Habitat use, distribution and breeding ecology of the globally threatened Rudd's Lark and Botha's Lark in eastern South Africa

摘要

Habitat use and breeding ecology of the threatened and poorly known Rudd's Lark Heteromirafra ruddi were studied in south-eastern Mpumalanga, South Africa, from October 2002 to April 2004. Data were also collected incidentally on the equally poorly known Botha's Lark Spizocorys fringillaris. Rudd's Larks establishing territories at the start of the summer breeding season selected grassland of lower than average height. Although grass in these territories had reached average height by the late breeding season, grassland selected by birds could still be distinguished from unoccupied grassland using a combination of other habitat variables. Botha's Lark was encountered less frequently than Rudd's Lark, but was always encountered along transects that also held Rudd's Lark, indicating a degree of overlap in habitat selection. However, the two species appeared to differ in nest site selection; Rudd's Lark nests were most frequently built in unburned grass and Botha's Lark nests on recently burned land. First egg dates of 93 Rudd's Lark nests ranged from late October to late March, with peak laying in January and February. Most clutches were of three eggs, and both incubation and nesting periods appear long for a lark, at 13-14 d and 13 d, respectively, for both species. Average nesting success, estimated using an extension of the Mayfield method, was around 30%, but showed a significant decline as the breeding season progressed and was lowest during the peak nesting period. Clutch size was significantly smaller in Botha's Lark ( median = 2) and nesting took place significantly earlier, largely on land recently burned. Botha's Larks largely abandoned the study area after a short and possibly curtailed breeding season. Predation was the main cause of nest loss in both species and examination of the remains of dummy eggs identified mongooses, rodents and snakes as the main predators. Late burning of grassland might shorten the potential breeding season of Rudd's Lark and lead to a peak of nesting that coincides with high predator numbers. The earlier nesting of Botha's Lark suggests that this species may have been even more severely affected by a shortening of the breeding season. A model of Rudd's Lark potential distribution confirms previous suggestions that there might be a population of the species in the north-eastern Free State and identifies possible new sites elsewhere.