Land use and breeding ecology of a renosterveld endemic bird: the Agulhas Long-billed Lark Certhilauda brevirostris
Agricultural expansion and intensification are among the leading contributors to biodiversity loss. Ground-nesting birds are especially vulnerable. Understanding the distribution and nesting requirements of a species is important, particularly if that species exists almost entirely within a human-modified landscape. The Agulhas Long-billed Lark Certhilauda brevirostris is a mediumsized passerine endemic to South Africa's Overberg region, an area extensively cultivated for crops and livestock production. The aim of this study was two-fold: to better understand patterns in landscape occupancy of this species as related to a set of biotic and abiotic variables, and to investigate the breeding ecology of this lark. To investigate the first question, I conducted 10–minute point counts at 51 sites regularly spaced in the core distribution of Agulhas Long-billed Lark. Points were spaced along small rural roads quarterly between October 2020 and January 2022. Agulhas Long-billed Larks were recorded at 58% (n=204) of 351 counts. Occupancy models were used to determine how detection was related to survey variables (temperature, wind speed and start time). Occupancy was then modelled against site variables (percentage renosterveld and riverine vegetation, and amount and type of fence line vegetation). Detection probability was estimated to be 0.67, giving an occupancy probability at sample sites of 0.91. Detection was negatively correlated with an increase in wind speed and temperature. Agulhas Long-billed Lark occupancy was greater when there was more renosterveld within a 250 m radius of the point count. It was positively associated with renosterveld along fence lines and a combination of renosterveld and riverine vegetation. To investigate the breeding ecology of this lark, extensive field visits over two years were conducted to establish baseline breeding ecology data. Over two nesting seasons, 29 Agulhas Long-billed Lark nests were found. Nesting started in winter (July) and continued until mid- summer (December). Most nests (66%, n=19) were in renosterveld with the remainder in human-modified landscapes. Nests were a shallow cup placed on the ground, wellconcealed at the base of a small bush or grass clump. Nests were monitored using video footage obtained from camera traps. The mean clutch size was 2.7 ± 0.5 (SD; median=3, range 1–3, n=20). Only the female incubated (n=10), and the incubation period was 16 days (n=1). The mean number of chicks hatched was 1.9 ± 0.8 (median=2, range 1–3). Two chicks fledged 13 and 17 days after hatching. Both sexes provisioned chicks. Provisioning rate was related to chick age and time of day but not brood size. Nesting success was low, with only 14% of broods fledging. Predation was the main cause of nest failure, with eight species of nest predators identified. A preference for nesting in renosterveld highlights the need for protection of this endangered habitat type. Although apparently well-adapted to this transformed landscape, the occupancy and breeding ecology results indicate that certain landscape features need to be preserved and that Agulhas Long-billed Lark will not be immune to unchecked land use change, especially given that, as a range-restricted endemic, the lark has limited displacement options.
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