill renestfollowinga nesting
failure, althoughthe number of nestingattemptsor renestingintensity
varieswithin and amongspecies(Geupel and Desante 1990, Martin and
Li 1992). Reconstruction
beginsalmostalways at a new site within 10
d and the new nest is likely to be farther away from the previousnest
the earlier in the nestingcyclethat failure occurred(citationsin Martin
1992). Multi-brooded speciesmay begin anothernestin as little as 8 d
514]
T. E. MartinandG. R. Geupel
J.Field
Ornithol.
Autumn 1993
after fiedging a prior nest. Sometimesthe female will begin nestingwhile
the male is still tendingthe fledglingsof the previousbrood(Burley 1980,
Smith and Roff 1980).
Nest finding can be a difficult and frustratingtask;patienceis the most
important asset.An observershouldset a goal of trying to find at least
one nestevery day. More than one nestwill be found on many days,but
if at leastone nestcan be found eachday the numbersof nestsobtained
over the season will
accumulate
NEST
and frustration
will
be minimized.
MONITORING
Each nest found should be checkedevery 3-4 d to determine if it is
still active(with eggsor young)or hasfailed. Exceptjust after egg-laying
and near hatching and fledgingevents,it is not necessaryto checkthe
nest contents. Instead, check the nest from a distance; if an adult is on
the nest, do not flush it. Gareful and highly conscientious
attentionto
checkingnestsis critical for data quality becausethe numberof daysthat
nestsare observedwith eggsor youngis usedto calculatedaily mortality
rates, the most effective measure of nest success(Hensler and Nichols
1981; Mayfield 1961, 1975). Moreover, nestingoutcomeis difficult to
determinewith increasinglengthof time betweennestchecksandvariation
at this stagecan bias estimatesof nest success.The fledgingdate should
be identified as the date of the last visit on which nestlingswere observed
in the nest.Do not extrapolatepastthe last date that youngwere observed
exceptwhen the averagenestingcycleduration is usedto determinethe
fledgingdate from the known initiation date. Otherwise,an upward bias
on Mayfield estimatesoccurs.Prior to the field season,a sheetof information that summarizesthe general clutch size, length of the incubation
period, and length of the nestlingperiod for every speciesthat occurson
the studysitesshouldbe prepared.This information aids anticipationof
hatching and fledging events.
Flaggingor othervisiblemarkerscanincreaserisk of predation(Picozzi
1975) and, hence,shouldbe usedwith caution.When possible,memorize
the area and write a descriptionof how to find the nest using compass
bearingsand distanceestimates(paces)from obviouslandmarksor flagging placed greater than 10 m from the nest. Another solutionis to grid
permanentlyall studyplotswith numberedstakesat 25 or 50 m intervals
dependingon the densityof the vegetation;25 m intervalsare usually
best(seeRalph et al. 1993 for informationon establishingpermanently
marked plots). Nest location can be describedfrom these permanent
markers.
Nest cardsare usedto recorddata about the nest site and nest activity.
The Gornell Laboratory of Ornithology (159 SapsuckerWoods Rd.,
Ithaca, New York 14850) maintains a national nest card database and,
thus, their card or some similar variant should be used. All observations
of nestsshould be recordedon the nest card, including visits when no
activitywas noted.Noting lack of adult activityis particularlycriticalfor
canopy or cavity-nestswhere nest contentscannot be checked.All this
Vol.64,No.4
Finding
andMonitoring
Nests
information is neededfor calculatingnestingsuccess(see also Bart and
Robson1982). Recordedinformationshouldincludedate,time, presence
of adultsand activityof adults(e.g., incubating,feedingyoung,flushed
from nest).Also, any time the nestis approachedcloseenoughto seethe
contents,they should be noted on the nest cards (number of eggs,or
number and age of nestlings).Age of the nestlingshelps determination
of nestfate in somecasesby providinginformationon lengthof time that
nestswere active. Also, data should be summarizedby successat each
nesting stage (egg-laying, incubation and nestling) and, thus, accurate
recordsof thesestagesare needed.When possible,data should include
date of first egg, clutch completiondate, hatchingdate, day of banding
(if banded)and fledgingdate. Careful and detailedobservations
should
be recordedif a nest predation event is observedin action. If the nest
appears inactive based on observationsfrom a distance, it should be
approachedto verify mortality. In the caseof canopynests,mirrors attachedto telescopingpoles (we use window-washingpoles)can be used
to checknestcontentsof nestsup to 10 m off ground.If the nestappears
depredated(eggsor young removed)then checkthe nest structureand
immediatearea aroundand underthe nestfor evidenceof predation.Look
for holesin the bottomof the nestcup.Any evidence(e.g.,shellfragments,
hole in nest,nesttorn up) shouldbe fastidiouslynotedon the card. When
the young fledge,they commonlyperch on the side of the nest thereby
flatteningthe nestand they leavefecal droppingsin the nestor on the
edgeor groundand suchshouldbe notedaspossibleevidenceof successful
fiedging. When a nest is thought to have fledged, however, observers
shouldtry to verify by watchingfor fledglingsor parentsfeedingfledglings
or by hearing parentsgiving alarm or distresscalls or young begging.
This activity usually occursnear the nest site becausefledglingsoften do
not movevery far in the first coupleof days.Somespeciessuchas RufoussidedTowhees (Pipilo erythrophthalmus),
however,may move as far as
100 m in lessthan a few hours. Care must be exercisedin classifying
nest fate becausesomespeciesor individualsmay carry food up to 24 h
or longerafter predationof their nest.This behaviormay be exacerbated
by unrelatedfiedgingsfrom neighboringterritories.Descriptiveconfirmatory evidenceof fiedgingshouldbe notedon the nest cards.
PRECAUTIONS
FOR
MINIMIZING
HUMAN-INDUCED
MORTALITY
Locatingand monitoringnestshave the potential to reducenestsuccess
(Gotmark 1992) but with properprecautionssuchbiasescanbeeliminated
or minimized (Martin and Roper 1988, Nicholset al. 1984, Willis 1973).
Some investigatorsuse camouflagenetting over their headsor attached
to camouflagedhats to reducedisturbanceto birds. Initial locationof the
nest normally createsthe most distressto adult birds and disturbanceto
the nest site becausesubsequentvisits are brief. Someevidencesuggests
that predationratesare higher on the first or early visitsthan subsequent
visits (Bart 1977, Nolan 1978, but seeBart and Robson1982), perhaps
causedby the disturbanceduringlocatingthe nest.Thereforethe following
516]
T. E. MartinandG. R. Geupel
J.Field
Ornithol.
Autumn 1993
guidelinesare suggestedwhen attemptingto locate nests.(1) Distress
calls by adults shouldbe minimized and never allowed to continuefor
over5 min. (2) Do not approacha nestwhen any potentialnestpredator,
particularlya visually-orientedpredator(e.g.,corvid)is present.(3) Minimize disturbanceto the area around the nest. (4) Do not get closeto
nestsduring nest building; birds will abandonif disturbedprior to egglaying, particularly during the early part of a season.
To lower the probabilityof predationor broodparasitismduring checks,
we recommendthe following precautions.(1) Check the nest from as
greata distanceas possible.Use binocularsto seethe femaleor contents
of the nestor get on logsand look from aboveinto the nestwhen possible
to minimize proximity and disturbancenear the nest. (2) Disturb the
birds and area as little as possible.Move to nestsin different paths on
subsequentvisitsand use a path that is quick, quiet and that minimizes
disturbanceto the vegetation;paths in the vegetationfrom broken stems
or smashedgrass/forbscan cue possiblepredators.Never leave a dead
endtrail to the nest.Do not return on the samepath but continuewalking
in a differentdirectionaway from the nest.If avianpredatorsare common,
checkotherbusheswithout nests.Always assumea predatoris watching.
(5) Be quick and accurateduring nest checksand nestlingbanding. If
the nest must be approached,minimize the amount of time spent near
the nest examining the contentsbecausethe more time spentat nest the
more scentthat is left for olfactorypredators.(4) Minimize the number
of observersvisiting the nest (no photographers).(5) Use a pen or stick
to check neststo prevent human scentfrom being left on or near a nest.
VEGETATION
MEASUREMENT
As soonas a nestingattempt terminates (successful
or unsuccessful),
completethe nest card and then measurethe vegetationassociated
with
the nest. Be careful at the beginningof the season(May to early June),
as an empty nest may not have had eggslaid yet; somespeciesor individuals will delay as long as 8 d betweencompletingnestsand laying
eggs.Do not bothernestsat this stage,unlessit is certaina nestingattempt
was made and failed.
Vegetationshouldbe measuredfor the nestsubstrateand surrounding
patch. Vegetationin the patch surroundingthe nest can provideinformation on microhabitatchoices.Speciesthat choosethe sameplant species
asa nestsubstratemaychoose
differentmicrohabitattypes(Martin 1993c,
unpubl. data). Moreover, vegetationin the habitat patch surroundinga
nestmay exert a stronginfluenceon probabilityof mortality.For example,
numbersof potential nest sites(stemsof the same size and plant species
asusedfor the nest)in the patchsurroundingthe nestmay affectpredation
risk (Martin 1988c, 1992, 1993c;Martin and Roper 1988). Hence, determinationof habitat patchpreferencesis importantfor developingland
managementguidelinesand testinghabitat selectiontheories.Comparisonsof nest patch characteristics
to unusedpatchesor to patchesused
acrossthe range of speciesmay provide important insight into habitat
Vol.64,No.4
Finding
andMonitoring
Nests
[517
preferences
(e.g.,seeJameset al. 1984;Knopf et al. 1990;Martin 1988c,
1992, 1993c;Martin and Roper 1988). Standardizedvegetationsampling
methodsshouldbe usedto allow comparisonsamonglocationsand investigators.Details of the vegetationsamplingprotocolsusedby the national BBIRD programare availablefrom Martin upon request.
In conclusion,nest-monitoringplots can providevaluable data on the
habitat influenceson nestingproductivityand possiblecausesunderlying
populationtrends.Constant-effortmist-nettingschemescan providean
index of annual productivity(Ballie et al. 1986, DeSanteand Geupel
1987)andalsosomeinformationonadultandjuvenilesurvivorship.
These
methods,however,do not necessarily
provideinformationon the typesof
habitat conditionsthat facilitate increasednesting productivity.Nestmonitoring is more labor-intensivebut providesdirect information on
both productivityand habitat conditionsthat facilitate maintenanceof
viable populations,therebyprovidingdirect land managementinformation. Moreover, nest-monitoringis the only way to ascertainthe rate and
consequences
of cowbird parasitism. Finally, nest-monitoringprovides
badly neededdata on life history traits of species,which allows identificationof bottlenecks
in the demographyof speciesand, also,when taken
togetherwith nestingsuccess
may provideimportantinsightinto vulnerability of populationsto disturbance(seeMartin 1993a).
ACKNOWLEDGMENTS
We thank a large number of field assistantsfor help in learning how to teachpeoplethe
art of finding and monitoring nests.L. Garner, S. Garner, J. D. Nichols. D. Petit, C. J.
Ralph, C. S. Robbins and R. M. Mannan provided helpful commentson earlier drafts.
Martin's work wassupportedby National ScienceFoundation(BSR-8614598, BSR-9006320)
and the U.S. Fish and Wildlife Service.Geupel'swork was supportedby the membersand
board of the Point ReyesBird Observatory,Chevron Corporation,and cooperationof the
Point Reyes National Seashore.This is contribution Number 1 for the BBIRD program
and Number
536 for PRBO.
LITERATURE
BALLIE,S. R.
CITED
1990. Integated population monitoring of breeding birds in Britain and
Ireland..Ibis 132:151-166.
, R. E. GREEN, M. BRODY, AND S. W. BUCKLAND. 1986.
An evaluation of the
Constant Effort Sites Review Group to the Ringing Committee of the British Trust
for Ornithology. BTO, Beech Grove, Tring, Hefts, United Kingdom.
BART,J. 1977. Impact of human visitationson avian nestingsuccess.Living Bird 16:187192.
--,
AND D. S. ROBSON.1982. Estimatingsurvivorshipwhen the subjectsare visited
periodically.Ecology63:1078-1090.
BURLEY,N. 1980. Clutch overlap and clutch size:alternative and complementaryreproductive
tactics. Am.
Nat.
115:223-246.
DESANTE,D. F., AND G. R. GEUPEL. 1987. Landbird productivity in central coastal
California: the relationshipto annual rainfall and a reproductivefailure in 1986. Condor
89:636-653.
GEUPEL,G. R. 1993. Wrentit (speciesaccount). In D. Shutford, ed. Marin County
breedingbird atlas: a natural history of Marin Co. breedingbirds. Occidental Press,
Bolinas,California, in press.
518]
--,
T. E. MartinandG.R. Geupel
J.Field
Ornithol.
Autumn
1993
AND D. F. DESANTE. 1990ß Incidence and determinants of double brooding in
Wrentits.
Condor
GOTMARK, F.
Ornithol.
92:67-75.
1992. The effects of investigator disturbance on nesting birds. Current
9:63-104.
HENSLER,G. L., ANDJ. D. NICHOLS. 1981. The Mayfield methodof estimatingnesting
success:a model, estimators and simulation results. Wilson Bull. 93:42-53.
HIGGINS,K. F., L. M. KIRSCH,ANDI. J. BALL,JR. 1969. A cable-chaindevicefor locating
duck nests.J. Wildl. Manage. 33:1009-1011.
JAMES,F. C., R. F. JOHNSTON,
N. O. WAMER,G.j. NIEMI, ANDW. J. BOECKLEN.1984.
The
Grinnellian
KENDEIGH,S.C.
niche of the Wood
Thrush.
Am.
Nat.
124:17-47.
1952. Parental care and its evolution in birds. Illinois Biol. Monogr.
22:1-357.
KNOPF,F. L., J. A. SEDGWICK,
ANDU. B. INKLEY. 1990. Regional correspondence
among
shrubsteppebird habitats. Condor 92:45-53.
LABISKY,R.F. 1957. Relation of hay harvestingto duck nestingunder a refuge-permittee
system.J. Wildl. Manage. 21:194-200.
LACK,D. 1968. Ecologicaladaptationsfor breedingin birds. Methuen and Co., London,
United Kingdom. 409 pp.
LYON,B. E., ANDR. D. MONTGOMERIE.1987. Ecologicalcorrelatesof incubationfeeding:
a comparativestudy of high arctic finches.Ecology68:713-722.
MARTIN, T. E. 1986. Competition in breeding birds: on the importanceof considering
processes
at the level of the individual. Current Ornithol. 4:181-210.
. 1988a. Processes
organizing open-nestingbird assemblages:
competitionor nest
predation?Evol. Ecol. 2:37-50.
ß 1988b. Nest placement:implicationsfor selectedlife-history traits, with special
reference
to clutch size. Am.
Nat.
132:900-910.
ß 1988c. On the advantageof being different: nest predation and the coexistence
of bird species.Proc. Natl. Acad. Sci. USA 85:2196-2199.
ß 1992. Breeding productivity considerations:what are the appropriate habitat
features for management?Pp. 455-473, in J. M. Hagan and D. W. Johnston,eds.
Ecologyand conservationof Neotropical migrant birds. Smithson.Inst. Press,Washington, D.C.
ß 1993a. Nest predationamong vegetationlayers and habitat types:revisingthe
dogmas.Am. Nat. 141:897-913.
1993b. Evolutionary determinants of clutch size in cavity-nestingbirds: nest
predationor limited breedingopportunities?Am. Nat., in press.
ß 1993c. Nest sitesand nestpredation:new perspectives
on old patterns.BioScience
43:523-532.
--,
AND P. LI. 1992. Life historytraits of cavity- versusopen-nestingbirds. Ecology
73:579-592.
--,
AND J. J. ROPER. 1988. Nest predation and nest site selectionof a western
population of the Hermit Thrush. Condor 90:51-57.
MAYFIELD,H. F. 1961. Nesting success
calculatedfrom exposure.Wilson Bull. 73:255261.
ß 1975. Suggestionsfor calculating nesting success.Wilson Bull. 87:456-466.
MCDONALD,M. V., ANDR. GREENBERG.1991. Nest departurecallsin female songbirds.
Condor
93:365-373.
NICE, M.M.
New
York
1937. Studiesin the life historyof the SongSparrow. I. Trans. Linn. Soc.
4:1-247.
NICHOLS,J. D., H. F. PERCIVAL,R. A. COON,M. J. CONROY,G. L. HENSLER,ANDJ. E.
HINES. 1984. Observerfrequencyand success
of mourning dovenests:a field experiment.
Auk
101:398-402.
NOLAN, V. 1978. The ecologyand behavior of the Prairie Warbler Dendroicadiscolor.
Ornithol. Monogr. 26:1-595.
PICOZZI,N. 1975. Crow predation on marked nests.Journal of Wildlife Management
39:151-155.
Vol.64,No.4
FindingandMonitoring
Nests
[519
PIENKOWSKI,M.W.
1991. Using long-term ornithological studies in setting targets for
conservationin Britain. Ibis 133 suppl.:62-75.
PIMM, S. L., H. L. JONES,AND J. DIAMOND. 1988. On the risk of extinction. Am. Nat.
132:757-785.
RALPH, C. J., G. R. GEUPEL, P. PYLE, T. E. MARTIN, AND D. F. DESANTE. 1993.
Handbook of field methodsfor monitoring landbirds.USDA Forest Service,General
Technical Report, Pacific SouthwestRes. Sta., Albany, California, in press.
RICKLEFS,R. E. 1969. An analysisof nestingmortality in birds. Smithson.Contr. Zool.
9:1-48.
ROBBINS,
C. S., J. R. SAUER,R. S. GREENBERG,
ANDS. DROEGE. 1989. Populationdeclines
in North American birds that migrate to the Neotropics.Proc. Natl. Acad. Sci. USA
86:7658-7662.
SHERRY,T. W., AND R. T. HOLMES. 1992. Population fluctuationsin a long-distance
Neotropical migrant: demographicevidencefor the importanceof breedingseasonevents
in the American Redstart. Pp. 431-442, in J. M. Hagan and D. W. Johnston, eds.
Ecologyand conservationof Neotropical migrant birds. Smithson.Inst. Press,Washington, D.C.
SILVER,R., H. ANDREWS,ANDG. F. BALL. 1985. Parental care in an ecologicalperspective:
a quantitative analysisof avian subfamilies.Amer. Zool. 25:823-840.
SI•^CI4,R. D. 1976. Nest guarding behaviorby male Gray Catbirds. Auk 93:292-300.
SMITH, J. N. M., AND D. A. ROFF. 1980. Temporal spacingof broods,brood size, and
parental care in Song Sparrows (Melospzzamelodia).Can. J. Zool. 58:1007-1015.
SOUTHERN,W. E. 1958. Nesting of the Red-eyed Vireo in the Douglas Lake Region,
Michigan. Jack-Pine Warbler 36:105-130.
TEMPLE, S. A., AND J. h. WIENS. 1989. Bird populations and environmental changes:
can birds
be bio-indicators?
Amer.
Birds
43:260-270.
WHITCOMB, R. F., C. S. ROBBINS,J. F. LYNCH, B. L. WHITCOMB, M. K. KLIMKIEWICZ,
ANDD. BYSTRAK.1981. Effectsof forestfragmentationon the avifauna of the eastern
deciduousforest. Pp. 125-205, zn R. L. Burgessand D. M. Sharpe, eds.Forest island
dynamics in man-dominated landscapes.Springer-Verlag, New York, New York.
WILLIS, E. 0.
Auk
1973.
Survival rates for visited and unvisited nests of Bicolored Antbirds.
90:263-267.
ZERBA,E., AND M. L. MORTON. 1983. The rhythm of incubationfrom egg-layingto
hatchingin Mountain White-crowned Sparrows.Ornis Scand. 14:188-197.
Received17 Dec. 1992; accepted25 Feb. 1993.