Power line collision risk in bustards 449
important areas for the great bustard were of the small con- figuration and only a few had medium configuration, which could explain the absence of collision records involving this type of power line and the consequent predicted low colli- sion risk. Our findings also suggest that power line configuration
may interact with habitat features: power lines with a large configuration posed a higher collision risk to little bustards in areas with intermediate levels of open habitat (c. 20– 65%), compared to the small and medium configurations. This may be because the little bustard tends to use areas with less suitable or fragmented habitats during the non- breeding season (Silva et al., 2007), when the species also tends to fly at heights with higher collision risk (Silva et al., 2014). The influence of power line configuration on bustard
collision risk suggests that distribution power lines, usually much lower and with a smaller collision risk area, are less risky to these birds than transmission lines. However, the total length of the distribution grid is much larger: in Alentejo region there are c. 13,483 km of distribution power lines (Silva et al., 2014)vs 1,239 km of transmission lines. The distribution grid as a whole may thus represent an important mortality source despite the lower risk posed by individual lines. Our results suggest wire marking devices have a signifi-
cant but small effect in reducing collisions for the little bustard. Previous studies showed that wire marking devices have a limited effect on bustard species, and only large spirals were found to have some effect on the great bustard (Janss & Ferrer, 1998; Barrientos et al., 2012). The data ana- lysed in our study were insufficient to evaluate the effect of wire marking on the great bustard, as most of the trans- mission power lines crossing its main range had mark- ing devices, making it difficult to separate habitat and mitigation effects. This could explain why the model fitted without imposing a monotonic trend suggested that power line sections marked with spirals posed a higher risk to the species.
Implications for bustard conservation and power line monitoring
The main determinant of collision risk for the great and little bustard is the proportion of open habitat in the area surrounding the power line. Therefore, the best mitigation measure for future transmission power lines is to avoid routing them through areas with large expanses of open farmland habitat. For existing lines, replacing the aerial wires with underground cabling would be the best solution to pro- tect bustards in open farmlands (i.e..50%of open habitat), at least in Special Protected Areas that are important for both species. However, this is difficult to implement because of the high cost and potential legal and technical challenges
(Raab et al., 2012; Bernardino et al., 2018). Where under- ground cabling is not possible, we recommend the adoption of technical configurations with smaller pylons, a reduced number of wire levels (with fewer cables displaced verti- cally) and shorter distances between top and bottom wires. Additionally, all transmission lines crossing areas with .20% open habitat in a 5 km buffer should have marking devices to increase their visibility. Although this mitigation measure appears to have only a small effect on these species it can reduce the number of fatalities. The choice of wire marking device should be based on the best evidence avail- able, balancing the effectiveness and durability of avail- able devices (Bernardino et al., 2018). Experimental designs focusing on bustard species, based on a before–after con- trol–impact approach, should be used to identify the best devices for this bird group. The high prevalence of mortality caused by collision with
power lines in both bustard species (Marcelino et al., 2018; Palacín et al., 2017) indicates that reducing such anthropo- genic mortality is likely to have a positive effect on their po- pulations. Mitigation is particularly important for the little bustard, whose population has halved over the last 10–14 years (Silva et al., 2018). Our results also show that the likelihood of finding a
carcass increased with survey effort, particularly for the great bustard. Although these are larger birds and thus more likely to be detected during carcass surveys (Ponce et al., 2010), great bustard collisions are less common and a higher survey effortmay be needed to detect
them.The spe- cies occurs in lower numbers than the little bustard and its fatality pattern is temporallymore scattered, particularly out- side Special Protected Areas. Therefore,monitoring schemes focussing on bustards should include regular carcass surveys throughout the entire spring, summer and autumn.
Acknowledgements This research was funded by FCT (Funda- ção para a Ciência e a Tecnologia) and REN—Redes Energéticas Nacionais, in the scope of the REN Biodiversity Chair. ATM was funded by FCT doctoral grant SFRH/BD/100147/2014 and JPS with a contract DL57/2016. FM was funded by REN and FCT (IF/01053/ 2015), and RCM by a post-doctoral grant funded by REN and FCT, both under the REN Biodiversity Chair.
Author contributions Study design: ATM, JPS, JP, FM; data collec- tion: ATM, RCM; data analysis: ATM, FM; writing: ATM, FM; revision: all authors.
Conflicts of interest None.
Ethical standards This research abided by the Oryx guidelines on ethical standards and did not require specific ethical or other approvals.
References
ALONSO, H., CORREIA, R.A., MARQUES, A.T., PALMEIRIM, J.M., MOREIRA,F.&SILVA, J.P. (2019) Male post-breeding movements
Oryx, 2021, 55(3), 442–451 © The Author(s), 2020. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605319000292
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164
