Chimpanzees live in a community, i.e. a group of individuals (males, females and offsprings) sharing the same home range. However, in the same forest, there are usually several communities of chimpanzees and each of these communities have their own home ranges. Indeed, chimpanzees are highly territorial animals. Each adult individual seems to know the limit of their territory and the ones of the neighboring groups. Intruders found in a community home range can, sometimes, easily be killed by the residents. Therefore, members are often patrolling in the edge of their home range, looking for potential intruders. When patrolling, chimpanzees can look for different things: (1) Food and water: it is common that some feeding trees or others resources (water sources, clay piths, ...) are shared by several communities; (2) Boarding territory: the individuals check for they territory and how safe it is; (3) Increase their territory: they are looking to other communities to push them away (often through killings); (4) Mating: males can look in the edge of their territory for potential stranger female to mate. They can sometimes make “prisoners”, trying to bring a stranger female into their community. This was observed in both Budongo communities. At this time, males surrounded a female and spent the day with her. In Sonso, an adult male, Duane, came back after some months with three subadults females in estrus.

A chimpanzee community is led by an alpha male controlling all affairs of the community, as well as an alpha female for female related affairs. There are sexual differences in term of territoriality in chimpanzees. Indeed, males are philopatric, i.e. they are born and live for their entire life in the same community, while females migrate in another neighboring community. Migration is a natural strategy to avoid incest and consanguinity. However, in Budongo Forest, in both Sonso and Waibira communities, it is common to see native females staying in the community they are born in. Incest between daughters and males seems to be inexistent as no daughters have ever been observed to mate with their fathers (known after genetic analysis).

Males being philopatric, they are using their entire home range and protect it. This is their core-area. Males will use only a part of the territory when: (1) they are young, after the death of their mothers. Then, they will use their mothers’ territory; (2) they are following a specific female of their interest in her own territory. In this case, they disappear for several weeks. It is recurrent with some males, such as Musa in Sonso or Ben, the Waibira former alpha. They might visit these females for different reasons: (2a) avoiding mating competition with other males; (2b) look for their preferred female partner (even if she is not in estrus); (2c) consortship when they are in estrus; in these cases, they are sometimes looking for an area far away from the rest of the community, and not in the territory of the females, where other males can also find them. We also observed this often with specific dyads in Budongo forest with for example Kasongoire and Rachna, and Ben and Arua in Waibira, and Zalu and Eve, and Kato and Kewaya in Sonso.

Females, on the other hand, have their own small home ranges in the community territory (See Figure 1) where they stay with their offsprings. This means that we know where to look for them. There are different hypothesized reasons why females have their own territory: (1) Protection from the males: males are chaotic and are often aggressing the females. Therefore, by staying alone, females avoid aggression and risk of infanticide of newborns; (2) Food availability and feeding competition: often, females are joining a feeding patch when males are not around or when they left the area, especially if they are peripheral females, once again to avoid aggression and have a better access to resources; (3) “Peace of mind”: female stay outside of the community politics (aggression, competition, noise…).

Sometimes, females with strong bonding share the same home range or overlap with the territory of another female, especially around resources (rich food patch or water point). They are also often travelling and foraging together. For example, Anna, Flora and her daughter, Faith, stay together in South of Sonso territory. Gloria, Tanja and Otyo are usually often found together as well.

In term of spatial dispersion and territoriality, we observe core and peripheral females. This seems to be induced by female dominance: central females seem to be higher ranking individuals than peripheral ones. In addition, some home ranges are transmitted between mother and daughter in Sonso, i.e. when mothers are dying, their daughters are keeping the same territory. It was observed with Faith and Faida, who stayed in their mother’s territory after she passed away. Young offsprings always stay in the mother’s range until their sexual maturity (~9-14 years for males; ~12-15 years for females). Sons will then start to follow adult males and daughters will abandon the home range for some days if in estrus or forever, migrating to another community. However, it was already observed that some mothers don’t let their daughter migrate. For instance, during an intercommunity encounter between Sonso and Kamira communities, Rafia was observed trying to follow Kamira individuals but her mother, Ruhara, did not allow her to leave.

After migrating, new females don’t have a specific territory. Some of them will stay in the periphery of the territory because they have migrated from a neighboring community and seem to want to stay as far as possible from the boundaries with their native community. For instance, Kethy, Nora and Monica, three females native from Sonso and now Waibira residents are staying in the North of Waibira territory (at the opposite of Sonso edges). Other immigrants, before being accepted/integrated as residents in their new community, will use the entire community home range. In this period, they will find difficultly to be accepted and often be aggressed by some resident individuals, mainly because of reproductive competition. It has been observed for example, between Ramula and the new arrived Otyo in Sonso. With time, immigrants will bond with the resident individuals showing them some support during these aggressions. For instance, Oakland, a central female, adopted Nambi after her daughters migration. Nambi became a central female as well. This might have been a strategy from Oakland who decided to stick to Nambi, after realizing she was the alpha and can bring her some protection and privilege. On the other hand, it seems that immigrants coming from the same community/direction seem to bond with each other. This has been observed in Sonso with Anna, a new immigrant, who bonded with Melissa and Flora. Sometimes, some resident young females will try to migrate in a neighboring community, but unsuccessfully and they will come back to their native community. This happened with a young female from Waibira, Rachna who spent 2 months in Sonso before going back to Waibira to stay there. In another case, Sula, migrated from Waibira to other communities for short periods, but always came back. Interestingly, she was recently observed associating with a new migrant (still unnamed and known as SF1, Stranger Female 1). One can hypothesize that during their short stays in other communities, females associate with some other young females who may migrate to their community in the future. Then Sula and SF1 may bond because they have met in SF1’s community in the past.

Females are seen moving in the entire home range when sexually receptive (i.e., in estrus), as they are forced to move to look for potential mate. In these cases, females can even trespass the boundaries of the community territory, in the hope to find potential mate from a neighboring community. This is a risky behavior, as being sired by another community can result to infanticide by the males (and sometimes, the females) of their own community. In addition, as females are staying together for their “peace of mind”, perhaps, a female in estrus always leaves the territory to avoid attracting all males who can disturb other females with whom they share their home range.

Here, if we compare female territoriality in the two Budongo communities, we observed interesting differences (see Figure 1 above). Indeed, we can clearly see that females’ home ranges in Sonso are more clearly distinct than in Waibira, which are highly overlapping. We also observed more central females in Waibira (NOR, NEV, TIB, RIT, MON, SUL, KIP and TAT) than in Sonso (NB and KL). These differences can be explained by several hypotheses: (1) Habituation and research level: Waibira community was habituated more recently than Sonso individuals, where more projects focusing on females have been conducted. Therefore, females are still less habituated than in Sonso and this may impact our knowledge of their accurate distributions; (2) Territoriality surface: Sonso territory is smaller than Waibira one (respectively 7 km2 and 12 km2). This could explain why female territory in Waibira are larger; (3) Food availability: Sonso is showing a rich food availability all year round. At the opposite, Waibira chimpanzees are more dependent of some specific feeding species. Therefore, females may overlap more in Waibira because they are concentrating in specific rich food patch; (4) BCFS camp is situated right in the core area of Sonso territory, creating a gap zone. This may impact the centrality of females in Sonso, some females avoiding this zone. All in all, despite our current knowledge and the above-mentioned hypotheses, a concise conclusion cannot be taken. Therefore, further comparative investigation is needed to better understand territoriality in Budongo females.

Conclusion

In the present paper, we discussed territoriality in females and examined how sexual receptivity, social politics, and resources availability are impacting this territoriality. We also illustrated this territoriality in the two neighboring communities of the Budongo forest, Sonso and Waibira, and described the main differences and their potential explanations. Both communities’ core territories are well known and defined by specific grids (trails). However, in both communities, individuals are often travelling “off-grid” or even disappeared for some weeks without being found in their respective territories. In addition, by their spatial proximity, both territories are sometimes overlapping according to food-availability. This, combined with the fact that, as a fusion-fission species, chimpanzees are facing continuous territorial pressure lead by politics with other neighboring communities, make us realized that we are still far to being able to clearly define the edges of both communities’ territories.  Therefore, on-going research is still conducted and our statements in this paper need to be verified. Furthermore, the fact that these territories are larger than we know, makes understanding them even more important to conservation strategies.