Weight and external measurements of Red foxes (Vulpes vulpes) from sw spain

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Weight and external measurements of Red foxes (Vulpes vulpes) from

SW Spain
Estación Biológica de Donana, Consejo Superior de Investigaciones CientIjIcas, Sevilla, Spain
Red foxes (Vulpes vulpes) show a high variability in body size, in parallel to their wide­

spread distribution, which was used as an example or as a deviation (DAvis 1977; KOLB

1978) of ecogeographical rules (MAYR 1963). Nevertheless, this tendency was evaluated in relatively small areas, compared to the whole geographical distribution of the species. In spite of being one of the most well-studied carnivore species in most aspects of their eco­ logy and behaviour, no reliable information is available on red fox body size for most of its complete range. In the present report, we present the weight and external body mea­ surements of one of the southern-most populations of Vulpes vulpes. Our results provide basic information upon which geographic variation on a continental scale could be investi­ gated.

Foxes were captured in the Donana area in Southwestern Spain (37°O0’ N, 0690’ W)

during the course of fox control programs from 1988 to 1992. The climate is Mediterra­

nean with Atlantic influence, with mild and wet winters and hot and dry summers. Body weight and five external measurements were taken: (1) Maximum body length (maximum

length from the tip of the snout to the dorsal edge of the perineum was recorded); (2) Tail length (from the dorsal edge of the perineum to the tip of the tail, excluding fur); (3) Hindfoot length (from the edge of the calcaneum to the tip of the third phalange, with the phalanges extended); (4) Ear length (from the base of the tragus to the tip of the pin­ na); and (5) Shoulder height (from the top of the withers to the tip of foreleg).

The age of foxes was determined by counts of cementum annuli in premolars and by cursory examination of complete dentition, which was sufficient for young foxes. Only foxes older than about seven months were included in the study. For each sex, juveniles (from seven to twelve months) and adults (older than one year) were considered sepa­ rately. Weights of pregnant or lacting females were not considered. We were not able to perform all measurements in all individuals. Sexual dimorphism was evaluated through the ratio male measurement/female measurement. For weight we used the cube roots of original values. For all comparisons we used the Student t-test (ZAR 1984). Significant dif­ ferences were considered when p < 0.05.

A total of 161 red foxes was measured. Adult males were significantly larger and

heavier than vixens in all the measurements (Tab. 1). The juvenile class showed a similar

pattern, but significant differences were observed only in liindfoot length and shoulder

height (Tab. 1). Adult males were significantly heavier (t = 4.19, p < 0.01) and larger than juvenile males for head and body length (t = 4.81, p <0.01) and hindfoot length (t = 2.85, p <0.01). There were no significant differences between adult and juvenile females for all body measurements or weight.

Table 1. External body measurements and weights for juvenile and adult red foxes from Donana Na­ tional Park. Mean value (X), standard deviation (SD), sample size (n), and the significance level (p) of mean differences between male and female measurements for both age categories.

Males Females

Juveniles (7—12 month old)

Measurements X SD n X SD n p

Weight (g) 5051 1199 18 4706 642 22

Head and body (mm) 659 45 18 648 29 23

Tail (mm) 382 36 18 377 25 22

Shoulder height (mm) 385 36 18 366 14 20

Hindfoot(mm) 151 9 18 145 8 23

Ear(mm) 97 5 18 96 5 22

Adults (> 1 year old)

Weight (g) 6330 968 64 5124 854 60

Head and body (mm) 708 36 65 659 29 57

Tail (mm) 392 32 65 375 28 59

Shoulder height (mm) 401 22 59 370 16 60

Hindfoot (mm) 157 7 65 145 6 61

Ear (mm) 100 7 58 94 6 54

Significance levels: —: p > 0.05, *: p <0.05, **: p < 0.01

Sexual dimorphism was significant only in adults for all measurements (p < 0.01 in all comparisons), with an average sexual dimorphism of 1.08, quite similar to that obtained from the data provided by KOLB and HEwsoN (1974) for Scottish (1.05) and English (1.07) red foxes, and by LUND (1959) for Norwegian specimens (1.05). Following RALL5’ (1976) criterium, this sexual dimorphism would be small and typical for mammalian spe­ cies exhibiting long-term pair bonding, like the red fox (KLEIMAN 1977). The absence of sexual dimorphism in the juvenile class, together with the absence of size differences be­ tween juvenile and adult females, suggest that females reach their adult body size in their first year of life, while males continue to grow, a fact that is typical in mammals where males are larger than females (RALL5 1976).

Red foxes from Donana are larger than predicted by Bergmann’s rule (MAYR 1963),

based only on a geographical basis. Male and female red foxes are lighter than Swiss equivalents (Laps and WANDELER 1983; WANDELER and LOps 1993) (7 080 and 5930 g for Swiss males and females, respectively). The same is true for Scottish foxes (KOLB and HEwsoN 1974) (7300 and 6200 g for males and females, respectively). Nevertheless, Do­ ñana foxes are larger in body measurements but rather similar in weight compared with their conspecifics from England (KOLB and HEwsoN 1974) (head and body length: 671 and 627 mm, weight: 6700 and 5400 g, for males and females respectively). These resu!ts provide additional evidence on size variability in the red fox, not fully explainable by single causes (KOLB 1978).

The authors are grateful to R. LAFrrrrE, F. AYALA, T. RUEDA, P. FERRERAS, J. ALDAMA, ISIDRIN and A. D0NAIRE for the capture of the red foxes. Funds were provided by the Instituto para Ia ConservaciOn de Ia Naturaleza (ICONA) and Dirección General de Ciencia y TecnologIa; Project PB9O-1080. The manuscript was criticized by Dr. J. A. DONAZAR, H. OKARMA, and I JUSTE.
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Authors’ address: Dr. ALEJANDRO TRAVAINI and Dr. MIGuiI. DELIBES, Estación Biológica de Doñana, CSIC, Apartado 1056, E-41080 Sevilla, Spain.

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