**1. Introduction**

#### **1.1 Vegetation change and birds' distribution**

One of the most important concerns in conservation is the cause of change in species abundance and diversity in various vegetation types over time. Conservation relies in part on protecting species in legally fixed areas, but protection is jeopardized if species leave those areas and move into other areas where they are more vulnerable. For example, there is evidence of range shifts in Tanzanian birds [1].

There has been a recent expansion of geographical range in savanna birds such as the White-bellied Go-away-bird *Criniferoides leucogaster* and Taita Fiscal *Lanius dorsalis* (A. Nkwabi pers. obs.). These are dryland species previously confined to the drier north-east areas of the East African central plateau but have now

spread westwards into the much moister parts of the Serengeti National Park by crossing the birds' barrier of the eastern Rift Valley wall and the associated crater highlands [2, 3].

Another species that has shown changes in distribution is the Black-throated Barbet (*Tricholaema melanocephala*) whose center of distribution was the savanna surrounding the Wembere grasslands, south of the Maswa Game Reserve [4]. This species has spread north into Serengeti National Park in 2004 and up to date, such change in birds distribution resulted due to a change in density of its main vegetation such as *Vachellia tortilis* and *Vachellia robusta* woodland, which was low in the 1970s but had increased by the early 2000s (Prof. A. R. Sinclair pers. com.).

#### **1.2 What causes a change in bird species' geographical range?**

There are several possible causes for bird changes in geographical distribution and range. Natural vegetation succession, wildlife grazing, and human activities are all possible causes. Change in vegetation in the Serengeti National Park has been well documented [5–8]. Park vegetations have experienced major changes, alternating between open grassland and dense woodland. However, how these vegetation structure changes influence animal distribution, particularly birds is not well documented. Such influences are important for the conservation and management efforts of birds.

The structure of African vegetation is predominantly determined by rainfall, fire, nutrients, and grazing of herbivores [9, 10]. Bird distributions may be related to these differences in vegetation structure due to gradients of latitude, elevation, and isolation [11, 12]. Vegetation structure is known to have a major influence on the abundance and diversity of birds [11, 13–15] and this applies to the Serengeti National Park [16, 17]. Bird species diversity generally increases with increased foliage height, diversity, or increased woody vegetation [18]; vegetation species composition (or floristic) may also strongly affect bird communities [19]. Furthermore, individual bird species often demonstrate strong preferences for certain vegetation types, thus permitting vegetation parameters to describe bird habitats [20].

The diversity of bird species is a function of the diverse and complex vegetations of the Serengeti National Park in which the bird species respond to differences in the structural components of vegetation and availability of food [16, 21, 22]. Ecological studies have described the Serengeti National Park over the past 40 years and much is known about the impact of natural and human disturbances on large mammals [23]. The resource requirements of some species of birds in the Serengeti National Park have been documented [16, 22, 24, 25]. The impact of natural and human disturbances through small-scale agriculture and human habitation on birds has been reported by Estes [21], Sinclair et al. [26], and Nkwabi et al. [27] who examined the influence of disturbances, such as burning and grazing, on bird distribution within the Serengeti National Park.

Studying birds in the Serengeti National Park will open a room for birds-tourism activities and conserve vegetation dynamics. This chapter examines how differences in vegetation structure might influence the richness, abundance, and diversity of birds in the Serengeti National Park. It is firstly predicted that *V. tortilis* and *V. robusta* increase the abundance and diversity of bird species than *Commiphora* spp. Secondly, predicted that *Vachellia drepanolobium* and *Vachellia seyal* increase the abundance and diversity of birds than grassland areas. Thirdly, predicted that bird abundance and diversity decline with changing grass height from tall to short grass.
