85
Es ima ing ela i e densi y o an in asi e ungula e in a
biodi e si y ho spo using d one-based he mal ideo su eys
Julia Wi czuk1, S anisław Pagacz1, Romain Alliod2
1 Museum and Ins i u e o Zoology, Polish Academy o Sciences, Twa da 51/55, 00-818 Wa saw, Poland
2 Eco one NC SARL, 8 ue du capi aine bois, 98800 Nouméa, New Caledonia (F )
Co esponding au ho : Julia Wi czuk ([email p o ec ed].pl)
Copy igh : © Julia Wi czuk e al.
This is an open access a icle dis ibu ed unde
e ms o he C ea i e Commons A ibu ion
License (A ibu ion 4.0 In e na ional – CC BY 4.0).
Resea ch A icle
Abs ac
New Caledonia’s unique e es ial habi a s – p ima ily moun ain ain o es and scle ophyll o es –
ace signi ican h ea s om in asi e ungula es, pa icula ly Ja an dee (Rusa imo ensis), in oduced
in he 19 h cen u y and now widesp ead. Since dee a e an impo an game and ood sou ce o lo-
cal communi ies, he managemen s a egy aims o mi iga e hei de imen al impac on ecosys ems
while main aining popula ions a le els ha con inue o suppo hun ing. To achie e hese objec i es,
e ec i e and eliable popula ion moni o ing me hods a e essen ial. Unmanned ae ial ehicles (d ones)
equipped wi h he mal senso s ep esen a po en ially supe io al e na i e o con en ional g ound-
based me hods o ungula e in en o ies, pa icula ly in emo e and di icul - o-access a eas. In his
s udy, we explo ed he easibili y o using a o o -wing d one and a he mal came a o es ima e he
ela i e densi y o Ja an dee in wo p o ec ed a eas: Domaine de Dé a (7,319 ha) and Pa c p o incial
des G andes Fougè es (8,098 ha). Visual line-o -sigh ligh s we e conduc ed a e sunse a al i udes
o 80 and 100 m abo e g ound le el, wi h he came a ixed a 40° o 0° angles. In Dé a, we su eyed
10 sampling blocks, and in G andes Fougè es, 4 blocks (each anging om 56 o 92 ha). In he p e-
dominan ly open sa anna a ea o Dé a, he es ima ed ela i e popula ion densi y was 116 dee /km2
(SE = 26.8), wi h some blocks exceeding 400 dee /km2. In con as , in he dense canopy ain o es o
G andes Fougè es, he ela i e densi y was 7 dee /km2 (SE = 2.8), wi h a local maximum o 18 dee /
km2. Di e ences in dee coun s be ween consecu i e ligh s o e he same blocks (wi h ime gaps o
less han 100 minu es) we e mino , demons a ing ha d one su eys a e highly epea able – an essen-
ial quali y o a eliable popula ion moni o ing p og am. To de ec a 25% popula ion educ ion wi h
a s a is ical powe o 0.8, su eying 10 sampling blocks was su icien in he high dee densi y sa anna
a ea, whe eas app oxima ely 28 blocks would be equi ed in he ain o es . The logis ics o d one
ope a ions we e ela i ely s aigh o wa d in he sa anna; howe e , in he ain o es , we encoun e ed
p ac ical di icul ies, including a limi ed numbe o sui able ake-o si es and es ic ed isibili y due
o he dense canopy co e . Despi e hese obs acles, he me hod p o ed o be an e ec i e and e icien
app oach o moni o ing dee popula ions in he challenging landscapes o New Caledonia.
Key wo ds: Ja an dee , New Caledonia, Rusa dee , Rusa imo ensis, he mal in a ed came a, un-
manned ae ial ehicle, wildli e moni o ing, wildli e su ey
Academic edi o : Sand o Be olino
Recei ed:
3 May 2025
Accep ed:
14 Sep embe 2025
Published:
10 Oc obe 2025
Ci a ion: Wi czuk J, Pagacz S, Alliod R
(2025) Es ima ing ela i e densi y o
an in asi e ungula e in a biodi e si y
ho spo using d one-based he mal
ideo su eys. NeoBio a 103:
85–106. h ps://doi.o g/10.3897/
neobio a.103.157791
NeoBio a 103: 85–106 (2025)
DOI: 10.3897/neobio a.103.157791
Ad ancing esea ch on alien species and biological in asions
A pee - e iewed open-access jou nal
NeoBio a
86
NeoBio a 103: 85–106 (2025), DOI: 10.3897/neobio a.103.157791
Julia Wi czuk e al.: The mal d one su eys o in asi e Ja an dee in New Caledonia
In oduc ion
Biodi e si y loss is cu en ly one o he p ima y challenges in na u e conse a ion.
I is d i en by habi a deg ada ion, clima e change, as well as compe i ion and p e-
da ion by alien in asi e species (Vi ousek e al. 1997; Le eu e 2006; Kings o d e
al. 2009; IPBES 2019). The nega i e impac o non-na i e animals is pa icula ly
p onounced on isola ed oceanic islands (Cou champ e al. 2003; Russell and Kue -
e 2019). Thei unique, p edominan ly endemic ege a ion, which o en e ol ed
wi hou p essu e om la ge mammalian he bi o es and he e o e did no de elop
adequa e de ense mechanisms, is especially ulne able o he p esence o human-in-
oduced domes ica ed o wild ungula es (Bowen and Van Vu en 1997). Mo eo e ,
in he absence o na u al p eda o s, he bi o e popula ions can expand apidly, pos-
ing an inc easing h ea o island ecosys ems. Consequen ly, con olling in asi e
he bi o es is a c ucial conse a ion p io i y on islands (Cou champ e al. 2003).
New Caledonia is a Paci ic a chipelago loca ed abou 1,500 km eas o Aus a-
lia. I is cha ac e ized by excep ional biodi e si y and a high numbe o endemic
species. O he mo e han 3,300 na i e ascula plan species ound he e, 75%
a e endemic (Mo a 1993; Isna d and Ja é 2024; Munzinge e al. 2025), and
he a chipelago is conside ed one o he mos impo an biodi e si y ho spo s on
Ea h (Mye s 1988; Mye s e al. 2000). The mos aluable e es ial habi a s o
G ande-Te e, he a chipelago’s la ges island – opical ain o es s (83% o en-
demic species) and d y scle ophyll o es s (57% o endemic species) – a e se e ely
h ea ened by mining, logging, i e, ag icul u e (ca le g azing), and in asi e spe-
cies (Mi e meie e al. 2004; Isna d and Ja é 2024). While ain o es s s ill co e
much o he ha d- o- each inland a eas a highe ele a ions, he small emnan s o
he scle ophyll o es s ha ha e su i ed, sca e ed wi hin sa annas along he wes
coas , occupy only 2% o hei o iginal a ea (Bouche e al. 1995).
Ja an dee (Rusa imo ensis), also known as Rusa dee , we e in oduced o G ande-
Te e in he 1870s. Due o hei high adap abili y, as well as he lack o compe i-
o s and p eda o s, he species quickly sp ead h oughou he island. Cu en ly, hei
abundance is es ima ed a se e al hund ed housand indi iduals (Ba iè e and Fo
2021), wi h he highes densi ies eco ded along he wes coas o he island (de
Ga ine-Wicha i sky e al. 2004). The species is now lis ed as one o he majo p io -
i y in asi e species (Conse a oi e d’espaces na u els de Nou elle-Calédonie 2017).
The highly nega i e impac o dee on he endemic lo a is obse ed bo h in he
emnan s o he scle ophyll o es (Bouche e al. 1995; Ga gominy e al. 1996; de
Ga ine-Wicha i sky and Spaggia i 2008; Mansou ian e al. 2018) and in he moun-
ain ain o es s (Le Bel e al. 2001; T on e al. 2024). Dee des oy endemic plan
species and impede o es egene a ion h ough b owsing, deba king, and ampling.
They also con ibu e o he sp ead o in asi e plan species by ac i ely dispe sing hei
seeds (de Ga ine-Wicha i sky and Spaggia i 2008). Se e e o e g azing causes soil e o-
sion and nega i ely a ec s wa e esou ces on he island (T amie e al. 2021). Addi-
ionally, local a me s a e conce ned abou he damage caused by dee o pas u es and
ag icul u al c ops (Ba iè e and Fo 2021). Al hough he impac o Ja an dee on he
island’s ecosys ems is undoub edly nega i e, hey also ep esen a signi ican sou ce
o game mea o local communi ies, and dee hun ing is an impo an pa o hei
cul u e (de Ga ine-Wicha i sky e al. 2004). Fo his eason, he species canno be
ea ed solely as a pes o be e adica ed om he island. Ins ead, i is necessa y o man-
age he popula ion in a way ha minimizes i s nega i e e ec s on biodi e si y and ag-
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NeoBio a 103: 85–106 (2025), DOI: 10.3897/neobio a.103.157791
Julia Wi czuk e al.: The mal d one su eys o in asi e Ja an dee in New Caledonia
icul u e while main aining i a a le el ha p ese es i s social signi icance. Achie ing
such goals equi es e ec i e and eliable me hods o popula ion moni o ing.
The Ja an dee popula ion managemen s a egy adop ed in New Caledonia
ocuses con ol e o s on 10 designa ed p io i y a eas ha a e pa icula ly aluable
o biodi e si y and p o ide essen ial ecosys em se ices, such as hose c i ical o
he wa e cycle (Conse a ion In e na ional and Conse a oi e d’espaces na u els
de Nou elle-Calédonie 2016). In h ee o hese a eas, egula moni o ing and in-
ensi e p o essional dee con ol ha e been planned wi hin he amewo k o he
PROTEGE p ojec (Paci ic Communi y 2025). Based on p e ious expe ience wi h
dee su eys in New Caledonia (de Ga ine-Wicha i sky and Sain -And ieux 2003;
Roques-Roge y 2008) and he esul s om es s conduc ed unde he in asi e un-
gula e con ol plan launched in 2008 (Ba iè e and Fo 2021; Fo and Ba iè e
2021), he s a egy ecommends moni o ing popula ions using indi ec me hods
ha measu e dee impac on he o es , along wi h di ec animal obse a ions o
es ima e abundance indices and iden i y a eas o dee concen a ion.
Due o he noc u nal ac i i y o Ja an dee and he limi ed access o he su ey a -
eas, he mal came a obse a ions conduc ed om unmanned ae ial ehicles (d ones)
a e conside ed he mos p omising new moni o ing me hod. P e ious s udies in
empe a e o es s ha e shown ha de ec ing la ge mammals in d one-acqui ed he -
mal image y is possible e en in ela i ely dense coni e s ands (Wi czuk e al. 2018).
Tes s o e cap i e dee enclosu es ha e u he demons a ed ha his app oach can
p o ide accu a e animal coun s (Bea e e al. 2020; McMahon e al. 2021; Zabel e
al. 2023). The me hod has also p o en eliable unde na u al condi ions, wi h d one
su eys p oducing consis en esul s when conduc ed alongside o he dee densi y
es ima ion me hods – such as pelle -g oup coun s and came a apping (McMahon
e al. 2022; Baldwin e al. 2023; Finnegan e al. 2024). Mo eo e , d one ligh s in
di icul moun ainous e ain ha e been epo ed o be much mo e easible and e -
ec i e han g ound-based obse a ional su eys (T inh-Dinh e al. 2024).
The pu pose o his s udy was o es whe he d one-based he mal ideo su -
eys could be an e ec i e me hod o moni o ing he Ja an dee popula ion in he
challenging landscapes o New Caledonia. Following p elimina y ligh s o de e -
mine op imal ligh pa ame e s, we es ed he me hod in wo o he island’s main
habi a ypes – open sa anna and dense canopy ain o es – and aimed o es ablish
a me hodological ounda ion o u u e dee in en o ies in New Caledonia and
simila en i onmen s.
Me hods
S udy a eas
The esea ch was conduc ed on G ande-Te e (16,372 km2), he main island o
New Caledonia. The island has a opical clima e wi h wo seasons: a d y season
( om mid-Ap il o mid-No embe ) and a ainy season ( om mid-No embe o
mid-Ap il) (Fo sing and Dumas 2021). A e age mon hly empe a u es ange om
20 o 26 °C, and mon hly p ecipi a ion a ies om 55 mm in Oc obe o 271 mm
in Ma ch (Wo ld Bank 2025). The island is spa sely popula ed, wi h an a e age
popula ion densi y o abou 15 inhabi an s pe km2. The e a e no na i e mammals
on he island excep ba s. Besides he in asi e dee and e al pig (Sus sc o a), he
island is also inhabi ed by domes ic ca le, goa s, and ho ses.
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NeoBio a 103: 85–106 (2025), DOI: 10.3897/neobio a.103.157791
Julia Wi czuk e al.: The mal d one su eys o in asi e Ja an dee in New Caledonia
The choice o he s udy a eas was s ongly in luenced by COVID-19 pandemic
es ic ions, as mos o he moun ain ain o es p io i y zones designa ed o dee
managemen we e inaccessible due o he lockdown.
The i s s age o he esea ch in ol ed es ligh s o es ablish he op imal ligh
al i ude and came a angle. These we e conduc ed a a p i a e hun ing and ca le
a m, La Co onniè e, Bouloupa is (21°51.23'S, 165°54.65'E). The p ope y (350
ha) ea u es hilly e ain wi h ex ensi e plains and woodlands. Fo he es ligh s,
we chose la , g assy a eas wi h nume ous dee .
The su ey ligh s o es ima e ela i e dee densi ies we e conduc ed in wo p o-
ec ed a eas: Domaine de Dé a and Pa c p o incial des G andes Fougè es (Fig. 1).
The su ey a eas we e selec ed o ep esen wo di e en ecosys ems o he island.
Domaine de Dé a (21°33.55'S, 165°20.05'E) is a 7,319 ha a ea loca ed on he
wes coas o he island. The e ain is hilly, wi h ele a ions anging om 0 o
383m a.s.l. and a mean slope o 12°. The a ea is domina ed by sa anna – g ass-
lands and sh ub wi h discon inuous ee co e (Figs 1, 2). Spa se o es s include
he la ges emaining pa ches o scle ophyll o es in New Caledonia.
The Pa c p o incial des G andes Fougè es (21°36.55'S, 165°45.15'E) is si ua ed
app oxima ely in he middle o he island’s cen al moun ain ange. The pa k co -
e s 4,546 ha, bu wi h a 700 m bu e a ound he pa k bounda ies included, ou
esul ing s udy a ea was 8,098 ha. The ele a ion anges om 157 o 718 m a.s.l.,
wi h a mean slope o 21°. The a ea is domina ed by opical ain o es , in e spe sed
wi h pa ches o sh ubs and g assland sa annas (Figs 1, 2).
Figu e 1. Land co e o he wo s udy a eas and loca ions o sampling blocks o Ja an dee (Rusa imo ensis) he mal d one su eys in
New Caledonia: Domaine de Dé a (A) and Pa c p o incial des G andes Fougè es (B); bo h a eas a e shown a he same scale.
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Julia Wi czuk e al.: The mal d one su eys o in asi e Ja an dee in New Caledonia
D one and senso
The ligh s we e conduc ed using a Ma ice 300 RTK quadcop e (DJI, Shen-
zhen, China). The d one is powe ed by wo li hium polyme ba e ies (capaci y
5,935mAh), enabling a ligh endu ance o up o 40 minu es. The maximum
ligh speed is 23 m/s, and he d one is esis an o winds up o 12 m/s. The ake-
o weigh is 9 kg, including wo ba e ies, a gimbal, a came a, and a pa achu e.
De ailed d one speci ica ions can be ound on he manu ac u e ’s websi e (h ps://
en e p ise.dji.com/ma ice-300).
The d one was equipped wi h a hyb id RGB/ he mal in a ed came a, he Ze-
nmuse H20T (DJI, Shenzhen, China). The he mal componen o he came a
ea u ed an uncooled, mic obolome e ocal plane a ay de ec o (640 × 512 pixels,
12 μm pixel pi ch, spec al ange 8–14 μm) wi h a 13.5 mm ocal leng h, /1.0
lens. The came a was moun ed on a downwa d gimbal, wi h he came a’s ho i-
zon al axis aligned pe pendicula ly o he ligh pa h. Video iles (30 Hz) in mp4
o ma we e sa ed on an SD ca d; he eco ded scenes we e also iewed in eal ime
on he d one’s emo e con olle . Geo e e encing da a and ligh pa ame e s we e
s o ed in STR (SubRip Tex Sub i le) iles.
Es ablishing op imal ligh al i ude and came a angle
The quali y o ideo da a acqui ed by d ones s ongly depends on he ligh al i-
ude abo e he g ound and he angle o he came a. Bo h o hese a iables a ec
he g ound sampling dis ance (GSD, i.e., pixel size) and he size o he came a’s
ins an aneous ield o iew ( ideo oo p in ) (Bu ke e al. 2019). The lowe he
ligh al i ude, he smalle he GSD, imp o ing he abili y o dis inguish small
de ails in he image y. Howe e , his comes a he cos o educing he image oo -
p in size, and hus su ey e iciency, as mo e ime is equi ed o co e he same
a ea (Fig. 3). To ensu e high de ec abili y and accu a e iden i ica ion o animals in
he mal imaging, he he mal signa u e o an animal should be a leas 10 pixels
long (Wi czuk e al. 2018; Bu ke e al. 2019). As he a e age body leng h o Ja an
dee is be ween 130 and 170 cm, he maximum accep able GSD should be 13 cm.
Because o he a iabili y in GSD caused by he came a angle and opog aphy, we
applied a conse a i e ule ha he GSD should no exceed 10 cm.
Figu e 2. Landscapes o he wo s udy a eas o Ja an dee (Rusa imo ensis) he mal d one su eys in New Caledonia: Domaine de Dé a
(A) and Pa c p o incial des G andes Fougè es (B).
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NeoBio a 103: 85–106 (2025), DOI: 10.3897/neobio a.103.157791
Julia Wi czuk e al.: The mal d one su eys o in asi e Ja an dee in New Caledonia
Figu e 3. G ound sampling dis ance (a he cen e o he came a’s ield o iew) and oo p in a ea (came a’s ins an aneous ield o iew)
o a ange o ligh al i udes (70–120 m) and came a angles (0–50°). Fo some combina ions o al i udes and angles, he esul ing g ound
sampling dis ances exceeded he 5–12 cm ange and a e no shown. A combina ion o 80 m al i ude and a 40° came a angle p o ides a
g ound sampling dis ance o < 10 cm while maximizing he oo p in a ea.
To assess he di e ences in ideo quali y acqui ed a a ange o al i udes (70–
120m) and came a angles (0–50°), we conduc ed es ligh s a La Co onniè e
a m in May and Sep embe 2021 (Fig. 4). Reco ded ideos we e isually inspec -
ed, and each al i ude–came a angle combina ion was a ed based on he le el o
de ail enabling easy de ec ion and iden i ica ion o dee while maximizing he
oo p in a ea. F om his analysis, we es ablished ha he op imal pa ame e s o
su ey ligh s we e 80 m al i ude abo e g ound le el and a 40° came a angle. These
se ings esul in a GSD esolu ion o ~9 cm (in he cen e o he came a’s ield o
iew) and a ilmed s ip wid h o abou 76 m (calcula ed based on he o mulas
p o ided by Bu ke e al. 2019).
Du ing su ey ligh s o e he ain o es , we also collec ed da a using a 0° came a
angle (poin ing di ec ly downwa d) o enhance de ec ion o animals obscu ed by
ees. Fo hese ligh s, al i ude was inc eased o 100 m o main ain he desi ed GSD
o ~9 cm. These al e na i e se ings esul ed in a na owe ilmed s ip wid h o 59 m.
Su ey ligh ope a ion de ails
A Dé a, ligh s we e conduc ed om 23 o 25 Sep embe 2021, and a G andes
Fougè es on 4 and 5 Oc obe 2021 (Table 1). The su ey ligh s we e ca ied ou a
nigh , om sunse (a ound 7 PM) o app oxima ely 1 AM (NCT), as oppo unis-
ic obse a ions indica ed ha dee become mo e ac i e a ound sunse , when hey
eme ge om o es s o eed in adjacen g asslands, wi h ac i i y dec easing a e
midnigh . A simila ac i i y pa e n was obse ed in samba dee (Rusa unicolo )
in oduced o Aus alia (Com e e al. 2022).
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Julia Wi czuk e al.: The mal d one su eys o in asi e Ja an dee in New Caledonia
Figu e 4. Video ames showing Ja an dee (Rusa imo ensis) he mal signa u es cap u ed by a d one a di e en al i udes and came a
angles: 80 m, 50°, 44 indi iduals (A); 80 m, 0°, 52 indi iduals (B); 120 m, 50°, 132 indi iduals (C); 120 m, 0°, 79 indi iduals (D). Inse s
show close-ups o selec ed he mal signa u es om he op and bo om pa s o he images (no e he di e en scales in he op and bo om
sec ions o images eco ded wi h a 50° came a angle). Videos we e eco ded du ing es ligh s a La Co onniè e a m, Bouloupa is, New
Caledonia, in May and Sep embe 2021.
A each s udy a ea, we selec ed sui able ake-o si es o d one ope a ions ha
o e ed ehicle access and clea isibili y o he su ounding e ain o ensu e ligh
sa e y and simpli y logis ics. Simul aneously, we aimed o choose loca ions ha
ep esen ed he ull ange o habi a s occu ing wi hin he s udy a ea. Impo an ly,
si e selec ion was independen o he dee dis ibu ion.
In he Dé a s udy a ea, we sampled a o al o 10 blocks, which anged in size
om 56 o 92 ha (mean 77 ha). The blocks we e eached om i e ake-o lo-
ca ions. In he G andes Fougè es s udy a ea, we sampled ou blocks (63–84 ha,
mean 70 ha), eached om h ee ake-o si es (Figs 1, 5).
The size o he sampling blocks was de e mined by wo cons ain s: he equi e-
men o isual line-o -sigh ligh s – he d one had o emain wi hin 1,800 m o he
ope a o (as pe ou de oga ion) – and he need o e ain a leas 20% o he d one’s
ba e y a e su eying a sampling block o ensu e a sa e e u n. Gi en he a iabili y in
ake-o si e condi ions (openness, isibili y, and opog aphy), he numbe , loca ion,
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Julia Wi czuk e al.: The mal d one su eys o in asi e Ja an dee in New Caledonia
Table 1. De ails o ligh s and he numbe o Ja an dee (Rusa imo ensis) de ec ed du ing he mal d one su eys in New Caledonia. Di -
e ences in he su eyed a ea be ween ligh epe i ions in he G andes Fougè es a e due o a ying ligh al i udes (80 m and 100 m) and
came a angles (40° and 0°) used o each ligh .
S udy a ea Sampling block Numbe o ligh s Da e S a imes A ea su eyed (ha) De ec ed indi iduals
Dé a A1 2 25.09.2021 19:02, 20:38 85, 85 47, 64
A2 2 25.09.2021 19:32, 21:07 84, 84 66, 73
B1 2 24.09.2021 19:04, 21:02 60, 60 44, 56
B2 2†24.09.2021 19:37, 21:29 93, 44 237, 154
B3 2 24.09.2021 20:22, 21:56 85, 85 211, 191
C1 2 25.09.2021 22:25, 22:55 70, 70 121, 120
D1 2 23.09.2021,
24.09.2021
23:27, 0:42 79, 79 17, 19
D2 2 24.09.2021 0:15, 1:11 83, 83 28, 33
E1 1 23.09.2021 19:27 84 77
E2 2 23.09.2021 18:52, 20:14 88, 88 98, 68
To al 811, 678 946, 778
G andes
Fougè es
F1 2 04.10.2021 19:03, 20:12 57, 45 10, 8
F2 2 04.10.2021 19:36, 20:42 75, 53 2, 2
G1 2 05.10.2021 18:55, 19:23 62, 44 0, 1
H1 2 05.10.2021 0:32, 1:03 58, 48 4, 4
To al 252, 190 16, 15
†Second ligh incomple e
and ligh pa hs o sampling blocks we e planned du ing ieldwo k o maximize co -
e age and minimize he isk o losing communica ion wi h he d one.
The ligh pa hs wi hin he sampling blocks had he o m o pa allel ansec s
(Fig. 5) anging in leng h om 0.2 o 1.4 km (mean 1.1 km, SD = 0.19 km). Each
block con ained 6 o 11 ansec s. The spacing be ween non-o e lapping ilmed
s ips was abou 10 m. The o al leng h o all ansec s was 106.5 km in Dé a and
32.2 km in G andes Fougè es.
Fo mos o he sampling blocks (12 ou o 14), su eys we e epea ed wice (Table
1). Howe e , due o echnical p oblems a one o he emaining blocks (Dé a B2),
he second su ey was incomple e, and one block (Dé a E1) was su eyed only once.
Su ey ligh s o e a single block las ed be ween 18 and 25 minu es, excluding
he ime equi ed o he d one o a el om he ake-o si e o he sampling
block and back. The in e al be ween he i s and second su eys anged om 8
o 100 minu es (mean 54 minu es).
In Dé a, bo h su ey epe i ions we e conduc ed a an al i ude o 80 m wi h he
came a ixed a a 40° angle. In G andes Fougè es, he i s su ey was also conduc -
ed om 80 m a a 40° came a angle. Howe e , since he a ea was mainly co e ed
by dense canopy o es , he second su ey was conduc ed wi h he came a ixed a
0° and a an al i ude o 100 m o enhance animal de ec abili y. The d one’s speed
anged be ween 8 and 10 m/s.
The su ey missions we e p og ammed using Mission Planne so wa e (A du-
Pilo ) and lown au onomously, wi h only ake-o and landing pe o med manually.
Fligh pa ame e s and he d one’s loca ion we e moni o ed by he pilo on a g ound
con ol s a ion and he sc een o he emo e con olle . Each block was in ended o
be su eyed using one pai o ba e ies; howe e , we assumed he mission would be
in e up ed and he d one e u ned o he ake-o si e i he ba e y cha ge d opped
o 20%. Du ing all ligh s, he d one was obse ed by a second pe son – he spo e .
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Video analysis
Videos we e e iewed manually by wo independen obse e s using he Full Mo-
ion Video (FMV) plug-in o QGIS (Raga 2021). This plug-in allows o he
analysis and isualiza ion o d one ideos wi hin a geog aphic in o ma ion sys em
(GIS) en i onmen . FMV equi es me ada a compa ible wi h he Mo ion Imag-
e y S anda d Boa d (MISB); howe e , he STR me ada a gene a ed by he H20T
came a a e no MISB-compa ible. To o e come his, we de eloped a Py hon sc ip
o con e he STR iles o he equi ed o ma .
While e iewing iles in FMV, when a dee o g oup o dee was de ec ed, we
ma ked i s loca ion, o he cen e o he g oup, by placing a poin on he ideo dis-
play (signa u es o which iden i ica ion was unce ain we e omi ed). This ac ion
simul aneously c ea ed a co esponding poin on he map laye , which was la e
sa ed in ESRI shape ile o ma . Fo each de ec ion, we eco ded he imes amp,
numbe o animals, and obse ed beha io in an Excel sp eadshee . Beha io (gen-
e alized a he g oup le el) was classi ied in o one o ou ca ego ies: 1) unning,
2) walking, 3) mo ing (i.e., emaining in he ini ial loca ion bu changing body
posi ion), o 4) s ill.
Figu e 5. Dis ibu ion o Ja an dee (Rusa imo ensis) du ing he he mal d one su ey in h ee sampling blocks (B1, B2, B3; i s ligh )
a he Domaine de Dé a s udy a ea, New Caledonia. To al numbe o dee de ec ed: 44 (B1), 237 (B2), 211 (B3). Backg ound image:
Gou e nemen de la Nou elle-Calédonie / DITTT / Se ice opog aphique.
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Julia Wi czuk e al.: The mal d one su eys o in asi e Ja an dee in New Caledonia
Ae ial he mog aphy can be eco ded as ideo iles o s ill images. Ou expe i-
ence om he cu en s udy, as well as om p e ious esea ch (Wi czuk e al. 2018;
Pagacz and Wi czuk 2023), indica es ha ideo da a o e signi ican ad an ages.
The mo emen o animals cap u ed on ideo helps dis inguish hei he mal sig-
na u es om o he simila ly sized ho objec s, he eby aiding in de ec ion and
ecogni ion. Addi ionally, ideo eco ded a 30 ames pe second – compa ed o
he ypical one image pe second o s ill image y – o e s a highe p obabili y o
de ec ing animals, pa icula ly in o es ed a eas, by cap u ing mul iple iews o
a gi en loca ion om shi ing d one pe spec i es. I is also impo an ha ideo
oo age allows obse a ion o animals’ esponses o he d one and he di ec ion o
hei mo emen , which – i no andom – may lead o biased popula ion es ima es.
Limi a ions
D one-based su eys p o ed o be less e ec i e in dense canopy ain o es s han in
open a eas. In New Caledonia, howe e , his limi a ion is less signi ican , as ain o es s
co e only abou 20% o he island (Allenbach 2021), while sh ubs and g asslands
accoun o o e 55% (Gou e nemen de la Nou elle-Calédonie and Obse a oi e
de l’En i onnemen en Nou elle-Calédonie 2019). To enhance su ey e ec i eness
in moun ainous ain o es p io i y zones, we ecommend planning sampling blocks
in a eas whe e closed-canopy o es co e does no exceed 50% and alloca ing g ea e
sampling e o o adjacen sa anna a eas whe e dee end o cong ega e o o aging.
The mal d one su ey limi a ions also ela e o he echnical aspec s o da a
analysis. The ideos cap u ed du ing ou su eys we e manually e iewed using an
open-sou ce FMV plug-in o QGIS. This so wa e is basic and lacks se e al use ul
ea u es. Fo ins ance, while i is possible o c ea e a GIS poin laye indica ing
dee loca ions by selec ing poin s in he ideo display window, i is no possible
o simul aneously assign a ibu es such as g oup size o animal beha io . These
a ibu es mus be en e ed and sa ed ex e nally in sp eadshee so wa e, which is
bo h ime-consuming and p one o e o s. The ime equi ed o e iew a ideo o
app oxima ely 40 minu es ( eco ded o e an a e age-sized sample block o abou
70 ha) anges om 60 o 90 minu es, depending on he numbe o dee de ec ed
and he ope a o ’s expe ience. The p ocedu e is highly a iguing, making i di i-
cul o e iew mo e han wo ideo iles consecu i ely. The solu ion would be an
au oma ic ideo analysis using deep lea ning algo i hms (Sudholz e al. 2021).
While comme cially a ailable so wa e enabling objec de ec ion and acking in a
geog aphic con ex is limi ed and expensi e (e.g., he FMV o A cGIS P o om
ESRI), de eloping new, o iginal so wa e equi es ime and he employmen o
highly quali ied pe sonnel. In any case, i is i s necessa y o c ea e a da abase o
aining, es ing, and alida ing he de ec ion/classi ica ion algo i hm. The da a
collec ed du ing his s udy p o ide a good s a ing poin o building such a da a-
base and also o e an oppo uni y o de elop a i s e sion o he algo i hm, laying
he g oundwo k o u u e in es men in i s de elopmen . Upcoming dee su eys
in New Caledonia a e expec ed o be analyzed using deep lea ning algo i hms,
which should signi ican ly educe he ime equi ed o da a analysis.
The low esolu ion o commonly used he mal senso s (640 × 512 pixels) is an-
o he limi ing ac o . To achie e an accep able le el o de ail in he ob ained imag-
es, he ligh al i ude mus be ela i ely low (≤ 100 m), which limi s he s ip wid h
and educes he e iciency o he su eys. Howe e , ecen ly in oduced high- eso-
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Julia Wi czuk e al.: The mal d one su eys o in asi e Ja an dee in New Caledonia
lu ion he mal came as (1280 × 1024) o e he possibili y o inc easing he ligh
al i ude wi hou he cos o de ail loss. Addi ionally, lying a highe al i udes may
help o e come communica ion issues caused by he e ain, he eby ex ending he
e ec i e ange o d one su eys. I is only a ma e o ime be o e high- esolu ion
came as become s anda d in wildli e esea ch, ele a ing he quali y o d one-ac-
qui ed he mal imaging o an en i ely new le el.
The inal limi ing ac o is egula ions. A e yea s o cons an changes, egula-
ions ega ding he use o d ones a e now well es ablished. Howe e , o ensu e he
sa e y o all ai space use s, he ules o d one ope a ions emain qui e es ic i e.
In mos cases, conduc ing nigh ime wildli e su eys will equi e holding a p o es-
sional d one pilo license and applying o exemp ions ha allow nigh ope a ions
a he desi ed al i ude o dis ance. These egula o y p ocedu es can be cumbe -
some, depending on he loca ion and he applican ’s expe ience. The e o e, wildli e
manage s planning d one su eys should be awa e ha ob aining he necessa y
pe mi s can be ime-consuming. The high equi emen s o d one ope a o s, com-
bined wi h he high cos o he equipmen , mean ha s akeholde s will usually no
be able o conduc su eys independen ly. Ins ead, hey will need o ou sou ce he
se ice o a well-equipped and expe ienced ex e nal con ac o .
Conclusion
D ones equipped wi h he mal came as a e an e ec i e ool o assessing he el-
a i e densi y o in asi e Ja an dee in he challenging landscapes o New Caledo-
nia. The ime e iciency, e i iabili y o he da a, and highly ep oducible su ey
p o ocol make d one su eys a much be e op ion han al e na i e g ound-based
me hods. The s aigh o wa d in e p e a ion o he da a and he s ong demon-
s a i e alue o he ideos acili a e social accep ance o dee managemen ac ions
– especially p o essional dee con ol – by local s akeholde s, such as landowne s,
esiden s, ibal cus oma y au ho i ies, and poli icians. Fu he imp o emen s o
he me hod will equi e he de elopmen o so wa e o au oma ic ideo analysis
and he use o high- esolu ion he mal came as.
Acknowledgmen s
We a e g a e ul o Pa ick Ba iè e, Ma co Zacca oni, and an anonymous e iewe
o hei aluable commen s and edi s on he i s d a o he manusc ip . This
s udy was ca ied ou as pa o he PROTEGE p ojec (Paci ic Te i o ies Re-
gional P ojec o Sus ainable Ecosys em Managemen ). We hank he eam a he
Agence néo-Calédonienne de la Biodi e si é (ANCB), esponsible o implemen -
ing PROTEGE p ojec ac ions in New Caledonia conce ning in asi e ungula es,
in pa icula Ca ole Wéma, Gé aldine Bidau, Maxime Lebou eille , and Pa ick
Ba iè e. We also acknowledge he ANCB’s “In asi e Ungula es” echnical g oup,
which se es as he PROTEGE p ojec ’s s ee ing commi ee o issues ela ed o
in asi e dee , e al pigs, and e al goa s. Ou hanks ex end o he Paci ic Commu-
ni y (SPC) and he Sec e a ia o he Paci ic Regional En i onmen P og amme
(SPREP), he delega ee and co-delega ee o he PROTEGE p ojec , espec i ely.
We also wish o hank Jocelyn Amice, Di ec o o SEM Mwé A a a he Domaine
de Dé a; Ch is ophe Schall, Manage o Pa c p o incial des G andes Fougè es; and
Philippe Bou gine, owne o he hun ing and ca le a m La Co onniè e.
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Julia Wi czuk e al.: The mal d one su eys o in asi e Ja an dee in New Caledonia
Addi ional in o ma ion
Con lic o in e es
The au ho s ha e decla ed ha no compe ing in e es s exis .
E hical s a emen
No e hical s a emen was epo ed.
Use o AI
No use o AI was epo ed.
Funding
The esea ch was conduc ed unde he PROTEGE amewo k (Paci ic Te i o ies Regional P ojec
o Sus ainable Ecosys em Managemen , Theme 4 “In asi e Alien Species,” h ps://p o ege.spc.in /
) and inanced by he Eu opean Union unde he 11 h Regional Eu opean De elopmen Fund
(EDF), he New Caledonian “Agence Ru ale,” and he p o incial au ho i ies.
Au ho con ibu ions
Julia Wi czuk: concep ualiza ion; o mal analysis; in es iga ion; me hodology; w i ing – o iginal
d a (lead); w i ing – e iew and edi ing, isualiza ion
S ansław Pagacz: concep ualiza ion; da a cu a ion; o mal analysis; in es iga ion; me hodology;
w i ing – o iginal d a ; w i ing – e iew and edi ing; isualiza ion.
Romain Alliod: concep ualiza ion; da a cu a ion; unding acquisi ion; in es iga ion; me hodol-
ogy; esou ces.
Au ho ORCIDs
Julia Wi czuk h ps://o cid.o g/0000-0003-0808-1768
S anisław Pagacz h ps://o cid.o g/0000-0002-0650-9575
Da a a ailabili y
All o he da a ha suppo he indings o his s udy a e a ailable in he main ex .
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