Robert E. Simmons

Climate change and birds: perspectives and prospects from southern Africa

Global climate warming, now conclusively linked to anthropogenically-increased CO2 levels in the earths atmosphere, has already had impacts on the earths biodiversity and is predicted to threaten more than 1 million species with extinction by 2050. Climate change in southern Africa is expected to involve higher temperatures and lower rainfall, with less predictability and a greater frequency of severe storms, fires and El Niño events. The predicted changes to birds in Africa — the continent most at risk from climate change — have hardly been explored, yet birds and many other vertebrates face uncertain futures. Here, in one of the first focused analyses of the correlates of climate change vulnerability in southern African birds, we offer a wide-ranging perspective on which species may be most at risk, and explore which traits may influence the adaptability or extinction risk of bird species. Our review suggests that small nomadic species with short generation times may be least at risk. While larger-bodied species may be physiologically buffered against environmental change, their longer generation times may make them less able to adapt evolutionarily to climate change. Migrant species, and those with specialised feeding niches such as pollinators, are also predicted to be at risk of population declines, based on low ability to adapt to new environments when introduced there as aliens. Species with small ranges (<50 000km2) restricted to the two southern African biodiversity hotspots most at risk from climate change — the Cape Floral Kingdom and the Succulent Karoo — are ranked according to low, medium or high risk of extinction. Those restricted to mountain slopes, mountain tops or islands, and those occurring mainly at the southern or western extremes of these biomes, are ranked as highest risk. These include endemic sunbirds, warblers and rock-jumpers — none of which are currently recognised Red Data species. Using climate envelopes we modelled the possible range shifts by 2050 of three pairs of species found in habitats considered to be at risk: fynbos, mountain and arid Karoo. All six species lost substantial portions of their range (x = 40%), with the montane Drakensberg Rock-jumper Chaetops aurantius losing most (69%). Significant reductions of available climate space in all species may interact with life history characteristics to threaten many southern African bird species unable to shift geographic range or adapt to novel resource conditions. We conclude with a list of research priorities and testable hypotheses which may advance our understanding of the complex influence that climate change is likely to have on African, particularly southern African, birds.

Trends in numbers of Cape Cormorants (Phalacrocorax capensis) over a 50-year period, 1956–57 to 2006–07

Abstract The population trend of Cape Cormorants (Phalacrocorax capensis), a species endemic to southern Africa and that feeds mainly on shoaling pelagic fish, is described for a 50-year period, from 1956–57 to 2006–07. The main breeding localities for the species are grouped in three regions in the Benguela upwelling ecosystem: guano platforms off central Namibia, islands off southern Namibia and islands off South Africas Western Cape Province. From 1956–57 to 1978–79, the numbers breeding off Namibia increased, as a result of increased availability of breeding space and adequate supplies of food. In the same period, numbers remained stable in the Western Cape. Numbers decreased off southern Namibia in the early 1980s and off central Namibia in the early 1990s, when environmental perturbations reduced the availability of food. Numbers decreased in the Western Cape in the early 1990s, following periods of scarcity of anchovy (Engraulis encrasicolus), an important prey item, and an outbreak of avian cholera caused by the bacterium Pasteurella multocida. They remained low as cholera outbreaks continued and some pelagic fish were displaced to the east beyond the foraging range of breeding Cormorants. The overall population of Cape Cormorants was of the order of 100000 pairs in 1956–57, increased to ∼250000 pairs in the 1970s, but reverted to ∼100000 pairs in 2005–06.

What precipitates influxes of wetland birds to ephemeral pans in arid landscapes? Observations from Namibia

Simmons, R.E., Barnard, P.E. & Jamieson, I.G. 1998. What precipitates influxes of wetland birds to ephemeral pans in arid landscapes? Observations from Namibia. Ostrich 70 (2): 145–148 The ability of wetland birds to rapidly find and exploit ephemeral pans is well known in and lands, but the episodic nature of such events means that the methods employed are poorly understood. Birds may: (i) wander randomly until wetlands are found; (ii) predict rainfronts and rainfall using changes in pressure gradients as cues; or (iii) follow rainfronts directly and descend onto pans as they fill. Observations from isolated pans in Namibia during the first rains indicate that wetland birds follow rainfronts, and descend onto pans as they fill. In one 30 ha pan, 37 birds of 5 species had arrived one day after filling and in another 50 ha pan over 300 birds of 13 species were attracted within 3 days of filling. Wetland birds, like migratory raptors, therefore, follow rainfronts, andMaywander locally thereafter. How specie...

Black Harrier Circus maurus of the Fynbos biome, South Africa: a threatened specialist or an adaptable survivor?

Black Harrier Circus maurus is a rare southern African endemic that may have lost over 50% of its core breeding habitat in the last century as a result of extensive land transformation by agriculture, invasive alien vegetation and urbanization in the Fynbos biome. We partially surveyed both the western (Swartland) and southern (Overberg) coastal plains of south-western South Africa, over 3 years (2000–2002) for breeding Black Harriers, and found a distinctly polarized distribution. Nests were concentrated either along the coastal strip or inland in montane habitats, and generally absent from heavily cultivated and transformed inland plains areas. Limited evidence (direct observations, prey remains) suggests that harriers forage in cereal croplands but generally do not breed in these modified environments. We recorded breeding success at nests in coastal (Dune Thicket) and montane (Mountain Fynbos) habitats. Harriers bred successfully along the coast and nests were aggregated in loose colonies around wetlands. Harriers in montane environments bred poorly, took a wide range of prey, and were subject to high levels of nest predation. We propose that Black Harriers have been displaced from lowland Renosterveld and Fynbos habitats (characterized by better foraging and nesting opportunities), primarily by the advent and spread of cereal agriculture. The conservation and future research implications of this hypothesis are discussed.

Anthropogenic activities influence the abandonment of Bearded Vulture (Gypaetus barbatus) territories in southern Africa

ABSTRACT Developing an effective conservation strategy for a critically endangered species relies on identifying the most pressing threats to the species. One approach to elucidate these threats for a long-lived animal with high territorial fidelity is to identify factors associated with territorial abandonment. The Bearded Vulture (Gypaetus barbatus) has declined dramatically in southern Africa over the past few decades, with nearly 50% of known territories being abandoned. In this study we examine the evidence for 3 hypotheses: that territorial abandonment was associated with (1) human impact, (2) food availability, or (3) climate change, or a combination of these. Model selection was used to determine the relative importance of 7 covariates within the home range of an adult pair, an area of 10 km radius (314 km2) around each nest. Our analyses provided strongest support for the human impact hypothesis, with abandonment more likely in territories with more power lines and higher densities of human settlements. Additionally, within Lesotho, southern Africa, there was some support for the food shortage hypothesis, with territories more likely to have remained occupied where they had a greater number of feeding sites within close proximity. Our data provided no support for the hypothesis that climate change may be driving abandonment through a direct impact of elevation or nest site aspect. Our results are in accordance with the main causes of mortality: poisoning and power line collisions. We suggest that conservation measures should focus on limiting the development of further human settlements and power lines within 10 km of occupied territories, applying mitigation measures to existing power lines and increasing law enforcement and education in areas still occupied by the species.

Declining coastal avifauna at a diamond-mining site in Namibia: comparisons and causes

A review of Namibian shorebird densities over two decades and two additional visits to the coastal diamond-mining areas at Elizabeth Bay, southern Namibia, were undertaken to assess the long-term influence of mining activity on density of shorebirds (Charadrii) and particularly threatened African Black Oystercatchers Haematopus moquini and Damara Terns Sterna baleanarum. Oystercatcher numbers remained relatively stable over 25 years, with some recent declines relative to previous surveys along the beach, while that of other shorebirds showed dramatic declines. Density of shorebirds fell 4.3-fold from 220 birds/km to 41 birds/km, relative to similar (pre-mining) surveys 25 years previously. Over the last nine years birds have declined from 12 to nine species. Control sites on nearby sandy beaches over the same (nine-year) period showed no such declines. From the mid-1970s (pre-mining), Damara Terns also declined from 20 breeding pairs to 2–7 breeding pairs between 1996 and 2002; they have remained stable elsewhere in Namibia. Mining activity does not directly impact the known tern nesting sites, but reduced tern numbers have occurred since 1.5 million m3 of fine sediments have been deposited annually into the bay. Observed foraging success of terns at Elizabeth Bay in 2002 was lower than recorded elsewhere in southern Africa, and independent data indicates that the abundance and biomass of their surf zone fish prey is lower in Elizabeth Bay than the nearest control site. Fish availability may also be reduced because most fish occurred within the sediment plume. The decline of the mollusc-eating component of shorebirds can also be explained by the disappearance of the White Mussel and other shellfish favoured by oystercatchers. I conclude that releasing sediment into the bay is detrimental to coastal avifauna and simple conservation measures are given that could reverse and allow further (experimental) study of the reasons for the trends found.

The value of the Black Harrier Circus maurus as a predictor of biodiversity in the plant-rich Cape Floral Kingdom, South Africa

Determining the efficacy of using indicator species to predict the spatial location of biodiversity hotspots is one way of maximising the conservation of biodiversity in already threatened habitats. Recent evidence from Europe suggests raptors can play such an indicator role, so we tested this approach with a globally threatened southern hemisphere species, the Black Harrier Circus maurus. We asked if this species, found in South Africa’s mega-diverse Cape Floral Kingdom, breeds in habitat fragments that were more diverse in terms of small mammals, birds and plants than unoccupied fragments of similar size. Renosterveld is a highly fragmented habitat that has lost . 90% of its original extent and remains only on privately-owned lands. Surveys of small mammals, birds and plants undertaken in 20 fragments in the Overberg region, South Africa, revealed nine with breeding harriers and 11 without harriers. Harrier-occupied fragments were associated with a 3.5 fold higher number of bird species and higher small mammal species richness than unoccupied ones. There was a lower abundance of most plants in occupied patches, except for red grass Themeda triandra which is an indicator of pristine renosterveld. Vegetation structure was significantly different, with harriers nesting on patches with taller, more open vegetation. While the diversity trends were not statistically significant, a positive trend between the presence of harriers and higher abundance of red grass – as an indicator of the more pristine state of the patch, suggests that harriers might allow biodiversity managers a heuristic approach for selecting the remaining patches of pristine renosterveld. The need for intensive sampling of several taxa leads to small samples and a lack of clear-cut trends for these top predators as indicators of plant diversity.

A molecular phylogeny of the harriers (Circus, Accipitridae) indicate the role of long distance dispersal and migration in diversification

The monophyly of the raptorial Circus genus (harriers) has never been in question, but the specific status of many, often vulnerable island endemic, taxa remains uncertain. Here we utilise one mitochondrial and three nuclear loci from all currently recognised Circus taxa (species and subspecies) to infer a robust phylogeny, to estimate the divergence date and to reconstruct the biogeographic origins of the Circus group. Our phylogeny supports both the monophyly of Circus and polyphyly of the genus Accipiter. Depending on the rate of molecular clock used, the emergence of the harrier clade took place between 4.9 and 12.2mya which coincides with the worldwide formation of open habitats which extant harriers now exploit. The sister relationship of the Northern Harrier C. cyaneus hudsonius and the Cinereous Harrier C. cinereus contradicts previous classifications that treated the former as conspecific with the Hen Harrier C. cyaneus cyaneus. Thus both should be elevated to species status: C. hudsonius and C. cyaneus. Further, the African Marsh C. ranivorus and the European Marsh C. aeruginosus Harriers emerge as sister species. The remaining marsh harriers exhibit very little genetic diversity, and are all recently diverged taxa that exhibit allopatric distributions. Considering their sister relationship and geographic proximity, we recommend treating C. approximans and C. spilonotus spilothorax as subspecies of C. approximans. For C. spilonotus spilonotus C. maillardi maillardi and C. maillardi macrosceles, their plumage and morphometric differences, phylogenetic relationship and geographic distributions make lumping of these taxa as a single species complicated. We thus propose to recognise as separate, recently evolved species: C. spilonotus, C. maillardi and C. macrosceles. Biogeographic inferences on the ancestral origin of harriers are uncertain, indicating that the harriers emerged in either the Neotropics, Palearctic or Australasia. We are, however, able to show that speciation within the harriers was driven by long range dispersal and migration events.

Protecting Damara Terns Sterna balaenarum from recreational disturbance in the Namib Desert increases breeding density and overall success

Because resources and funds available for the conservation management of many threatened species are limited, it is important to determine the effectiveness of different conservation measures aimed at protecting threatened species. The globally Near Threatened Damara Tern Sterna balaenarum breeds on anthropogenically disturbed beaches on the central coast of Namibia. We assessed the effectiveness of conservation measures on the breeding numbers, densities and success of Damara Terns in a loose colony among small barchan dunes on the central Namibian coast. Nests were monitored daily during the 2001/02 and 2002/03 breeding seasons. Information notices were erected during the 2001/02 breeding season and vehicle access was restricted to prevent human disturbance in the colony during the 2002/03 season. Nest numbers and density doubled in the second season, but breeding success decreased significantly from 83% to 67%. This unexpected result probably arose from increased densities attracting more predators. Despite this decrease the protection measures increased the number of chicks hatching from the area by 71%. In conjunction with two previous studies of protection from off-road vehicles we conclude that Damara Terns benefit from reduced disturbance and prefer to nest on undisturbed beaches.

Rainfall and food availability as factors influencing the migration and breeding activity of Namaqua Sandgrouse, Pterocles namaqua

This study examines whether rainfall and its effects on food availability control the timing of migratory movements and breeding activity in the Namaqua Sandgrouse, Pterocles namaqua. Namaqua Sandgrouse exhibit a pattern of partial migration between two late-summer-rainfall regions, birds spending the summer months in the Nama Karoo and the winter months in the Kalahari. Across southern Africa, the breeding season for this species is unexpectedly variable, and not consistently correlated with periods of peak food availability. The main egg-laying periods in the late-summer-rainfall regions are: (a) in northwestern Namibia from January–May with a peak in May, (b) in southwestern Namibia in any month with a peak in July, (c) in the Kalahari from June to December, and (d) in the Nama Karoo from September to December. Breeding in the Nama Karoo often starts five months after food becomes abundant, and extends into the start of the rainy season, when food availability can reach the lowest levels in the annual cycle. This suggests that some factor(s) other than proximate food availability is/are involved in determining the timing of movements and breeding in this species, at least in some regions. The possible complicating influences of biannual breeding, moulting, adult nutritional reserves and seasonal variation in nest predation pressure are discussed. We conclude that further long-term monitoring throughout the range of the Namaqua Sandgrouse is required to unravel the potential contribution of three factors (food availability, pottern of migratory movement and risk of nest predation) to the timing of migratory movements and breeding seasons in this species.