Mduduzi Ndlovu

Understanding the ecological drivers of avian influenza virus infection in wildfowl: a continental-scale study across Africa

Despite considerable effort for surveillance of wild birds for avian influenza viruses (AIVs), empirical investigations of ecological drivers of AIV prevalence in wild birds are still scarce. Here we used a continental-scale dataset, collected in tropical wetlands of 15 African countries, to test the relative roles of a range of ecological factors on patterns of AIV prevalence in wildfowl. Seasonal and geographical variations in prevalence were positively related to the local density of the wildfowl community and to the wintering period of Eurasian migratory birds in Africa. The predominant influence of wildfowl density with no influence of climatic conditions suggests, in contrast to temperate regions, a predominant role for inter-individual transmission rather than transmission via long-lived virus persisting in the environment. Higher prevalences were found in Anas species than in non-Anas species even when we account for differences in their foraging behaviour (primarily dabbling or not) or their geographical origin (Eurasian or Afro-tropical), suggesting the existence of intrinsic differences between wildfowl taxonomic groups in receptivity to infection. Birds were found infected as often in oropharyngeal as in cloacal samples, but rarely for both types of sample concurrently, indicating that both respiratory and digestive tracts may be important for AIV replication.

Investigating Avian Influenza Infection Hotspots in Old-World Shorebirds

Heterogeneity in the transmission rates of pathogens across hosts or environments may produce disease hotspots, which are defined as specific sites, times or species associations in which the infection rate is consistently elevated. Hotspots for avian influenza virus (AIV) in wild birds are largely unstudied and poorly understood. A striking feature is the existence of a unique but consistent AIV hotspot in shorebirds (Charadriiformes) associated with a single species at a specific location and time (ruddy turnstone Arenaria interpres at Delaware Bay, USA, in May). This unique case, though a valuable reference, limits our capacity to explore and understand the general properties of AIV hotspots in shorebirds. Unfortunately, relatively few shorebirds have been sampled outside Delaware Bay and they belong to only a few shorebird families; there also has been a lack of consistent oropharyngeal sampling as a complement to cloacal sampling. In this study we looked for AIV hotspots associated with other shorebird species and/or with some of the larger congregation sites of shorebirds in the old world. We assembled and analysed a regionally extensive dataset of AIV prevalence from 69 shorebird species sampled in 25 countries across Africa and Western Eurasia. Despite this diverse and extensive coverage we did not detect any new shorebird AIV hotspots. Neither large shorebird congregation sites nor the ruddy turnstone were consistently associated with AIV hotspots. We did, however, find a low but widespread circulation of AIV in shorebirds that contrast with the absence of AIV previously reported in shorebirds in Europe. A very high AIV antibody prevalence coupled to a low infection rate was found in both first-year and adult birds of two migratory sandpiper species, suggesting the potential existence of an AIV hotspot along their migratory flyway that is yet to be discovered.

Host associations, biogeography, and phylogenetics of avian malaria in southern African waterfowl.

The relevance of spatial variation in the environment and host communities for parasite community composition is poorly documented, creating a need for additional case studies from which general principles can be developed. Avian malaria in southern African waterfowl has not previously been studied. As a first step towards documenting and understanding its biogeography, we used PCR and molecular sequencing techniques to analyse 454 blood samples from Afrotropical ducks from 5 different locations (spread around the subregion) for avian malaria. Fifty-five blood samples were positive for one or more genera of haematozoa. The regional infection rate across all sites and sampling periods was 12·1%. Nine individuals carried dual infections containing multiple haematozoa. Fifteen different cytochrome b haplotypes among 52 positives (3 samples failed to sequence) and 61 total sequences were found. Eleven haplotypes closely matched Plasmodium, whereas 4 were more similar to Haemoproteus. Five distinct haematozoan clades were identified. Haemoproteus parasites appeared to be more host-specific than Plasmodium, which occurred at every sampling location and in every host species examined. There were no significant differences in overall parasite prevalence attributable to either site or species, although Plasmodium and Haemoproteus occurrences differed by site-species combination and the borderline significance of our test for between-site variation (P < 0·06) implied that with a larger sample size, differences in parasite prevalence among locations might be detectable.

Satellite Telemetry of Afrotropical Ducks: Methodological Details and Assessment of Success Rates

Despite widespread and increasing use of solar-powered satellite transmitters to tag wild birds, there are few published articles that detail how transmitters should be attached to different species and even fewer assessments of the overall field success of telemetry projects. The scarcity of this information makes it difficult to plan and budget for telemetry projects effectively. In this paper we present relevant information from a study involving a total of 47 individual ducks of two Afrotropical anatid species, Egyptian Goose, Alopochen aegyptiaca, and red-billed teal, Anas erythrorhyncha, using solarpowered GPS satellite transmitters of two different sizes (30 g and 22 g, respectively) at three very different southern African sites (Strandfontein wastewater treatment works in the Western Cape Province of South Africa, Barberspan Nature Reserve in the North West Province of South Africa, and Lake Manyame in north-central Zimbabwe). We present a full description of harness design and attachment and a survivorship analysis of the transmitters. Our results suggest that the 30 g units last longer than the 22 g units, with approximately 60% and 30%, respectively, of these PTTs (position tracking terminals) lasting longer than a year; 45% and 5%, respectively, lasting longer than two years; and 20% and 0%, respectively, lasting longer than three years. We strongly encourage the publication of comparable data sets so that future studies that rely on telemetry data can be planned with a realistic set of assumptions and limitations in mind.

Linking avian communities and avian influenza ecology in southern Africa using epidemiological functional groups

The ecology of pathogens, and particularly their emergence in multi-host systems, is complex. New approaches are needed to reduce superficial complexities to a level that still allows scientists to analyse underlying and more fundamental processes. One promising approach for simplification is to use an epidemiological-function classification to describe ecological diversity in a way that relates directly to pathogen dynamics. In this article, we develop and apply the epidemiological functional group (EFG) concept to explore the relationships between wild bird communities and avian influenza virus (AIV) in three ecosystems in southern Africa. Using a two year dataset that combined bird counts and bimonthly sampling for AIV, we allocated each bird species to a set of EFGs that captured two overarching epidemiological functions: the capacity of species to maintain AIV in the system, and their potential to introduce the virus. Comparing AIV prevalence between EFGs suggested that the hypothesis that anseriforms (ducks) and charadriiforms (waders) drive AIV epidemiology cannot entirely explain the high prevalence observed in some EFGs. If anseriforms do play an important role in AIV dynamics in each of the three ecosystems, the role of other species in the local maintenance of AIV cannot be ruled out. The EFG concept thus helped us to identify gaps in knowledge and to highlight understudied bird groups that might play a role in AIV epidemiology. In general, the use of EFGs has potential for generating a range of valuable insights in epidemiology, just as functional group approaches have done in ecology.

Influence of moult and location on patterns of daily movement by Egyptian Geese in South Africa

Abstract The daily movements of 18 Egyptian Geese (Alopochen aegyptiaca) in South Africa were recorded using satellite telemetry. General additive mixed models were used to explain the distances moved by the birds at different times of the day, correcting for sex, site, season and individual. Distances moved by birds in the mesic, winter-rainfall, south-western region (Strandfontein) of South Africa were compared with movements in the semi-arid, summer-rainfall region (Barber-span) of northern South Africa. Moulting birds all remained at single wetlands during moult, displayed crepuscular patterns of activity and nocturnal retreats to safety. At the end of moult, birds dispersed away from moulting sites. The longest daily distances travelled by individuals took place mainly just before moult was due to start or within the first 10 days after completing moult, providing strong evidence that Egyptian Geese undertake moult migrations. The daily pattern of movement was strongly skewed, with >70% of flights being short (<10 km) and longer flights mainly occurring at night (88%). There were considerable differences in patterns of dispersal between birds at the summer-rainfall site and the winter-rainfall one. Summer-rainfall birds undertook long-distance movements between wetlands whereas Winter-rainfall birds appeared to move randomly and over short distances.

A Study of Moult-Site Fidelity in Egyptian Geese, Alopochen aegyptiaca, in South Africa

Little is known about moult and moult-site fidelity of African waterfowl. Satellite telemetry and uniquely engraved colour-rings were used to study moult-site fidelity of Egyptian geese marked at two sites in South Africa — Barberspan in the summer-rainfall region and Strandfontein in the winter-rainfall region. Twelve Egyptian geese were tagged with satellite GPS PTT transmitters while moulting at Barberspan and Strandfontein during 2008 and 2009, and a further 527 were colour-ringed between June 2007 and March 2009. Bi-monthly point counts of Egyptian geese and scans for colour-ringed birds were made at each study site from July 2007 until June 2010, resulting in 139 individually colour-ringed geese being re-sighted during the study period. We explored Egyptian geese dispersal distances away from the study sites and modelled moult-site fidelity from colour-ring return rates corrected for survivorship, sampling period efficiency and colour-ring detectability estimates. There were 12% and 29.7% colour-ring return rates for geese ringed at Barberspan and Strandfontein, respectively. Four of five moulting birds tagged at Barberspan with satellite transmitters returned to Barberspan to moult the following year. Two of these same birds moulted at Barberspan in the third year while the other two moulted elsewhere. One out of seven Egyptian geese satellitetagged at Strandfontein returned to the same site to moult the following year. One bird moulted at a nearby pan (5 km away), two moulted at estuaries less than 30 km from Strandfontein and one bird moulted at a farm dam 56 km away. Two birds satellite-tagged at Strandfontein did not moult the following year and returned to moult at Strandfontein in the third year. The moult-site fidelity model suggested that a minimum of 16% of Barberspan birds and 51% of Strandfontein birds returned to the same wetland to moult the following year. The apparent low moult-site fidelity at Barberspan suggested by colour-ring resightings may reflect the small number of birds colour-ringed at the site.

Birdcall lures improve passerine mist-net captures at a sub-tropical African savanna

Field research techniques are constantly evolving to meet the needs of the scientific community. There is a growing need for field biology studies to shift towards increasing efficiency and quality of results while simultaneously decreasing cost in both the researcher’s time and resources. I tested the efficacy of using multiple recorded birdcall lures (n = 172 species) to improve mist-net captures at a subtropical African savanna setting. Capture success was compared between passive and birdcall enhanced mist-nets during winter and summer seasons. Results suggest that the use of birdcalls does significantly increase the total number of birds caught in both seasons and also increases the diversity of passerine species. Conventional passive mist-nets without an audio lure were initially productive but their capture rate subsequently decreased as sampling days progressed. Birdcall lure enhanced mist-nets had a constant capture output during the summer season. The most responsive birds to audio lures were gregarious species (e.g. Pycnonotus barbatus, Dryoscopus cubla, Prionops plumatus, Phoeniculus purpureus, Turdoides jardineii and Lamprotornis chalybaeus) and the aggressive Dicrurus adsimilis and Acridotheres tristis. I conclude that birdcall lures can be used in summer and winter seasons to improve mist-net captures especially for studies focusing on gregarious and aggressive passerine species in a sub-tropical African savanna setting.

Geographic variation in factors that influence timing of moult and breeding in waterfowl

Waterfowl flight-feather moult is expected to occur when energy is not needed for breeding and when a suitable safe habitat is available. Flight-feather regrowth is an energetically costly stage in the annual cycle of waterfowls. In this study, we tested the hypothesis that moult will coincide with the time of year when food and aquatic habitats are most abundant. We investigated how the timing of rainfall relates to the timing of breeding and flight-feather moult in five common southern African waterfowl at two sites in South Africa with opposite rainfall regimes (one summer, one winter). We then incorporated published data to compare and contrast the relative timing of breeding and moult in southern hemisphere (southern African and Australian) waterfowl with northern hemisphere (European and North American) species. Our results showed that southern African waterfowl breed in the wet season and moult during the dry season. Tadorna cana was an exception, breeding in the dry season and moulting during the wet season in the summer-rainfall area. There was also a long lag period between peak breeding and peak moult in southern hemisphere waterfowl species, the longest lag being that of birds in the summer-rainfall area. By comparison, northern hemisphere waterfowl species breed and moult during the warm season, with a shorter lag period between peak breeding and peak moult compared to southern hemisphere species. We concluded that waterfowl in southern Africa (with the exception of T. cana), southeast Australia, Europe and North America time their breeding period to coincide with peaks in the availability of both food and breeding sites. Northern hemisphere species moult where chances of predation are low, when temperatures are warm, and before food and aquatic habitats approach their winter minima. By contrast, southern hemisphere waterfowl delay the onset of moult until the dry season, opting to moult when both food and aquatic moulting habitats are scarce.

Body Mass and Pectoral Muscle Size Changes in African Waterfowl During Moult

Body mass and organ size dynamics during flight-feather moult vary among waterfowl species. To better understand adaptations of the African waterfowl, we measured how body masses of Spur-winged Goose (Plectropterus gambensis),South African Shelduck (Tadorna cana), Yellow-billed Duck (Anas undulata), Red-billed Teal (Anas erythrorhyncha) and Southern Pochard (Netta erythrophthalma) change during flight-feather moult. We further assessed how pectoral muscle size of Spur-winged Goose and South African Shelduck varied during the same period of flight-feather moult. Our results indicate that Spur-winged Goose and South African Shelduck underwent atrophy and subsequent regeneration of the pectoral muscles, while their body mass decreased at the onset of moult and later stabilized from the time when flight feathers were two-thirds grown until moult was completed. Body mass of Yellow-billed Duck and Red-billed Teal decreased from the onset of moult until the mid-point but thereafter increased rapidly, returning to pre-moult levels by the time moult was completed. Southern Pochard gradually lost mass from the start of moult almost until moult completion, at which time mass increased slightly.We conclude that African waterfowl exhibit different fluctuations in body mass and pectoral muscle size during flight-feather moult. Taken together, these findings suggest that no single hypothesis can fully explain the interspecific differences in the moult strategies of African waterfowl as reflected in changes in body and pectoral muscle conditions.