Lutra . \()I .39 . I 996

VARIABII .ITYANL) SEASONALITYIN SPRAINTING BEHAVIOUR OF OTTERSLUM 1 ON A HIGHIAND RIVER IN CENTRAL EUROPE

b y

ANDREAS KRAN Z

ABSTRACT

3 : i

I 'hr use of the nuinber of spraints as indicators of (sma ll-s(ale) habitat uti lization and popu lation dens i ty in ot-

t e r s Li dra I udra i s cu n t r oce rs ial . l'ariabili ty a nd seasonal change s o f spra int numbe rs have n o t been quanti fi ed in

C rnu i l a nd Easte rn F. urope , but t h ey are a pr e req uisite fo r u sing sprai n ts i n a n efiec[ive ma nn ee Mo reover, fi nd-

in };s in Ce n U a l r: uru pe m ay h e l p explai n s raso n al sp r ain l in g in ge ne ra L S pr ainting b e h av i o m of ott ers was s tudie ti

ot an u lig u U a phi c hi ghlxnd river , occ upied bc a r es id entolt ce p opti l a ti on .

- Spr ain ti n g brh uvfour w as seas o na l , wi t h m a ny s Nr aint s occ turing front O er o ber to March a nd few s praint s

f rum t une t o S ep tru i ber .

- In O c t obrr a nd Nove mber , the m o nth s s h o wing hi g h sp raintiug xctiv i iy witli lild e variation a n d u s u a lly c h ai=

ac t e rizrd by st a bl r wi • al h e r co nditi o n s, 90%, u Eth e surveyed st retc h os (> 60 0 m long, > 3 m wide ) pruvide d Iheo r-

eti ca l inte r s pra int di stan ces (= nieres o f ri ver scann e d d h ide d by total spra int numbe r) of Iels th an 4 3 m and 3 6

m , re s pec ti ce ly . li is suggr s ted th ai in thi s sraso n a nd i n thi s ty p e o f h a bitat , inter spra int Bi sta n c es have a 9 0 %

probabi l ity of be i ng w i thm these tigures along rieers occupicd bv an cstab l ishrd popu l ation .

- Incrr ascd poptilation den s ity c uin c idrd i% ith m o er s pr ain is, bui thi s was n o t signifi ca nt .

Kcvtivo rds: Lutra lufrri , CrnU'al Etu'o pe, marking behaviour, seasonuli n', p o pttl at i o n m o nil o rin g .

1 . I ntroduction

Otter spraints (faeces) are considered a valuable means to record the presence of ot-

ters (e .g ., Mason & Macdonald, 1986 ; Kranz, 1990; Reuther, 1993) . The significance of

the number of spraints as indicators of (small-scale) habitat utilization and populationdensity is controversial (Kreuk et al ., 1986 ; Kreuk & Conrov, 1987 ; Mason & Macdon-ald, 1987; Conroy & French, 1991) . Spraints are easy to Eind and in many cases repre-

sent the only possible approach to study the species . Direct observations are limited toa few habitat types and regions (e .g . Shetland), and more sophisticated methods likeradio-telemetry are expensive, limited by legai restrictions, and usually provide onh

case studies . Hence, quantification of sprainting behaviour displayed by an established

otter population is a prerequisite for using spraints in an effective mannee . Besidesthese methodical aspeers, findings in Central Europe compared witti those in other

areas might provide clues for zuiderstanding seasonal changes in spraint numbers ingeneral .

To date, detailel investigations ofsprainting behaviour have heen conducted 0111v inWestern Europe . Sprainting behaviour was found to he seasonal, with a maximum be-tween November and March and a minimum between July and September (Macdonald& Mason, 1987 ; Conroy & French, 1991 ; Kreuk, 1991) . No information is available ot]seasonal sprainting behaviottr in Central and Eastern Europe .

ihc Icf1 f i i reg ru und .

P hoto I . 1~~Jm .i l ci c~, (dt r cicli : V uni ih c ric<r Ii lc inc r Fianip, iri i h i rad itiun :i l omer spxa i niing s i ~~- ot] i hklok l, til

Lul ra . ml . '11), I '. I S I( i i

h.uii p_, illi Ih , ~ "drifilc . .nul pi-J ,

li n lu ;1 . 1(i,1 , li U .n Il n i n, i h l~ n„i I\1, - ili n ,lli lig i<< iri i .- . :si rli I t n . u is mrt' block i l ic st i'e .inl in

wi li i cr , su ihat praintiu g vitcs typsUrttm bccwn e ~luudcd .

36 Lutra, vol. 39, 194) 6

The aims of this study veere to :

(a) identify seasonal sprainting behaviour along a Central European river ;

(b) quantify the variation of spraint numbers found along a stream inhabited by a resi-dent otter population ;

(c) test whether a change in population density of an established population is likely to

he detected by a change in sprainting behaviour .

`L . Study area

The study was conducted along the upper stretch of the river Kamp, one of the mais

tributaries of the Danube in Lower Austria . This region (700 m a .s .l .) is situated 100 kin

west-northwest of Vierma in the highlands Galled Waldviertel, which consist of' granitoand gneiss .

Otter presence has been documented since the 1970s (Tv-aas, 1981), and there is no

hint that the species ever abandoned the area . The catchment area comprises 610 kir',with the main tributaries Zwettl and Kamp, the laffer splitting up into the Kleiner and

Crosser Kamp . The rivers are surrounded by pine and spruce forests, interspersed by

patches of farmland (mostly grassland) . Otter reproduction has been confirmed 1»~tracks annually since 1988 (oven unpublished data) . According to Racer-Cross (1989),

the mais dief of otters here is trout Salmo trutta f. Jàrio and grayling "1'{atimallus thymalbi .s.

3. Material and method s

A 1-km stretch of river (Al : photos 1-3) was selected for the long-term investigation(1988-1994), preceded by one vear of familiarization witti the study area and witti find-

iug spraints (Kram, 1990) . This stretch on the river Kleiner Kamp is situated 22 km

downstream its origin and comprises a catchment area of 140 km- ; the s[ream is 7-15 mwide here . Granito rocks provide a frequent alternation of pools and riffies . This stretch

has one bridge and the inflow of a tiny trickle (30 cm wille) . Banks, rocks and sand-

banks veere scanned by walking the river witti high rubber boots .

A sprainting site was defined as a physical unit - like a single rock or landbank - irre-spective of sire . All sprainting sites veere mapped and numbered . The age oC sprainis

was estimated according to Bas et al . (1984) : venfresh= moist and witti typical smelt (up

to 5 days), medium-old = dry spraint, bat stilt witti typical otter odour (6-14 days), and old= dry and without or almost without smelt, compact or breaking up info single compo-

nents ; single bones or scales (fraginents of spraints) veere excluded . In the following,

verg fresh and medium-old spraints are popled and Galled fresh unless stated otherwisc .

This stretch of river was monitored witti the same effort for leven vears . Successive

surveys veere always separated by at least 14 days, to minimine double counts of freshspraints . Old spraints veere excluded from the analysis vetion comparing different sea-

sons, because they are top mach influenced by the preceding weather (detrimental im-

pact of rain etc . : Kranz, 1995) . The total nurnber of spraints found at 88 sprainting sitesduring 64 surveys was 3,126 (70% on 65 different rocks, 19% (>n 15 sandbtinks, 10% on

two inlands, and 1% at six sites on the spil of the baraks) . The vear was divided info six

periods of two months (December/January', Februatv/March, etc .), and seasonal

sprainting patterns veere tested by tising Dtinn's test 1 (llunn, 1964), lee t<iblc• I .

l . u m i . vul . :V l, ISI<, lli :~i

Another 15 stretches (tota l 2 1 km) with simi lar features, d istributed over t he total

catchment area of 6 1 0 km2, veere monitored twice in 1990 . Th is provided an opporaill-

ity to confirm the find i ugs Erom the s ingle stretch, since seasona l changes i n spra i nt

nmnbers along one particu l ar stretch could also be the resu l t of a seasoma l shift i n

range i i se . The l ength of these stretcher ranges from 0 .6 to 2 .7 km (average 1 .4 km) . In

Ju ly 1 990, 472 spraints veere finund there, in November 1 990 another 2,076 .

1 . Result s

Fig . 1 plots very fresh and med ium-o l d spraints during 64 surveys, conducted alongth(- l -km stretch along the river pleiner Kamp (AI ) . Spraint numbers found disring the

six bimonth l y periods are shown in boxp l ot diagrams in fig . 2 . Dunn's test 1 ident i ficd

s i gnificant differenter i n numbers of fresh spra ints between each bimonth ly period

f rorn October to March (cold periods) and the per iod, J une/ July . Ano t her s ignificant

d ifferente was detected between the periods August/September and October/Novenr

ber (lor details, ree tabl e 1 ) .

'rh(, spra int numbers found a l ong the 1 5 stretcher disu-ibuted over the tota l catch-

ment area support the find ings trom the s i ngle stretch Al . I n 13 cases [here veere mant

more fresh spraints in November than in J u l y° ; in on ly two cases, one co i nc i d i ng w it ti rec-

ords of 'a female accompanied by cubs, the oppos i te was truc (fig. 3) . The sprain t num-

bers Trom these 15 stretcher veere compared witti the correspond i ng numbers from the

single stretch A I . This required transformiilg spraint numbers fownd along stretches

with diffèrent l engths. Numbers veere expresled in metres of surveyed river

( t neU-es/numbers of spra i nts = m/sp) . I n J uly the average distante (med i ae) of freshspra ints at Al was 1 33 m/sp (every 1 33 metres there was a fres h spraint) ; at the 1 5

stre t c hes the average was 25 0 m /sp . In Novembe r , the average di s t a n te at Al was 33

ni/sp, whi le at the 1 5 stretc her i t was 41 m/sp. The exact va lces for ~ ul~, Oc tober and

November are listed, logether witti va lces of t he 90th percent ile, in table 2. The 90th

percentile indicates the distante withm which a sing le spraint is found witti a probabil-

i ty of 90% .Finally, the numbers of fresh spraints found disring eleven surveys i n 1 989/90 along

the 1-km stretc h Al veere aompared witti eleven seasonally corresponding surveys in

14)43/94 (fig . 4) ; this was dove in order to identity a change in spra inting activitv ; du-

-ing that per i od the popu lation had expanded its d i str i bution in th is and neighbour i ng

river svstems . I ndeed, more spra ints veere íound disring 1993/94 (n)edian = 20) than i n

1989/90 (mediae = 13), btu th i s differente was not significant (Manun Whitney 11-test,p= 1 .574) .

5 . Discussion

Only fresh spraints (max . 1 4 davs) veere used to quant i fi° seasona l spra i nting beha-

vi011r . I t would not have been feas ible to ure on l y very fi-esh spra i nts (max . 5 davs), be-

causc thee otters would not have had enough t ime to visit a particular area (Er l inge,

1967; own obse t vations), even though such short intervals would have yie lded even

mort s i m il a r wea the r cond itions .

38

a

Number of surveys per month

Luua , vol . 39, 199 6

Fig . 1 . N um bcrs o f cc n l i cs h and m cd iun ru l d s pra i n ts found ako n g a 1- km s t ret c h of ricc r (s u c t ( h Al) Bur i n}; l i l

s un,evs be ttve rn 19 88 a nd 1 99-1 . S un evs veere se pa r a te d b c at l i u t 1 1 da c s, to mini m izr doubl e ruunl s ( in sam e

m o n 1 h s s urveys wc r r clo ne mo re od e n than in oth e rs e .g . ] anu a i~° t hree ti enes dwing uren vcars, Fe bruau v to ur

ti en es, rtc .) .

Sprainting behaviow- in Central Europe shows the same seasonality as in the marine

and freshwater habitats of Western Europe . Kruuk (1991) discuses th ree hypothesesregarding the seasonality of sprainting behaviour on [he Shetland Islands :

( 1 ) The seasonal sprainting behaviour has a sexual function .

Krtiuk rejects this hypotheses because there is no overa ll difference between sexes,

and because the pattern of seasonal spra inting is a lso found in England, where breed-ing is ❑on-seasonal (Macdonald & Mason, 1 987), whereas in Shetland brecding is sea-sonal ( Kraak & (:onroy, 1 987) . I n Central Europe breeding i s, according to my oven da-

ta, not strictly seasonal, births occur at least from March to November, probab l y veetb a

maximum in August and September (oven unpub l ished data), about two mon t hs l a t er

than in Shetland . I n Saveden the peak breed i ng time is spring (Erlinge, 1967), bu[there scems to be the same scasonal sprainting pattere as in Shetland, Eng l and andAustri a .

(2) The seasonal sprainting behaviour bas a territorial function .

Kruuk does not entirely reject t h is, but there are stroeg arguulents against it : spraintsare not concentra t ed on territoria] bottndaries, and 32% of sprain t s had onlv a short po-

J F M A M J J A S 0 N

I . utra , vol . 39 , 1 996

c

Cl.

3 9

Fig. 2 . F rcq ucncv (list ribwi un u f li rs h spx a i n t s fo und slang a Lk m s u ct c h dtu in g 64 sui~rvs : ih e vca r was di\ id c d

in to bim o n t hl ~ pcri u ds ; Ihc buxplu t s c ha r ac~e rize th e medi ao s, m in p e rcen i il es an d u t uli crs (= ra r e c~enis:

m anv o r cri v t èw s pr a in t + ) o f th(- s p ra in t di sti ibuli o n in cach p rri od .

tential function, because they veere deposited with in the iutertidal zone . Kram (1990)

found no obvious c lusters of spraints along alt 8-km stretch of river, wh ich could have

been interpreted as marking of territorial boundaries . I n contrast, spraint ntuubers

changed fregiieiitly witp i n these 8 km .

(3) The seasonal sprainting behaviour indicates the Case of resources .

Kruuk favours this hypothesis the sprainting peak in Shetland coincides witti love

food availability in late winter . Another important resource along coasts is fresh walei-

(Kruik & Balharr-v, 1990) ; however, no distinction was made between sprainting on th e

Oct/Nov Dec/Jan Feb/Mar Apr/May Jun/Jul Aug/Sepn = 17 n = 8 n=7 n=8 n = 1 2 n=12

40

1000

900

800

~ 700

Q 600N

Q 500

12 400

300

200

100

0Stretches

Lutra, vol . 39, 1 996

July

Novembe r

Fig . 3 . Fres' h sp ra ini s fix e nd i n july and Nove mbe r 1 9 40 a l on g 1 5 st re t r h rs, d i s ti ibul ed over Ihe total (al( 11111c111

arca of6 1 0 km ', co nfi rm the scasonal s p ra in i in g ac ti vi ty as fo imd alo ng th e s in gle surtc h A I ; i n o rd er to co m par e

spr ain l num b ers along su'r tc h rs o f different I e n gt h , spra in t numbers are expresle d as m e U 'es u f r iv et sca n n ed di-

c id e d b y' ch r number of s pra i n t s found (aug(- Bi s t a n ces in ]ulv, s ho rt in Nuvembrr ) .

9

8

7

~ 6

~ 5

4

3

2

1

0

0

0

1989 /90 1993 /94

Fig . 4. N w n b ers < ill ies h sp ra iut s found B o rin g 11 siunres in 1 9851/yU were love r (me d i : in = 13) th an I hu se o f 11

se a.so na l curres N o nding stnveys in 1 993/9 4 ( m e dia n = 20) .

Luu -a, vo l . 39, 19 4 6 11

Feb . /Mar. Apr . /May Jun . /Jul . Aug . /Sept . Oct./Nov .

Dec . /Jan . 0.16 2 .39 3.69** 2.81 0 . 21

Feb . /Mar. 1 .95 3 .36* 2.52 0 . 01

Apr ./May 1 .30 0.42 2 . 34

J un ./Jul . 0.99 4 . 23***

Aug . /Sept . 3.16*

T abic I . Uifli, rrnccti in scasunal spraint ntunbe rs (Duon's test L Dttnn , 1964), critica! trvahi t- s : u . .:,„ 2 .9 3 lol

p< O . OFi ' : u, . ,= 3 .$ I fier p< 0 .0 I ° : u .,.., _ :3 .99 tbr p< 0 .00 l- .

July (fresh) 15 stretches

July (all spraints) 15 stretches

July (fresh) stre tch Al

July (all spra ints) s tretch Al

October (fresh) stre tch A I

October (a ll spraints) s tretch Al

November (f resh) 15 stretcher

November (a ll spraints) 15 s tretcher

November (f resh) stretch Al

November (a ll spraints) stre tch AI

median

m / sp

250

59

133

56

51

25

41

14

33

17

90th percentile

m /s

900

223

245

98

120

43

217

36

62

27

1:ah lr '? . Med iati ;uid <.lOt h per(ent il v inl ers p raiu1 di,s i auces a l ou} ; su e i clies o 1 an ol i gu u oph i c hi g lil a nd neer i n

s u m n re r and autumn . Fi g tu us k i n 1 i r s h (= up to 14 J aps old sp ra inis) a nd all spr ai nt s in c ludin g old o]](- .% al t- li su . d .

42 Luua. \ ul . 39 , 1 99 6

spore and at fresh water pools, many of which are quite far away Erom the spore . Accord-

ing to this hypothesis, there should be a significant difference between spraint num-bers associated with Bood and spraint numbers associated with fresh water, because

fresh water is equally available year-round or even more in the wet winter, whereas fish

is not . However, if food is the dominant resource governing spraiuting behaviour, is it

likely that lood availability is simultaneously at a minimum in England, Spelland, Swe-

den and Austria, where prey species, habitat and climate are obviously different~ De-creasing water temperaturen make fish lens mobile and pence Basier available to otters .

In Austria, sprainting behaviour on trout rivers increases in October, at least olie nionth

before ice could have au e ffect tzpon the accessibility of fish . In addition, the same pat-tern is obvious on rivers inhabited mainly by cyprinids, and in commercial fish ponds .

These ponds maiuly produce care and fond is abundant as long as heavy ice does not

restriet access to the water; sprainting behaviour is not related to the eitent of ice cover

on these ponds . Hence, though lood availability may govern sprainting patterns in Sliet-

land, this does not neem to explain the same pattern in Central Europe . The peak (Oc-

tober to March) probably coincides with several factors :

(a) cubs have left their deus and move around with th e females; pence, the number ofotters is temporarily higher than during the rest of the year .

(b) Fema les are increasingly ready to mate again .

(c) Lower water temperaturen in winter are responsib le for higher feeling demands

and pence more sprainting.

These three factors combined might account for an iiicreased sprainting activity be-

tween October and May . The significant drop in spraints in June and Jiily (somewhat

lens pronounced in August and September) could reflect the season in which newly

born cubs are still inside the lens and in which females actively suppress sprainting

(Green et al ., 1984), in order to avoid attracting the attention of male otters (infanti-

cide: Kruuk, 1995) or potential other predators . Human ontdooi- activities along

streams in slimmer have frequently been stressel as having a negative impact on otters,

which was thought to he reflected in a decrease of spraint numbers (Mason & Macdoti-

ald, 1986) . In this study, the lack of fresh spraints (they veere absent in Jtily at six out of'

18 stretchen and almost zero along another five stretchen) was not related to human dis-

turbance; witpin neven years, only once a fisherman was encountered, and canoeing or

rafting lid not take place .Oerober and November veere selected in order to define typical spraint numbers and

their variation along au oligotrophic highland rivet, inhabited by an established popu-

lation . At this time sprainting activity is high and variation rasher love ; also weather con-

ditions are stable, which maken surveys lasting for several weeks feasible . It spotlid he

kegt in mind that sprainting behaviour in November is somewhat higher thaii in Octo-

ber (table 2) ; pence, figuren for both months should he regarded separately . Inter-

spraint Bistances exceeding 36 m in November and 43 m in October are suggested to

indicate either a lower otter density, or a habitat rarely used by otters (error 10 % ; error

5% if investigating two stretchen) . In oligotrophic highland rivers these valoen could

serve as a simpte density index, distinguishing between high and love otter densities .

IuUna , vo I .39 , 1996 13

There was lens sprainting activity in 1989/90 than in 1993/94 ; the differente was not

significant, however. This coincided with an expansion of the otter population during

these years in the surveyed region at large (Kranz, 1995) . In the investigated catchment

area otters have expanded their range : in 1994 otters regularly used a stretch of 6 km

further downstream, which was only rarely used in 1990 . Furtherrriore, they have re-

conquered another catchment area next to the river Kamp . Hence, an increasing pop-

ulation density may have a positive effect on sprainting behaviour .

acKNowi.r. DcE Mr:N T s

am esprcialltgratrt u l to M . Taborski for his criticism on the manuscript and ad v~icr concerning stadstics, as

well as to J . Conrov . H . Gossuw and R . Schmidt . The study was partly finainced bv the Austrian Sci e nce Foundation

(NWF Project No . P08742-IVIO) and the Hunters' Association (Zentralstelle (3s t eneichischrr Landesjagdverbiin-

d c ) ,

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l ' ni~ c rs ih of Agri cultiu 'e/ BO K L' V i e nn a

P rter)or danstrassc 76

1 1 9 0 Wi c n , Au s tri a