Approach to the social structure of a wild rabbit (Oryctolagus cuniculus, L.1758) population in reproductive time. DÍEZ C., GARRIDO J. A., BARTOLOMÉ D. J., OLMEDO J. A., GAUDIOSO V. R.
Dpto. de Producción Animal II, Fac. de Veterinaria, Univ. de León. 24071. León (España). dp2cdv@unileon.es
III INTERNATIONAL SYMPOSIUM ON WILD FAUNA (ISCHIA, ITALY)

INTRODUCTION

Wild rabbit (Oryctolagus cuniculus, L.1758) is one of the most emblematic species of the Iberian Peninsula, being main food of species so outstanding as the Imperial Iberian Eagle (Aquila Adalberti) or Iberian Linx (Linx pardina), which depends on it directly, for its survive. Now a day, the specie's situation can be described as bad (Calvete, 2001). This marked recession's causes can be justified by several factors, as epizooties (myxomatosis or haemorrhagic virical disease), habitat alterations, hunting activity's increase or increment of opportunist's predators. Even this way, still exist some populations that are in satisfactory situation, like it's the case of the one analyzed in this work.

OBJECTIVS

The main objective of this study is to know, in a certain way, some basic parameters of the social structure of an adult wild rabbit population, which is in expansion. Sex-ratio, weight and pregnant dues percentage were analysed just after the animals were captured.

MATERIALS AND METHODS

Study area.- The work was carried out in a game zone, which is in the north of County of Valladolid (Spain), with about 700-720 m high. It presents a continental extreme weather, and about 360 mm/year pluviometry. Predominant vegetation is composed by cereal lands, with barley (Hordeum distichom) and wheat (Triticum aestivum). Another species, which are cultivated, are leguminous as medic (Medicago sativa). Also, as permanent vegetation, there is an important reforested zone with pine trees (Pinnus spp.) Animals.- 77 adult wild rabbits were studied. The capture was carried out with nets and by means of the traditional practice of "hunting with ferret" (Mustela putorius) (Photo 1). All captures were done during the month of February, moment in the one which, as the continental weather which is present in the study area, the animals are in the beginning of the reproductive time. All animals' sex was determined after their capture using external genitals identification method (Saenz de Buruaga et al, 1991). All animals were weighed too, helped by a dynamometer with a precision of 25 g. Moreover, dues were examined to know if they were pregnant using abdominal touching method. To carry out the statistical analysis, was used the computer program STATISTICA 4.5 © for Windows.

RESULTS AND DISCUSSION

1. Sex-ratio and pregnant index:

   Of the total of analyzed animals, 30 turned out to be male and 47 female, obtaining a sex-ratio clearly slanted toward the females, with a percentage relationship of 61% females and 39% males, and then sex-ratio was 2:3 (Graph 1). These results differ with those of Boag (1992), who find more males than females, and sex-ratio about 2:1. This fact can also be explained in great measure by the difference in the capture methods used. This author's method was based on the hunt with shot-guns, and analysis of dead animals. With this method males´ captures are bigger (BOAG, 1992). This is increased when populations are into reproductive time (VON HOLST et al. 1999). Moreover, our facts are plenty similar as Von Holst et al. (1999), who say that wild rabbits live in social groups of about four males and six females. However, sex ratio which was found is smaller than used by Myers (1958) in his studies in enclosures, where he used 75% females and 25% males.

   

2. Pregnant index:

   It was determined 27 cases of positive pregnant, 16 negative and 4 doubtful, in those we couldn't determine it accurately, being obtained about 57% pregnant females, 34% empty and 9% with doubts. This index is a few bigger than described by Soriguer (1995) and similar to the one registered by Trout and Smith (1995), always in the same season of the year. It is very important, also, the marked difference found with the valour registered by Boag (1992), who, in February, finds an index of about 14% of pregnant females, although it could be due to his study is carried out in a population affected by myxomatosis, disease that could have negative effects on reproductive parameters (BENITO, 2001).

3. Weight analysis:

   Medium weight obtained for the total of animals was about 1300 g., being about 1260 g for the males and 1318 g for the females, with standard deviation about 102,88 and 124,96. This total medium valour comes closer a lot to the one published by Delibes (1995), who describes a weight of about 1250 g in north Spain wild rabbits, also establishing a falling scale in the weight of the wild rabbits, from the North of Europe, to Andalusian (Spain) rabbits that would be the smallest rabbits. Weight was located between 1100 and 1550 g. for the males, while in the case of the females between 1000 and 1600 g. (Graph 2), being therefore, lightly minor in males, that in females with embryos. Registered weights` variance analysis for males and females presents F(1,75) = 4,52 throws p<0,05, appearing therefore, between both groups, significant differences. These results can be explained in function of the pregnant index, that indicates us than a high percentage of females are pregnant, that makes that their weights increase.

BIBLIOGRAFÍA

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