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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. 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Received17 Dec. 1992; accepted25 Feb. 1993.