**2.6 Grass height measurement and grass cover estimates**

The grass layer included both grasses and forbs, but as the grass was usually the dominant group, the term "grass" was used in the following analysis and the data from grasses and forbs were pooled. Measurements of grass height were obtained

#### *Vegetation and Avifauna Distribution in the Serengeti National Park DOI: http://dx.doi.org/10.5772/intechopen.106165*

in all habitats where birds were counted. At each of the plots, grass height and grass cover were estimated. A small hole was made at the center of the plastic plate of 37 cm diameter and inserted in a 1 m ruler, which was placed vertically in the grass, and detailed explanations of the method on how to prepare and use a plastic plate were well explained by McNaughton [35]. The plastic plate rested on the surface of the grass, and its position on the meter ruler was recorded as the standardized grass height [35]. Three height measurements were made and the average was used for each plot, only three points were selected in each plot due to the large area coverage in the Serengeti National Park and surrounding areas. Grass cover was estimated by direct observation and recorded as a percentage cover. Measurements were taken during dry and wet seasons from February 2010 to April 2012.

#### **2.7 Data analysis**

Birds were classified according to feeding guild (insectivores, granivores, omnivores, and frugivores) and foraging guild (ground vs. tree canopy feeding) [36, 37]. Bird species that spent time on ground foraging were grouped as ground feeding and those that spent time on trees searching for food were termed as tree feeding [36, 37]. All ground, aerial, water, and tree canopy feeding birds were recorded, but the analysis concentrated on ground- and tree-feeding birds because the study concentrated on habitat structure in the terrestrial environment. All bird species that fed on insects, seeds, and fruits, and foraged either on the ground or in the grass layer were classified as ground-feeding birds; and all species that foraged in bushes, shrubs, and tree canopy were classified as tree-feeding birds [38, 39]. Ground-feeding birds were also sorted based on the grass height they were associated with.
