Factors Affecting Group Size and Vigilance Behaviour of Maasai Giraffe (Giraffa camelopardalis tippelskirchi) on the Serengeti-Ngorongoro Ecosystem, Tanzania

Eivin Røskaft,Tomas Holmern,Wilfred N Marealle

doi:10.37284/eajenr.2.1.133

Abstract

This study investigated the factors affecting different group sizes of Maasai giraffe (Giraffa camelopardalis tippelskirchi) in the Serengeti-Ngorongoro ecosystem. The study was motivated to test the following hypotheses: 1) in a given group, the sex ratio of males to females with calves is related to group size; 2) group size affects vigilance behaviour; 3) illegal hunting influences group size and vigilance behaviour; and 4) group size differs in different habitats, being larger in woodlands during the wet season and in riverine habitats during the dry season. A negative relationship between the ratio of the proportion of adult males to females with calves and group size was observed, whereas the proportion of females and calves increased with group size. The proportion of vigilant individuals decreased with an increase in group size. Habitat, risk of illegal hunting and proportion of calves in the group was found to be significant contributors to an increase in vigilance behaviour. However, the results do not support the hypotheses that seasonality and habitat preference affect group sizes of the Maasai giraffes. Emphasis should be put on anti-poaching efforts on males and nursery groups, especially in areas with a high risk of illegal activities.

Highlights

This study investigated the factors affecting different group sizes of Maasai giraffe (Giraffa camelopardalis tippelskirchi) in the Serengeti-Ngorongoro ecosystem
Living in groups is a common phenomenon in many animal species; some herbivores form herds, some fish species form schools, many birds live in colonies and some animals live in large, extended family groups (Krebs, 2009)
The Serengeti contains a range of vegetation types where the northern sections are characterised by rolling, wooded savannah; south-eastern parts features almost treeless plains; the western corridor is a wooded region mostly covered by the savannah woodland, while further to the east, the terrain rises steeply to massif highlands and forested areas (Kideghesho et al, 2006; Magige, 2008)

Summary

Introduction

Living in groups is a common phenomenon in many animal species; some herbivores form herds, some fish species form schools, many birds live in colonies and some animals live in large, extended family groups (Krebs, 2009). How a species comes to live in groups and group size is formed depends upon the evolutionary advantages associated with living in groups. This includes but not limited to having many eyes or collective detection. Mating and reproductive success are frequently considered to be higher in animals living in groups as found in the ‘‘lek’’ system in Ugandan kob (Kobus kob thomasi), Kafue lechwe (Kobus leche kafuensis), and Topi (Damaliscus korrigum). This allows for mate choice for ‘‘good genes’’ by females (Buechner & Roth, 1974; Nefdt & Thirgood, 1997; Bro-Jorgensen & Durant, 2003)

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