Agulhas long-billed lark (Certhilauda brevirostris) densities, population estimates and habitat association in a transformed landscape

Abstract

The effects of agricultural landscape transformation and subsequent habitat associations have been little studied for the Agulhas long-billed lark (Certhilauda brevirostris), a regionally threatened species in the Overberg, Western Cape, South Africa. Point count surveys were conducted throughout the Overberg using distance sampling techniques. We calculated bird density and extrapolated this to a population range estimate of between 203 000 and 368 000 individuals. Using generalised linear modelling of habitat variables from the point counts, we found that the birds prefer short vegetation, regardless of habitat type or cover. Broad-scale habitat association patterns were examined using SABAP2 data to determine if reporting rate (a measure of abundance) was correlated with the proportion of natural habitat within each pentad, finding that reporting rates were lower for areas with large patches of natural vegetation and extensive road access. It remains inconclusive whether agricultural practices benefited Agulhas long-billed larks, or whether these practices mimic historical ecological processes, but the population appears secure and even increasing with the status quo.

Keywords: agricultural transformation, Alaudidae, distance sampling, endemic species, fynbos, habitat selection