Birds

When wild birds are mentioned in connection with electricity supply, it is not about the influence of low-frequency electric and magnetic fields. Rather, it is about the fact that they can collide with wind turbines, power lines, and their masts in flight and die. In order to prevent bird strikes on power lines, visible bird protection markings have been used on the conductor cables for years. The effectiveness has been proven for many species ^[1].

On medium-voltage pylons with small distances between the pylon and its line wires, especially large bird species such as birds of prey, owls, and storks can easily trigger a short-circuit and suffer a fatal electric shock. On the other hand, birds use power lines as a safe perch, and many species, including storks and birds of prey, like to nest on electricity pylons. In the process, they are exposed to low-frequency fields. Their effects have so far been investigated in the field in only a few studies.

A recent review ^[2] compares negative and positive impacts of power lines on bird populations. The greatest danger comes from collisions and electrocution. Their frequency depends on the size and behaviour of the respective bird species as well as on the weather and technical parameters of the electricity pylons. Another negative factor is reduced breeding success. This is partly attributed to magnetic fields but also to the fact that nests on electricity pylons are often more exposed to weather conditions (e.g. heavy rain, wind, and sun) than nests on trees in the forest. Another negative factor is the barrier function as a result of the visibility of the power lines and the removal of vegetation below the power lines. In contrast, power lines also have positive effects on bird populations. They are used by many species as perching and resting places with a good overview (e.g. whether an enemy is approaching or food is visible) or as gathering places for flocks of birds. Many bird species successfully breed on electricity pylons. Power lines can also serve as linear landmarks for orientation.

Another review ^[3] describes changes in behaviour, reproduction, and growth in some species of raptors and songbirds that breed near power lines. The effects are not uniform and overall do not imply a consistent negative impact of power lines on breeding success.

In southern Portugal, the population density and breeding behaviour of little bustards (Tetrax tetrax) were studied in relation to the landscape in 2003–2006. Power lines proved to be an important influencing factor that greatly affected the occurrence of bustards. The cause here is not magnetic fields but rather the fragmentation of the otherwise open steppe landscape ^[4].

Work on hawks nesting in brood boxes on electricity pylons ^[5] shows that the young developed equally well in both exposed and non-exposed nests. The blood count and the concentration of the hormone melatonin were also unaffected by the magnetic fields. The magnetic flux density in the exposed nests was measured and ranged from 1 to 25 µT.

Great tits (Parus major) ^[6] breeding under power lines laid more and larger eggs than unexposed tits. Whether this was caused by the magnetic field or the habitat under the power lines remains unclear. Breeding success remained unchanged. The magnetic flux density in nests under power lines was about 0.2 µT; in distant nests, it was only about 0.6 nT.

Another paper shows that corridors below power lines provide special habitats for some songbird species in particular (e.g. warblers and sparrows), where species diversity and numbers of individuals increase ^[7].

Birds can perceive the Earth’s magnetic field

Migratory birds and many others (possibly all bird species) can perceive the Earth’s static magnetic field and orientate themselves accordingly. Research in this area is far from complete. However, current knowledge suggests that birds may use up to three independent organs to perceive the Earth’s magnetic field ^[8]. Special light receptors (cryptochromes) in the retina of migratory birds react to the orientation of the magnetic field. The basis is the influence of the magnetic field on radical pairs. Another sensory organ, which contains magnetite (iron oxide), is possibly located in the beak and reacts to the magnetic flux density ^[10]. However, the functionality of this organ is called into question ^[11]. Recently, a third magnetic field receptor in the inner ear of the pigeon was experimentally proven and explained by physical calculations; the mechanism of action of this is based on electromagnetic induction ^[12].

DC power lines

In the course of the power grid expansion, DC power lines are also planned on land; these will be surrounded by static electric and magnetic fields. It is possible that the magnetic fields, if their magnetic flux density reaches the range of the Earth’s magnetic field (about 48 µT), are perceived by birds and influence the behaviour in the immediate vicinity of the power lines.

References

[1] Mercker M (2021) Wirksamkeit von Vogelschutzmarkierungen an Freileitungen - methodische Überlegungen zu Versuchsaufbau, Auswertung und Übertragbarkeit empirischer Feldstudien. Naturschutz und Landschaftsplanung. 53(9): 32-38.

[2] D'Amico M, Catry I, Martins RC, Ascensao F, Barrientos R, Moreira F (2018). Bird on the wire: Landscape planning considering costs and benefits for bird populations coexisting with power lines. Ambio.

[3] Fernie KJ, Reynolds SJ (2005) The effects of electromagnetic fields from power lines on avian reproductive biology and physiology: a review. J Toxicol Environ Health B Crit Rev. 8(2): 127 - 140.

[4] Silva JP, Santos M, Queirós L, Leitão D, Moreira F, Pinto M, Leqoc M, Cabral JA (2010) Estimating the influence of overhead transmission power lines and landscape context on the density of little bustard Tetrax tetrax breeding populations. Ecological Modelling, 221(16) : 1954–1963.

[5] Dell'Omo G, Costantini D, Lucini V, Antonucci G, Nonno R, Polichetti A (2009) Magnetic fields produced by power lines do not affect growth, serum melatonin, leukocytes and fledging success in wild kestrels. Comp. Biochem. Physiol. C Toxicol. Pharmacol. 150(3):372 - 376.

[6] Tomás G, Barba E, Merino S, Martínez J (2012) Clutch size and egg volume in great tits (Parus major) increase under low intensity electromagnetic fields: A long-term field study. Environ. Res. 118(1): 40 - 46.

[7] Hrouda J, Brlik V (2021) Birds in power-line corridors: Effects of vegetation mowing on avian diversity and abundance. J Vertebr Biol 70(2): 21027.21021-21027.

[8] O'Neill P (2013) Magnetoreception and baroreception in birds. Dev. Growth. Differ. 55(1): 188 - 197.

[9] Hore PJ, Mouritsen H (2016) The radical-pair mechanism of magnetoreception. Annual review of biophysics 45: 299-344.

[10] Fleissner G., Stahl B., Thala, P, Falkenberg G, Fleissner G (2007) A novel concept of Fe-mineral-based magnetoreception: Histological and physicochemical data from the upper beak of homing pigeons. Naturwissenschaften 94, 631 - 642.

[11] Treiber CD, Salzer MC, Riegler J, Edelman N, Sugar C, Breuss M, Pichler P, Cadiou H, Saunders M, Lythgoe M, Shaw J, Keays DA (2012) Clusters of iron-rich cells in the upper beak of pigeons are macrophages not magnetosensitive neurons. Nature 484 (7394): 367 - 370.

[12] Nimpf, S, Nordmann, GC, Kagerbauer, D, Malkemper, EP, Landler, L, Papadaki-Anastasopoulou, A, Ushakova, L, Wenninger-Weinzierl, A, Novatchkova, M, Vincent, P, Lendl, T, Colombini, M, Mason, MJ, Keays, DA (2019). A putative mechanism for magnetoreception by electromagnetic induction in the pigeon inner ear. Curr Biol 29(23): 4052-4059 e4054.