Variation of group size among African buffalo herds in a forest‐savanna mosaic landscape

Abstract

Documenting within species group size variation is important to completely understand social organization within species and to interpret variation among species. Here, I investigated group size of African buffalo Syncerus caffer over 2 years in a heterogeneous landscape. African buffalo use closed continuous forest and vast open savannas, and anecdotal observations suggest that habitat type influences their social structure. While the Cape buffalo Syncerus caffer caffer is well studied, few data exist for the forest-dwelling Syncerus caffer nanus. I observed forest buffalo at Lope´National Park, Gabon, and examined variation of group size. Eighteen forest buffalo herds used the study area with an estimated population of 342 individuals ($5 buffalo km À2 ). The mean group size for the 18 herds was 12 AE 2 (range of means= 3-24), considerably smaller than Cape buffalo herds. For eight radiocollared forest buffalo, the mean group size was stable, varying little with time of day, across seasons, or between savanna and marsh habitat. However, herd size varied widely across herds, from fewer than 10 individuals in the smallest herds to more than 20 buffalo in the largest. Large herd size is associated with home ranges that contain substantial areas of open habitat, and thus more food resources than forested habitats.

Spatial properties of a forest buffalo herd and individual positioning as a response to environmental cues and social behaviour

“…Sexual segregation has also been observed in other ungulates (e.g., bighorn sheep; Ruckstuhl 1998;Ruckstuhl and Neuhaus 2000;Ruckstuhl and Kokko 2002). On the contrary, as evidenced in previous studies (Melletti et al 2007a, b;Korte 2008bKorte , 2009 forest buffalo herds live in quite stable groups and members are mainly permanent part of it. In this 2 years study the male was always observed inside the herd.…”

“…Studies of various species have shown that under conditions of increasing predation risk, animals form larger and denser groups (Spieler 2003;Hoare et al 2004). Korte (2008b) found unusually high number of observations of old buffaloes and this suggests probably low predation pressure on adult while food resources probably influenced group size more than predation. Moreover, there is some evidence that feeding competition can simultaneously have a dilution effect, increasing the overall distance among individuals within a group to decrease foraging interference (Wrona and Jamienson 1991;Parrish and Hamner 1997;Krause and Ruxton 2002).…”

“…Magurran 1993;Parrish and Hamner 1997;Ruckstuhl 1998;Krause and Ruxton 2002;Ruckstuhl and Kokko 2002;Turner et al 2005;Hay et al 2008;Korte 2008b;Morrell and Romey 2008). These factors include feeding and foraging efficiency, energy expenditure, the time spent on vigilance behaviour, predation risk, group size, sexual segregation and reproductive opportunities.…”

“…Exogenous factors, such as the presence of predators (Hamilton 1971;Beecham and Farnsworth 1999;Krause and Ruxton 2002;Hoare et al 2004;Ioannou et al 2007;Ioannou and Krause 2008) or various conditions (e.g., time of day, season, temperature, the probability of food acquisition, synchronizing activity budgets: Perry 1995a; Parrish and Hamner 1997;Ruckstuhl 1999;Chesson 2000;Gerard et al 2002;Korte 2008b) are common mechanisms that can trigger animal aggregation, increase group size and cohesion and decrease attack success. In several species (e.g.…”

Spatial and temporal changes in group dynamics and range use enable anti‐predator responses in African buffalo

“…Similarly, in the lowland forests of Congo and the mixed forest-savanna of Gabon, both areas expected to be predator free (Bauer et al 2003), buffalo herds average fewer than 50 individuals (Sinclair 1977, Korte 2008. The majority of the abovementioned populations were estimated to be a similar size to the current population in Main Camp, so population size effects cannot explain the differences observed currently …”