Southern African Bird Atlas Project Research Articles

Bird atlas in action: using citizen science data to generate population trend alerts in Hessequa, South Africa

Citizen science data are rapidly transforming the conservation landscape. Targeted participatory citizen science initiatives generate nuanced data capable of monitoring trends in populations and generating early warnings for species and habitats experiencing significant declines. In the Hessequa Atlasing Area, Western Cape, South Africa, citizen science 'atlasers' involved with the Second Southern African Bird Atlas Project (SABAP2) have worked with scientific leadership since 2014 to improve the quality of bird atlas data in their region for species monitoring. In this study, we used reporting rates from SABAP2 checklists in the Hessequa Atlasing Area to calculate changes in range size and relative abundance for the 165 most commonly reported species in the region. We used a seven-tier alert system and broad habitat categories to sort species by priority for conservation action. Our results showed that wetland and marine associated species are experiencing the greatest declines in range and relative abundance in the Hessequa Atlasing Area, whilst urban and grassland associated species are largely increasing. We discuss how observed changes in populations may be used to guide conservation action and provide recommendations for scientists and non-scientific community members on engaging with and responding to the changes highlighted in each of the seven alert levels provided.

Is climate change causing the range contraction of Cape Rock‐jumpers (Chaetops frenatus)?

AbstractSpecies distribution models often suggest strong links between climate and species' distribution boundaries and project large distribution shifts in response to climate change. However, attributing distribution shifts to climate change requires more than correlative models. One idea is to examine correlates of the processes that cause distribution shifts, namely colonization and local extinction, by using dynamic occupancy models. The Cape Rock‐jumper (Chaetops frenatus) has disappeared over most of its distribution where temperatures are the highest. We used dynamic occupancy models to analyse Cape Rock‐jumper distribution with respect to climate (mean temperature and precipitation over the warmest annual quarter), vegetation (proportion of natural vegetation, fynbos) and land‐use type (protected areas). Detection/non‐detection data were collected over two phases of the Southern African Bird Atlas Project (SABAP): 1987–1991 (SABAP1) and 2008–2014 (SABAP2). The model described the contraction of the Cape Rock‐jumper's distribution between SABAP1 and SABAP2 well. Occupancy probability during SABAP1 increased with the proportion of fynbos and protected area per grid cell, and decreased with increases in mean temperature and precipitation over the warmest annual quarter. Mean extinction probability increased with mean temperature and precipitation over the warmest annual quarter, although the associated confidence intervals were wide. Nonetheless, our results showed a clear correlation between climate and the distribution boundaries of the Cape Rock‐jumper, and in particular, the species' aversion for higher temperatures. The data were less conclusive on whether the observed range contraction was linked to climate change or not. Examining the processes underlying distribution shifts requires large datasets and should lead to a better understanding of the drivers of these shifts.

Long-term trends from Citizen Scientists: 24 years of breeding success data of African Oystercatchers Haematopus moquini in the Garden Route

Long-term data on breeding success in beach-nesting birds in southern Africa are scarce. Citizen science projects have risen to the forefront of large dataset collection efforts globally, with several local projects helping us unpack long-term trends for species in southern Africa. A long-term monitoring project on African Oystercatcher Haematopus moquini breeding success in parts of the Garden Route on the south coast, conducted by the Lakes Bird Club, enables us to determine whether conservation efforts are positively influencing the species there. Since the onset of the study in 1997/1998, there has been a steady increase in the number of breeding pairs at Knysna and Sedgefield, but not at Brenton-on-Sea. A similar increase in hatching success is recorded, with an overall increase in the number of fledglings per adult pair over the area throughout the study. Collectively, this indicates that some local and national conservation efforts, such as the beach driving ban and awareness campaigns like #ShareTheShores, have been successful, leading to positive trends in these parameters for this species. This article highlights the usefulness of long-term datasets for corroborating outcomes from other large datasets, like the Southern African Bird Atlas Project 2.

Temporal Dimensions of Data Quality in Bird Atlases: the Case of the Second Southern African Bird Atlas Project

Temporal Dimensions of Data Quality in Bird Atlases: the Case of the Second Southern African Bird Atlas Project

Human infrastructure, surface water and tree cover are important drivers of bird diversity across a savanna protected area-mosaic landscape

ContextProtected areas are important in mitigating threats to biodiversity, including land conversion. Some of the largest protected areas are located in biodiverse savanna systems where a mosaic of land-uses exist beyond their borders. The protected areas located in such systems are often host to threatened species and diverse animal communities. In spite of the ecosystem services birds provide, we do not know how functionally and evolutionary diverse the community is in north-eastern South Africa, or what the drivers of such diversity are inside and outside one of the world’s largest savanna protected areas: Kruger National Park (KNP).ObjectivesFirstly, we aimed to investigate how bird species richness, functional richness, phylogenetic and beta diversity (including its components), and rarity differed across the KNP protected area and its adjacent mosaic. Secondly, we aimed to investigate the habitats and proximity to the KNP boundary that drove patterns across three biodiversity metrics. We also investigated whether differences in sample sizes of the citizen science data we employed, impacted results in a significant manner.MethodsTo investigate our aims, we used bird species records from the Southern African Bird Atlas Project 2 (a citizen science project that collects data at a 5 min latitude by 5 min longitude resolution), and for elucidating drivers of community composition, we used a finer scale remotely sensed product.ResultsHuman infrastructure, water sources and tree cover were overall the most significant and strongest drivers of bird diversity in the region; however, the patterns were complex. Specifically, we found that species richness was strongly and positively influenced by seasonal water and infrastructure mostly inside the protected area (KNP). Most significantly and somewhat concerning, though, were the strong negative effects that infrastructure had on bird functional and phylogenetic diversity inside KNP and, to a lesser extent, inside the mosaic. Seasonal water had a similarly strong but positive effect on species richness in the protected area, a random sub-sample of the former and the mosaic. Tree cover also had a negative and significant effect across the region on phylogenetic diversity and was the strongest driver of this diversity metric.ConclusionsOur results displayed the significant but negative influence that relatively little infrastructure had on bird functional- and phylogenetic diversity inside the KNP protected area despite its positive effect on species richness. Water sources across the protected area-mosaic landscapes also significantly affected regional savanna bird community richness. An increase in tree cover negatively affected phylogenetic diversity inside and outside the protected area as well as the mosaic: a similar finding to other studies in South African savanna systems. We showed the importance of habitat heterogeneity, specifically its components such as infrastructure, freshwater systems and tree cover, and how these impact independently and differently on bird communities across a large biogeographical savanna region.

A utilization distribution for the global population of Cape Vultures (Gyps coprotheres) to guide wind energy development.

The rapid development of wind energy in southern Africa represents an additional threat to the already fragile populations of African vultures. The distribution of the vulnerable Cape Vulture Gyps coprotheres overlaps considerably with wind energy development areas in South Africa, creating conflicts that can hinder both vulture conservation and sustainable energy development. To help address this conflict and aid in the safe placement of wind energy facilities, we map the utilization distribution (UD) of this species across its distributional range. Using tracking data from 68 Cape Vultures collected over the last 20 years, we develop a spatially explicit habitat use model to estimate the expected UDs around known colonies. Scaling the UDs by the number of vultures expected to use each of the colonies, we estimate the Cape Vulture population utilization distribution (PUD) and determine its exposure to wind farm impacts. To complement our results, we model the probability of a vulture flying within the rotor sweep area of a wind turbine throughout the species range and use this to identify areas that are particularly prone to collisions. Overall, our estimated PUD correlates well with reporting rates of the species from the Southern African Bird Atlas Project, currently used to assess potential overlap between Cape Vultures and wind energy developments, but it adds important benefits, such as providing a spatial gradient of activity estimates over the entire species range. We illustrate the application of our maps by analyzing the exposure of Cape Vultures in the Renewable Energy Development Zones (REDZs) in South Africa. This application is a scalable procedure that can be applied at different planning phases, from strategic, nationwide planning to project-level assessments.

A review of the conservation status of Black Stork Ciconia nigra in South Africa, Lesotho, and Eswatini

Summary Across South Africa, Lesotho, and Eswatini, long-term citizen science atlas data have suggested concerning declines in the population of Black Stork Ciconia nigra. Unlike the Asian and European populations, the southern African Black Stork population is described as resident and is listed as “Vulnerable” in South Africa, Lesotho, and Eswatini. Here we report on surveys of historical nesting locations across northern South Africa, finding evidence for nest site abandonment and limited evidence of recent breeding. We undertook detailed species distribution modelling within a maximum entropy framework, using occurrence records from the BirdLasser mobile app. We cross-validated the models against information in the Southern African Bird Atlas Project (SABAP2) database, highlighting Lesotho as an important potential breeding area. Additionally, we used SABAP2 to assess population trends by investigating interannual patterns in reporting rate. Comparing current reporting rates with those from SABAP1 (1987–1992), we found that there has been a dramatic decrease. We noted that a large proportion of the population occurs outside the breeding range during the breeding season, suggesting a considerable non-breeding population, especially in the extensive wildlife refuge of the Kruger National Park. The slow declines observed might be indicative of a population which is not losing many adults but is failing to recruit significant numbers of juveniles due to limited breeding. Using densities derived from transect surveys, we used predictive models to derive estimates of breeding range carrying capacity and a population estimate, which suggested declines to numbers around 600 for this subregion. Minimising disturbance at breeding sites of this cliff-nesting species and improving water quality at key population strongholds are pathways to improving the status of the species in the subregion.

A comparison of migrant and resident bird population changes in South Africa using citizen science data: trends in relation to Northern Hemisphere distribution

Many species of migratory birds have been declining on the Palearctic-African flyways in recent decades due to human population pressure and land-use intensification. Models predict that the declining trends of migratory birds will continue into the foreseeable future across much of Africa, likely exacerbated by climate change. While sub-Saharan Africa is viewed as less important for these migrants than the Sahel, the region still receives many migrant species. We use the citizen science Southern African Bird Atlas Project data sets (SABAP1 and SABAP2) to determine relative change between atlas periods (1987–1991; 2007–2021). Firstly, we validate our metrics of population change on a dataset of 581 species that occur frequently in South Africa, Lesotho and Eswatini by examining change in relation to migratory status (Palearctic, Intra-Africa or Resident) and other species’ traits. We found greatest declines in migrants but with magnitudes not as great as expected, with largest relative decreases for Palearctic migrants, and little difference between Intra-Africa migrants and residents. Declines were best described by size independent of migratory status, even when controlling for phylogeny. For the set of Palearctic migrants, we then examine if change is related to Northern Hemisphere distribution. We found greater decreases for birds with breeding grounds in southern Asia (India and south-eastern Asia) relative to Europe. These results are useful for conservation agencies wishing to extend ties to relevant researchers and conservationists in these regions, and highlights potential challenge areas for this set of birds on their breeding grounds.

Bucking the trend: the African Black Oystercatcher as a recent conservation success story

The African Black Oystercatcher Haematopus moquini is a charismatic, southern African near-endemic, wader species, that is often seen as a flagship species for coastal bird conservation, as it was recently down-listed regionally to Least Concern on the IUCN Red List of Threatened Species. To celebrate this rare conservation success story, BirdLife South Africa named it the 2018 Bird of the Year and ran a year-long programme in collaboration with the Nature’s Valley Trust highlighting aspects of the species’ biology, current threats, and conservation success. We used data collected by the Southern African Bird Atlas Project (SABAP1 and SABAP2) to examine changes in the species’ range and relative abundance, both in the records between the two projects, as well as trends within the SABAP2 sampling period (2008–2017). This case study enabled us to assess whether such metrics can accurately reflect abundance and distributional changes in a species. We found increases in the reported range and the reporting rates between the two Atlas projects, and that the SABAP2 reporting rate was stable. Regionally, across four coastal categories, the reporting rate was lowest in KwaZulu-Natal, though this region also showed an increase in the probability of reporting during the SABAP2 period. While corroborating the recent change in the species’ conservation status, we also provide good evidence that the long-term SABAP data can be used successfully to assess population trends and range changes over time.

Invasion of Psittacula krameri in Gauteng, South Africa: are other birds impacted?

Anthropogenic activities have resulted in the dispersal of many species beyond their natural range and there is ongoing concern over their impacts on native ecosystems. However, these interactions are hard to disentangle from the effect of human-driven habitat alterations. Psittacula krameri (Rose-ringed Parakeet) is a recent coloniser in the heavily modified province of Gauteng, South Africa. We analysed this species across the region to assess its colonising status and potential impact to-date. Using presence data from the Second Southern African Bird Atlas Project (SABAP2) for the parakeet as well as a selected subgroup of 49 other bird species (potential competitor and control species), occurrence patterns in the province for the period of July 2007–June 2017 were determined. Reporting rates for species in SABAP2 were used as a proxy for relative abundance. While the parakeet’s range and abundance increased significantly, only two species showed a significant reporting rate decline in areas of parakeet occurrence. These declines persisted across a wider area where parakeets were not found. Broader-scale Gauteng reporting rate trends, not replicated in the parakeet range, were noted for nine other species, suggesting that the changing avifaunal composition in the anthropogenically transformed Gauteng may instead be driven by habitat change. A large proportion of species can be considered as newcomers to this largely modified ecosystem, and the possibility of vacant niche filling is strong in this case. In the context of novel ecosystems such as urban areas, a terminology based on adaptability rather than nativity status is encouraged.

Implications of geographical range changes and resultant sympatry for three Accipiter hawks on the Cape Peninsula, South Africa

Some invasive species are known to compete with and even displace indigenous species. Two Accipiter species historically indigenous to eastern South Africa have colonised the Cape Peninsula in the south-west of the country and have become sympatric with a third local Accipiter species. We investigated the changes in the occurrence reporting rates of all three species on the Cape Peninsula between 1982 and 2018 using data from the Atlas of the Birds of the Southwestern Cape and from the two data collection periods of the Southern African Bird Atlas Project (SABAP1 and 2). We found that the Black Sparrowhawk Accipiter melanoleucus has become more abundant and that the African Goshawk A. tachiro and the historically local Rufous-breasted Sparrowhawk A. rufiventris have declined since the invasion of the Cape Peninsula by Black Sparrowhawks, suggesting that the latter species has outcompeted and at least partially displaced the other two species. Although that may be the case, since the three species seem to have relatively stabilised population sizes after 2010 this could suggest progressive resource partitioning with a level of ecological isolation following the initial dominance interactions. Since the westward expansion of the ranges of the Black Sparrowhawk and the African Goshawk along the southern coastal region of South Africa were most likely facilitated by anthropogenic alteration of the landscape ultimately leading to the sympatry of the three species on the Cape Peninsula, we suggest that this is therefore a case of indirect human-caused alien invasion.

Bird Distribution Dynamics - African black oystercatcher in South Africa

This is another paper on bird distribution dynamics in Biodiversity Observations. The objective of this series of papers is to report on the ranges of bird species as revealed by the Second Southern African Bird Atlas Project (SABAP2, 2007 onwards) and to describe how their ranges have changed since the first bird atlas (SABAP1, mainly 1987 /- 1991), about two decades apart. The African Black Oystercatcher Haemetopus moquini is neither considered a Red-listed species globally nor regionally however, this endemic and iconic bird was expected to decline due to a variety of anthropogenic and natural influences hence, it received much attention from the scientific community. SABAP data supported the findings of some previous projects that looked at both oytsercacther distribution, dispersion and feeding ecology along South Africa's (SA) coastline as well as that of the alien Mediterranean Mussel Mytilus galloprovincialis. Possible reasons for a relatively recent and northern presence along the SA coastline could be due to southern populations experiencing food shortages during the breeding season that result in seasonal dispersion or carrying capacity on the mainland has been reached. Inside the /oystercatcher's breeding range, the alien mussel serves as an additional food source that probably explains the largest SABAP2 reporting rates along the southern regions of the coastline as this area coincides with the /mussel's distribution range.

Efficient Bayesian analysis of occupancy models with logit link functions.

Occupancy models (Ecology, 2002; 83: 2248) were developed to infer the probability that a species under investigation occupies a site. Bayesian analysis of these models can be undertaken using statistical packages such as WinBUGS, OpenBUGS, JAGS, and more recently Stan, however, since these packages were not developed specifically to fit occupancy models, one often experiences long run times when undertaking an analysis. Bayesian spatial single‐season occupancy models can also be fit using the R package stocc. The approach assumes that the detection and occupancy regression effects are modeled using probit link functions. The use of the logistic link function, however, is algebraically more tractable and allows one to easily interpret the coefficient effects of an estimated model by using odds ratios, which is not easily done for a probit link function for models that do not include spatial random effects. We develop a Gibbs sampler to obtain posterior samples from the posterior distribution of the parameters of various occupancy models (nonspatial and spatial) when logit link functions are used to model the regression effects of the detection and occupancy processes. We apply our methods to data extracted from the 2nd Southern African Bird Atlas Project to produce a species distribution map of the Cape weaver (Ploceus capensis) and helmeted guineafowl (Numida meleagris) for South Africa. We found that the Gibbs sampling algorithm developed produces posterior samples that are identical to those obtained when using JAGS and Stan and that in certain cases the posterior chains mix much faster than those obtained when using JAGS, stocc, and Stan. Our algorithms are implemented in the R package, Rcppocc. The software is freely available and stored on GitHub (https://github.com/AllanClark/Rcppocc).

Modelling bird atlas reporting rate as a function of density in the southern Karoo, South Africa

The relationship between true population density and abundance indices derived from atlas data can be used to estimate population size, a metric that is vital for assessing the conservation status of animal species. However, this relationship remains understudied. Meanwhile, there is growing concern for the avifauna of South Africa's arid southern Karoo region, which is threatened with an increasing frequency of heat waves as well as the expansion of infrastructure in association with uranium mining, renewable energy production and shale gas extraction. We calculated density (individuals km−2) for 49 bird species using data from a standardised distance-sampling survey conducted across 64 pentads (sampling areas of approximately 81 km2) in the southern Karoo region. Reporting rates from the Southern African Bird Atlas Project (SABAP) were explained by individual density for 32 of the 49 species using logistic regression models, and for 37 species using group (cluster) densities. Within this set of species, there was a positive correlation between mean reporting rate and log-transformed mean density in a linear model that included log-transformed mass as a covariate. For seven species with a high uncertainty associated with their density estimates (high relative standard error), we found that we could use our model to produce intuitively reasonable density estimates based on their SABAP2 reporting rates. This relationship suggests that where density estimate–reporting rate relationships for communities are known, they are useful for cross-checking density estimates. We illustrate the utility of this relationship by calculating population estimates for a set of species, and discuss the importance of SABAP2 for conservation purposes in the Karoo.

Common Starling Sturnus vulgaris expansion in South Africa

The Common Starling Sturnus vulgaris has progressively expanded its range in South Africa since its introduction into Cape Town in the late 19th century. In the past few decades it has extended this range into Gauteng province. Using data from the Southern African Bird Atlas Project 2, this paper examines the spread and relative abundance changes for the species across South Africa over the past 10 years, with a detailed look at the recently-colonised Gauteng. Across South Africa, the Common Starling's distribution has shifted, and grown. As it spreads north along the coastline and northwards inland, some of the former range has been lost. In Gauteng, the species has shown a range and abundance expansion over the same period. If the observed trends are to continue, this species is likely to eventually become a prominent species across the entire country, and further north into the sub-region. However, the potential impact that this species has on indigenous avifauna is unknown and, in the face of rapid anthropogenic change, remains to be investigated.

Quantifying the decline of the Martial Eagle Polemaetus bellicosus in South Africa

SummaryHuman populations in Africa are growing at a faster rate than in any other region; this growth will exert increasing pressures on the continent’s wildlife resources and declines in wildlife are already being observed. Species occupying higher trophic levels may be amongst the most useful indicators of this pressure and raptorial birds have already proven to be particularly useful in highlighting problems with their environment. The Martial Eagle is an African endemic which is thought to be declining and was recently uplisted to globally Vulnerable, although data on population trends are almost entirely lacking. The Southern African Bird Atlas Project (SABAP) 1 and 2 are citizen science projects that represent a rare opportunity, within an African context, to quantify population changes over a 20-year period. We use data from these surveys to explore changes in reporting rates for this species in South Africa between SABAP 1 (1987–1992) and SABAP 2 (2007–2012) at the scale of quarter-degree grid cells. Previous research suggests that such comparisons accurately reflect changes in breeding numbers for this species. We found an overall decline in reporting rates of c.60%, with more cells showing loss or declines (75%) than those showing colonisation or increases (25%). No differences in reporting rate change were found between provinces, suggesting a relative uniform decline across the country. There were, however, differences between biomes with declines recorded in all biomes apart from Albany Thicket, Succulent Karoo and Fynbos (south-western biomes). Declines differed inside and outside protected areas, with larger declines outside (64%) than inside (42%) protected areas, although even within large protected areas significant declines were observed. These results support the uplisting of the species’ conservation status and suggest that even within protected areas the species is not immune to the drivers of decline.

Predicting the distribution of the Vulnerable Yellow-breasted Pipit (Anthus chloris) using Species Distribution Modelling

ABSTRACTThe Yellow-breasted Pipit (Anthus chloris) is endemic to the eastern escarpment of South Africa, marginally entering eastern Lesotho. This species is classified as globally Vulnerable due to a perceived decreasing population size and loss of habitat. We employed Species Distribution Modelling to investigate the predicted range of this species to determine whether additional purportedly suitable habitat exists where this species may be found, and to assess the degree to which habitat loss has affected this species. We used a database of 250 independently obtained and verified sightings to predict the summer breeding distribution of this species and compare our verified sightings and predicted range to the sightings currently in the Second Southern African Bird Atlas Project (SABAP2) database and the latest regional conservation assessment. Our models closely approximate the current distribution of the Yellow-breasted Pipit, and suggest that most of the purportedly suitable habitat is occupied, at least at the macro scale. Our models further suggest that the Eastern Cape Province does not hold much suitable habitat for this species, and that the purported range contraction in this region may have been overestimated.

The second Southern African Bird Atlas Project: Causes and consequences of geographical sampling bias.

Using the Southern African Bird Atlas Project (SABAP2) as a case study, we examine the possible determinants of spatial bias in volunteer sampling effort and how well such biased data represent environmental gradients across the area covered by the atlas. For each province in South Africa, we used generalized linear mixed models to determine the combination of variables that explain spatial variation in sampling effort (number of visits per 5′ × 5′ grid cell, or “pentad”). The explanatory variables were distance to major road and exceptional birding locations or “sampling hubs,” percentage cover of protected, urban, and cultivated area, and the climate variables mean annual precipitation, winter temperatures, and summer temperatures. Further, we used the climate variables and plant biomes to define subsets of pentads representing environmental zones across South Africa, Lesotho, and Swaziland. For each environmental zone, we quantified sampling intensity, and we assessed sampling completeness with species accumulation curves fitted to the asymptotic Lomolino model. Sampling effort was highest close to sampling hubs, major roads, urban areas, and protected areas. Cultivated area and the climate variables were less important. Further, environmental zones were not evenly represented by current data and the zones varied in the amount of sampling required representing the species that are present. SABAP2 volunteers' preferences in birding locations cause spatial bias in the dataset that should be taken into account when analyzing these data. Large parts of South Africa remain underrepresented, which may restrict the kind of ecological questions that may be addressed. However, sampling bias may be improved by directing volunteers toward undersampled regions while taking into account volunteer preferences.

Early warning systems for biodiversity in southern Africa – How much can citizen science mitigate imperfect data?

It is a hard reality that virtually all countries, no matter how well resourced, take conservation and land use decisions based on highly patchy and imperfect data - if indeed any data at all. Despite a mushrooming of scientific evidence and journals in the past decade, and open-access provision of many expensive global datasets, developing countries in particular often have to make do with inaccurate and coarse-scale global data, in the absence of targeted, local data to solve immediate conservation problems. To what extent can citizen science data compensate for the patchiness of conventional government-gathered scientific data in order to support planning, policy and management? We demonstrate how southern Africa's citizen science-based “early warning system for biodiversity” is used to support land-use planning and conservation decisions, including Red List, strategic and project-based environmental impact assessments and national protected area expansion and implementation strategies. This system integrates volunteer-based species atlases such as the Protea Atlas Project and Southern African Bird Atlas Project (SABAP), species population monitoring such as the Custodians of Rare and Endangered Wildflowers (CREW) project, and site-based rapid assessment and monitoring such as MyBirdPatch and BioBlitz. Countries in southern Africa are on a sharp continuum of research capacity, funding, political engagement and own datasets. Yet there is the capacity for adaptive management systems based in significant part on civil society volunteerism. Crucially, these must be underpinned by statistically sound, simple, repeatable scientific protocols, which are still rare in Africa.

Using independent nest survey data to validate changes in reporting rates of Martial Eagles between the Southern African Bird Atlas Project 1 and 2

Repeat monitoring is vital to measure biodiversity change. However, monitoring protocols may change, as survey techniques improve or different questions are asked. Such modifications may cause difficulties when examining changes in wildlife populations. The Southern African Bird Atlas Project (SABAP) 1 and 2 are repeat national bird surveys undertaken 20 years apart. These surveys therefore offer unrivalled potential to examine bird population changes in an African context. However, changes in protocols, both spatially and temporally, between the two surveys have raised concerns over using these data to infer population changes. In this study we use independ- ent nest survey data to test whether changes in reporting rates of Martial Eagles in the Kalahari Gemsbok National Park between the two SABAP surveys were reflected in real change in numbers of nesting pairs. From 11 quarter degree squares (QDS), covering c. 8 000 km2, both SABAP and nest surveys suggested a near identical 44% decline. Levels of agreement were weaker at the individual QDS scale, although in 67% of cases the direction of change was the same using both surveys. These results suggest that comparisons in the reporting rates between SABAP 1 and SABAP 2 accurately reflect changes in the breeding population size of this species.