food habit os f the otte irn the centra sierrl amoren a ... · acta theriologica vol. 29 32,...

A C T A T H E R I O L O G I C A Vol. 29, 32: 383—401, 1984

Food Habits of the Otter in the Central Sierra Morena (Cordoba, Spain)1

Pedro LÔPEZ-NIEVES & José A. HERNANDO Casal

López-Nieves P . & H e r n a n d o J . A., 1984: Food hab i t s of t h e o t te r in the C e n t r a l S i e r r a M o r e n a (Cordoba, Spain) . Acta theriol. , 29, 32: 383—401 [Witn 4 Tao les & V t i g s . j

T h e food h a b i t s of t h e o t te r Lutra lutra (Linnaeus, 1758) have been s tudied by t h e ana lys i s of the i r f aeces in bo th : Guade lmez and Cuzna r ivers , in S i e r r a Boye ra Reservoir , a n d a s t r e a m called Garcia , all s i t ua t ed in t h e C e n t r a l S i e r r a Morena . T h e diet va r i e s l i t t le, being composed of six m a i n categories of p r e y l is ted h e r e in o rde r of i m -p o r t a n c e in t h e d ie t : f i sh amph ib ians , rept i les , insects , b i rds a n d m a m -mals . I n f o u r zones s tudied , t h e ex i s t ence of seasonal va r i a t ions in t h e die t h a s b e e n obse rved . Dur ing t h e w e t season, f i sh cons t i tu te t h e p r inc ipa l n u t r i t i o n a l source b u t t h e n lose i m p o r t a n c e w h e n con t ras t ed w i t h t h e r e s t of t he p r e y f o u n d in t h e low per iod. The changing of t h e season, a s m a d e c lear by the P r inc ipa l Componen t s Analys is <PCAJ, is s h o w n to be m a r k e d in t h e r i ve r s t h a n in the r e se rvo i r . I n t h e same w a y local v a r i a t i o n wh ich exis ted chief ly b e t w e e n the food in t h e t w o r i v e r s a n d in t h e r e se rvo i r a n d co r robora ted by t h e P C A and Stepwise D i s c r i m i n a n t Analys i s (SDA) w e r e observed . The composi t ion of the diet is p r inc ipa l ly in f luenced by t h e ava i lab i l i ty of t h e resources a n d t h e p r e f e r e n c e w h i c h the o t te r has t o w a r d s ce r ta in species.

[ D e p a r t a m e n t o de Zoología, F a c u l t a d de Ciencias, Univers idad de Córdoba , Córdoba , E s p a ñ a ]

1. I N T R O D U C T I O N

The study in Europe of the otter 's food, Lutra lutra (Linnaeus, 1758) by the examination of the food remains found in their excrements has been carried out in several habitats: in Sweden {Erlinge, 1967, 1968, 1969), in Ireland (Fairley, 1972; Fairley & Wilson, 1972) and in Great Britain (Stephens, 1957; Hewson, 1973; Webb, 1975; Jenkins et al, 1979; Jenkins & Harper, 1980; Mason & Mac Donald. 1980 and Wise et ai., 1981) amongst others.

The bibliography about the otter 's diet on the Iberian Peninsula is very limited. At the present t ime the only work which contributes quantitative and qualitative data based on the analysis of digestive tracts and excrements is that carried out in Galicia (the NW of the Peninsula) by Callejo et. al. (1979).

In view of such a limited bibliography the prime objective of the 1 Th i s p a p e r has been g r a n t e d by C.A.I.C.Y.T. No. 237/81.

[383]

384 P. Lôpez-Nieves & J. A. Hernando

present study, was to determine the otter 's diet, in a zone where its existence could apparently be endangered due to the irregular water flow in the water courses to which it is tigthly bound. It has been used multivariate analysis techniques, to study the food of this species with the aim of determining in a more objective and realiable way the local, monthly and seasonal variations as well as the factors which provoke them.

S t u d y a r e a . In o rder to de t e rmine t h e o t te r ' s diet in t h e Cen t ra l S ie r ra Morena , two r ive r s : Guada lmez a n d Cuzna, belonging to d i f f e r e n t hyd rog raph ic bas ins ; a s t r e am: Garc ia , wh ich is a t r i b u t a r y of t he r ive r Cuzna, and the S ie r ra Boyera Reservoi r , s i tua ted a t t h e h e a d w a t e r s of River G u a d i a t o (Fig. 1) we re chosen. T h e c l ima te of th is zone, classif ied as M e d i t e r r a n e a n sub -humid , p rovides a l imited a n d h ighly i r r egu la r w a t e r f low, leaving the w a t e r concen t ra ted , t h roughou t t h e l eng thy d ry season ( f rom the middle of M a y to the midd le of

Sep tember ) in pools isolated one f r o m t h e o ther . Apa r t f r o m the S ie r r a Boyera Reservoir , t he t h r e e r e m a i n i n g sampl ing zones

a r e s i tua ted in a r e a s scarcely in f luenced by the h u m a n popula t ion , a n d w h e r e the M e d i t e r r a n e a n type t e r m o p h y l e vege ta t ion belonging to t h e Querceta ilicis (C.E.B.A.C., 1971) class p redomina tes , whi ls t t h e r i ve rbed of t h e w a t e r w a y s is p ro tec ted by a th ick maqu ia .

A n a l y s i s of sp ra in t s a n d da t a processing. T h e e x c r e m e n t s w e r e collected fo r tn igh t ly in t h e f o u r indicated zones, fol lowing a f i xed course, f r o m April , 1979 to March , 1980.

The c leaning of t he scats w a s car r ied out fo l lowing t h e me thod descr ibed by Webb (1976). T h e ident i f ica t ion of the r e m a i n s w a s ca r r i ed out w i th use of guides, keys a n d by type collection c rea ted for th is purpose , a n d which w e based on the fol lowing s t ruc tu re s : ve r t eb rae , pha ryngea l t ee th , bone radi i , j aw bones, p reopercu la and opercula bones, and on the ex t remi t ies , scales, skins, f e a t h e r s and exoske le tons of insects.

In o rder to p resen t the da t a w e have fo l lowed the m e t h o d employed by Er l inge (1967, 1968 and 1969) and o ther au tho r s (Stephens, 1967; Rowe-Rowe, 1977 c; Mason & MacDonald , 1980; a m o n g others) in which the da ta a r e expressed as a pe rcen tage of the re la t ive f r e q u e n c y of a p p e a r a n c e . The r e m a i n s of a p rey found in an e x c r e m e n t a r e cons idered as belonging to a single cap tu red specimen. The total cap tu red p rey of a ce r ta in species is g iven by t h e sum tota l of all scats conta in ing the r e m a i n s of the species.

The va r ia t ion of the f ish popula t ion in the a rea w h e r e t h e scats w e r e collected in the S ie r ra Boyera Reservoi r w a s car r ied out by m e a n s of sampl ing wi th ne t s — t w o t r a m m e l ne ts and two gill nets — which w e r e checked eve ry 12 hours in o rder to avoid sa tu ra t ion . The data ob ta ined w e r e conver ted by m e a n s of f i sh ing e f fo r t index (Ricker, 1975), w i th two ne ts being used to avoid his select ivi ty. I n o rde r to m e a s u r e t h e diet p r e f e r ence index of Iv lev (1961), in according to Cock (1978), was used :

2. METHODS

Ne/Se—N/S P= w h e r e

Ne/Se+N/S

Food habits of the otter 385

Fig. 1. Pos i t ion of t he p rov ince of Córdoba a n d of t h e f o u r zones sampled . A: River Guada lmez , B: River Cuzna . C: Garc ia S t r e a m . D: S ie r r a Boyera Reservoi r . The le t t e r s E (Córdoba) a n d F (Galicia) indica te the places where , a t t h e p r e sen t

t ime, t h e diet of the o t t e r has been s tudied on the Ibe r i an Peninsula .

Ne — is t h e n u m b e r of p r e y t y p e I ea t en ; N — is t he n u m b e r of p rey ini t ia l ly p re sen t ; Se — the to ta l n u m b e r of p r e y ea ten and S — is t he t h e to ta l n u m b e r of p r e y ini t ia l ly p resen t .

As for t h e mu l t i va r i an t me thods , t h e Pr inc ipa l Componen t s Analys is (PCA) a n d the S tepwise Disc r iminan t Analys is (SDA) w e r e used to s tudy the spec imens collected in the four zones cons idered m o n t h l y and seasonal ly . The a im of P C A w a s to a t t a in t h e o rder ing of t h e seasons a n d months , us ing the percen tages of a p p e a r a n c e of each ca tegory of p r e y in the d i f f e r e n t sampl ing a r ea s as va r iab les ,


in o rde r t o detect t h e i n t e rna l s t r u c t u r e of t he da ta a n d o rde r t h e m into t r e n d s of i n d e p e n d e n t va r i a t ion . T h e a i m of t h e SDA was, by m e a n s of t h e f o r m a t i o n of ap r io r i g roups in t h e sampl ing zones, t o detect^ in r e l a t ion to the prey, t h e p e r c e n t a g e of success or e r ro r in the f o r m a t i o n of t h e said g roups a n d also t o de tec t t he i r d i f fe rences . T h e p r o g r a m m e s used w e r e BMDP4M (PCA) a n d BMDP7M (SDA) (Dixon, 1975) f r o m t h e Min i s t ry of Educa t ion a n d Science p r o g r a m m e s l ib ra ry .

R E S U L T S

During the study period a total of 2,145 scats were collected, whose distribution throughout zones and months is shown in Table 1.

The diet of the otter in the Central Sierra is composed of six main categories of prey: fish, amphibians, reptiles, insects, birds and mam-mals, listed in order of importance in the diet (Table 2), In the four sampling areas, considered individually and for the whole of the zone, fish were the most captured prey, with percentages varying between 70.56*/o and 82.69°/» of the total captures. The fish was represented in

T h e n u m b e r

Tab le 1

of e x c r e m e n t s collected in t h e f o u r sampl ing zones in each mon th .

Mon th G u a d a l m e z

Rivers

Cuzna Garc ia S ie r r a Boyera

Reservo i r Tota l

Apri l 34 1 11 64 110 May 55 55 5 41 151 J u n e 70 73 0 78 221 J u l y 86 115 0 66 267 Aug. 49 107 0 104 260 Sept . 46 81 0 94 221 Oct. 12 65 2 58 137 Nov. 60 15 9 92 176 Dec. 68 84 6 106 264 J a n . 31 71 3 44 149 Feb. 39 29 0 41 109 March 47 18 0 15 80

Total 597 709 36 803 2145

the diet by three families: Cyprinidae, Centrarchidae and Cobitidae (in the Garcia stream and the River Cuzna the Centrarchidae family did not appear). The first of these families provided the major i ty of the fish captures. Amphibians — all of the captures referr ing to Rana ridibunda — constituted the second important capture in the diet, except in the reservoir, where the birds took this place. Reptiles, especially Natrix maura, and insects too formed an important par t in the diet. On the other hand, only few mammals were captured.

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It was in the reservoir where the greatest variety and quanti ty of prey was recorded, whereas the last recorded was in the Garcia stream, where almost all the captures centred on fish, above all on Chondrostoma polylepis willkommi.

1. The Monthly and Seasonal Variation of the Diet in the Different Habitats

The monthly and seasonal variation of the diet was studied in all zones except the Garcia stream, in view of the limited number of scats collected there and irregulari ty of their distribution throughout the year.

(a) The River Guadalmez. The monthly variation of the different categories of prey can be proved that f rom May to July fish captures decreased drastically whereas there was an increase in N. maura, R. ri-dibunda and above all in birds captures, which displayed a clear season-ality in being captured (Fig. 2). The basis of the diet was constituted by leuciscus cephalus which maintened its relative f requency of ap-pearance above those of the remainder of the prey, except in June, when they coincided with the maximum displayed by N. maura. During

FR%

Fig. 2. The m o n t h l y d i s t r ibu t ion of t h e r e l a t ive f r equenc i e s (FR%>) of t he p r e y cap tu red in the River Guada lmez . A. sapidus, M. salmoides a n d S a u r i a a r e exc luded

due to the i r l imi ted pe rcen tage .


A M J J A S O N D J F M

Fig . 3. T h e m o n t h l y d i s t r i b u t i o n of FR°/o, of t h e p r e y c a p t u r e d in t h e R ive r Cuzna . A. sapidus, O. cuniculus a n d S a u r i a a r e e x c l u d e d b e c a u s e of t h e i r l ow FR°/o.

a very definite period of time — f rom September to November — a limited quanti ty of Micropterus salmoides was captured. The greater part of N. maura, R. ridibunda, birds and insects captures took place at a time when the river levels were low.

(b) The River Cuzna. Just as the monthly variation occurred in the River Guadalmez, so too did it occur in the River Cuzna, and in this zone it took place in a more marked form (Fig. 3). As in the previous zone, L. cephalus maintained its relative frequencies of appearance fairly constant throughout the year. In general, the most important fish captures took place f rom August to March, although from April to June more Cobitis paludicola were captured. The dominant prey, with regard to fish, was Barbus sclateri, amounting to 50%> of the total captured prey in January . In this zone birds were infrequent prey of the otter, ap-pearing in a small proportion in the diet f rom August to January . N. maura and R. ridibunda were distributed throughout the year ap-


proximately the same as in the River Guadalmez. The only Oryctolagus cuniculus was captured in this zone.

FR%

Fig. 4. T h e m o n t h l y d i s t r ibu t ion of FR%> of t h e p r e y c a p t u r e d in the Sierra , Boyera Reservoi r . R. alburnoides, C. paludicola, Sau r i a a n d m a m m a l s a r e exc luded

because of thei r low FR%>.

(c) The Sierra Boyera Reservoir. In the monthly variation of the relative frequencies of appearance of the different prey it has been observed that fish constituted the basis of the diet during the whole year (Fig. 4). When the frequency of appearance (FR°/o) of a species decreased there was a corresponding increase in another, allowing the year to be divided up into three periods, in which dominated alternitavely Cypri-nus carpio, M. salmoides and Ch. polylepis willkommi. The rest of the fish species were captured in a smaller quanti ty. The rest of the vertebrates and insects which completed the diet were distributed with different frequencies throughout the year, without standing out part i -cularity at any time, as occurred in the two zones dealt with previously. Birds were an exception, displaying higher frequencies in Summer and


Autumn. It was in this zone that the highest capture percentages of birds and mammals was found, representing at the same time the greatest specific diversity.

FR%

Fig. 5. The m o n t h l y d i s t r ibu t ion of FR°/o of t h e p r e y cap tu red dur ing the s t u d y in the Cen t ra l S ie r re Morena . R. alburnoides, S a u r i a and m a m m a l s a r e exc luded

because of the i r low FR%>.

(d) The Central Sierra Morena. For the whole of the Central Sierra Morena the monthly variation of the different species was subject to the distribution pat terns which were displayed individually in the dif-ferent areas considered (Fig. 5). For example, the frequency of ap-pearance of fish as a whole, decreased at the time understood, between May and July, when the captures of N. maura and R. ridibunda in-creased. As occurred in the two rivers, the captures of L. cephalus were produced in a fair ly stable way during the whole year. The limited captures of mammals occurred f rom April to September.

2. Comparison of the Diet in the Different Sampling Zones

(a) Monthly variation. For the samples of the diet considered monthly — with the exception of the Garcia stream which produced a limited amount of excrements — the PCA acquired in the first f ive


axes 75.9°/o of the total accumulated variance (Table 3), wi th 28.0%, 18.1°/o and 12.7°/o corresponding respectively to the first three axes. The adequacy mean of the samples gathered was 0.57 (Dziuban & Shirkey, 1974; Dziuban et al., 1979).

Table 3

Non r o t a t e d f ac to r s of t h e 17 va r i ab le s f o r f ive f i r s t componen t s w i t h cons idered month ly . For i n t e rp r e t a t i on those w i t h a n abso lu te va lue super ior t h a n 0.50 h a v e

been chosen, a n d they a r e boldfaced .

Var iables F A C T F A C T F A C T F A C T F A C T 1 2 3 4 5

1 C. carpio - . 5 5 2 .672 .127 .051 .184 2 M. salmoides .553 .433 .190 .171 .526 3 B. sclateri .618 - . 1 2 6 .477 .110 .370 4 C. polylepis .462 - . 3 0 6 .400 .150 .480 5 L. cephalus .873 —.083 - . 0 8 5 - . 1 6 6 .024 6 R. alburnoides - . 2 8 8 .477 .682 .142 - . 3 4 5 7 C. paludicola .861 .232 - . 1 3 4 - . 0 9 0 .035 8 Uniden t i f i ed c ipr inids .644 .010 .230 .141 - . 3 3 0 9 Natrix maura .471 .647 - . 3 9 2 - . 0 8 1 - . 2 5 2

10 Uniden t . Sau r i a .325 .410 - . 1 3 5 .683 .006 11 R, ridibunda .802 .452 - . 0 9 0 .000 - . 0 3 8 12 Insects .365 .620 - . 4 0 1 - . 0 7 0 .036 13 Birds - . 3 5 7 .637 - . 1 8 0 - . 2 8 6 .303 14 A. sapidus .225 .421 .618 - . 3 6 6 .030 15 Rattus sp. - . 2 5 1 .487 .568 - . 2 5 1 - . 2 1 5 16 M. musculus - . 6 5 2 .210 .152 .854 —.064 17 O. cuniculus - . 4 5 1 - . 1 4 7 - . 2 6 3 .084 - . 4 6 5

Var iance , °/o 28.0 18.1 12.7 9.6 7.5 C u m m u l a t i v e var iance , % 28.0 46.1 58.8 68.4 75.9

After rotation, the existence of three groups was shown on the graph defined axes I and II (Fig. 6A). One group characterized by its strong positive polarity around axis I and which is composed of the species which displayed a greater f requency in the dry seasons of the rivers, formed by: R. ridibunda, N. maura, C. paludicola and insects. A second group composed of the variables which gather together with high values on axis II and are prey were more abundantly present in the excre-ments gathered in the reservoir, formed by: C. carpio, M. salmoides and birds. Finally a thrid group formed of the variables with cluster together around the coordinates centre and in which appear prey which were found together and with greater regularity in the rivers and reservoir.

The months are separated into three groups by PCA (Fig. 6B): one group (G. 1), separated from the rest by axis I, is constituted of the months in which the rivers offered less water and is dominated by the prey with high values on axis I (R. ridibunda, N. maura, C. paludicola


Fig. 6. The o rde r ing of t h e p rey (A) a n d t h e m o n t h s (B) b y m e a n s of PCA on axes I a n d II, exc lud ing the Garc ia S t r e a m . T h e p r e y a re expressed as in Tab le 3. T h e m o n t h s a r e indica ted wi th two le t te r s : t h e capi ta l cor responding to the m o n t h (March, J u l y a n d Augus t have an apos t rophe) a n d the second le t te r to t'he River

G u a d a l m e z (a), River Cuzna (b) and S ie r r a Boyera Reservoi r (d).

and insects). Another group is principally formed during autumn and spring of the reservoir, and in which dominated by C. carpio, M. sal-moides and birds. The third group is formed by the rest of the months (G. 3) and is dominated by l'ess characteristic prey for each zone.


(b) Local variation. The SDA (Fig. 7) distinguishes the three functional zones f rom the principal prey which form the monthly diet in each of them. The ellipses of equiprobability calculated at 95% success rates, reveal that the rivers come close to each other and to the reservoir, and, at the same time remain separated f rom it by the canonical variable Y. The prey which characterized the otter 's nourishment in the reservoir was C. carpio and in the two rivers L. cephalus and B. sclateri.

Fig. 7. Ell ipses of equiprobabi l i ty , ca lcula ted a t a 95% succes ra te , f o r t h e m o n t h s of sampl ing ca r r i ed out in the rese rvo i r a n d in the bo th r ivers . T h e symbols cor respond to those in f i g u r e 6 fo r t h e mon ths . VC X and VC Y: Canonica l va r i ab les X a n d Y. Ga : T h e G u a d a l m e z River ; GB: The Cuzna River a n d GC:

T h e S ie r r a Boyera Reservoi r .

3. The Food Preference in the Diet of the Otter in the Sierra Boyera Reservoir

The food preference in the otter 's diet, with regard to fish, has been studied in the Sierra Boyera Reservoir, following the evolution of the fish population, by means of sampling with nets, throughout the study year (Table 4) and it has been compared by the otter in this place during the same period of time (Table 4B) (Erlinge, 1967; Wise et al., 1981).

The annual fluctuation in the C. polylepis population, the most abun-dant species in the reservoir, was evident, and there existed a period, June to August and November, when no capture of this species took place with nets. The M. salmoides population was maintened regularly

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in the zone sampled and in terms of numbers it was the second important species in the reservoir. The R. alburnoides and C. carpio populations appeared in lesser number with almost all of the captures later taking place in July. Only three speciemens of B. sclateri were captured in the year.

It can be observed a priori that the most captured prey by the otter — M. salmoides and C. carpio — were not the most abundant in the environment, and that a preference existed towards certain species, as made clear by Ivlev's index (Table 4C). Apart f rom C. polylepis and R. alburnoides to which the otter displayed a negative preference, the remains had a positive preference with the maximum corresponding to B. sclateri.

DISCUSSION

Despite the limited water flow and the lengthy low water period in the water courses of the zones studied, the number of scats gathered in the study year was fairly high. It was precisely in the months when the rivers' waters were at their lowest, that the greatest quanti ty of excrements were collected (apart f rom Garcia stream which dried up completely). When the otters became concentrated in the limited water zones, this lead to an increase in their density and so to an increase in the number of excrements deposited (Jenkins & Burroughs, 1980) and collected.

The otter 's diet in the Central Sierra shows slight diversity with regard to the species captured — 17 categories of prey counted as op-posed to the 33 of Callejo et al, (1979) and 28 of Erlinge (1967) — since it exploits in an almost exclusive way the freshwater environment which is poor in species in our zones. Despite this, the exploitation is carried out in a fairly effective way, as the otter obtains almost all of its food f rom this environment. The full exploitation of the resources gives place to the differentiation of the diet between the different zones sampled, due to the resources of the environment or to the species towards which the otter has a preference. These factors give place to the existance of characteristic prey for each zone. Thus the most characteristic in the reservoir were M. salmoides and C. carpio and the two in the river were L. cephalus and B. sclateri, as the SDA made clear.

A similarity was observed between the diet in the two rivers and a differentiation observed with respect to the diet in the reservoir, which is made clear by the PCA and the SDA.

The seasonal changes were more marked in the river currents than in the reservoir. But despite the fluctuations and the populational dy-


namics which certain animals displayed and which had an influence on the composition of the diet when the number of possible prey varied (Wise et al., 1981), the scarcity of water in the water currents had a decisive influence on the diet. In the Sierra Boyera Reservoir, since the quant i ty of water is almost constant, it does not have an influence upon the fish populations, nor upon those of other prey, and its density of specimens is due to their dynamics, biology or other factors. When Spring and Summer arrived, the number of amphibians and reptiles increased and the early elements in the birds and mammals populations appeared which lead to potential prey increase for the otter. The diet was enriched by other prey besides fish, but without the quant i ty of fish captures being diminished in such considerable way as in the rivers, since the density of these new prey was limited when compared with the density of fish and with the great volume of water in the reservoir.

In the rivers, the scarcity of water in the low water period and the formation of isolated pools, compelled the fish to migrate to f ree zones or, as occurred with the remaining categories of prey, to become con-centrated in these pools. The inferior swimming abilities of R. ridibunda and N. maura compared to those of fish, made them more easily captured by otter (Erlinge, 1968) which found an important source of food in them during this period.

The greatest insects captures were all beetles, with the exception of two Grillotalpa grillotalpa. These insect capture together with captures of R. ridibunda and N. maura were produced precisely in the low water period when advantage was taken, as we have already stated, of the great concentration of the latter in the limited water zones.

Reptiles constituted an important prey in the otter 's diet in the Central Sierra Morena, where the highest percentages of reptile captures were found, with those of Callejo et al., (1979) being somewhat smaller in Galicia. This constitude a differentiating feature in the diet on the Iberian Peninsula with respect to the rest of Europe.

The results obtained from the birds present a greater diff iculty of interpretation, since the food remains could not be identified in their entirety. Nevertheless the presence of feather belonging to Anas platy-rhynchos, Gallinula chloropus and Fulica atra could be detected. The River Cuzna and Garcia Stream, offer limited open zones and few aquatic birds and, because of this, the captures were limited or null. On the other hand they were more plentiful in the River Guadalmez and the Sierra Boyera Reservoir where the captures had greater impor-tance. The movements and migrations of the birds and the appearance of early elements in the populations (Wise et al., 1981) had an influence on the captures which caused their seasonality.


Mammals are an occasional prey of the otter in the Central Sierra Morena as is demonstrated by the limited percentage in which they appeared in the diet, which contrast with the 13,3% obtained by Cajellb et al.} (1979) in Galicia, the highest for the whole Lutra genus. As occurs with reptiles and amphibians the preference towards aquatic species is evident, since the majori ty of the captures were centred upon A. sapidus and Rattus sp., which prowl near the bank, among the reeds and bul-rushes of the reservoir — the place where the capture of the lat ter originated. The limited number of mammals captured may be due, in part at least, to competition with other mammals, especially Vulpes vulpes, which are plentiful' in the zone (Erlinge, 1969 and 1972; Jenkins & Harper, 1980; Wise et al, 1981).

Fish, considered both as separate species, and together, represented the most important prey in the otter 's diet in any period of the year, although they were subject to monthly and seasonal variation. It was in the rivers where the greatest difference between the quantity of fish captured in the dry season and the wet season was registered, because of the reasons already explained. For the whole of the Central Sierra Morena the same phenomenon was observed.

In the diet of otters in both rivers the regular presence of L. cephalus stood out throughout the whole annual cycle. This is due to the fact that this species is a particular exploiter of the river's habitats. The most captured fish in the River Cuzna was B. sclateri since the otter takes advantage of the concentrations of this fish in the deep pools on this river 's bed (B. sclateri foods f rom riverbeds), whereas the River Guadal-mez does not offer any of these pools. It was noticed in both rivers that C. carpio was not present which may be due to the fact that this species is characteristic of still, deep waters (Castello, 1980). The presence of some M. salmoides captures in the River Guadalmez was probably due to the fact that they moved up from the nearby Zujar Reservoir, where they had been introduced artificially to exploit the river 's food resources.

The remaining species which complete the diet displayed fluctuations which are probably due to the particular biology and dynamics of the fish populations, unknown at this time on the Iberian Peninsula.

Although C. polylepis was the most abundant species in the reservoir, M. salmoides and C. carpio were the most eaten. Moreover, a clear pref-erence existed towards B. sclateri, together with the existance of three periods in the year, with each one dominated by one species. This makes it clear that the most captured prey was not always the most abundant in the environment (Erlinge, 1967; Frined, 1978). The causes for the preferred capture of a certain prey and the monthly fluctuations include factors such as the biology and dynamics of the prey (Erlinge, 1967;


Callejo et al., 1979; Wise et al., 1981) the greatest vulnerability and least ability to escape, their activity, the size of the fish (Erlinge, 1967; Rowe-Rowe, 1977a, b; Jenkins et al., 1979), the situation of the prey (Wise et al., 1981) and the clarity and temperature of the water (Rowe- Rowe, 1977a, b).

We can sum up be saying that in the Central Sierra Morena both seasonal and monthly variations were observed which were produced in the same way as those observed in Great Britian (Jenkins et al., 1979; Jenkins & Harper, 1980; Wise et al., 1981) and in Sweden (Erlinge, 1967) but in a contrary way to those which occurred in Galicia (Callejo et al., 1979).

A local variation could be observed too between the otter 's food in the rivers and in the reservoir, which was due to the seasonal variation and to the prey caused principally by amphibians and reptiles, and to the existence of dominant or characteristic prey in the diet of each area. The composition of the diet in our zone is influenced by several factors: (1) The availability of the resources, as is shown by the exploitation of the prey which displayed a marked seasonality and the existence of dominant prey in the diet, which coincided with their abundance in the environment. (2) The preference towards certain species — B. sclateri, C. carpio and M. salmoides — as was evident in the case of the reservoir. (3) The seasonality which certain prey displayed and which gave place to a seasonal variation in the diet. (4) The irregular system of the rivers, which creates a concentration of certain species in the zones with water. (5) The dynamics and biology of the prey populations.

Acknowledgement s : The au tho r s wish to be expres s the i r g r a t i t ude to Prof . Dr. C a r m e n Bach and Dr . Miguel Delibes f o r t he i r in te res t ing suggest ion a f t e r t h e cr i t ical read ing of t he manusc r ip t , to D. Car los Fe rnandez -De lgado fo r his h e l p and also to the Univers i ty of Sevil le 's Cen t ro de Cálculo (Calculat ion Cent re) fo r t he he lp given in the da ta processing.

R E F E R E N C E S

1. Cal le jo A., Gui t ian J., Bas S., Sánchez J . L. & Cas t ro A., 1979: P r i m e r o s datos sobre la dieta de la nu t r i a , Lutra lutra (L.), en aguas cont inenta les d e Falicia . Donana , Act. Vert. , 6: 191—202.

2. Castel ló V., 1979: Ic t io fauna del r ío Guad ia to : Es tud io de la población de ba rbos (B. barbus sclateri Stein.). Memor ia de L icenc ia tu ra . Univers idad de Córdoba . Córdoba. 54 pp.

3. C.E.B.A.C., 1971: Estudio agrobiológico de la provinc ia de Córdoba. Madr id : 1—401.

4. Cock M. J . W., 1978: The assessment of p re fe rence . J . Anim. Ecol. 47: 817—832.


5. Dixon W. J., 1975: BMDP. Biomedica l C o m p u t e r s P rog rams . Univers i ty of Cal i forn ia Press . Berke ley . Los Angeles .

6. Dz iuban Ch. D. & S h i r k e y E. C., 1974: W h e n is a cor re la t ion m a t r i x appropia te fo r f ac to r analys is? Psychol . Bull., 81: 358—361.

7. Dziuban Ch. D., S h i r k e y E. C. & Peeples T. O., 1979: A n inves t iga t ion on some d is t r ibu t iona l charac te r i s t i c s of the m e a s u r e of sampl ing adequancy . Educ. Psychol. , M e a s u r e m e n t , 39: 534—549.

8. Er l inge S., 1967: Food hab i t s of t he F i sh -o t t e r , L. Intra L., in Sou th Swedish habi ts . Vil t revy, 4: 371—438.

9. Er l inge S., 1968: Food s tudies on cap t ive o t t e r s (L. Intra L.). Oikos, 19: 259—270.

10. Er l inge S., 1969: Food hab i t s of t h e o t t e r (L. lutra L.) a n d the mink (M. vison) in Sweden. Oikos, 20: 1—7.

11. Er l inge S., 1972: In te rspec i f ic r e l a t ions b e t w e e n o t te r (L. lutra) a n d mink. (M. vison) in Sweden . Oikos, 23: 327—335.

12. Fa i r l ey J . S., 1972: Food of o t t e r s (Lutra lutra) f r o m Co. Galway, I re land, a n d no tes on o ther aspects of the i r biology. J . Zool., Lond., 166: 469—474.

13. Fa i r l ey J . S. & Wilson S. C., 1972: A u t u m n food o t te rs (Lutra lutra) on the Agivey River , Coun ty L o n d o n d e r r y , N o r t h e r n I re land . J . Zool., Lond., 166: 468—469.

14. F iend G. R., 1978: A compar i son of p r e d a t o r ,scat ana lys is w i t h convent ional t echn iques in a m a m m a l su rvey of con t ras t ing hab i t a t s in Gipps land, Victoria. Aust . Wildl . Res., 5: 75—83.

15. Hewson R., 1973: Food a n d feed ing hab i t s of o t t e r s Lutra lutra a t Loach P a r k , no r th - ea s t Scot land. J . Zool., Lond., 170: 159—162.

16. J e n k i n s D. & B u r r o w s G. O., 1980: Ecology of o t te rs in N o r t h e r n Scotland: III . The use of faeces as indica tor of o t te r (L. lutra) dens i ty a n d dis t r ibut ion. J . Anim. Ecol., 49: 755—774.

17. J e n k i n s D. & H a r p e r R. J., 1980: Ecology of o t t e r s in N o r t h e r n Sco t land : II. Ana lys i s of o t te r (L. lutra) a n d m i n k (M. vison) f aeces f r o m Deeside, NE Scot land in 1977—78. J . Anim. Ecol., 49: 737—754.

18. J e n k i n s D., Walke r J . G. K. & McCowan D., 1979: Ana lyses of o t t e r (Lutra lutra) f aeces f r o m Deeside, NE Scot land . J . Zool., Lond., 187: 235—244.

19. Iv lev V. S., 1961: E x p e r i m e n t a l ecology of the f eed ing of f ishes . Yale Univers i ty Prees . N e w Haven .

20. Mason C. F . & MacDonald S. M., 1980: The w i n t e r diet of o t te r (Lutra lutra) on a Scot t ish sea loch. J . Zool., Lond. , 192: 558—561.

21. Ricker W. E., 1975: Compu ta t i on a n d i n t e r p r e t a t i o n of biological s ta t i s t ics oi f i sh popula t ions . Bull . Fish. Res. Boars . Can., 191: 1—382.

22. Rowe-Rowe D. T., 1977a: P r e y c a p t u r e a n d feed ing behav iour of South A f r i c a n ot ters . The L a n n a r g e y e r , 23: 13—21.

23. Rowe-Rowe D. T., 1977b: Var ia t ions on t h e p r e d a t o r y behav iou r of t h e clawles o t t e r . The L a m m a r g e y e r , 23: 22—27.

26. R o w e - R o w e D. T., 1977c: Food ecology of o t t e r s in Nata l , Sou th Afr ica . Oikos 28: 210—219.

27. S t e p h e n s M., 1957: The n a t u r a l h i s to ry of t h e o t te r . T u m b r i d g e Wells. Ken t 28. Webb J . B., 1975: Food of t he o t te r (Lutra lutra) on t h e Somerse t levels'.

J . Zool., Lond., 177: 486—491. 29. Webb J . B., 1976: O t t e r spra in t analysis . A n occasional publ ica t ion of the

M a m m a l Society. London.

Stosunki pokarmowe wydry 401

30. Wise M. H., L i n n I. J . & K e n n e d y C. R., 1981: A compar i son of t'he f eed ing biology of mink , Mustela vison, a n d ot ter , Lutra lutra. J . Zool., Lond., 195: 181—213.

Accepted, June 30, 1984.

P e d r o L Ô P E Z - N I E V E S & José A. H E R N A N D O Casai

S T O S U N K I P O K A R M O W E WYDRY W C E N T R A L N E J S I E R R A MORENA (KORDOWA, HI SZP AN IA )

Streszczenie

B a d a n i a n a d s k ł a d e m p o k a r m u wydry , Lutra lutra (Linnaeus, 1758) p r o w a d z o -no n a pods t awie ana l i zy ka łu . Ma te r i a ł zb ie rano n a d b rzegami rzek G u a d a l m e z i Cuzna , s t r u m i e n i a Garc i a oraz wokół zb iorn ika wodnego S ie r ra Boyera , w C e n -t r a l n e j S i e r r a Morena (Tabela 1; Ryc. 1). Jeżel i chodzi o r o d z a j p o k a r m u , d ie ta w y d r y była m a ł o zmienna i sk łada ła się z ryb , p łazów, gadów, owadów, p t a k ó w i s s aków (Ryc. 2—5). W czterech b a d a n y c h s t r e f ach wys t ąp i ł y j ednak p e w n e sezo-n o w e różnice w składzie d ie ty (Tabela 2, 3). W okres ie o b f i t u j ą c y m w deszcze, g łówne źródło p o k a r m u s t anowią ryby , k tó rych udzia ł znacznie zmnie jsza się, g d y w o d y zaczyna być mało . Z m i a n y sezonowe diety oceniono p rzy pomocy ana l i zy k o m p o n e n t ó w g łównych i s twierdzono, że są one znacznie wyraźn ie j s ze w r z e k a c h niż w zb iorn iku w o d n y m (Ryc. 6). P r z y pomocy tego samego tes tu oraz ana l i zy d y s k r y m i n a c y j n e j , oszacowano różnice w p o k a r m i e w y d r ży jących w b a d a n y c h r z e k a c h i n a zalewie w o d n y m (Ryc. 7). Sk ład żeru u w a r u n k o w a n y jest g łównie jego dostępnością o raz wybiórczością w y d r y w s t o s u n k u do pewnych g a t u n k ó w (Tabela 4).

food habit os f the otte irn the centra sierrl amoren a ... · acta theriologica vol. 29 32,...

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