Department of Zoology, University of Cape Town, Cape Town, 7700, SOUTH AFRICA.
This study investigates the population genetics and behavioural ecology of the Greywing Francolin, Francolinus africanus, and identifies factors which influence the distribution and abundance of this important gamebird. It also develops scientifically sound management strategies which should allow the maintenance of populations at levels which will produce sustained and economically viable hunting yields as a co-product of agriculture.
Examination of genetic variability based on allozymes disclosed estimates of average within-population heterozygosity higher than that for most birds, and for all other galliformes for which data are available. Thus, Greywing apparently have a high degree of population stability and large effective population sizes. Indirect estimates of migration and several significant allele-frequency differences between nearby coveys suggest that there is a greater degree of genetic subdivision among Greywing populations than among populations of other birds. However, although the data suggest that populations are genetically differentiated on a large geographical scale, they also indicate that there is considerable dispersal, which produces outbred subpopulations on a fine geographical scale. Greywing therefore have a wealth of genetic variability that may 'buffer' populations against environmental changes, responsible hunting and/or short-term demographic bottlenecks. They also appear to undergo sufficient migration so that recruitment from adjacent populations will ensure population stability in hunted areas.
The timing of breeding in the Greywing is strongly correlated with the initiation of annual rains in the summer-rainfall, grassland regions of Natal, Lesotho and the eastern parts of the Orange Free State and Cape Province. However, in the winter rainfall, Fynbos Biome of the southwestern Cape Province, the Greywing's nesting period is contracted and follows immediately after the cessation of the rainy season. The main causes of nest failure in Greywing populations on the Stormberg Plateau were predation by small carnivores and crows, and destruction by management fires. In order to minimize the effects of hunting on Greywing reproductive output, the hunting season should be from 15 April to 31 July 1in the summer-rainfall region and from 1 April to 30 June in the winter-rainfall region (currently 1 April-15 July in the Cape Province and 31 May-31 August in Natal). For the same reason, grasslands in the summer-rainfall region should not be burned later than the end of August.
Growth and development of young Greywing is rapid, with linear body measurements and plumage development approaching asymptotic values within 12 weeks. Sexual dimorphism was not significant in the development of young Greywing, and body mass was too variable to be reliable as an estimator of age. Linear body measurements and moult patterns are recommended for accurate age estimation of Greywing up to 12 weeks, with primary feather replacement reliable for aging at least up to 20 weeks. These techniques will be used to age birds in hunting bags for estimating annual variation in production and reproductive success.
Calling is strongly correlated with the annual social cycle, remaining at high levels from August to April. Calling was most frequent at sunrise, and was negatively correlated with wind speed. Comparison of calling frequency and population density showed that call counts (especially during March-April) can be used to estimate changes in year-to-year population density, as well as within-season variation among areas.
Greywing were not equally distributed over the land surface. As was reported by Mentis & Bigalke (1981a) for Greywing populations in the Natal Drakensberg, inherent landscape features, e.g. ridges, shelves, slopes and valleys, also influenced habitat partitioning of Greywing on the Stormberg Plateau. Furthermore, vegetation structure (i.e. successional stage of grasslands) is the primary factor influencing distribution of Greywing populations (Mentis 1992; Chapter 6), and annual variation in summer and autumn arthropod abundance is the primary diet-related influence on abundance of Greywing.
Most Greywing hosted helminths, and infestation was independent of host-sex. Although no pathological conditions were found, high overall prevalence, and seasonal peaks in worm burdens could pose potential threats to Greywing populations. Particularly if these parasites are density dependent on the host population, and Greywing numbers are increased by manipulative management, as was displayed by Red Grouse Lagopus lagopus populations in Scotland and northern England (Hudson 1986).
Investigation of the haematozoan parasites of Greywing again showed no evidence of pathogenic effects. However, the presence of Plasmodium juxtanucleare in 11% of Greywing examined might contribute to mortality rates because most of the infected birds showed chronic infection. This parasite species has not previously been recorded in southern Africa.
Analysis of commercial Greywing hunting effort, efficiency and impact on Greywing populations showed that hunter effort and skill were not significantly different between years, and that hunter satisfaction Las significantly correlated with the number of Greywing seen. Furthermore, comparison of the mean population density of areas shot at progressively higher percentage off-take showed significant reduction of the population in the year following the hunt, where above 50% of the population was removed. Therefore, for sustainable, economically viable hunting, groups of between four and seven hunters should be offered 50-65 Greywing per hunt, and populations should be hunted only once per season removing no more than 50% of a covey.
Investigation of the effects of hunting on population and genetic structure suggests that although annual density cycles for hunted and unhunted Greywing populations were similar, hunted populations experienced a 'pulse' of immigration immediately after hunting and bred earlier. Nevertheless, average levels of allozyme heterozygosity for hunted and unhunted populations were identical (H = 0,076). Furthermore, the hunted populations displayed similar levels of outbreeding to those for unhunted populations. Therefore, although a 'pulse' of local immigration followed hunting, which apparently results in relatively fewer migrants into unhunted populations; I conclude that the effect of hunting at present levels of offtake (40-50% of the population) on Greywing Francolin populations has no apparent long-term influence on their genetic structures.