Experimental shifting from harem defence to territoriality in rutting red deer

Female defence (harems) is the usual strategy for red deer stags, Cervus elaphus, in most populations (Lincoln & Guinness 1973; Clutton-Brock et al. 1982) but in some areas in Spain harem defence co-exists with the defence of mating territories (Doñana National Park: Carranza et al. 1990; Carranza 1992). A possible explanation for why territoriality has so far been observed only in Mediterranean areas of southern Iberia is that in those ecosystems resources are exceptionally scarce and patchily distributed at the end of the extremely hot summer, when the rut takes place. Those areas in southern Iberia where resources are scarce during the rut but are not clumped in particular patches provide an opportunity to test whether an experimental concentration of resources would produce a shift from female to resource defence. To test this point, we chose an area where the common strategy of red deer stags was harem defence and experimentally provided food at particular points. This produced a concentration of females and induced males to shift from the defence of harems to the establishment of small territories. Our study area was covered by Mediterranean forest (genera Quercus, Pinus, etc.), scrub (Cistus, Erica, Pistacia, Arbutus) and meadows, and located in the Cijara Game Preserve (Badajoz, Spain). We observed simultaneously two areas (A and B) of about 15 ha each, during the last 3 h before dusk (typically between 1530 and 1830 hours GMT, the period of maximum daylight activity; see Carranza et al. 1991), during the rutting periods of 1990 and 1991. The rutting season in this area typically lasts about 30 days, from late September to late October. In each area, two observers in a hide made (1) scan-sampling records (Martin & Bateson 1986) at 1-min intervals of the spatial positions of all individuals (males and females), plotting them on a 1:2000 map, and (2) continuous focal-group (Altmann 1974) observations on interactions involving adult males either with other males or with females, again plotting them on a map. We used the instantaneous distribution of females at 1800 hours (estimated peak of activity) every day to calculate the distribution and density of females. Adult males were individually recognized by the shape and branching pattern of their antlers. The behaviour of males defending a territory instead of a mobile harem has been explained elsewhere (Carranza et al. 1990). We considered the rutting area of a given male as the minimum convex polygon including 90% of his locations during the rutting period. The territory (defended area, typically fully included within the rutting-area polygon) was determined by connecting the outer points where defensive activities were recorded (see Carranza et al. 1990). The number of females (harem size) held by a male per day was added up for all the days on which the male held females during the rut. This total number of females was then used as a measure of the male’s success in gathering females. In both areas, the rut of 1990 was a control, and in 1991 we experimentally delivered food (alfalfa) from the beginning of the rut at three points every day (one pack of about 30 kg per point per day), at about 1500 hours, before the main afternoon activity of the animals. During the rut of 1990 all males defended mobile harems in area A. Apart from sporadic visitors (less than 3 days stay), the area was used by six harem-holding males. The mean rutting area used by these males was 0·96 ha (&0·74 ). The males stayed between 4 and 14 days in the area (average 7), and none of them was observed defending any territorial boundaries. In 1991, the distribution of females was clumped around the feeding points, and seven males used rutting areas of 0·19 ha on average (&0·09 ), and actively defended small territories (500–5000 m). The effect of food was extremely rapid. On the first day that the food was provided, females spent most of the time feeding at the food points, two adult