Researcher: Henriette Cornelia PotgieterRegion: Namibia
BackgroundBiodiversity Transects in Africa (BIOTA) commissioned Dr. Rob Simmons to do bird surveys in Namibia from 2007-2010. He found that riverbeds across a rainfall gradient from the east (average annual rainfall 420 mm) to the dry west (128 mm) become increasingly important in sustaining both species richness and abundance in an arid environment.
He recommended that land managers and conservation managers conserve all dry river lines in arid Namibia. The dynamics of habitat mosaics and bird diversity will contribute to management recommendations, as will migration and spatial avoidance as key features of adaptation.
Climate change causes increasing temperatures and aridity in the southern African subregion, necessitating a greater understanding of conservation threats and ecosystem responses to them. This project will study behavioural adaptations of bird species that survive where water is scarce and unpredictable, yet water demands are high. Surface water is not available at the study sites. How do they survive in an environment where many similar species do not? The project will look in detail at how the birds utilise riparian vegetation: which parts of it they use most and for which purposes.
ObjectivesThis study aims to contribute to conservation management and policy decisions in Namibia by understanding why some bird species persist in very hot, arid environments where other, similar, species do not survive at all.
Namibia has established a number of river basin management forums and the study results will be valuable for basin management decision-making. This is further of value because of the pressure on water resources held in ephemeral river aquifers – a better understanding of the response of riverine ecosystems to environmental change will help determine risks due to water extraction.
It is necessary to understand which behavioural traits increase a bird species’ survival chances in an arid environment and to study in detail how populations are affected by changes in their habitat if conservation managers want to address birds’ vulnerability to habitat changes, whether those changes are anthropomorphic or due to climate change. Relevant habitats need to be conserved on suitable scales.
This project aims to establish a link between bird species and local climatic variables. For successful conservation interventions, it is imperative to know in detail how populations are affected by differences in stress management. The southern African subregion is already experiencing an increase in temperatures and more desiccation is predicted; it is therefore highly relevant to know how some species or populations have already adapted to the predicted changes in habitat.
MethodologyUsing the BIOTA rainfall gradient (an east-to-west drop in mean annual precipitation of 270 mm across 260 km), three river sites will be studied on the westernmost farm, Rooiklip, 142 km from Windhoek at 244 degrees and with a mean annual rainfall of 128 mm.
Two or three bird species that persist across the rainfall gradient and occur in the rivers of Rooiklip will be chosen for focal sampling. If practical, the three species should have similar food needs and different body sizes.
One other BIOTA farm may be chosen to repeat the surveys as comparison with a river in a wetter environment. Whether it is practical to survey two farms will be decided during pilot study in July.
Each follow is 5 – 10 minutes. Information for each follow: time, species, # individuals, distance from observer, height in vegetation, lateral position in vegetation, vegetation height, foliage and thorns, state of canopy, vegetation species, sun/shade, temperature at bird position. Every 30 seconds, the activity/behaviour of the bird will be noted with extensive comments.
Timing: One survey will take place in winter, and one in hot summer. Duration of each will be 26 days; longer if necessary. Observations are made in riverine vegetation. Data recorded on a Dictaphone, birds observed through binoculars. GPS points mark each site. Every day, data is transferred to a spreadsheet.
- Do they forage only until it gets too hot and at what temperature does that happen?
- Which species seek shade first?
- Which exhibit panting/wing drooping first?
- At which temperature do they show heat stress?
- Where do they seek shade – in tree or on ground?
- Arboreal species – do they choose thorn trees for protection or more shady trees to reduce heat stress?
- Is there a drop in foraging yield that corresponds with increasing temperature?
- Do open area birds enter the river as it gets hotter and if so, at what temperature?
- What do open area birds do once they are in the river – it is assumed that they use river vegetation for thermoregulation and also predator evasion?
- Which parts of riverine vegetation are utilised and for what purposes?
The results will be written up for an M.Sc. dissertation, to be published through Northwest University.