Jessica M. Shaw

Estimating the impacts of power line collisions on Ludwig’s Bustards Neotis ludwigii

Ludwig’s Bustard Neotis ludwigii , endemic to Africa’s south-west arid zone, is susceptible to collisions with overhead power lines. Limited data from the south-eastern part of its range suggest that this factor may threaten its survival. We estimated transmission line collision rates for Ludwig’s Bustard across its South African range to assess the effect of this mortality on the population. Conservatively, collision rates averaged at least 0.63 ± 0.12 fatal collisions per km of transmission line per year, with relatively little regional variation. Despite being less abundant, the larger males were more collision-prone than females, which might account for the female-biased population. Extrapolating collision rates across the range of the species suggests that 4,000–11,900 birds are killed annually on high-voltage transmission lines. Actual mortality on overhead lines is probably much greater, given biases in carcass detection (crippling, scavenging and habitat biases), as well as the fact that our estimate excludes mortality on lower voltage distribution lines and telephone wires. Given an estimated global population of 56,000–81,000 birds in the late 1980s, the demographic invariant method suggests that such mortality is unsustainable. This result supports the recent upgrading of the conservation status of Ludwig’s Bustard from ‘Least Concern’ to ‘Endangered’, and highlights the need for further research on this problem.

A preliminary survey of avian mortality on power lines in the Overberg, South Africa

Avian mortality on power lines in South Africa is currently recorded on the Central Incident Register (CIR), which is a collation of incidentally reported cases. The true scale of the problem is unknown, so we report here on a survey of representative power lines in the Overberg region of the Western Cape. On the 199 km surveyed, 123 birds of at least 18 species were found. Collisions were more common than electrocutions, apparently killing 88% of the birds found on distribution lines. Large terrestrial birds were the most numerous victims, with large numbers of Blue Cranes Anthropoides paradiseus and Denhams Bustards Neotis denhami killed. In comparison with mortality rates from the CIR, we estimate that only 2.6% of power-line mortalities are reported, emphasising the importance of systematic surveys in quantifying mortality and directing mitigation. Our survey highlights the general hazard that power lines pose to avifauna, and the urgent need for further research into the population impacts of the high incidence of collisions.

Estimating scavenger and search bias for collision fatality surveys of large birds on power lines in the Karoo, South Africa

Bird collision mortality associated with power lines is a global conservation challenge, but periodic carcass counts along power lines underestimate actual mortality because of survey biases. We conducted a scavenger trial over 90 days and three observer detection trials after 1, 48 and 90 days using 44 wild goose carcasses to identify explanatory variables and estimate correction factors for these biases. Scavenging activity was high but mostly occurred in situ; only 16% (95% binomial CI 5–27%) of carcasses were removed by the end of the 90-day trial period (all within the first three weeks). Observer experience did not significantly affect detection rate, with experienced observers locating 75% (95% CI 68–83%) of carcasses compared with 67% (95% CI 58–75%) by naïve observers. Vegetation height, distance from the line and carcass spread were significant explanatory variables. The pattern in detection rate linked to carcass age was variable; there were fewer detections after 48 days, but rates at day 1 and day 90 were similar for experienced observers because bleached bones were highly visible. This suggests that long survey intervals are acceptable for the detection of large bird carcasses in arid environments such as the Karoo where collisions are infrequent but widespread events.

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

Ludwig’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.

Winter Scavenging Rates Under Power Lines in the Karoo, South Africa

Bird mortality from collisions with power lines, wind turbines and other infrastructure is a global conservation problem (Drewitt & Langston, 2008; Jenkins, Smallie & Diamond, 2010). Millions of birds are thought to die annually this way, but calculating accurate fatality figures is extremely difficult (Drewitt & Langston, 2008). Fatality rates are normally estimated from periodic carcass searches, e.g. under representative sections of power line, but alone these can give misleading underestimates of true rates (Smallwood, 2007; Ponce, Alonso, Argandona, Fernandez & Carrassco, 2010). Several bias factors should be taken into account to allow for carcasses missed through removal by scavengers or decomposition (scavenger bias), varying levels of observer efficiency/different habitat types (search bias) and injured birds that die away from the search area (crippling bias; Bevanger, 1999). In South Africa, the power grid is extensive and expanding (www.eskom.co.za), and there is expected to be a proliferation of wind turbines in coming years (Jenkins, 2010).Power lines already pose a threat to several threatened bird species e.g. Blue Cranes, Anthropoides paradiseus (Shaw, Jenkins, Smallie & Ryan, 2010), Ludwig’s Bustards, Neotis ludwigii (Jenkins et al., 2011) and Cape Vultures, Gyps coprotheres (Boshoff, Minnie, Tambling & Michael, 2011). However, to really understand the impacts of such mortality, survey biases for large birds in the South African environment need to be assessed. In preliminary search and scavenger bias experiments conducted in the Hantam Karoo in summer 2011 (Schutgens, Shaw & Ryan, 2014), only 16% of experimental carcasses were removed (although most were scavenged in situ). However, scavenger bias may vary seasonally (Prosser, Nattrass & Prosser, 2008; Flint, Lance, Sowl & Donnelly, 2010). In this study, we repeat the experiment at the same locality in winter. We use camera traps to identify the scavenger guild, as they have been successfully used to monitor carcass removal experiments elsewhere (e.g. Bumann & Stauffer, 2002; Smallwood, Bell, Snyder & Didonato, 2010).

Trapping and capture myopathy in Ludwig's Bustard

Banding and deploying tracking devices are important techniques to study birds of conservation concern, but require that individuals can be safely and efficiently caught and handled. We describe the trapping techniques used to catch Ludwigs Bustards (Neotis ludwigii) in the Karoo, South Africa, for a satellite tracking programme aiming to better understand the movement biology of this poorly known and threatened bird. Trapping sites on transformed land used as congregation sites were difficult to locate for these nomadic and partially migratory birds, but six of nine prospective trapping trips were successful. Although labour-intensive, extensive deployment of leg nooses coupled with guide-lines to direct birds proved effective. We caught 12 bustards at four sites across the Karoo over 37 trapping days in 2010–2012. Success was male-biased, with only two females caught. Noose traps were safe, with no injuries to captured birds. However, in common with other studies, we encountered problems with capture myopathy after handling five bustards; two subsequently died and three recovered.We designed a ‘harnessing chair’ to reduce the risk of capture myopathy, but still encountered problems. We recommend noose traps with guide-lines to catch other large, wary birds in open environments where there is some predictability of habitat use,but caution against long handling times and trapping in extreme temperatures.