Makumba Group Interactions and Other Published Studies

(1) How were interactions and their levels distributed throughout the data collection period? (2) How did the Makumba group interactions that occurred in 2007 compare to published studies at other gorilla sites?

Multisite comparator responses were grouped into „aggressive and avoid‟ or tolerant behaviours based on descriptions in Table 4.2. Comparing interunit responses during interactions across

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sites and gorilla species must be done with caution, as the definitions used by different sites or researchers are not standardised, such that directly comparing results can lead to inaccurate conclusions. Typically, aggressive and avoidance responses are separated, although this technique can cause errors when comparing across sites. For example, in Karisoke distant communication involving chest-beats and hoots was defined as avoidance [Sicotte, 1993]

whereas in Lossi, avoidance was defined as „moving quietly away from a group or solitary male‟

[Bermejo, 2004]. Additionally, agonistic and avoidance responses are not always mutually exclusive [i.e. Parnell, 2002b]. In this study, Makumba exhibited both aggressive and avoidance behaviours during the same interaction 11 times. Aggressive and avoidance categories were therefore pooled together for the multisite comparison. A similar problem occurs with the tolerant category, with researchers at several sites defining tolerance as completely ignoring another gorilla unit‟s attempt to communicate [Bermejo, 2004; Cipolletta 2006; Doran-Sheehy et al., 2004; Magliocca & Gautier-Hion, 2004; Robbins & Sawyer, 2007] and others such as Lopé [Tutin, 1996], defining tolerance as displaying without movement out of the interaction area.

Parnell [2002b] further subdivided tolerance into „ignore‟, where no reaction was recorded, and

„tolerate‟, where individuals spent time in close proximity (within 30m) without displays and with or without affiliation. Some sites do not provide a detailed definition [Sicotte, 1993; Doran-Sheehy, 2004] simply stating behaviour as „mingling‟ or „tolerating‟ or „ignoring‟ without additional description. Standardisation issues are further compounded as observation hours, study sites (bai versus forest environments), habituation levels, number of study groups (many versus one focal group) and interaction independence ratings differ (Parnell, 2002b; Sicotte, 1993; Section 4.3.2).

The Makumba group data for the multisite comparison was based on the 44 interactions recorded during observation sessions in 2007. Ten of these interactions started in the early morning as evidenced by disrupted nesting patterns, ranging and as evidenced by Makumba‟s behaviour upon observer contact suggestive of an ongoing interaction. As it is possible that a critical response may have occurred before the researcher began recording on these days (i.e.

patrol or movement out of the area due to interaction), categories for this cross-site comparison were based on the 34 interactions where exact response patterns were known.

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Table 4.2 Definitions Used for the Makumba Group Interactions

Response Description

Aggressive & Avoid (a) Chest-Beating with/without Patrol, Contact, or Movement, or Silence with/without Patrol or Movement

(b) Chest-Beating with Patrol, Contact or Movement, or Silence with Patrol or Movement

Tolerant (a) Attempt to Communicate by Extragroup Males Completely Ignored by Makumba

(b) Chest-Beating without Movement or Patrol or Contact

4.3.7 Peak Interaction Month July and Silverback-Group Dynamics

This is a multi-tiered question that involved: (a) providing detailed insight into events surrounding the start of high level interactions which led to Etefi‟s (recently matured natal female) transfer out of, and then eight days later, back to the Makumba group; (b) determining the relative influence of fruit availability to the peak interaction period July; (c) determining the effects of peak interaction month July on the Makumba group‟s core and home range; (d) determining patterns of movement and resource use during the events surrounding Etefi‟s transfer period, and; (e) determining overlapping nesting patterns in relation to peak interaction period July, and during interaction events surrounding Etefi‟s transfer period.

These questions have been explored by providing a full narrative describing the progression of events directly from my field notes, and by showing nest patterning and daily group movement patterns from July 1st-July 17th (the period leading to the build up, transfer and eventual return of Etefi). Fruit abundance scores are detailed in Chapter 2. For information on nest site data collection see Chapter 2. In order to allow for comparative measurements of home range size, a 250m x 250m grid was superimposed on the map [Cipolletta, 2003]. Ranging data were split into two periods: January-July before and during peak interaction period; and August-December after peak interaction period, although high level interactions continued at decreased rates throughout the remaining five months of the study period. Core and home range areas were

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calculated according to Cipolletta‟s [2003] methods, modified from Watts [1998]. Home range was calculated as the sum of all 250m x 250m quadrants entered by the group, and core area was calculated as the sum of quadrants that, in descending order of entry number, cumulatively accounted for 75% of the group‟s total quadrant entries. Ranging data were available for 365 days in 2007. The Makumba group never slept at the same nest site twice during 2007. Nests were considered to be overlapping when they occurred within the same 166m x 166m quadrant.

As this also occurred infrequently, sample sizes were too small to run any statistical tests, although observations are discussed.

Autocorrelation of ranging data, a major statistical problem in attempting to relate range use to resources or the presence of other groups [De Knegt et al., 2010], was explored using nest site placement (N = 166). Since only one nest was constructed per day, the distance between successive nests indicates the potential for spatial constraints in ranging – measured on a continuous basis. Nest site placement within the mapped areas (Chapter 2, Figures 2.5 and 2.6) was compared with ranging data (Section 4.4.6, Figure 4.5). Although nest site placement followed an overall similar pattern to daily ranging, the gorillas never nested in the same place twice, and rarely nested in overlapping quadrats (Section 4.4.7). These results suggest that while ranging and nesting were obviously constrained by the possible distance that could be travelled between successive nests, they were not strictly dependent on each other in successive events. As such, I analysed continuous ranging on a daily basis in relation to interactions.