Foraging ecology
Marine foraging and its effects on activity budgets in a wild-foraging troop of chacma baboons on the Cape Peninsula
Chacma baboons are found in a variety of habitats across southern Africa and are known to feed on a diverse array of plant- and animal foods. In most cases, baboon troops are restricted to foraging in terrestrial environments and thus consume only terrestrial plants and animals. The baboons of the Cape however, are unique, in that roughly half of the troops on the Peninsula occupy home ranges which include coastal land. These animals therefore have access to the marine intertidal zone and the plants and animals that are found there. Anecdotal reports suggest that Peninsula baboons spend a great deal of time at or near the coast and make extensive use of the marine food resources available to them.
Despite the novelty of marine foraging and its potential influence on the activity budgets and foraging behaviour of baboons, few studies investigating this behavioural phenomenon have been conducted. The few studies that have included marine foraging in their subject-matter have neither provided details on the frequency and duration of marine-foraging bouts nor investigated the possible factors which affect this behaviour.
The aims of this study are to investigate how a free-ranging Peninsula troop with unlimited access to the marine environment incorporates marine food items into their diet, and whether or not the addition of this high-quality food has affected other aspects of their behaviour. This research could therefore only be conducted on one of the Peninsula troops that is known to marine forage and has unlimited access to the marine intertidal zone. Furthermore, the study troop should ideally be a troop that does not consume human foods as this would undoubtedly have profound effects on the behaviour of the troop in question.
Study animals
There are currently only two troops on the Peninsula that do not consume any human foods, namely the Klein Olifantsbos troop and the Kanonkop troop. Both of these troops occupy home ranges in the Cape of Good Hope section of the Table Mountain National Park that allow them unlimited access to the marine intertidal zone. The Kanonkop troop was chosen as the study troop for this project as this troop had been partially habituated for previous research, and the locations of some of their sleeping sites were already known.
Fieldwork sessions
As marine intertidal organisms are periodically submerged, the amount of time during which the baboons are able to access marine organisms varies both on a daily- (with high and low tides), and monthly basis (through cycles of spring and neap tide). The troop will be followed through full lunar tidal cycles to determine whether the temporal variation in the availability of this high quality food resource impacts on its inclusion within the diet of a troop. In order to perform seasonal comparisons, data will be collected over four months (one month during each season) between June 2009 and March 2010.
Data collection
All data are collected while following the troop on foot, from sleeping site to sleeping site, on a daily basis during designated field seasons. Once a marine-foraging bout has begun (when the first individual starts feeding on marine organisms), the number of individuals marine-foraging is recorded every minute until the bout is finished (when the last individual stops feeding on marine organisms). A hand-held GPS unit is used to determine the geographical coordinates of the locations where the bout began and ended.
While following the troop, observers also collect faecal samples and food samples for stable isotope analyses. These samples are frozen until they can be processed back in the lab.
General behavioural data are collected by means of instantaneous scan samples, carried out every ten minutes starting on the hour. During each scan, all visible individuals are identified according to sex and age-class (where possible) and their activity state and current habitat type occupied are recorded. Scan data are recorded using Cybertracker software Cybertracker installed on Fujitsu-Siemens Pocket PCs. At the beginning of each scan, the geographical coordinates of the estimated centre of the troop are determined using a hand-held GPS unit.
Data analysis
The marine foraging scan data will be used to ascertain how much time the troop spends marine foraging, and how bout frequency and length vary through tidal cycles and seasons. Once this has been determined, possible links between environmental factors such as tide height, swell height, and wind direction, and frequency and length of marine foraging bouts will be investigated. Food- and faecal samples will be processed in the lab and then analysed using an isotope ratio mass spectrometer in order to determine the stable isotope ratios of these samples. These data will be used to determine whether or not the marine foods which the baboons consume present a clear signal in the baboonsÂ’ faeces. If this proves to be the case, then the stable isotope ratios will be used as complementary data in analyses of seasonal variation in marine foraging frequency. Analyses of general scan data will reveal how these baboons allocate time to different activities and, in conjunction with analyses of GPS data, also how they divide their time amongst different habitats. Further analyses of GPS data will be used to determine the ranging patterns of the troop.
Volunteer opportunities
Two of the four fieldwork sessions (June and September 2009) have already been completed, and volunteers have already been selected for the Summer fieldwork session (January 2009). There are however, openings for volunteers who wish to assist with data collection during March 2010. Volunteers must be able to cover the costs of transport to South Africa and board and lodging while in the country. If you have training and/or experience in field biology and/or primatology and are interested in working on the project please contact Matthew Lewis (matthew.lewis@uct.ac.za).
