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Corel la, 2000, 26(4): 110-113
MOVEMENTS OF TWO EXPERIMENTALLY DISPLACED BROWNTREECREEPERS Ctimacteris picumnus lN A MATRIX OF WOODLAND AND
PASTURE
CAREN B. COOPER
Deparlment of Biology, Virginia Polytechnic Institule and State University, Blacksburg' VA' USA 24061
-Cunent address: Comell Lab of Ornithology, 159 Sapsucker Woods Road' Ilhaca' NY' USA 14850
Received: 3 Odober 200 l
previous work found that Brown Treecreepers Climacteris picumnus werc unable to disperse to isolated
"ooaiunJpit"t ", in the New England Tablea-nis, nortnern t'tew south Wales .l attempted.to understand dispersal
O"n*ar|.iy i"si"g how Brown -Treecreepers
react to landscape patterns while moving l radio-tagged two male
eio*n fr""dr""p"rJ on their resident territories and released them on territgries two kilometres away l expected
lo jolro* it " return patns ol tnese birds across i matrix of pastures and woodlands within hours ol release The
male that I moved to a new terntory "-n""i"o oir""try to the original territory by woodlands returned within.four
days. The mate that I moved to u n"* Griiory *ntn'ras isotatelO kom the irriginal territory by d*t:9 l9ry
.9iqnoi return. rne post-release movements ol both males were confined to woodlands. These obseftations
reveal
f," tirit"o .ou,j."nt behaviour of male Brown Treecreepers and provide anecdotal sr'idence that non-wooded
habil,at rs a barrier to dispersal in this species
INTRODUCTION
The mechanisms by which habitat fragmentation affe.ts the
Dersislence of wildlife populattons have been a major focus
of research and debate in ionseruation biology Exp€rimental
reseauch has revealed a wide range of species-specificresponses to habitat fragmentation (reviewed by Debinski and
Holt 20OO). Habitat degradation as well as edge and isolationeffects vary in importance in their contribution to thepersistence of different species. Experimental and theoreticalitudies suggest that fragmentation can disrupt natal dispersal(Askins el al. 19901 Hanison and Bruna 1999; Cooper andWalters 2002a) and lower reproduction and survival (l-ovejoy
et aL. 1984;Lyrch and Whigham 1984; Saunders et al. l99I).Whereas lowered reproduction and survival arise through edgeeffects that ar€ known to operate primarily by nest Parasitismand predation (Lovejoy et cl. 1984; Lynch and Whigham1984: Saunders et al. l99l), it is unknown exactly howisolation effects disrupt dispersal.
Theoretical studies of isolation effects hinge on untestedassumptions concerning dispersal behaviour, including howbarriers to dispersal and movement behaviour vary amongspecies. Bird movements occur at several scales: withinterritories, between territo es, and between seasonal ranges.Because many passerines migrate between seasonal ranges,it may seem counter-intuitive that smaller-scale movementscould be disrupted by habitat fragmentation, but the scantempirical evidence available suggests otherwise formigratory forest songbirds (Dunning er al. 1995; Desrochersand Hannon 1997), a variety of residents (Machtans e/ al.1996; Sieving et al. 1996: St. Clair e/ cl. 1998), and fbrshort-distance migrants (Haas 1995) in North America andland birds in Australia (Saunders and deRebeiva 1985).
The Brown Treecreeper Climacteris pictlmnrs is a non-migratory, co-operatively breeding passerine that inhabitsEucalyptus woodlands. The species forms territories
ranging from l. l-10.? hectares (mean = 4.4 ha, Std = 2 5)
(Co-oper er al., in review) in open woodlands, sometimes
incorporating small areas of cleared land (e g roads) and
rhey irequently forage at least uP lo 30 metres into open
plslures bordering woodland patches or wooded slreams(pers. obs.). Thus, their short-range movements (wltnln
tirritory) are not inhibited by cleared land Nevertheless,
Brown Treecreepen are declining because isolation of
habitat remnants disrupts dispersal. Cooper and Walters(2002a) found that females were unable to fill breedingvacancies in isolated patches, but bred successfully in suchpatches when experimentally relocated there.
Dispersal could be disrupted by several mechanisms. For
example, birds may be unwilling to enter novel, interveninghabitats (Creenberg 1983); they may enter these habitatsbut experience eleYated mortality rates (Matthysen andCunie 1996); or they may enter these habitats, but have avery low probability of locating suitable habitat patches ina human-dominated matrix. Cooper et al. (2002) \sed' aspatially explicit simulation model of Brown Treecreeperpopulation dynamics in the New England Tablelands tobetter understand how dispersal movements may interactwith the configuration of habitat in the landscape. In aneffort to develop movement rules for the model, I soughtto observe how Brown Treecreepers react lo various
habitats while moving across the landscape.
Studies of invertebrate movements suggest thatobservations of individual behaviour at edge boundariescan predict the movement and distdbution of a speciesamong habitat types (e.g. Haddad 1999; Jonsen and Taylor2000). From observations of foraging Btown Treecreepers,I expected that cleared land was not a complete barrier tomovement. Because dispersal behaviour is almostimpossible to observe, I attempted to manipulate BrownTreecreepers into performing movements on an inter-territorial scale by displacing territorial birds two kilometres
' 110
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December,2002
and following their rerurn paths. I had previously observedBrown Treecreepers moving at least 500 metres in less thanhalf an hour during forays (Cooper, unpubl. data) andassumed they had homing abil ify l ike many otherpasserines. Therefore, I anticipated that each bird wouldreturn to its territory within hours of release.
NIETHODS
For th is manipulat ion. I iden! i f ied scveral pairs of terr i tor ies inlvoodland parchcs approximatcly 40 kilometres west of Armidale. NewSouth Wales (30"2?'5, l5 l '13 'B). I p lanned to d isplace mate BrownTleecrecpcrs between each pair of tcrritories and observe their retumpalhs. Hcre I repo( on the only two displacem€nts lhat I underlook,havi g cnded the experimen! afler the rwo displaccmenrs rev€aled moreI imi lcd moveDrent behaviour lhan I expected.
C. B. Cooper: Movements of experimentally displaced Brown Treecroepers 1 1 1
The frrst pair of territories (referred (o as rhe Direct disDlacement)$ere 2 l i lometres apa srrh rhc srrdigh( l ine Jr. lance compri\ed olwoodlauds (Fig. l). The second pair of territories (referred to as rheCircuilous displaccmcnt) were also 2 kilometres aparl, but with thestraiBht line dislance comprised of mostly cleared land, yet lheternlones were connected by woodlands through a circuitous route (Fig.l) For the Circuitous displacement, both rerrirories bordercd clearedIand or scattered trees and the displaced male frequently foraged incleared land or roads prior 1o displacement.
In Brown Treecreepers, females are the predominan! dispersing sex. Irelocaled helper males rarher rhan females in order to avoid breaking upbrccding pairs and lC) minimize lhe risk to flcdging success. On 9Novembcr of thc 1996 breeding season (for the Direct displacement) andl9 November 1996 (for the Circuitous displacement), a field assishot andI fitted two helper males wjth mdio,transmitters (0.90 g, Holohil Sysrerns,Ltd.) and a unique combinaliofl of colour bands. Transmilters wereatlached wrth leg hamesscs as described by Rappole and Tipron (1991).
Figx.r: !-Map ol hndcover types and dLsplacement ft'utes- Dotted ava reprepnts woodland pat.hes (>s0 trces/tn), white atea rcprcynts scauered trees( 1 0-50 treer'4n) and harched atea re p re sents cleared land. woodlandi in li! rBion c ontain hi gh densities of B twn Treec repe r te rrtories ( circles ),et'cpt woodhtuis to the south o.f the Dire.t Displacement. B&\e of arnvts indi.a;e E original tlnitory and iu point of orroi inai"or" ttrc disptaced
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C. B. Coopet: Movements ol experimentally displaced Brown Treecreepers Corel la 26(4)112
Males were placed in a c loth bag and moved f rom thci r respecl lve
resident territory 1o territories 2 kilomelres away in a wcsterly direclion(Fie. l). For ea;h bird, wc observed it as continuously as possible from
aain unrit durk until we no longer received a radio transmission When
the rrdio signal was los!, we checked the originrl terrilory for the bird's
relurn each day.
RESULTS
Neither bird was able to return home readily The male
that underwent the Direct displacement vocalized upon
release and was immediately detected by other Brown
Treecreepers. The resident birds attacked and chased the
displaced male unti l he left their territory He was
freouentlv detected and chased trom other tsrrltorles as
wel'I. He roosted the night of release in an area of young
trees where there were no Brown Treecreeper terrltorlgs'
He t rave l led lo lhe edg.e , . , f wood lands . bu t never en tered
cleared land. The next day, he was detected by Brown
Treecreepers while intruding on lheir tenrlory During the
en.uins i ls.ht, his lran'mitrer was pulled off We lost sight
of the -male
and did not see him on his original territory
until lbur days after release.
The male that underwent the Circuitous displacament was
never detected by other Brown Treecreepers He rarely
vocalized and froze and pressed himself close against a tree
trunk whenever Brown Treecreepers came near' He made
repeated fo rays o f aPprox imate ly I k i lomet res ln every
direction comprised of woodtands. yet spenl much of his
time resting on logs and foraging on the ground^at the
release site. He wai last seen on the fourth day after his
release in the late afternoon at the release site, after which
we no longer received a signal from the transmitler'
DISCUSSION
These observa t ions sugges l lha t movemenl o f ma le
Brown Treecreepers is strongly affected by habitat
structure. Unfortunately, I cannot determine whether this
inference applies to females, whose dispersal beha-viour is
more crit ical to Population dynamics than that of males
Male Brown Treecriepers rarely disperse beyond their natal
territory, generally obtaining a breeding vacancy by
inherit ing their natal tenitory or by budding (claiming a
oortion of therr natal tenitory) (Noske 1980; Doerr and
boerr 2000: Cooper er al 2002t
If female movements are also restricted by cleared land,
then breeding vacancies in isolated patch€s should remain
unfil led and competit ion should be high for breeding
vacancies among connected woodland patches Further
more. the population in fragmented habitat should slowly
decline due to lack of recruitment This finding is
consistent with the observed response of Brown
Treecreepers to habitat fragmentation (Walters er 41 1999;
Cooper er al. 2002; Cooper and Walters 2002b) Brown
Tteecreepers are declining in isolated patches Breedingvacancies remain unfi l led in isolated patches' but not inpatches which are relatively contiguous and in a matrix ofscattered trees rather than cleared land (Cooper and Walters2002a).
Because many passerines have homing ability, I expectedBrown Treecreepers to return quickly to their original
territory. Because Brown Treecreepers foraged in pastures,
I expected displaced birds to move across cleared land if
necessary. Why were both expectations unmet? It is
diff icult to discern the reason that displaced male Brown
Treecreepen had diff iculty returning to their original
territoriei. One interPretation is that cleared land is a
barrier to between-teritory movements Several hypotheses
could accounl for the discrepirncy between this interpretation
and lhe observarions thal Brown Treecreepers frequently
forase in cleared land. The first hypothesis is that Brown
Tree"creepers may enter cleared land when it is a familiar
area. bui not when it is a novel location The second
hvDolhesis is lhal Brown Treecreeper foraging movements'
rnitii.h oft"n occur on the ground (Walter et al 1999)' can
occur in cleared land, but dispersal movements' or any
medium-range movements, may involve travelling from tree
to tree. Several other understory birds are reslstant to move
inlo open areas tBierregaard cr 4i lgg2: Desrochers and
Hannon 19971 St . C la i ie r a / 19s8) l f th is hypothes is - i s
correct, then whether individual behaviour at edge
boundaries can predict movement and distribution of
nro*n t .""t."p"ts appears dependent on the motivational
itate of the inaividu;i when observed ln other words'
when observations at edges are of birds with the motlvatlon
to disperse, then the observations may translate lnto
oreA ic i ion t o f movements in f ragmented landscapes ''However. ,* hen the obser\'ations at edges are of bird5 wilh
the motivation to forage, then the observations may not
translate to larger scale movements
A second interpretation of why both my expeclation were
unmet is that Brown Treecreepers lack homing ability'
Under this scenario, the male in the Direct displacement
lrealment may have returned home only because he w"s
released in *u, u nurro* linear strip of woodlands and he
happened to move in the general direction of his territory
rath'er than away from it. If Brown Treecreepers generally
iorav up to I iilometre from their territofies, then after
. *o io r ine lo r I k r lomet re in the d i rec t ion loward h is
orisinal ienitory, the Direct dtsplacement male would have
bein rn familiai sunoundings. Conversely' lhe male in the
Circuitous displacement treatment would not be in familiar
sunoundings from his 1 kilometre forays unless he had
forayed I kilom"tre into cleared land and scattered trees
Nevertheless, because post-release moYements of both birds
were confined to woodlands, these anecdotal observations
still suggest that Brown Treecreepers do not enter cleared
land for between-territory movements.
The two displaced reecreepers differed in their Yocal
resDonse and detectability after release. There may have
been pre-existing differences in behavioral tendencies
between these two individuals. If this were the case' the
male lhat underwenl lhe Circuitous displacemenl appeared
more able to disperse (because he avoided detection when
intruding on tenitories) than the male that underwent the
Direct displacement. Therefore' if individual differences
were partly responsible for the patterns observed, it should
have been more likely for the male that underwent the
Circuitous displacement to return. It is also possible that
the differences were a consequence of the breeding stageof the receiving territory. The male that underwent the
Direct displacement was released on a tenitory with
nestlings, it which time parents actively defend territories,whereas the male that underwent the Circuitous displacement
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December,2002
was released on a tenitory with fledglings, at which timeterribry boundaries are rarely defended (pers. obs.).
if Brown Treecreepers do not disperse through clearedland. then an intervening habitat of scattered trees orwoodland corridors are necessary for dispersal betweenwoodland remnants.
'fhe conservation of Australian birds
will beneflt from more resgarch to determine theIelationship bet*een bird movements and the compositionof habitats in the landscape.
ACKNOWLEDGMENTS
I lh ink J. Lyons for the discussrons of re locat ing b ' rds thr t insplredmy,r t lempr at th is exper iment. Many thanks 10 A. Sl ikkel ibr spcndinglong hours in rhe f ie ld radio- t racking bi rds lhat seldom nrove. J.
C-ranford. C. I laas. B. Jones. J. Wal tcrs and J webster helped plan lh isresearch. A. Bennett . R. Bishop, E. Doen and J. Waltcrs helpcd improverhis manuscript. J. Wlhcrs provided the radio-transmillers. I also thankH. Ford for provid ing Iogist ical support iD carry ing oul lhc f lc ldresearch. The New South wales Cenler for La d Management kindly
f t .anted access to : tcr ia l photographs ol lhe study regron. Financralsuppo( was provid€d by Signra Xi , a Graduale Research andDevclopme0l Progran g.ant f rom VPI : tnd SU, a Nat ional ScienceFou0dal ion Disscrt i l t ion lmprovement Grant (DE8-9801083), and thcH. T. Bailey Foundadon oi VPI and SU. The University of New EnglandAnimal Ethics Comnri r te€, dre Austra l ian Dird and Bar Banding Scheme,and the NSW Nalional thrks and Wildlife Service granted permissionibr this experiDcnt. Finally, I thirnk the landown€rs lbr permilling (hiswork on thcrr pruperty.
REFERENCES
Askins, R. . \ . , Lynch. J. F. . rnd Grccnberg. R (1990). Popula!ondecl ines in ln igratory b i rds in eastern No(h Amcr ica. Cr l fenrOnittul 1t 1-5'7
I l ierreg.urd, Jr . R. O . Lovejoy. T. E . Kapos, V, dos Santos. A. A. andHutchings, R. W. (1992). The bio logical dynamics of t ropicalrxinforesl liagments. an)s.i. {2: 856-8()().
( looper. C. B. rnd Wal lers, J. R. (2002a). Exper imenial evidence ofdisruplcd dispcrsal causing dccl ine of an Auslra l i rn passcr inc inlfagmented habilat. C.)nr. Ar., 16: l-8.
Cooper- C. B and wllllers, J. R. (2002b). Habitat and landscape effectson Browo Treecreeper distribution: independent elfects of woodlandloss a d f tagmental ion al mul t ip le scales. Ard. Crn. l . 105: l -10.
Cooper, C. B., Wallers, J. R. and Ford, H. A. (2002). The demographyof Brown Treecreepers io connected and isolated, large and smal lwoodland patbcs. Enw l02t 249-256.
Cooper, C. ts . Wahers, L R. and Priddy, J. Effects of landscape pattemson dispersal success: a s i Inulat ion of Brown Treecreeper populat iondynamics in a spatially realistic landscrpe. Ecological Applications:in press.
Debinski , D. M and Hol( , R. D (2000). A survey and overview ofhabitat liagmcnlation experiments. Conr. Biol. llt 342-355.
l )esrochers, A. and Hannon, S. J. (1997). cap crossing decis ions byforest songbirds du. ing the posf f ledging per iod. Cdnr. Bld l . 11:r 204 I2 t0 .
C. B. Coaper Movements o{ experimentally displaced Erown Treecreepers 1 1 3
Doerr , V. A. J. and Doerr , E. D. (200t) . Brown Treecreepcr ' In'Handbook of Australian, New Zealand and Anhrctic Birds, Vol. 5:Tlran! flycatchers to Chals.' (Eds P J. Higgins, J. M. Pctcr and w
K. Steele.) (Oxford Univers i ly Press, Melboume.)Dunning, J. B, Jr , Borgel la, R. i r . , Clemenls, K. and Mcft t , G. F (1995)
Patch isolation. corridor effects, and colonizadon by a resident spanowin a managed pinc vr'oodland. Con!. Biol.9:512-550
Greenberg, R. (1983). The ro le of neophobia in determining the degreeof foraging spccialization in some migrant warbler. Arn. Ndr. 122:444453
Haas, ll. A. (1995). Dispersal and use of corridors by birds in wooded
patches on an agricultural iandscaPc. Cont. Riol.9t 845 1354
Haddad. N M (1999) Coddor use prediclcd from behaviors al hab'ht
boundanes. Arr. Ndt. t5!t 215-227Harison. S. and Brunr. E. (1999). Habital fragmenlation and large scale
conservalion: what do we rcelly know tot srre? E.ograpltr 22i
225-232.Jonscn. l. aod Taylor. P D. 12000J. CaLopteryt damselfly dispersions
lrising from multiscale responses to landscape struclure. C{rnr. !iol.
J(2):,1 [online] URL: http://www.consecol.org/vol'1/isszart4Lovejoy. T. 8. , Rankin. J. M., Bierregaard. R. O., Brown, K S
Emmons, L. Il. and Van der Voort. M. E. (1984). Ecosystem decay
of Amazon forest remnants. In 'Ext inct ions (Ed. M. H. Nikechki) .
Pp. 295-325. ( t jn ivers i ty of Chicago Press, Chicago, IL, USA.)Lynch, J F. and whigham. D F. (1984). Effects of foresl fragmentation
on breeding bird communrlies in Maryland, USA. Ant. alrnr' 28:287 -324.
Machtans, C. S. , Vi l lard, M. 'A. and Hannon, S J. (1996). Use ofriparian buffer strips as movement corridors by forest birds. Cdnr.Bid. r0:1366-1319.
Ma(hysen, E. and Curr ie, D. (1996). Habi tat f ragmcf l ta l ron reduceddisperser success in juvcnilc nulhatches Silrd err.?d?d: evidence lrompatcms of lerritory establishment. ErcEruphy 19t 6'7-12.
Noske. R. A. (1980). Cooperat ive breeding by l reecreepers. t ru 80:35-36.
Rappole, J. H. and' f ipton, A. R. (1991) New hamess design for theattachment of radio uansmi(ers to small Dasserincs. J. Fi(ld Omitllol.6 2 : 3 3 5 3 3 7
Saunders. D A. and deRebeiva, C I ' . (1985). Turnover in breeding bi rdpopulations on Roltnest Island. Weslern Australia. A !t. WiLll. Res.lzt 461 1'7'l .
Saunders. D. A. , Hobbs, R. J. and Margules, C. R. (1991). Bio logicalconscquences of ecosystem lragmenlation: A review Corr. aiol. 5:l 8 3 2 .
Sieving, K. 8. , Wi l lson, M. F. and De Santo, T. L. (1996). Habi tatbarners to movement of understory birds in fragmented south-remperalr ra in l^re. t . l r i I l - l : o4. !a4q
St. Cla i r . C. C. . Ddl is le. M., Desrochers, A. and Hannon, S. (1998).winler responses of forest b,rds to habitat corndors and gaps. Crn.r.t..rl. [oflline] 2(2): 13. URL: h!!p://ww w consecol. org/vol2/iss2/art I 3
Wal lers, J. R. , Ford, H. A. and Cooper, C B. (1999). Var iat ion inpopulation s(ruclure and ecology of brown lreecreepers belweencontiguous and fragmented woodland: a preliminary assessment. Brol.Cons.9Ot l3-2O.