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

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

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

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.

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