Methods of Censusing Red fox (Vulpes vulpes) populations
Abstract
Estimating absolute or relative numbers in red fox populations is not an easy task. Although a range of methods has been described, neither an optimal nor a universally accepted technique has been found. Moreover, none has been tested on populations of known size. We reviewed the efficiency of fourteen indices of fox abundance classified into two groups: (a) methods where individuals are captured and marked, which include ear tagging or similar conspicuous markings, toe clipping, radioactive tagging of faeces, radio-tracking, and statistics from hunting and trapping; (b) methods not requiring capture, which include both direct methods (nocturnal counts, unsystematic observations, and drive censuses), and indirect methods (den counts, transects for track, scat counts, and scent stations). As a rule, statistics are rarely applicable to populations estimates. Methods involving capture are expensive but provide more accurate estimates than the second group of indices, which are not suitable for paired comparisons from one year to another. Management and wildlife specialists should have in mind such restrictions when considering their goals and the required level of accuracy. Finally, we recommend the simultaneous utilization and comparison of several methods (one from each group, as proposed in a double sampling strategy) for optimum evaluations.
Full text
Hysl i ,
(n.s.)
3
(1991): 199
-
214
A i
I
Simp. I d. Ca ni o i
METHODS
OF
CENSUSING RED FOX
(VULPES VULPES)
POPULATIONS
METODI
DI
CENSIMENTO
DELLA VOLPE
(VULPES
WLPES)
JUAN
F
RAN
C
I
S
C
O
BELT-
(*),
MIGUEL
DELIBES
(*)
&
JAIMP,
R.
RAW
(**)
ABSTRACT
Es ima ing absolu e
o
ela i e numbe s in ed
ox
popula ions is no an easy ask. Al hough a
ange
o
me hods has been desc ibed, nei he
an
op inid no a uni e sally accep ed echnique has
been ound. Mo eo e , none has been es ed on popula ions
o
known size. We e iewed
he
e iciency
o
ou een indices o
ox
abundance classi ied in o wo g oups:
(a)
me hods whe e
indi iduals a e cap u ed and ma ked, which include ea agging o simila conspicuous ma kings, oe
clipping, adioac i e agging o aeces, adio- acking, and s a is ics om hun ing and apping;
(b)
me hods no equi ing cap u e, which include bo h di ec me hods (noc u nal coun s, unsys ema ic
obse a ions, and d i e censuses), and indi ec me hods (den coun s, ansec s o ack, sca coun s,
and scen s a ions).
As
a ule, s a is ics a e a ely applicable o popula ions es ima es. Me hods
in ol ing cap u e a e expensi e bu p o ide mo e accu a e es ima es han he second g oup
o
indices,
which a e
no
sui able o pai ed compa isons om one yea o ano he . Managemen and
wildli e specialis s should ha e in mind such es ic ions when conside ing
hei
goals and he
equi ed le el o accu acy. Fmally, we ecommend
he
simul aneous u iliza ion and compa ison
o
se e al me hods (one om each g oup, as p oposed
in
a double sampling s a egy)
o
op imum
e alua ions.
Key wo ds: Census me hods,
Vulpes
ulpes,
Canidae.
RIASSUNTO
La
alu azione della consis enza di una popolazione di Volpe, median e censimen i assolu i
o
ela i i,
b
di di icile soluzione. T a i di e si me odi di con eggio impiega i, nessuno si
è
i ela o
o imale
e
uni e sale. Tu a ia nessuno
è
s a o ulilizza o pe popolazioni
di
consis enza no a. Qui
esaminiamo la alidi à
di
14
me odi impiega i pe
il
calcolo di indici di abbondanza, ipa endoli in
due g uppi: (a) me odi che implicano la ca u a e
il
ma camen o degli animali median e ma che
au icola i
o
con assegni simila i, ampu azione delle alangi, adioiso opi ile abili nelle eci, colla i
adio eleme ici e me odi che
si
basano sulle s a is iche ena o ie e sui appolaggi; (b) me odi che
non ichiedono la ca u a degli animali e che igua dano sia ile amen i di e i (con eggio no u no,
awk amen i casuali, censimen o in ba u a), sia indi e i (con eggio delle ane, con eggio delle
imp on e e delle eci
su
pe co si dc ini i, s azioni odo i e e). Ra amen e l'analisi s a is ica
è
applicabile alle s ime della consis enza delle popolazioni.
I
me odi che implicano la ca u a degli
animali
sono
mol o impegna i i
in
e mini di empo
e
cos i, ma o niscono s ime più accu a e ispe o
a quelli del secondo g uppo che non sono ada i pe la compa azione dei da i da un anno all'al o.
Ques i limi i anno a en amen e conside a i in elazione aiie inali à e
ai
g ado di p ecisione che si
in ende aggiunge e. Noi sugge iamo l'impiego simul aneo di più me odi
di
censimen o
(almcno
uno
pe ciascun g uppo), pe una compa azione inc ocia a dci da i e pe o ene e una s ima co e a
della consis enza.
Pa ole chia e: Me odi di censimen o,
Kdpes
ulpes,
Canidae.
(*)
Es aci6n Biolbgica de Doiiina,
CSIC.
Apdo.
1056.
E
-
41080
Se illa, Spain
(**)
Dp o. Ciencias Exac as
y
Na u alcs,
IPO,
Casilla
933,
Oso no,
Chile
I
NTRODUCTION
We will use he e m census in a b oad sense. Censuses a e commonly aimed
no
so
much a de e mining he ac ual numbe s o indi iduals in a popula ion
(O e on, 1971; Da is and Wins ead,
1980),
bu a he a es ima ing an index
o
abundance om a ce ain sampling size. This allows he compa ison o a eas on a
empo al and/o spa ial basis. In any case he p oposed a ge is no easily
achie able and i
is
expensi e.
No
one
me hod, among he many desc ibed in he
li e a u e, can
be
conside ed as he bes
o
he one always yielding op imal esul s.
Ail
o
hem ha e limi a ions and mos
o
he assump ions
upon
which sampling
p ocedu es a e based a e no usually me (Rau, 1988; Es es and Jameson, 1988).
Mo eo e , he e
is
ha dly a simple case whe e indexes ha e been compa ed using
popula ions
o
known
size
(e.g. Da is and Wins ead,
1980).
Two o he aspec s
o
censusing me hods dese e mo e a en ion han hey a e
commonly gi en. Fi s ly, he le el
o
accu acy (i.e. esolu ion) gi en
by
censusing
is
o en below accep able limi s. Rolley (1987) s udying his subjec in bobca s
(Lym
u us)
-
a medium sized ca ni o e
-
s a ed ha
no
single echnique has
p o en sensi i e enough o de ec ing changes smalle han
10
-
25%
wi hin a
popula ion.
Thus,
he e ec
o
any
ac o po en ially egula ing he popula ion
could no likely
be
de ec ed unless i would exceed his pe cen age. Secondly, he
ela ionship be ween cos o censusing and esul s ob ained is o en dis ega ded by
he esea che . Usually, he mos amilia me hod has he highes p obabili y
o
being chosen. Specialis s in e es ed in es ima ing Red
ox
abundance a a gi en
Tab.
1
-
Summa y
o
me hods e iewed in his pape
o
es ima ing popula ion size in
K ipes
ulpes.
~~ ~ ~~~
A.
-
METHODS REQUIRING CAPTURE
A.l.
-
Cap u e
-
ma k
-
ecap u e me hods (CMR)
i.
-
Conspicuous agging (ea
-
agging, colla ing e c.)
2.
-
Toe
-
clipping
3.
-
Radioac i e ma king
o
aeccs
A.2.
-
Home
ange
size
A.3.
-
S a is ics
5.
-
Hun ing Indica o o Popula ion Densi y
(HIPD)
6.
-
T ap
-
lines
B.
-
METHODS
WITHOUT
CAPTURE
€3.1.
-
Di ec me hods
7.
-
Nigh coun s
8.
-
D i e
census
9.
-
Non
-
sys ema ic obse a ions (sigh ings)
10.
-
Den
coun s
11.
-
T ack coun s
12.
-
Sca coun s
13.
-
Scen
-
s a ion ines
14.
-
O he
(
"
a
pos e io i
"
)
B.2.
-
indi ec me hods
200
place and ime need o know, a leas c udely, bo h he inpu equi ed and esul s
ob ainable om he a ailable me hods. Only in his way one can choose he mos
sui able me hod ascomp omise be ween his needs (i.e. goals, aims) and his
esou ce a ailabili y (i.e. money, helpe s, e c.).
This
pape is aimed a e ising ou een di e en me hods ha ha e been used
o es ima ing Red ox popula ions ei he by
us
a he Do iana Biological Rese e
(DBR)
(Rau e al., 1985a), o by o he au ho s in o he coun ies. We include
me hods applied o o he ca ni o es which can be adap ed o ox census, and we
ou line he p incipal ad an ages and limi a ions
o
each.
M
ETHODS
REQUIRING
CAPTURE
F om a p ac ical pe spec i e, me hods o es ima ing Red ox popula ions can be
classi ied
in o
hose ha equi e he cap u e o
indi iduals
and hose ha do no
(Tab.
1).
Among he
i s
g oup, he e a e
ob ious
di e ences
i
he esea che
himsel cap u es he animals and eleases hem a e wa ds (cap u e-ma k- ecap u e
modi ied),
o
i da a a e ob ained om cap u es ca ied ou wi h a wide ange o
echniques (e.g. hun ing and apping).
CAF'TURE-MARK-RECAPTURE METHODS (CMR)
Because
i
allows
many
possibili ies, his me hodology has been gi en a lo o
a en ion in he li e a u e (e.g. O is e
al.,
1978; Sebe , 1982; Whi e e al., 1982;
Mon gome y,
1987).
Ne e heless, oxes a e di icul o cap u e and e en mo e o
ecap u e,
so
ha his me hod canno be s ic ly applied. Ins ead, oxes should be
cap u ed and ma ked wi h di e en sys ems, which allow o iden i y o de ec
hem
om
a dis ance (S onehouse, 1978). The heo e ical basis
o
CMR
me hods has a
simple o mula ion:
in
a
popula ion o N indi iduals,
M
indi iduals a e cap u ed
and ma ked; om a subsequen sample
o
'In''
indi iduals o he same popula ion,
"me'
ma ked indi iduals a e ound. The size o he popula ion is hen gi en
by:
N
=
(M.n)/m
The p incipal assump ions a e: a) he popula ion
is
closed (Lincoln
-
Pe e sen
o
Schnabel p ocedu es can hen be applied, e.g. Todd e al., 1982, hough es ima o s
o open popula ions such as hose o Bailey, and Jolly-Sebe a e also a ailable,
e.g. Cla k, 1972; Caughley,
1977);
b) indi iduals a e equally ca chable, ha
is,
he
sample
is
homogeneously dis ibu ed among he popula ion,
bo h
be o e
cap u ing
and a e ma king. The socio
-
spa ial o ganiza ion o oxes
-
as
o o he ca ni o es
-
in alida es he second assump ion, and co ec ion ac o s a e necessa y (Bu nham
and O e on, 1979; Pollock, 1982; Pollock e al., 1985, among o he s).
An
addi ional p oblem conce ning his me hodology is he di icul y o es ima ing he
cap u e a ea, since he ange o mo emen s o indi iduals
is
o en
unknown.
Radio
-
acking can usually sol e his p oblem (G eenwood e al., 1985; Ku eld e
al.,
1987;
Babb and Kennedy, 1989).
201
CMR me hods yield absolu e es ima es o densi y (numbe indi iduals/ a ea).
As
a ule, any censusing me hod could yield an es ima e o he whole popula ion,
hough i seems mo e app op ia e
-
see below ansec me hods
-
o
conside
census esul s only as ela i e abundance es ima es (Kolb, 1982; Ebe ha d and
Simmons, 1987).
CMR
me hods
a e
po en ially use ul o sampling oxes i he unde lying
assump ions can be me .
CONSPICUOUS
TAGGING
Colou ed ags and o he ma ks ha a e di icul o see a nigh a e no sui able
o he Red ox, gi en i s noc u nal o c epuscula ac i i y. Howe e , e lec ing
ma ks (Macdonald, 1987) which can be li up om a dis ance, can be a e y use ul
aid. This me hod equi es open places equen ed by oxes and he possibili y o
a esea che o co e as la ge an a ea
as
possible.
A
DO iand Biological Rese e,
a
7,000
hec a es s udy a ea in he Do iana Na ional Pa k, Sou hwes e n Spain,
we
ma ked oxes wi h adio- ansmi e s i ed
o
e lec ing colla s (Deiibes a id
Bel an, 1986), bu he sca ci y
o
obse a ions (see below Sigh ings) due
o
hick
sh ubs made his me hod unusable. O he au ho s ha e ea - agged oxes, bu
unless a co ec ion is made o ag losses, his me hod may gi e e oneous esul s
(Hu be e
al.,
1976; Englund, 1980).
TOE
-
CLIPPING
Wildli e specialis s ha e used con olled inge ampu a ions
in
coyo es
(Canis
Zu um)
in o de o ecognize hei acks (Andel ,
1981;
Henshaw, 1981). The
popula ion can
be
es ima ed ai ly accu a ely om he a io o
"
no mal
"
o
"
ampu a ed
"
animal acks, bu his me hod is es ic ed o places and
ci cums ances whe e acks can easily be de ec ed (snow o sand ansec s, di
oads, e c.).
A
su gical ope a ion may also be conside ed une hical
on
c uel y
g ounds and because he animal
is
le wi h a pe manen handicap.
I
has he
ad an age ha se e al popula ion ca ego ies can be ma ked (by sex, by age,
indi idually, e c.), acco ding o he numbe and posi ion o he ampu a ed inge s,
which allows mo e eliable and s uc u ed es ima ions.
RADIOACTIVE
MARKING
OF
FAECES
Ma king o aeces wi h adioac i e iso opes has been in use o some wen y
yea s o es ima e popula ion size in qui e a numbe o species. I was i s
employed o census ox popula ions (Nellis e al., 1967) and hen o he ca ni o es,
wi h success (Conne and Labisky, 1985; C ab ee e al., 1985). Once cap u ed,
animals a e gi en an in amuscula o in ape i oneal injec ion
(5-100
mic ocu ies)
o
one o se e al combined adioac i e iso opes,
usually
Zd5
and
Cdl@,
bu
also
Ce1@, Co n and Mn'54. Iso opes a e chosen o hei low adio
-
oxici y
(mos o hem emi gamma adia ions), a mean physical and biological li e adjus ed
o s udy pe iod ( anging om some weeks o yea s), and he majo ou e
o
elimina ion o he iso opes h ough aeces, among o he cha ac e is ics (Pel on and
Ma cum, 1977; K uuk e al., 1980). I i e o he abo e ci ed iso opes we e injec ed
singly o in combina ion wi h any o he , up o
15
di e en indi iduals o coho s
o a wild popula ion could be ma ked, making i possible o ca y ou simul aneous
sampling o in apopula ion di e ences
in
habi a
use,
ood p e e ences, ma king
beha iou , e c. (Sibly and Smi h; 1985).
A
majo obs acle
o
his echnique, besides he co ec iden i ica ion o sca s, is
he way e i o y enu e sys ems by di e en indi iduals can in luence de ec abili y
o
aeces.
Fo
ins ance, a e i o ial ox may use mo e conspicuous places o ma k
han a ansien one; males may ma k in di e en places han emales and mo e
equen ly, e c. Once mo e, adio- acking would be an ideal complemen a y ool
(Mi chell-Jones e al., 1984; Conne and Labisky, 1985). Conside ing i s
ad an ages, adioac i e ma king o aeces p o ides a e y good app oach o
mee ing
he
assump ions o CMR me hodology because
o :
a) he s a is ical
independence
o
he ma king and ecap u ing phases
o
he echnique,
b)
he
ela i ely small selec i i y in ecap u e (i.e. low deg ee o he e ogenei y), and
c)
he ela i ely high ecap u e p obabili y,
HOME
RANGE
SIZE
This
is
p obably he mos common me hod applied o ca ni o e s udies, Ou
knowledge o hese elusi e mammals has d ama ically inc eased wi h he
de elopmen
o
adio- eleme y de ices (Pa ic e al., 1982; Kenwa d, 1987).
Densi y es ima es
(D)
a e ob ained om he equa ion:
whe e
H
is he mean indi idual home ange size popula ion, which can be
e alua ed by a ious algo i hms (S uwe and Blohowiak, 1989).
This me hod es ima es mhimum yield alues (i.e. i unde es ima es
he
popula ion), because i is assumed ha each home ange is used exclusi ely by one
animai. This is no always ue. Foxes li e
in
social g oups whose sizes a y in
ela ion
o
he abundance and spa ial dis ibu ion
o
esou ces (Voig and
Macdonaid, 1984; Doncas e and Macdonald, 1991). Thus, es ima es based on his
me hod mus be ea ed wi h cau ion, pa icula ly when sample biases a e
suspec ed (Laund é and Kelle , 1984).
In
ou s udy a ea, Red oxes we e adio acked and sampled wi h o he census
me hods a he same ime in o de o e alua e and imp o e di e en echniques.
Besides he di icul y no ed abo e, we ound ha his me hod could be misleading
because he seasonal a ia ions obse ed in home ange size we e no associa ed
wi h changes in absolu e densi y (Rau, 1988).
D
=
1/H
HUNTJNG
AND
TRAPPING
LINES
The numbe o oxes hun ed du ing spo , managemen
o
boun y ials o e a
whole coun y, s a e, e c. p o ides su icien in o ma ion
o
es ima e
HIPD
203
abundance index (Hun ing Indica o o Popula ion Densi y, Zimen, 1980). The
HIPD
o
simila indices show a high deg ee o eliabili y o de e niining
popula ion ends o e la ge a eas. Voig (1987) (see also Kolb and Hewson, 1980;
Kolb, 1982) has poin ed ou ha moni o ing o hun ing
o
apping cap u es is
likely o p o ide he bes es ima es
o
empo al a ia ion in he popula ion when
he da a come om la ge enough a eas, despi e some non
-
negligible p oblems (see
Smi h e al., 1984). P obably one o he mos signi ican handicaps is in he way
how hun ing and apping da a a e collec ed, being coun y dependen .
A
good
idea o he quali y o in o ma ion po en ially ob ainable is o be ound
in
he u
sales ables o No ak e al. (1987). O he no able s udies a e desc ibed in Jenkins
e
al. (1981), and
he
classic pape by El on and Nicholson (1942).
Zimen (1980) eco ded a close associa ion be ween empo al e olu ion
o
he
HIPD and abundance o abid oxes in he samples.
An
index could hus be
cons uc ed
a
pos e io i (see below) wi h adequa e adjus men s, o p edic ox
popula ion ends om he abid oxes hun ed.
We ema k,
as
a conclusion o his second ca ego y
o
me hods equi ing
cap u e o animals, he ela i ely low cos in ol ed i sui able da a (i.e. su ey plans
and egis a ion) a e collec ed, and he high eliabili y o hese me hods, al hough
some co ec ion ac o s (e.g. cap u e pe uni e o when hun ing e iciency, u
p ice, and o he a iables a ec he sample), mus be conside ed o in e p e ing
he da a.
M
E
T
H
O
D
S
WITHOUT CAPTURE
NIGHT
COUNTS
The p o ocol
o
his me hod can
be
summa ized as
ollows:
using
a
ehicle
equipped wi h a mo eable spo ligh , a leas wo pe sons make
a
ansec su ey
(40 km in A ois, 1981)
a
a cons an speed (10
kmhou ),
wi h eplica ions
(2
-
5)
o he ansec
on
consecu i e nigh s.
The me hod was i s designed o census lagomo ph popula ions, la e being
applied o ca ni o es in open habi a s (Wase , 1980). A ois (1981), and Schan z
and Libe g (1982),
among
o he s (see also Pandol i e al., 1991), ha e success ully
adap ed he me hod
o
es ima e ed ox popula ions. Lloyd (1980) desc ibed how
his me hod could be used in o es ed a eas well in e sec ed by oads:
"ln
such
places oxes in ields adjoining oads a e no dis u bed by passing ca s and
sigh ings can
be
made a ixed in e als along he oadside
...'I.
Ne e heless, se e al ac o s should be aken in o accoun
€o
a s anda dized
me hod. Fo example, A ois (1981) ound he mos a ou able condi ions o
census we e be ween 21.00
-
03.00
a he newmoon, wi h high cloud co e , and no
wind. O he ac o s he conside ed we e he annual cycle o ege a i e co e and
he s uc u e o he ox popula ion.
An
au umn census could be used o de ec he
inc ease in
ox
numbe s due
o
ec ui men and dispe sal, while
an
ea ly sp ing
es ima e would comp ise la gely b eeding indi iduals.
204
Nigh coun s can be con e ed o es ima es o absolu e densi y i : a) he ange
o isibili y
is
es ed each ime, and b) plo s o a known a ea a e sampled ins ead
o a ansec line (Schan z and Libe g, 1982). Time
uni s
( oxes coun edll-iou ) a e
p e e able o compa ing a eas ha di e
in
habi a composi ion. Ano he
a ia ion
on
he p ocedu e is o pa i ion a line ansec in o habi a segmen s. This
op ion could also imp o e possibili ies o da a analysis.
As
o any line ansec p ocedu e (Bu nham e al., 1980), a basic ule is o
s anda dize he sou ces o a ia ion associa ed wi h sampling e o (some
men ioned abo e, also he expe ience o s a , abo e all i nigh coun s a e
pe o med o se e al species simul aneously, e.g. p eda o s and p ey). Clea ly, one
o
he mos signi ican p oblems wi h nigh coun s is he g ea a ie y o ac o s
in luencing he use o space and ime by animals. Fo example, one could ask:
Wha pe cen age
o
he
ox
popula ion is eally coun ed, (i.e. de ec able) by
spo ligh ing?
A
sui able co ec ion ac o has been calcula ed by adio
-
acking ed
oxes and de e mining he mean pe cen age
o
ime spen by se e al indi iduals in
open habi a s, whe e hey we e de ec able by spo ligh ing (Schan z and Libe g,
1982).
DRIVE
CENSUS
The animals a e d i en in o a delimi ed a ea by ained people, some imes
assis ed by hounds, and coun ed as hey c oss he obse e ’s line. O e on (1971)
ci ed
a
simpli ied e sion
o
his me hod by eplacing he obse e ’s line wi h a
sand ansec
(o
o he so ma e ial) om which he animal acks could la e be
iden i ied.
This
me hod can be used success ully
in
woodland o dense ege a ion co e ,
such Medi e anean sh ubland. Fo example, Telle ia and SAez-Royuela (1984)
es ima ed densi ies o ox and oe dee
(Cup eoh
cap ealus)
by sampling in plo s
o
75 hec a es o
oak
ha dwoods
(Que cus
obu ).
Howe e , he e o equi ed o
a sui able sample size ( hese au ho s conduc ed
35
d i e censuses), and also he
ime spen
in
o ganizing a su icien numbe o helpe s (obse e s, bea e s, and
hei hounds, e c.), should be conside ed when planning a d i e census. These
p oblems we e esol ed o SAez-Royuela and Telle ia (1988) who we e able o
p o i om hund eds o d i es o ganized
o
hun ing. Among he ad an ages o he
d i e census a e i s eliabili y and he possibili y o ob ain simul aneous da a on
o he animals, pa icula ly game species. I
is
impo an
o
no e ha he accu acy
o he esul s will be posi i ely co ela ed wi h he numbe
o
bea e s, and
nega i ely co ela ed wi h he size o a ea sampled (Telle ìa, 1986).
Undoub edly, he deg ee
o
dis u bance ha he d i e census in ol ed mus also
be conside ed; his
is
p obably no an ideal me hod o use in na u e ese es.
In
ou expe ience, we ha e ound
a
good app oxima ion be ween esul s
ob ained om d i e census ou o he limi s o Doiiana Na ional Pa k and hose
eco ded om o he densi y es ima o s p e iously de eloped
o
his a ea (see
below), a abou 1.7 oxes/km2.
205
SIGHTINGS
(NON
-
SYSTEMATIC OBSERVATIONS)
The basis o his me hod is o ge a egis a ion o any ox sigh ing in a gi en
a ea. Fo he analysis o such da a, sigh ings mus be e e ed o uni e o such
as he numbe o obse e s, ime spen in he ield, dis ance a elled, e c (Rau,
1988).
This
is
p obably he simples
o
all he a ailable me hods o es ima e ela i e
abundance o ed oxes, being especially ecommended o p o ec ed a eas, o
places whe e ield wo k is in p og ess ( esea ch, igilance, e c.). I implies many
man/hou s spen in he ield. Alien and Sa gean (1975), and Ha is and Rayne
(1986a)
employed sigh ings o oxes o calcula e abundance indices. Ne e heless,
he e y simplici y o his me hodology needs co ec ions
in
o de o alida e he
esul s and o ob ain ealis ic in e p e a ions o he da a. See o example Voig 's
(1987) commen s on he di icul ies in ol ed in de ining he co espondence
be ween a sigh ing index and
an
es ima e o ela i e abundance.
We ha e been able o de e mine
a
sui able adjus men o ou s udy a ea. Red
ox sigh ings due o keepe s, esea che s, and isi o s we e co ec ed agains
obse e numbe s. Iden i ica ion
o
animals wi h isual ags pe mi ed
us
o
calcula e he pe cen age o e-sigh ing
o
any indi idual. Finally, simul aneous
adio- acking da a we e used o es ima e p obabili y o a ox
-
c ossing di oad o
i eb eak inside i s home ange, whe e i was mos easily de ec able in he ield.
Compu ing hese ac o s,
Rau
(1988) ob ained a ox abundance index wi h ends
well acco ded wi h he ox densi y in Doiiana Biological Rese e as es ima ed by
o he mo e sophis ica ed me hods.
The me hod's economy, simplici y, easy s anda diza ion, and good adjus men
possibili ies wi h o he mo e eliable me hods, which a e also mo e expensi e (in
money and ime), a e good enough easons o using a da a base o ox sigh ings
as a measu e o popula ion ends.
This
app oach o densi y es ima o s has been
named
"
double sampling
"
(Ebe ha d and Simmons, 1987). Fox-sigh ings is only
one o he possibili ies (see below ack coun s), and can be applied
o
o he
species besides oxes.
DEN
COUNTS
Coun s
o
b eeding ox dens in la e sp ing o summe depending
on
he s udy
-
a ea (Lloyd, 1980), can be used o de e mine he absolu e abundance o he
species.
The
li e a u e
on
his subjec is ce ainly no lacking. The classic wo k o
Sa gean e al. (1975), p o i ing om he excellen isibili y o e hei s udy a ea
o coun s
o
ox dens om an ai plane, can be compa ed wi h coun s
accomplished on oo which equi es mo e s a , ield knowledge, e c. (S o m e
al.,
1976; Linds om, 1980; Hewson, 1986; P igioni e al., 1991).
P obably he majo ad an age o censusing oxes by coun ing hei b eeding
dens is he good le el o accu acy ob ained by his me hod. Sa gean e al. (1975)
de ec ed 84%
o
270
ox amilies
in
hei s udy a ea. Ob iously, some in o ma ion
206
has o be assumed such
as
he numbe o indi iduals pe den, e i o y size o a
ox
amily, e c. I he su ey is ca ied ou
on
oo , addi ional da a can be
egis e ed such as ood habi s o cubs e sus adul s (Delibes and Maiiez, 1984),
and compe i ion wi h o he species o den si es (Pigozzi, 1986). Den loca ion also
p o ides a good basis o u he wo k such
as
cap u ing (Zoellick and Smi h,
1986) and popula ion managemen (Zimen, 1980; Hewson, 1986).
TRACK COUNTS
IN
PERMANENT
TRANSECI'S
Di oads, i eb eaks, and o he simila clea ings a e commonly used by oxes,
o a elling, ma king, o es ablishing hei home ange bo de (Sa gean , 1972;
Fab igoulé and Mau el, 1982; Mau el, 1983, among o he s). This pa e n
o
space
use
is
no a cha ac e is ic unique o ed oxes. Pulliainen (1981) moni o ed annual
luc ua ions
in
ela i e abundance o ou species o ca ni o es, he ed ox
included, by skiing along
a
pe manen ansec o
6
kilome e s weekly du ing he
snowy season (No embe o Ap il). His esul s we e enhanced by simul aneous
obse a ions
on
oden ac i i y and habi a p e e ences
o
he ca ni o es du ing a
s udy pe iod long enough
-
13 consecu i e win e s
-
o desc ibe p eda o -p ey and
communi y dynamics. This me hodology has been used by Rau e
al.
(1985b) in
Sou hwes e n Spain (Do iana Biological Rese e)
o
es ima e ox densi y by ack
coun s
on
sand ansec s.
A
basic assump ion o his me hod is ha a linea ela ion exis s be ween he
numbe o acks (o o he signs) de ec ed and he ela i e abundance o he
species. Howe e , om ou expe ience, his is no always he case. F om
simul aneous adio- acking o oxes and su eying o a
1.2
km long sand ansec ,
a con e sion ac o was ob ained
o
ack/km o oxes/km (Se in e al.,
1987).
Each ox c ossed he ansec
3
imes
on
a e age in each 24 hou cycle. Howe e ,
he loca ion o he ansec g ea ly in luenced he esul s.
S ephenson (1986), and Schwa z and Becke (1988) ha e been in ol ed o
se e al yea s in de eloping simple echniques o es ima e popula ion ends in
Lynx
canadensis.
Thei design
is
a double sampling p ocedu e: simul aneous
moni o ing
o
lynx acks in snow ansec s and adio- acking
o
indi iduals du ing
24
-
48 hou s. Mo emen s
o
ma ked lynxes cons i u ing a andom subse o he
popula ion we e analysed by a ious me hods, including simula ion (Becke
in
p ess, in Schwa z and Becke , 1988).
SCAT COUNTS
IN
PERMANENT
TRANSECTS
The use o sca coun s o de e mine ox abundance has some simila i y wi h he
p e ious me hod:
a)
sampling is ca ied ou along delimi ed ansec s,
i
possible
pe manen in loca ion;
b)
a
s a i ied sampling design
is
also
p e e ed in o de o
a oid he e ec s
on
popula ion ends
o
seasonal changes in habi a use by oxes.
The sca coun p ocedu e, howe e , equi es special co ec ion ac o s (see below).
P obably no o he me hod has such long adi ion in he es ima ion o species
abundance (Kolb
and
Hewson, 1980; Pu man, 1984). Rau
e
al.
(1985a
and
b)
207
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