J RaptorRes.39(1):19-25 ¸ 2005 The Raptor ResearchFoundation, Inc.
INVESTIGATING
FLAMMULATED NEW
MEXICO
FALL
MOVEMENTS
OF HATCH-YEAR
OWLS (OTUS FLAMMEOLUS) USING
STABLE
HYDROGEN
IN CENTRAL ISOTOPES
JOHNP. DELONG 1 HawkWatchInternational,1800 S. WestTemple,Suite226, SaltLake City,UT 84115 U.S.A. TIMOTHY
D. MEEHAN 2 AND RUTH B. SMITH 3
Department of Biology,University of NewMexico,Albuquerque, NM 871Yl U.S.A. ABSTRACT.--The migratory patterns of Flammulated Owls (Otusflammeolus)are poorly understood.We predicted natal originsof hatch-yearFlammulatedOwls captured from August-Octoberin central New Mexico using stablehydrogen-isotope analysisof feathers.We collectedreference feathers (N = 22) from Utah, Colorado, New Mexico, and Arizona and describedthe relationship between the •D (stable hydrogenisotoperatio in partsper thousand[%o]) valuesin the feathersand the predicted•D values for precipitationwhere the featherswere grown. We then used this relationship to determine the potential origins of featherstaken from hatch-yearowlscapturedduring fall. We collapsedour resultsinto three categories.Owls in the first category (with the least negative•D values;N = 45) had featherisotoperatios that correspondedwith areasof central New Mexico and central Arizona, including the fall-bandingsiteitself.Owlsin the secondcategory(N = 10) likely originatedin northern New Mexico. Owls in the third category (most negative•D values;N = 2) originated either in the highestelevations of northern New Mexico, or more likely, in southern Colorado. These resultsindicated that someowls made at least200 km movementsto reach the studysite,but that most capturedowlslikely originated locallyor in adjacentmountain ranges. KEYWORDS: FlammulatedOwl; Otus flammeolus;stable-hydrogen isotopes; migrationpatterns;geographicalcatchment area.
INVESTIGACI6N DE LOS MOVIMIENTOS DE OTOI•IO DE OTUS FLAMMEOLUS EN SU A•O DE ECLOSItSNEN EL CENTRODE NEW MEXICO USANDOIS(STOPOSESTABLESDE HIDRtSGENO RESUMEN.--Lospatronesmigratoriosde Otusflammeolusson poco conocidos. En este estudio usamos anfilisisde is6toposestablesde las plumas para predecir los lugares de nacimiento de individuos de menos de un afio de edad de O. flammeoluscapturadosdesde agosto hasta octubre en el centro de New Mexico. Colectamosplumas de referencia (N = 22) en Utah, Colorado, New Mexico y Arizona y describimosla relaci6n entre los valoresde 8D (cociente del is6topo establede hidr6geno en partes por mil [%o]) en las plumasy los valorespredichosde 8D para la precipitaci6n de los lugaresdonde se desarrollaron las plumas. Luego usamos esta relaci6n para determinar el origen potencial de plumas tomadasde individuos capturadosdurante el otofio. Resumimosnuestrosresultadosen tres categorias.Las lechuzasen la primera categoria (con los valores de 8D menos negativos;N = 45) presentaron cocientesde pluma-is6topoque correspondieron alas fireasdel centro de New Mexico y del centro de Arizona, incluyendo el sitio de anillado de otofio. Las lechuzasen la segundacategoria (N = 10) probablemente se originaron en el norte de New Mexico. Las lechuzasen la tercera categoria (los valoresde 8D mils negativos;N = 2) se originaron o en las miximas elevacionesdel norte de New Mexico, o mils probablemente, en el sur de Colorado. Estosresultadosindicaron que algunas
Present addressand correspondingauthor: 2314 Hollywood Ave. NW, Albuquerque, NM 87104 U.S.A.; Emafl'
[email protected] Presentaddress:Departmentof Sciencesand ConservationStudies,Collegeof SantaFe, 1600 St. MichaelsDr., Santa Fe, NM 87505 U.S.A. Present address: 2252 Calle Cuesta, Santa Fe, NM 87505 U.S.A.
19
20
DELONG ET •L.
VOL. 39, No. 1
lechuzas realizaron movimientos de al menos 200 km para 11egaral sitio de estudio, pero que la mayoria de los individuos capturadosprobablemente se originaron localmente o en las cadenasmontafiosasadyacentes. [Traducci0n del equipo editorial]
Bird migration is a complex phenomenon that has attracted
considerable
research
attention
for
decades (Able 1999). The migration of some birds remains poorly understood, however. The Flammulated Owl (Otusflamme01us) is a small,nocturnal bird whose migration patterns are among the least known in North America (McCallum 1994). The
availableevidencesuggests that theseowlsare Neotropical migrants (McCallum 1994). This view is derived primarily from the near absenceof winter
igin, or are they primarily migrantsfrom far north of the local breeding area?Second,is the seasonal pattern of owl capturesrelated to the originsof the owls? Third, are there sex differences in seasonal
timing of capture or in natal origins? METHODS
Field Methods.The studysitewaslocatednear Capilia Peak in the Manzano
Mountains
of central
New
Mexico
(34ø42'N,106ø24'W;Fig. 1; DeLongand Hoffman1999).
We captured owls at two netting stationsspacedca. 200 m apart on the east and west sidesof the Capilia Peak Ridge. We lured owlsto the stationswith broadcastFlamThese negativeresultshavenot been accompanied mulated Owl callsplacedwithin an arrayof three to six by positivedata demonstratingwhere Flammulated mist nets (60-ram mesh). We opened mist nets 3-7 Owls in North America spend the winter. We que- nights/wk from 19 August-20 October 2002, for a total 51 nights of netting. We began netting ca. 0-30 min ried the Bird Banding Laboratory databaseand of after sunset and continued until 15-30 min before sunrecords
for Flammulated
Owls in North
America.
found that, through the year 2000, no band recov- rise, or for shorter periods if inclement weather forced
eries were obtained that directly documented the migratory movementsof Flammulated Owls. We investigatedthe natal originsof Flammulated Owls captured in the Manzano Mountains of central New Mexico using stable-hydrogen-isotope analyses.Briefly, the latitudinal gradient in stablehydrogen-isotoperatios (2H/•H) associatedwith
station closure.We generallyopened nets only during calm or moderately-windyperiods, avoidingperiods of high wind (exceedingca. 24 krn/hr). We collecteda contourfeatherfrom abouteveryother owl (N = 57) for use in the isotopeanalysis.Because isotope ratios in adult raptor feathers may not corre-
keratinof bird feathers(SDf)of individualscap-
Wildlife Genetics, Inc. (Nelson, British Columbia, Cana-
spond to local precipitation (Meehan et al. 2003), we
collectedfeathersonly from hatch-yearowls.Hatch-year FlammulatedOwlsleavethe nestin juvenal plumageand growingseasonprecipitation(SD/,)is reflectedin begin molting into formativeplumagewithin about 1 wk animal tissuesthat are grown in those areas (Hob- after fledging (Reynoldsand Linkhart 1987). When they son and Wassenaar1997). Although somehydro- are captured at the Capilia Peak banding station, most gen in tissuescan exchangewith atmospherichy- hatch-yearowls have not completed this molt (DeLong 2004). Therefore, we aged owls as hatch-yearsif they drogen (Wassenaarand Hobson 2000), for tissues showeda mix of juvenile and formative feathers and colsuch as feathers and hair these ratios are more or lected onlyjuvenile-plumagefeathersfor use in the staless locked into their structure and can be meable-hydrogen-isotope analysis. suredevenwhen the animal travelsgreat distances We took blood samplesfrom owlsfor sex determina(Chamberlain et al. 1997). Recent studies show tion. We collectedblood from the brachialvein usingthe tip of a needle and a capillary tube and transferred the that the ratio of stable-hydrogenisotopesin the sample into a microcentrifuge tube containing ethanol.
tured during migration can be comparedto maps da) analyzed the samplesand determined the sex of
these owls using the CHD gene (Griffiths et al. 1998).
of 8D/,to describethe approximate latitudeswhere Unlessalreadybanded,we banded all capturedowlswith
those feathers were grown (Meehan et al. 2001, Wassenaarand Hobson 2001, Kelly et al. 2002). Analysesof stable-hydrogenisotopesalso have revealed patterns of migratory movement in Neotropical migratory birds (e.g., leap-frog and chain migration; Kelly et al. 2002, Smith et al. 2003). We used stable-isotopeanalysisof Flammulated Owl feathers to answer three specific questions. First, are the owlscaptured at the banding station in the ManzanoMountainsof local or regionalor-
a uniquely-numbered aluminum leg band provided by the U.S. GeologicalSurvey. Reference
Feathers.
We
collected
reference
feathers
(N = 22) to calibratethe relationshipbetween8Dfand the 8Dpwhere the featherswere grown.We obtained Flammulated Owl feathersfrom sitesnear Ogden, Utah, and Colorado Springs,Colorado,where collaboratorscollected feathers from nestlingsin 2002. Additional reference featherscame from collectionmanagersat the Umversityof New Mexico and the Universityof Arizona, who provided us with feathersfrom studyskinsof hatch-year plumage Flammulated Owls taken in north-centralNew
MARCH 2005
ORIGINS OF FAI L-CAPTURED FLAMMULATED OWLS
21
Figure 1. Map of potential natal origins of hatch-yearFlammulated Owls captured in the Manzano Mountains, New Mexico, in 2002. Predictedprecipitationvalueswere divided into three categoriesand mapped to showthe potential locationswhere owlsin thosegroupsmay have originated. See Methods for further descriptionof map preparation.
Mexico
and
the
Chiricahua
Mountains
in southeastern
Flammulated Owl's range in the Rocky Mountain States. Laboratory Methods. We prepared feather samplesby first cleaning them of oils with a chloroform-methanol
We calculated the isotope ratios of non-exchangeable hydrogen in feather samples via comparative equilibration using keratin standardsafter Wassenaarand Hobson (2003). The isotope ratios of non-exchangeablehydrogen in keratin standardswere determined using steam equilibration methods (Wassenaarand Hobson 2000).
(2:1) solution (Wassenaar and Hobson 2000) and then
The keratin standards we used were black bear (Ursus
air drying them for 14 d to enable exchangeablehydrogen (13-22%) to equilibrate with laboratory-ambient moisture (Chamberlain et al. 1997, Wassenaarand Hobson 2000). We then packed feather clippings (0.18-0.20 rag) in silver capsules(3.5 x 5 ram; Costech,Valencia, CA, U.S.A.), pyrolized the samplesusing a Finnigan MAT TC-EA elemental analyzer (Thermo Electron Corporation, Boston,MA U.S.A.), and analyzedsamplehydrogen using a Deltae•usXL massspectrometer(Thermo Electron Corporation, Boston, MA U.S.A.) in continuousflow mode at the University of New Mexico Stable Isotope Laboratory.We used the following standardmodel to calculatewhole-sample8D and report 8D valuesin partsper thousand (%0):
americanus)fur samplesfrom Louisiana (non-exchangeable hydrogen•D = -58%0) and Alaska (-164%o). The comparative equilibration equation we used to convert whole-samplevalues to non-exchangeablevalueswas:
Arizona. Collection datesof museum skinsranged from 1959-95.
These
reference
feathers
cover
much
of the
•D = {(hydrogen-isotoperatio of sample) -' (hydrogen-isotoperatio of Vienna Standard
Mean
[VSMOW])
Oceanic
Water
- 1} x 1000.
The precisionof our analyses was$D _+3• (1 SD) based on repeated measurementsof internal laboratory standards.
•D! ...... h•g•ab•e = (•D!who•e•a,np• + 29.89)/0.65 We report both whole-sampleand non-exchangeablehydrogen-isotope ratios of reference and fall-collected feathers to facilitate comparisonwith other studies. Mapping Methods. We estimated the origins of owls captured in the Manzano Mountains by (1) calculatinga regressionmodel for the relationship between hydrogenisotope ratios in reference feathers and estimated grow-
ing season•Dp for reference-feather collectionsites,(2) usingthis regressionto predict growingseason•Dp for each feather sampled in the Manzano Mountains, and (3) using GeographicInformation System(GIS) analysis
to query growingseason•Dp, FlammulatedOwl geographic range, and North American biome maps to identify potential origins.
Estimated•Dpvaluesfor the predictiveregression and determination of origins were from the GIS-basedmodel of Meehan et al. (2004; http://biology. unm.edu/wolf/ precipitationD.htm). We digitized a geographic range
22
DELONG ET AL.
VOL. 39, NO. 1
Table 1. Stable-hydrogen-isotope ratiosin feathersare presentedfor referenceand fall-captured FlammulatedOwls
(SDf)values[%0]).Fall-capture feathers werecollected during2002in theManzano Mountains, NewMexico.Utah and Colorado referencefeatherswere collectedduring summer2002. New Mexico and Arizona referencefeathers were collected from museum skins (1959-95).
8Df+ SD LOCATION Reference
8Df+ SD
NON-EXCHANGEABLE
WHOLE-SAMPLE
MEAN
MEAN
HYDROGEN
HYDROGEN
N
LATITUDE
LONGITUDE
- 30%0 -75 _+ 9%0 -89 _+ 6%0 -98 -+ 4%0
- 50%0 -79 _+ 6%0 -88 _+ 4%0 -94 _+ 3%0
I 5 6 10
31.85 35.91 39.11 41.32
109.35 106.00 105.04 111.58
-52
-64
57
34.70
106.40
sites
Arizona New Mexico Colorado Utah
Fall captures Manzano Mountains
-+ 19%0
-+ 12%0
map for FlammulatedOwlsfrom McCallum (1994) and ManzanoMountainsusingnon-exchangeable 8Dr enteredthis into the GIS to limit 8D/,map queriesto valuesand referenceequation (1). There would be geographicregionsof North Americawhere Flammulated Owls breed. We used a digitized map of North Amer- no difference in our results between using equations (1) or (9), but we chose to proceed using ican biomes from Reichenbacher et al. (1998) to limit
8D/,mapqueriesto drymontaneconiferforests, the bi- equation (1). ome selectedby FlammulatedOwls (McCallum 1994).
Predicted8D•,valueswereplacedinto threecat-
Usingthe GIS,we selected 8D•gridcellsthatfell within the rangeof predicted8D/,valuesfor birdscapturedat egories.Categoryone rangedfrom -30 to -60%0 (N = 45), category two ranged from -60 to the banding station, and that occurred within both the owl's geographicrange and associatedbiome type (Fig. -70%0 (N = 10), and categorythree ranged from 1). We emphasizethat thesedata shouldbe viewedas a -85 to -95%0 (N = 2). When mapped, the three spatialhistogramrather than preciseestimatorsof natal origins.
categories of predicted8Dpdisplayed potentialna-
tal origins of captured Flammulated Owls that ranged from the immediate local vicinity of the The mean8Dfvalues for non-exchangeable and banding station up through the northwestern whole-samplehydrogenfrom owlsat the four ref- U.S.A. Owls in the first category (with the least erence sitesranged over 68%0 and were progres- negative8Dfvalues)had potentialoriginsin the sivelymore negativewith increasinglatitude (Table isolatedmountain rangesof west-centralNew MexRESULTS
1). The mean 8Dfvaluefor capturedowlsin the ico and east-centralArizona (Fig. 1). Hence, most
owls could have been local or from neighboring mountain ranges.Owlsin the secondcategoryhad potential natal originsestimatedat the higher elThe relationshipbetween 8D•, and reference feather8Drfor non-exchangeable hydrogen (//2 = evations of mountain ranges near the Manzanos Manzanos
was between
the mean values for south-
ern Arizona and northern New Mexico (Table 1).
and in northern
0.47) was estimated as:
8D/= 1.33(8D•,)+ 16%0.
(1)
New Mexico
and southern
Colo-
rado. Two owlswere placed in the third category
(withthe mostnegative8D/values)andhadpoten-
The standard errors for the non-exchangeable tial origins in either the extreme high elevations slope and interceptwere 0.13 and 95, respectively. of their breeding areasin northern New Mexico The relationship between8D•,and 8Dffor whole- or in an area stretchingfrom the RockyMountain front in Colorado up through northwesternstates samplehydrogen(/•2 = 0.48) wasestimatedas: suchas Oregon and Washington. 8D7 = 0.87(8D•,)- 19%0. (2) We captured most owlsin September,with few The standard errors for the whole-sampleslope owlscapturedafter the first week of October.The and intercept were 0.90 and 16, respectively. We seasonalpattern of owl captureswasnot related to
predicteda 8D•,valuefor eachowlcapturedin the 8Dfvaluesand,therefore,not likelyrelatedto the
M_ARCH 2005
OretINS
OF FALL-CAPTURED FLAMMULATED OWLS
23
New Mexico, with many owls potentially originating in the immediate local vicinity of the banding -20 ß station (i.e., Manzano Mountains). It is most likely that owls in the second category originated in northern New Mexico and southern Colorado, given that this area representsthe largestarea of potential origin. However, the second category in-60 cludes many areas close to the banding station, indicating that some owls in category two also are -80 from neighboringmountain ranges.If there is no directionality to the movements of Flammulated -100 Owls during September,then many of the owlsin categoriesone and two could haveoriginatedfrom throughout most of the montane areas of both -120 220 230 240 250 260 270 280 290 300 New Mexico and Arizona. In the third category, Julian Date there are two owls with isotope signatures that Figure 2. Relationshipbetween stable-hydrogen-isotopeplaced them anywherein a large geographicarea ratiosof feathers(gDf)andJuliancapturedatefor hatch- from the highest elevations in New Mexico up year Flammulated Owls capturedin the Manzano Moun- through Washington(Fig. la). tains, New Mexico, in 2002. These resultsare one of the first pieces of evidence that suggestsouthward migratory movementsin FlammulatedOwls.At leasttwo owlslikely originsof the owls (Fig. 2). However,the two owls originated north of New Mexico, making their in the third categorywere capturedtowardthe end movement to the banding station consistentwith of the banding season(mid-October;Fig. 2). It is what we would expect from migrating birds. Aspossiblethat theseowlswere comingfrom further suming that the direction of long-distancemovenorth than the other owls, suggestingthese two ments during the fall is to the south, then these owlswere undertakingmigratorymovementswhen two owls made movements of at least 200 km (and possiblymuch more) to arrive in the Manzanos. captured. Although our data provide new insightsinto the Therewasno differencein gD/values(t = 0.35,
l*
ø
øo ' %%" '
df = 31.8,P = 0.73) orJuliancapturedatebetween
movements
males and females (t = 0.61, df = 39.8, P = 0.54).
Mountains, our results are imprecise because of severalfactorsthat limit our ability to usehydrogen
Hence, there were no sex-specificdifferencesin the predictedorigins or timing of capturedowls. DISCUSSION
of Flammulated
Owls in the Manzano
isotopesto determine the origins of particular birds. These factors are particularly difficult to overcome
in the mountainous
states of the south-
westernU.S.A. and the southernRockyMountains. First, the latitudinal gradient in isotope ratios allows only coarse predictions of potential origins (Meehan eta!. 2001). Second, the latitudinal gradient in isotoperatios is complicatedin the southgDpinto three categories and mappedthe areas western U.S.A. due to proximity to the Pacific where thosevaluescould be found (Fig. 1). Using Ocean, the Gulf of California, and the Gulf of Mexthis approach, we offer three general statements ico (Dansgaard1964). Finally, the latitudinal graabout the potential originsof capturedowlsbased dient is complicatedby a negativerelationship beon the three mapped categories.In the first cate- tween elevation and isotope ratios (Poage and gory,we find owlsthat could have originatedfrom Chamberlain 2001, Bowen and Wilkenson 2002). much of the montane areas in Arizona and New This latter relationship makesit difficult to distinMexico (Fig. lb). There is no evidencethat young guish potential sourceareassuch as those at high Flammulated Owls make long-distancemovements elevations in the south from those at lower elevato the eastor west,so it is likely that the large ma- tions further north. Importantly,we used methods determinjority of captured individualsoriginatedin central that accountedfor the variousprocesses Our resultsindicate that hatch-yearFlammulated Owls captured during fall in the Manzano Mountains represent a combination of local and regional birds, and a small number of migrants from the north (Fig. la). We dividedour predicted
24
DELONG ET AL.
ing isotope ratios in local rainfall by mapping a
VOL. 39, NO. 1
ever, we identified potential natal areas for
relationship between8Dfvalues andestimated local capturedowlsthat were primarily local and region-
8D•,valuesratherthanassuming a simplelatitudi- al. Indeed, everysampledowl couldhaveoriginatnal relationship over the western United States. ed in New Mexico (although the two potential miDespite the limitations,this stable-hydrogen-iso-grantswould be from far northern New Mexico). tope analysishasproduceda very usefulpictureof We do not believe that this finding is a failure of the natal originsof owlscapturedin the Manzano the method. Stable-hydrogen-isotope analysisof Mountains, a picture that would be difficult to bird feathershas been usedsuccessfully to describe compile usingband recoveriesof a small, noctur- sourcerangesfor focal speciesat other migration nal bird. monitoring stations (Wassenaar and Hobson We also found no overall relationship between 2001). For example, a study on Sharp-shinned capturedateand 8Dfvalues(Fig.2). The absence Hawks (Accipiterstriatus)captured during migraof a relationship to indicate migratory patterns tion at the Manzano Mountains study site, using such as whether northern or southern birds pass proceduresidentical to those used in this study, through the sitefirst (Smith et al. 2003) may have confirmed that captured birds had originated resulted from the geographically-limitedsource acrossa wide latitude spanning New Mexico to population we sampled.There still may be inter- Alaska (Smith et al. 2003), similar to patterns inesting migratory patterns to detect if owls can be dicatedby long-termband-recoverydata (Hoffman
sampledfrom a larger portion of the range.The et al. 2002). two clearlysouthward-moving birdswere captured Fall movementsof young FlammulatedOwls in
in mid-October,suggestingthat October may be an New Mexico remain somewhat of a mystery. important time for longer movementsof young Whether Flammulated Owlscapturedduring fall in Flammulated
Owls in New Mexico.
This
restilt
is
consistentwith other viewson the timing of Flam-
the Manzano Mountains are local birds or dispersers from other parts of New Mexico is still un-
mulated Owl migration (McCallum 1994). How- known. Finally, answering the question of what ever,why we capturedthe bulk of the owlsin Sep- type of migratory movementsFlammulatedOwls tember and so few owls in October, despite nets undertake may require considerablymore effort. being open in late October, remains to be exBanding efforts that target potential wintering arplained. eas and other likely stopoverlocations(in particWe found no gender-specific differencesin capular where Flammulated Owls do not breed) may ture timing. We investigatedthispossibilitybecause shed light on this question, especiallyif used in many migrating raptors showgender-specificdifcombination with further isotopic analysisor geferential migration timing (DeLong and Hoffman netic markers that can match wintering or migrat1999). Such differences could mask seasonaldifing birds to potential natal areas. ferences in the origin of captured birds because
temporal separationof owls originating in the same locationscould make it difficult to accurately detect a relationshipbetweenowl origins and capture date. The absenceof a gender-specifictiming difference reduces the possibilitythat we overlooked a relationshipbetweencapture date and or•gin. It is alsolikely that timing diftkrencesbetween males and femaleswere not yet developedbecause
these owlslikely originatedrelativelycloseto the Manzanos.
The breeding range of Flammulated Owls extends
north
from
the
Manzano
Mountains
into
Coloradoand Wyomingand further northwestinto Utah,
Idaho,
Montana,
and Alberta,
Canada
(McCallum 1994). We anticipatedthat many captured owlswould have clearlycome from throughout the full latitudinal extent of their range; how-
ACKNOWLEDGMENTS
Primary financial supportwasprovidedby the USDA Forest Service,Cibola National Forest and Region 3, and the New Mexico Game and Fish Department Sharew•th Wildlife Program.Additional fundsfor the projectcame
fromJeanieandJodie Humber.BeverlydeGruyterat the SandiaRangerStation,and HowardGrossandJeff Smith at HawkWatch
International
were
instrumental
in ar-
ranging funding and logisticalsupportfor this project. WendyKing and Apple Snider conductedmost of the fieldwork. Bob Dickerman (University of New Mexico), Tom Huels (Universityof Arizona), Brian Linkhart (Colorado College), and Diane McCabe (U.S. ForestService, OgdenRangerDistrict) all providedjuvenileFlammulated Owl feathersfrom their studyareasor their university's studyskin collectionsfor use as isotopereference samples.The New Mexico Coffee CompanyprovidedAvalon© organic, shade-growncoffee to keep field staff awake.Keith Hobson, Robert Rosenfield,Jeff Smith, and
MARCH 2005
ORIGINS OF FALL-CAPTUREDFLAMMULATED OWLS
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movement
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Received29 January 2004; accepted15 October 2004
