Population size and trends of Ludwig’s Bustard Neotis ludwigii and other large terrestrial birds in the Karoo, South Africa

Abstract

SummaryLudwig’s Bustard Neotis ludwigii is globally ‘Endangered’ because of a projected population decline resulting from high collision mortality on power lines throughout its southern African range. Population monitoring is key to the effective conservation of threatened species, but there are no population trend data to confirm the impact of this mortality. We repeated extensive road and aerial census counts of Ludwig’s Bustards and other large terrestrial birds, previously conducted in the late 1980s, across the Karoo, South Africa. An aerial survey gave similar density patterns to a concurrent road count, suggesting that road counts are an adequate method for censusing Ludwig’s Bustards. In common with the 1980s surveys, there was a strong seasonal effect in the Succulent Karoo, with Ludwig’s Bustards abundant in winter and rare in summer. There was no evidence of a corresponding decline in the Nama Karoo in winter, but this probably relates to reduced detectability in the Nama Karoo in summer as there is evidence for large proportions of the population migrating between biomes. No relationship was found between the numbers of Ludwig’s Bustards and rainfall, perhaps because of larger scale rainfall patterns in the Karoo and/or because the species is not strictly nomadic. Compared with the 1980s, Ludwig’s Bustards were more strongly associated with transformed lands, which have increased marginally on road count transects. Using Distance, the current South African population is estimated at 114,000 (95% CI 87,000-148,000) birds, with no evidence for a population decline over the past two decades. Numbers of Blue Cranes Anthropoides paradiseus increased since the 1980s, corresponding with other data supporting this trend, but numbers of Karoo Korhaan Eupodotis vigorsii, Southern Black Korhaan Afrotis afra and Blue Korhaan E. caerulescens all decreased, raising concerns about the conservation status of these resident bustard species.

High power line collision mortality of threatened bustards at a regional scale in the Karoo, South Africa

“…We were surprised though to find no effect of cultivated land, given that bustards have some association with this habitat type (Shaw et al . ) and are likely to fly low when commuting to and from fields. However, any such effect may be scale‐dependent and these findings are only from one region.…”

“…, Shaw et al . ). The Karoo covers a vast area, with the winter‐rainfall Succulent Karoo to the west and the grassier Nama Karoo to the east (Dean & Milton ).…”

“…While the size of the global Ludwig's Bustard population is unknown, the latest South African population estimate is 114 000 (95% confidence interval (CI) 87 000–148 000) birds (Shaw et al . ). Other bustards are also at risk of power line collisions in the Karoo, including the Near Threatened Kori Bustard Ardeotis kori and endemic Karoo Korhaan Eupodotis vigorsii (Taylor et al .…”

“…1a) where it is thought to be both partially migratory and nomadic in response to rainfall. Over half of the global population is thought to occur in the South African Karoo, which is a semi-arid, relatively flat and largely treeless region (Hockey et al 2005, Shaw et al 2016. The Karoo covers a vast area, with the winter-rainfall Succulent Karoo to the west and the grassier Nama Karoo to the east (Dean & Milton 1999).…”

“…The Karoo covers a vast area, with the winter-rainfall Succulent Karoo to the west and the grassier Nama Karoo to the east (Dean & Milton 1999). While the size of the global Ludwig's Bustard population is unknown, the latest South African population estimate is 114 000 (95% confidence interval (CI) 87 000-148 000) birds (Shaw et al 2016). Other bustards are also at risk of power line collisions in the Karoo, including the Near Threatened Kori Bustard Ardeotis kori and endemic Karoo Korhaan Eupodotis vigorsii (Taylor et al 2015, BirdLife International 2016.…”