The nest and brood of the generalist African Pipit
The intense agricultural practices of developed countries are a major threat to birdlife, as is expanding agriculture in developing countries. But enhanced agricultural best practices can provide surrogate habitats for some bird species without compromising the economics of livestock farms. With best practice, farmlands can be rich in birds, and even support a diversity of species close to that of natural systems.
Grasslands are the world’s largest terrestrial ecosystem, covering 5.3 billion hectares, or 40% of the global land area. Two-thirds of grasslands are farmed, contributing to rangeland for domestic animals and livelihoods and food for billions of people. Grassland goods and services generate more than 90% of the world’s milk, 70% of the world’s mutton and 35% of the world’s beef. They also provide irreplaceable wildlife habitats and valuable ecosystem services, such as carbon storage and upstream water regulation for many major river systems.
Despite their uniform appearance, grasslands are one of South Africa’s most diverse ecosystems, supporting more than 3 300 plant species, 15 of the country’s 34 endemic mammals and 12 of the 40 endemic bird species, five of which are globally threatened. South Africa’s grasslands host five Ramsar wetland sites and comprise around 16.5% of the country’s land surface, but are one of the most threatened ecosystems, with more than 60% irreversibly transformed and only 2.8% formally protected (the Ramsar Convention is an international treaty for the sustainable use and conservation of wetlands, named after the city of Ramsar in Iran).
Moist highland grasslands in South Africa, of which only 1.5% are conserved, were historically maintained by winter and spring fires, probably at intervals of four years or more, and by summer grazing by migratory, medium-sized antelope. Today, these grasslands are managed by livestock farmers, who in most areas burn annually at the start of the rainy season, in early summer, coinciding with the onset of the breeding season for birds. The two major drivers of grassland disturbance — fire and grazing — have therefore been altered dramatically.
Research by the Percy Fitzpatrick Institute of African Ornithology at the University of Cape Town investigated how fire and grazing interact to influence communities of plants, invertebrates and ultimately, birds. The institute was identified as a Centre of Excellence in 2004 by the department of science and technology and the National Research Foundation.
The project’s scope included a nature reserve, various farming practices and communal lands that lack a managed fire regime. It was found that in terms of vegetation quality, burn frequency has an over-riding effect. Annual burning negatively impacts both plant species diversity and vegetation structure, and a combination of frequent fires and heavy grazing can result in a low, lawn-like sward.
Communal lands look much the same, even though fires are not managed, simply because grazing pressure is so high. Frequent burning also affects the diversity of invertebrates, with diversity being lowest in annually burned areas. However, in terms of food for birds, the pattern is somewhat different. Grasshoppers, which are the favoured food for many insectivorous birds, dominate the invertebrate fauna. They also respond positively to burning, and are most abundant at sites that have been burned in early summer, reaching peak abundance towards late summer.
The different responses of vegetation and invertebrates to management practices create a conundrum for birds. Food is most abundant in areas burned in the breeding season, yet the short grass sward provides little concealment for nests. These grasslands are rich in predators, with snakes being the main predators of eggs and chicks. If birds aggregate where food is abundant, then bird density may not mirror reproductive success, because predators easily locate nests in these sites. In other words, bird density may not provide an honest signal of bird performance.
Following up on more than 400 nests, we found that nest site selection and nest success are driven by vegetation structure, which itself is driven by management. For birds that build cup nests on the ground, nest success rates increase through the season, because predation rates fall as vegetation grows. Incorporating plant, insect and bird diversity data in analyses, we confirmed the importance of conserved areas for birds in moist highland grasslands. We showed unequivocally that current farm management practices have significant negative repercussions for bird abundance, species richness, nest density and fledgling output.
We further confirm that the increasingly popular use of “holistic” grazing practices in intact high altitude grassland systems can actually have a detrimental effect on grassland biodiversity. On the plus side, however, we found that some simple changes to management practices could translate into immediate biodiversity benefits without compromising the economics of livestock farms. If managers burn biennially or every three years in a patchwork, so that their farms contain grasslands of different “ages”, biodiversity benefits will be demonstrable and immediate.
Dr Rob Little works at the Percy Fitzpatrick Institute of African Ornithology at the University of Cape Town. Dr Ian Little is senior manager: habitats at the Endangered Wildlife Trust in South Africa