Within-territory density varied between 0.31 and 9.80 jackals km−2 (mean±se=3.50 jackals km−2±0.80, N=15) and decreased further from the colony (F(1,13)=20.270, R2=0.568, P=0.001), (Fig. 6). Within-territory density did not equate to the inverse of territory size because the number of adults within a territory varied. On the Namibian coast, a Cape fur seal colony forms a clumped and abundant year-round food resource that promotes a commuter system among the resident black-backed jackal population. All jackals in this study travelled to the colony to feed. Outside the colony, jackals displayed behaviour

indicative of territoriality and, during the jackals’ denning period, dramatic within-population check details variation in social and spatial organization was observed, with territory and group size increasing and within-territory density declining further from the colony. Jackals commuted up to 20 km from their den/resting site to the fur seal colony to feed; a system consistent with theoretical studies that describe an optimal distribution of animals between different areas offering varying levels of profitability (Fretwell & Lucas, Gefitinib mw 1970). Jackals leave areas of low prey availability to forage at the fur seal colony because the benefits of such trips outweigh the costs (Höner et al., 2005). The costs to commuting jackals of aggressive physical contact with resident pairs may be low. Fighting

between resident pairs and commuters was not observed during the study and is thus expected to be rare, with commuters avoiding territory holders, active dens and utilizing networks of common routes. Vocalizations by residents may play a role in reducing the probability of encounters (Sillero-Zubiri & Macdonald, 1998) and enable commuters to adopt appropriate, submissive behaviours should contact with territory holders be unavoidable. The benefits of travelling to the colony to forage are high. Marine material provides a protein and energy-rich food Ribonucleotide reductase resource (Rose & Polis, 1998) and jackals can consume large

quantities with minimal disturbance. Consequently, energetic returns may outweigh costs in energy expended by jackals living up to 20 km away. It is important to highlight, however, that the population at CCSR is not isolated. Jackals move up and down the coast and we have evidence, in the form of fur seal hair and teeth in jackal faecal deposits, that jackals over 30 km inland forage at the fur seal colony. As prey availability becomes increasingly scarce, one would expect that with increasing distance in any direction from the colony a point would be reached when commuting becomes unprofitable. Further research along this coastal, and coastal-inland gradient is required to identify optimal and maximum distances at which jackals sustain commuting behaviour. Previous studies have suggested that territoriality breaks down in the CCSR jackal population (Hiscocks & Perrin, 1988).