Power line routing and configuration as major drivers of collision risk in two bustard species

Abstract

Collision with power lines is a major cause of mortality for many bird species. Understanding the biotic and abiotic factors that increase collision risk is therefore important for implementing mitigation measures to minimize mortality, such as power line rerouting or wire marking. Here, we used collision events registered during - along  km of transmission power lines in southern Portugal to analyse spatio-temporal patterns and collision risk factors in two sympatric, threatened, and collisionprone species: the great bustard Otis tarda and the little bustard Tetrax tetrax. The occurrence of collisions was not uniform across space and time, and variations could be explained by the species' ecological requirements, distribution patterns and behaviour. Although both species fly considerable distances between areas of suitable habitat, collisions were far more likely in power line sections with . % (for the little bustard) or . % (for the great bustard) of open farmland habitat in the surroundings. Power line configuration was also important: taller pylons and those with a higher number of wire levels posed a higher risk for both species. Wire marking had a small but significant effect for the little bustard, reducing collisions risk. There was, however, no similar effect for the great bustard, possibly a result of limited data. Mitigation measures should be implemented to prevent bustard collisions, including adequate route planning, ideally avoiding areas with . % of open habitat. Line configuration and wire marking are particularly important where such localities cannot be avoided and power lines cross areas with a high proportion of bustard habitat, including outside protected areas.

The effects of powerlines on bustards: how best to mitigate, how best to monitor?

“…in Alentejo, Portugal, almost 10 times larger than that for transmission; Marques et al . 2021), potentially representing an overall higher mortality risk. Additionally, two or more transmission lines and distribution lines often run in parallel, making it difficult to establish the structure responsible for the collision.…”

“…The position (in a vertical or horizontal configuration), height and conspicuousness of wires all contribute an effect (e.g. Bevanger 1994, Marques et al 2021). Birds that fly in flocks appear to be at higher risk, possibly because the tendency to follow leaders overrides individual vigilance (e.g.…”

Changes in grassland management and linear infrastructures associated to the decline of an endangered bird population

“…Power lines are known to affect the spatial distribution of the little bustard, although it is not clear if the causal factor is an increased perceived predation risk (as power line poles are frequently used as perches by little bustard predators, such as large raptors) or neophobia 52,64 . Additionally, power lines represent a major cause of anthropogenic mortality for the species 40 , with high fatalities due to collisions with power line cables known to occur at the onset of the breeding season 45 . These mechanisms may explain the reduction of male density in areas with more power lines.…”

“…This is the highest mortality rate per collision with power lines ever recorded for a species. Morphological characteristics and bird sensorial perception are key species-specific features that explain such a high mortality rate 41 – 44 , but behavioural changes (as flocking behaviour or flight height) across seasons were also considered relevant 45 , 46 . In addition to mortality, little bustards also avoid the vicinity of anthropogenic infrastructures, mainly to roads and power lines 47 – 52 .…”

Diurnal and nocturnal movements of Kori Bustards in the Serengeti ecosystem

“…Though some Bustards perform night movements, they are prone to deaths because of powerline collisions and other infrastructures compared to Bustards that perform daytime movements. Deaths by collisions with powerlines are recorded among many different species (Bevanger 1994, Allan 2005, Marques et al 2021, Silva et al 2022. Therefore, a better understanding about the extent of nocturnal movements in large flying birds is particularly valuable in developing mitigation measures for when Bustards are more prone to such collisions.…”