Southern Carmine Bee-eaters (Merops nubicoides) – large, highly gregarious blue and shocking pink birds – are summer visitors and generally arrive in Zimbabwe in August to breed. These beautiful birds are conspicuous in their breeding as they form large colonies and dig many holes into steep riverbanks. When breeding, they are widespread in the major river valley systems and undergo rather complex movements before departing in December for post-breeding dispersal which first takes the population southwards to South Africa (where they do not breed) and Mozambique followed by a northward movement toward the end of the rainy season in March through the south-east lowveld back to their non-breeding quarters in equatorial Africa.
Interest in the species in this country dates back almost seventy years when BirdLife Zimbabwe was first formed and annual visits were made to a colony on the Mupfure River. Eventually this interest developed in 1963 to ringing the birds and in 1970 to the ornithology society beginning a project on mapping the status of the species. Already in those days, concern was voiced that the bee-eaters were suffering from human predation and from river damming schemes. In 1983, the mapping project was revived when the Southern Carmine Bee-eater was included into the Special Species Surveys of BirdLife Zimbabwe because threats to it were still recognised. It also soon became clear from the research being conducted that the species` stronghold in Zimbabwe was in the Zambezi Valley, downstream from the dam wall at Lake Kariba, both along the Zambezi River itself and also along its tributaries.
Much of the Zambezi River on the Zimbabwe bank is bounded by riparian woodland dominated by Acacia Albida. Some areas behind the fringe support a jesse bush or a mixed species layered dry forest, dominated by several types of tree, such as Combretum, Commiphora, Lonchocarpus, and Pterocarpus species with much of the whole valley floor being dominated by Mopane Woodland (Colophospermum mopane). One effect of the Kariba dam, and also of poor rainfall years is that many sand bars and islands have become `high and dry` in the river channel and overgrown by young Acacia Albida trees. On the Zimbabwe bank, the Zambezi River forms the northern boundary for six areas i.e. Hurungwe Safari Area, Chirundu Commercial Area, Mana Pools National Park, Sapi Safari Area, Chewore Safari Area and Dande Communal Land. These areas also depict the Zambezi escarpment on the Zimbabwe side; this escarpment is a rift feature and is the southern boundary of the Zambezi Valley. Many rivers cut through the escarpment, draining the higher ground to the south and flowing northwards to the Zambezi River. Both the main river and its tributaries have cut into their beds and formed many sheer sand cliffs in the process, due to erosion. This is where the nesting colonies of the Southern Carmine Bee-eaters are likely to be found. It is generally held that nesting in holes gives eggs and young a better chance of survival than nesting in the open. In the tropics, predators abound which is why so many birds here nest in holes. Bee-eaters are all earth-hole nesters but it is by no means a given that bee-eaters` hole nests always afford reliable protection. Egg-eating snakes, Spitting Cobras and Nile Monitors are amongst their major nest predators.
However, a bigger threat to the bee-eater colonies` breeding success is possibly due to bank collapse. Before Kariba dam was built, the natural stream flow in the Zambezi River downstream of the Kariba gorge was in continuous decline from about April/May to November/December. The bee-eaters were presumably adapted to that, fledging their youngsters in late November before the river seriously rose and flooded the nest holes. With the completion of the dam and the use of water flow through the turbines to produce electricity, there are now variations in flow, which continue to cause severe erosion of the riverbanks. The bee-eater colonies therefore experience fluctuations in water level, which is exacerbated by the passage of speedboats.
Another vulnerability shown by the birds during their breeding season in Zimbabwe is if there is a scarcity of insects at the end of our dry season (September and October), especially if the previous rainy season has been poor.
Since the late 1960s, human predation, mainly with snaring and birdlime, has been recorded at Southern Carmine Bee-eater colonies but these activities were generally engaged at a local level. In recent years, however, the demand for the bee-eaters` spectacularly-coloured feathers has escalated in Asian markets putting the colonies along the Zambezi under unprecedented threat. This threat is ominous in that it is driven by the promise of an economic return for poor people who have found little else to survive on – and will certainly prove unsustainable to the population of this exquisite species if left unregulated.
For information on birding hotspots around Zimbabwe check out the Birding Zimbabwe tab on www.birdlifezimbabwe.org