Data from: Drivers of bird species richness within moist high-altitude grasslands in eastern South Africa

Moist high-altitude grasslands in South Africa are renowned for high
avifaunal diversity and are priority areas for conservation. Conservation
management of these areas conflicts with management for other uses, such
as intensive livestock agriculture, which requires annual burning and
leads to heavy grazing. Recently the area has become target for water
storage schemes and renewable electricity energy projects. There is
therefore an urgent need to investigate environmental factors and habitat
factors that affect bird species richness in order to optimise management
of those areas set aside for conservation. A particularly good opportunity
to study these issues arose at Ingula in the eastern South African
high-altitude grasslands. An area that had been subject to intense grazing
was bought by the national power utility that constructed a pumped storage
scheme on part of the land and set aside the rest for bird conservation.
Since the new management took over in 2005 the area has been mostly
annually burned with relatively little grazing. The new management seeks
scientific advice on how to maintain avian species richness of the study
area. We collected bird occurrence and vegetation data along random
transects between 2006 and 2010 to monitor the impact of the new
management, and to study the effect of the habitat changes on bird species
richness. To achieve these, we convert bird transect data to presence only
data to investigate how bird species richness were related to key transect
vegetation attributes under this new grassland management. First we used
generalised linear mixed models, to examine changes in vegetation grass
height and cover and between burned and unburned habitats. Secondly, we
examined how total bird species richness varied across seasons and years.
And finally we investigated which habitat vegetation attributes were
correlated with species richness of a group of grassland depended bird
species only. Transects that were burned showed a larger decrease in
vegetation cover compared to transects that were not burned. Grass height
increased over time. Bird species richness was highest in summer compared
to other seasons and increased over time. Overall bird species richness
increased over the three summer surveys but species richness of birds that
prefer heavily grazed habitat showed little change over the three years.
Changes in bird species richness were best explained by the model with
grass height for combined species richness of grassland depended birds but
also for birds that prefer heavy grazing when treated alone. On one hand
birds that prefer moderate grazing were best explained by a null model.
However, overall bird species richness was better positively correlated to
grass height than grass cover or dead grass. We conclude that frequent
burning alone with relatively reduced grazing led to higher but less dense
grass, which benefited some species and disadvantaged others. We suggest
that management of this grassland use combination of fire and grazing and
leave some areas unburned to accommodates birds of various habitat needs.