Acta Theriol (2011) 56:189–198 DOI 10.1007/s13364-010-0008-7
ORIGINAL PAPER
Social organization in the Chinese water deer, Hydropotes inermis Gérard Dubost & Florence Charron & Aurélie Courcoul & Aurélie Rodier
Received: 17 May 2010 / Accepted: 7 September 2010 / Published online: 24 December 2010 # Mammal Research Institute, Polish Academy of Sciences, Białowieża, Poland 2010
Abstract The social organization of Chinese water deer was studied in a zoological park. Most adults lived together in the mixed zone, although other habitats were available. The overlap between individual areas was largest in females. In the mating season alone, less than half of the males established territories which overlapped in small spots where most encounters occurred. Females travelled freely throughout the entire available area, but nonterritorial males stayed between the territories. Except in males during mating season, very few physical contacts other than sniffing took place between individuals regardless of age, sex or status. Each animal lived alone and did not show attraction or aggressiveness towards congeners. Grouping was temporary with no durable link between individuals, not even between mothers and daughters older than 5 months. The solitary life of individuals on a common ground and the establishment of seasonal territories make the water deer unique among ruminants. The species appears to be no more social than the water chevrotain, an “ancient” species. This fits well with other characteristics of the species. Keywords Chinese water deer . Home range overlap . Territorial behaviour . Social interactions
Communicated by: Magdalena Niedziałkowska G. Dubost (*) : F. Charron : A. Courcoul : A. Rodier Muséum national d’histoire naturelle, EGB, UMR 7204, Ménagerie du Jardin des Plantes, 57 rue Cuvier, 75231 Paris Cedex 05, France e-mail:
[email protected]
Introduction The Chinese water deer (Hydropotes inermis, Swinhoe 1870) is a small cervid native to China and Korea. The presence of large canines in males, and not antlers, large auditory bullae and inguinal glands make the species unique among cervids (Haltenorth 1963; Nowak 1999). From molecular standpoint, it may be considered close to Capreolus capreolus (Randi et al. 1998). Although several studies have been conducted in the wild (Sun and Dai 1995; Sun and Xiao 1995; Sun 2002) and in captivity (Scherpe 1971; Feer 1982; Stadler 1990; Zhang 1996, 1998; Dubost et al. 2008), knowledge of its social life remains largely incomplete, particularly concerning the relations between individuals. This is regrettable considering the great originality of the species. Such investigations can be rarely undertaken in nature. Thus, the goal of this work was to study the spatial distribution of individuals and their social interactions in a zoological park. Although the conditions differed on some points from those existing in the wild and the interactions between individuals were probably more frequent than in nature, we assumed that the animals disposed of sufficient area to express the characteristics of the species in terms of search for contacts, choice of partners and grouping of individuals. A comparison with data obtained in another park should deepen our knowledge of the species. Observations could allow one to determine to what extent the behaviour and the sociality of the water deer fit with its other biological traits. Moreover, since many ethological studies have revealed interesting trends among artiodactyls, such a study seems pertinent because the species is reported as solitary, as are the most ancient extant ruminants. Thus, the water deer could represent an interesting exception among cervids. Lastly, knowledge of its social life is important when maintaining many
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individuals together for reintroduction purposes, since the species is classified as “vulnerable” by the IUCN.
Materials and methods The species is small-sized, with males lighter than females (14.0 kg vs 15.2 kg; Dubost et al. 2008). In nature, it inhabits tall reeds and grassy areas, travelling mostly alone (Haltenorth 1963; Bützler 1988; Sun and Dai 1995; Nowak 1999; Sun 2002). The study population spends the whole year with maras, red-necked wallabies and large birds in the Branféré Zoological Park (Bretagne, France) on 12.2 ha composed of 5 ha of mixed tall forest, dense bushes and short meadows, 2.2 ha of tall forest interspersed with bushes and 5 ha of short meadows with no or few trees (Fig. 1a). Throughout the year, the animals feed on natural grasses during both the day and the night, but a few individuals also eat supplementary pellets in winter. As in the wild (Sun and Xiao 1995), at the beginning of autumn some mature males (eight out of 18 in 2003) established individual territories in the mixed zone, the one most used by the females. Females and young could travel freely throughout the territories, but non-territorial males usually stayed between the territories, which corresponds to the social organization seen at Whipsnade, England (Stadler 1990), as in other places. At Branféré, as elsewhere, the reproductive cycle was well defined: most births took place during only 1 month (13 May–18 June). Each female usually give birth to 1–3 young. The individuals were weighed and marked during capture campaigns in 2002, 2003 and 2004 before the onset of the mating season (Dubost et al. 2008). Newborns were marked at 1 day of age or early in morning of the a) Vegetation
b) July
Fig. 1 Distribution of water deer at Branféré Zoological Park. a Vegetation, meadows (white), tall forest (vertical hatched), dense bushes (grey), watercourse (horizontal hatched), areas not available to the individuals (black). b Individuals encountered at beginning of
second day. Observations were undertaken in the two most important seasons of the same year (birth raising: 6 April– 31 August 2003; mating: 6 October 2003–31 January 2004). Each season was divided into three periods: birth season: pre-partum, from birth of each young to end of its third week (maximum care of young), and from the fourth to ninth week of age (declining phase of rearing); mating season: 6 October–15 November (males established territories), 18 November–19 December (maximum territorial behaviour, mating peak), and 1–31 January (end of mating). In each season, a survey of the whole area allowed us to locate the individuals in different habitats according to a grid of 30×30-m squares covering the entire area. The seasonal area used by each individual was also determined from all its locations. Home range overlaps were expressed as percentages of used areas. Since a matriarchal system is often at the base of social life in deer (Putman 1988), special attention was paid to interactions between five reproductive females and 43 partners of every sex and age, during five to eight continuous hours per day in birth season and in two daily sessions of 3 h each in the morning and afternoon in mating season. Each observation session started 1.5 months before the occurrence of the first corresponding event (birth or mating) and ended 1.5– 2.5 months after its maximum, that is, during three to five consecutive months each. This represented 333 h of observations in birth season (64–70 h/female) and 209 h in mating season (41–44 h/female). Individuals were observed by the focal sampling method (Altmann 1974). Focal individuals changed from day to day. Among the partners of these five focal females, the reproductive females were distinguished from non-reproductive ones, as were territorial males from non-territorial ones. Territorial males differed from non-territorial ones by their defence c) December
summer and; c end of autumn, none (white), less than the average number per square (diagonal hatched), from one to three times the average (grey), more than three times the average (black)
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of exclusive areas against other males in the mating season. Additional data were collected on young born to these focal females during the same seasons. Because the growth of young was very rapid (Dubost et al. 2008), the interactions between the mother and each young in birth season were studied at a shorter time scale than those between adults (e.g. from birth to 1 week, from 2 to 3 weeks, from 4 to 6 weeks and from 7 to 9 weeks) and always corresponded to an entire day of observation. Interactions between 12 males (seven territorial and five non-territorial) were also followed in both seasons in 2003 and in the mating season in 2004. All direct or short-distance interactions between individuals were considered in relation to their time, duration and the identity of the performer and receiver. In activity and at rest, individuals situated at less than 5 m from focal females were considered to be grouped with them, at more than 5 m of distance from other individuals the females were regarded as alone. This distance was arbitrarily determined from previous observations. Approaches and withdrawals were not retained. Likewise, odours, sounds and long-distance optical cues were omitted, since they were rarely indicative of relations existing between two given individuals. Counts were analysed with χ2, averages with the Student t test and correlations with the Pearson r coefficient. When samples were small and a normal distribution not assumed, the non-parametric Mann–Whitney U test was used for comparing two series and the correlations were made with the Spearman rank–order coefficient rs (Siegel and Castellan 1988).
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corresponded to a density of 7.0 individuals per hectare over the entire surface; however, density varied greatly among habitats, representing 11.7–12.5 individuals per hectare in the mixed zone vs only 2.4–4.2 in the meadows and 0.6–4.5 in the forest, depending on the season. The more an animal weighed, the larger the area it occupied regardless of age, sex or season: area (ha)=0.19 body mass1.14 (kg): rs11 =0.92, p
