The distribution and biology of nomadic birds in the Karoo, South Africa

Abstract

Dryland nomadic bird species, as a proportion of all bird species in a biome in southern Africa, are highest in the arid grassland and arid and semi‐arid Karoo in South Africa. Nomadic birds, of which the most widespread species is the greybacked finchlark Eremopterix verticalis (Smith), are most frequently observed in the north‐central and north western Nama Karoo. The species richness of nomadic species is inversely correlated with species richness of all bird species in the Karoo. Since the distribution of nomadic birds is in areas where rainfall is patchy, low (<250 mm per year) and aseasonal, this supports the idea that fewer species are able to cope with resources that are patchy in time and space, and that there has been selection for nomadism in the species that are able to use patchy environments. Species richness and abundance of nomadic birds is negatively correlated with rainfall amount but positively correlated with the coefficient of variation of the rainfall and with rainfall in autumn. The frequency of nomadic birds is inversely correlated with altitude range; nomadic species are most often recorded in structurally simple habitats (shrubland and grassland) on open plains. Most nomadic bird species in the Karoo are granivorous. Perennial desert grasses are important components of the habitat and diet of small nomadic granivores, and also provide nest sites and nest material. Nomadic birds can breed throughout the year, without a clearly defined ‘season’ in both the Succulent and Nama Karoo. Average clutch sizes do not differ significantly between resident and all nomadic species in the arid and semi‐arid Karoo. Nomadism is an evolutionary stable strategy for individual species only when extremes in environmental conditions are frequent enough, and unpredictable enough, to maintain movements to high resource patches or to maintain dispersal away from low resource patches. If high rainfall years are too regular or infrequent, or peaks in fluctuations of resources in the environment too low, or rainfall patches are randomly distributed, nomadism would not be maintained as part of the individual behaviour pattern.

Spatial Scaling of Prevalence and Population Variation in Three Grassland Sparrows

“…Nomadism is a special form of dispersal that is characterized by irregular movements of individuals, groups of individuals, or whole populations to different areas from year to year or within a season (Sinclair 1984, Dean 1997). Nomadism develops most commonly when limiting resources fluctuate spatiotemporally and become patchy and unpredictably available across a region (Sinclair 1984, Dean 1997.…”

“…Nomadism is the irregular or undirected dispersal of individuals following patchy and unpredictably available resources across a landscape (Sinclair 1984, Dean 1997. It is in effect temporal turnover of populations (Allen and Saunders 2002).…”

“…It is in effect temporal turnover of populations (Allen and Saunders 2002). Nomadism can occur among individuals, groups of individuals, or entire populations (Andersson 1980), and across multiple spatial scales (Dean 1997). It is most commonly observed in species that live in highly variable environments, such as the North American grasslands (Bragg 1995), where the ability to track resources (e.g., food or suitable nesting sites) and colonize new breeding areas quickly in response to changing environmental conditions is advantageous (Cody 1985, Igl andJohnson 1999) Dornak (2010) analyzed nomadism only at one spatial scale, so it remains unclear if these grassland sparrows are nomadic over multiple scales and (most importantly) at what scales the differences in prevalence between them are manifested.…”

Temporal biodiversity change in transformed landscapes: a southern African perspective

“…The focus has not only been on changes to biodiversity as a consequence of species entering the country, but also on traits, vectors and pathways that enable species from South Africa to alter biodiversity in other regions van Kleunen & Johnson 2007;). 19711973197519771979198119831985198719891991199319971999 Although biological invasions by animals have perhaps been less extensively investigated (though e.g. Robinson et al 2007;Shelton et al 2008), temporal changes at a number of spatial scales have been explored.…”

Variability between Scales: Predictors of Nomadism in Birds of an Australian Mediterranean-climate Ecosystem

“…Nomadism in birds has been relatively little studied, and surprisingly little is known of the ecological correlates of nomadism. Dean (1997) reported that nomadic species of the South African Karoo tended to be granivores, especially feeding on grass seeds, and further noted that nomadic species that feed on grass tended to be small. Davies (1984) found that nomads tend to feed on seeds or nectar, but also stated that some nomads are raptors, tracking rodent outbreaks.…”