Abstract
Background and Research Aims
Power lines are one of the main anthropogenic causes of bird mortality on a global scale, but research is scarce in some countries with a high diversity of birds, such as Mexico. In this study, we assessed the impact of bird collisions and electrocutions with power lines on avian communities at three wind farms located in three different states in Mexico.
Methods
Carcass searches were carried out at sites in Tamaulipas (4 months in 2021), Guanajuato (2 months in 2020, 4 months in 2021), and Oaxaca (55 months from 2014 to 2021).
Results
A total of 579 bird carcasses from 65 different species were recorded. The White-winged Dove (Zenaida asiatica) was the most frequently found species (282 records) across the three sites. When considering the number of species identified per family, Icteridae had the highest number of species at the Oaxaca site, Columbidae and Passerelidae at the Tamaulipas site, and Anatidae at the Guanajuato site. At the order level, Passeriformes had the highest number of species at the Tamaulipas and Oaxaca sites, and Anseriformes in Guanajuato. Of the total species recorded, 12 are within some category of risk according to Mexican legislation and the IUCN Red List, and 18 are migratory species.
Conclusions
Our results, together with evidence from previous studies, indicate that power lines represent one of the main causes of anthropogenic mortality in Mexico in terms of the number of affected bird species. Further research is urgently needed to explore the effect of power lines on bird populations in the country, particularly those at risk of extinction, and migratory species.
Implications for Conservation
The high diversity of species found to be affected in this study highlights the wide-ranging impact of these structures and the need to implement mitigation strategies at the three sites studied, particularly for the most affected species, the White-winged Dove (Zenaida asiatica).
Introduction
Both the establishment of communication and transportation structures in human societies and the development of structures for generating and transmitting electrical power represent numerous threats to biodiversity. Among the main threats are isolation of populations, habitat loss, death from collisions with vehicles, and death due to collision with and electrocution by power transmission and distribution lines (Balkenhol & Waits, 2009; Bernardino et al., 2018). Birds are one of the groups most affected by the latter threat; in fact, power lines are one of the main sources of avian mortality worldwide, and it is estimated that in the United States and Canada alone, they kill more than 60 million birds per year (Loss et al., 2015).
Power lines are associated with population decline in several avian species (see Biasotto & Kindel, 2018; Slater et al., 2020 and references therein), many of which are endangered (Dwyer et al., 2019; Guil et al., 2011), motivating an increase in the study of bird mortality associated with these structures around the world (Bernardino et al., 2018; Biasotto & Kindel, 2018). Moreover, the continuous growth of human settlements and the growing demand for electricity in modern societies together result in a 5% annual increase in power lines around the world (Jenkins et al., 2010). Therefore, it is essential to identify which species are affected, to better understand the impact of power lines on bird populations, and take action to reduce this impact.
Multiple studies worldwide have evaluated characteristics of bird mortality related to power lines. Among the main factors associated with collisions with power lines are as follows: (1) factors related to the characteristics of the individual birds (e.g., the ratio of the wing area to weight, age, flight behavior such as gregariousness, or in-flight displays related to the courtship process in large wingspan species (Janss, 2000); (2) characteristics of the site where the power lines are located (e.g., topography, vegetation, climate, visibility conditions); and (3) the characteristics of the power lines (e.g., number of wires, their height and diameter; Bernardino et al., 2018; Jenkins et al., 2010). However, there is a clear geographic bias in the evidence base, with numerous studies in Europe and North America (Bernardino et al., 2018; Loss et al., 2015), while some of the regions and countries with the greatest diversity (e.g., megadiverse countries) lack even basic information, such as which species are most affected (Guil & Pérez-García, 2022), that would enable a better understanding of the impact of these structures on avifauna, and support the development of strategies to reduce avian mortality.
Mexico has the 10th highest avian diversity of any country (Navarro-Sigüenza et al., 2014), but also has an extensive electrical grid that in 2004 included 746,911 km of power lines distributed throughout the country (Rosellón, 2007). This figure has continued to increase with the establishment of new power plants, urban expansion, and the move towards wind farms. For example, the Isthmus of Tehuantepec, one of the main migration routes for Neotropical birds (Cabrera-Cruz et al., 2017), is the region with the greatest presence of wind energy in the country, including 52 km of transmission lines and a place to expand to an estimated 145 km of power lines in the medium-term future (SEGOB, 2015). Despite the extension and imminent growth of electrical lines, we know of only five published studies that have evaluated the impact of power lines on bird mortality in Mexico. Four of the five studies were carried out in northern states of the country (i.e., Chihuahua, Baja California Sur, Sonora) between 1999 and 2006 (Cartron et al., 2000, 2005, 2006; Manzano-Fischer et al., 2007), and were mainly focused on the evaluation of bird mortality by electrocution, although in many cases it was not possible to determine the cause of death accurately (Cartron et al., 2006). Manzano-Fischer et al. (2007) identified 423 bird carcasses during their investigation in the state of Chihuahua, including: 24 Golden Eagles (Aquila chrysaetos), 28 Ferruginous Hawks (Buteo regalis), and one Bald Eagle (Haliaeetus leucocephalus), while 15 carcasses were found in Sonora and one in Baja California (Cartron et al., 2006). The authors highlighted the fact that methodological differences between studies prevented detailed comparisons.
Given the lack of information about the impact of power lines on bird species in Mexico and Latin America, and the imminent increase in the extension of power lines in regions of importance for threatened and Neotropical migratory species, we aimed to provide information on the species affected by power lines associated with three wind farms in Mexico, located in the states of Oaxaca, Tamaulipas, and Guanajuato. We carried out this study to use the findings to make an urgent appeal to social actors across Latin America to pay attention to this issue and establish a regional agenda that may serve as a basis for decision-making in the future, for the benefit of the regional avifauna.
Materials and Methods
Study sites
The fieldwork was carried out along power lines and power poles (namely hereafter as “power lines”) associated with wind farms in the states of Tamaulipas, Guanajuato, and Oaxaca, located in northeast, central, and southcentral Mexico, respectively (Figure 1). The specific characteristics of the power lines and the search methodology for each site are described below, but in general, the power lines did not have any type of line markers, and the searches were carried out along these structures to identify carcasses. When a bird carcass was found, the geographical coordinates were recorded and photographs were taken to identify the species and provide evidence of the record. In cases where only feathers were found (more than three feathers close to each other), these were used to identify the species, where possible. Additionally, all carcasses were removed to avoid recounting them in subsequent visits. Location and length of transmission lines sampled in the states of Tamaulipas (1), Guanajuato (2) and Oaxaca (3), Mexico.
Tamaulipas
The power line sampled at this site (midpoint of transect; 23° 25′ 53.68″ N, 98° 54′ 45.82″ W) had a voltage of 115 kV, a width of 6 m, and a height of 15 m from the ground. The sampled segment was 12.7 km long and was supported by 30 towers. The vegetation around the transmission lines and surrounding area was secondary vegetation of Tamaulipan scrub. Intensive searches were conducted both under the power lines and around the support towers. The searches were carried out by four people covering a 15-m wide transect under the power line. The stretch of power line was sampled twice a month from January to April 2021, and the total area sampled was 190,815 m2.
Guanajuato
The power line at this site (midpoint of transect; 21° 44′ 53.7″ N, 101° 15′ 8.37″ W) had a voltage of 230 kV, a width of 15 m, a height that varied from 9 to 20 m from the ground. The sampled segment was approximately 17.6 km long and had 53 towers. The area under and around the transmission lines area was mostly devoid of vegetation, but there were also some areas with a dense cover of nopal (Opuntia spp.). Water bodies were present on either side of the power line. Intensive searches were carried out under the power lines and surrounding areas by four people, covering an 18-m wide transect. Two sections, one 0.34 km long located between towers 21 and 22 and the other 1.56 long located between towers 39 and 43 could not be sampled due to the presence of dense scrub and nopal that impeded the search. The power line was sampled monthly from November to December 2020 and January to April 2021; the total area sampled was 317,594 m2.
Oaxaca
The power line at this site (midpoint of transect; 16° 30′ 47.28″ N, 94° 53′ 53.94″ W) had a voltage of 230 kV, a width of 6 m, and a height of 30 m from the ground. The sampled segment was approximately 21 km long and had 70 towers. The vegetation under and around the transmission lines was mainly cropland (mostly sorghum) and secondary deciduous forest vegetation. There was a network of crop irrigation canals in the area. Intensive searches were carried out by four people in a transect that ranged from 40 to 80 m wide, including the area under the power lines and around the support towers. The transect width depended on the density of vegetation and accessibility to private properties. One person searched below the transmission line and one person on each side 50 m away from the line. This transmission line was sampled on either one or two occasions per month, in 2014 (May–Aug, Oct), 2015 (May–Aug, Nov–Dec), 2016 (Apr–Nov), 2017 (Apr–Nov), 2018 (Feb–Mar, May–Nov), 2019 (Apr–May, Jul, Sept, Nov–Dec), 2020 (Jan–Dec, except Apr), and 2021 (Feb–Mar). The total area sampled was 511,340 m2.
Data Analysis
Once the data from the study sites were obtained, we compiled a list of the species recorded. To find whether each registered species had already been reported as being killed by power lines elsewhere in the world, we carried out a literature review using the search engines Google Scholar and Clarivate Analytics with the words “Bird” OR scientific or common name of each species on the list (including synonyms) AND “Collision” OR “electrocution” OR “Strikes” OR “Deaths” OR “Casualties” AND “Power Lines” OR “Transmission Power Lines” OR “Electric Power Lines” OR “Electric Wires.” We also explore all the combinations in Spanish. Additionally, to compile the list of species that have been reported as killed by electric lines in Mexico, we carried out a search in Google Scholar (June and July 2021) using the word combination “birds” AND “power lines” OR “collision” AND “Mexico.” We used rank-abundance curves to evaluate the differences between the numbers of recorded carcasses between species within sites (Magurran, 2004).
Results
Species with recorded carcasses associated with power lines in Mexico.
Migratory species = * (Zenaida asiatica is migratory in Oaxaca but resident in Tamaulipas and Guanajuato), endemic species to Mexico = +. Conservation categories: Mexican Government (SEMARNAT, 2010): A = Threatened; P = Endangered; Pr = Subject to special protection; E = Probably extinct in the wild; (International Union for Conservation of Nature IUCN, 2021): LC = Least Concern, NT = Near Threatened, VU = Vulnerable, NE = Not Evaluated. Fieldwork location: * = Oaxaca, ** = Tamaulipas, *** = Guanajuato.
ND = no data of casualties, Cause (C = Collision, E = Electrocution). Not id = not identified (only to family taxonomic level).
Taxonomic composition presented by families (a), and orders (b), of bird collision or electrocution records at three sites sampled in this study. Following to each name of families and orders are indicated the number of species.
According to Mexican legislation (SEMARNAT, 2010), three of the species affected by power lines are included in risk categories: two species (Mexican Duck [Anas diazi], and Limpkin [Aramus guarauna]) are classified in the category of “Threatened” (A; Amenazada), and one species (Orange-fronted Parakeet [Eupsittula canicularis]) in the category of “Subject to special protection” (Pr; Sujeta a Protección Especial); According to the Red List (IUCN, 2021) two species identified in our study (Northern Bobwhite [Colinus virginianus], and Eastern Meadowlark [Sturnella magna]) are classified as “Near Threatened” (NT), one species (Orange-fronted Parakeet [E. canicularis]) as “Vulnerable” (VU), and one (Mexican Duck [A. diazi]) has “Not been evaluated” (NE) (Table 1).
The results we found by site were as follows. In Tamaulipas, we found evidence of 66 bird deaths in the search area along power lines. We could identify 54 of these birds as belonging to 15 different species. We identified one carcass at the genus level (Setophaga), four at the family level (Columbidae), and we could not identify seven (Table 1). Of the total carcasses that we could identify to the species level, the most frequent was the White-winged Dove, with 38 records (∼70% of the total; Figure 3a). The families with the highest number of recorded species were Passerellidae and Columbidae, with three species each, and the order that presented the highest number of species was Passeriformes with eight, equivalent to 53.3% of the total (Figure 4a, b, Table 1). Rank-abundance plots for species with carcasses recorded in the sampled sites of Tamaulipas (a), Guanajuato (b) and Oaxaca (c), Mexico. The species codes are included in Table 1. a= Dendrocygna autumnalis, b= Mareca strepera, c= Mareca americana, d= Anas platyrhynchos, e= Anas diazi, f= Spatula discors, g= Ortalis vetula, h= Ortalis poliocephala, i= Colinus virginianus, j= Columbina inca, k= Columbina passerina, l= Columbina spp., m= Leptotila verreauxi, n= Zenaida asiatica, o= Zenaida macroura, p= Crotophaga sulcirostris, q= Morococcyx erythropygus, r= Geococcyx californianus, s= Chordeiles sp., t= Chordeiles acutipennis, u= Nyctidromus albicollis, v= Porzana carolina, w= Porphyrio martinicus, x= Aramus guarauna, y= Burhinus bistriatus, z= Gallinago delicata, a*= Leucophaeus atricilla, b*= Leucophaeus pipixcan, c*= Ardea herodias, d*= Ardea alba, e*= Egretta caerulea, f*= Bubulcus ibis, g*= Butorides virescens, h*= Nycticorax nycticorax, i= Eudocimus albus, j*= Platalea ajaja, k*= Coragyps atratus, l*= Cathartes aura, m*= Tyto alba, n*= Bubo virginianus, o*= Caracara cheriway, p*= Falco sparverius, q*= Eupsittula canicularis, r*= Pitangus sulphuratus, s*= Tyrannus melancholicus, t*= Tyrannus verticalis, u*= Tyrannus forficatus, v*= Corvus corax, w*= Polioptila caerulea, x*= Turdus grayi, y*= Mimus gilvus, z*= Mimus polyglottos, a+= Arremonops rufivirgatus, b+= Spizella passerina, c+= Junco hyemalis, d+= Melospiza lincolnii, e+= Sturnella magna, f+= Icterus spp., g+= Icterus spurius, h+= Icterus pustulatus, i+= Icterus gularis, j+= Molothrus aeneus, k+= Quiscalus mexicanus, l+= Seiurus aurocapilla, m+= Geothlypis philadelphia, n+= Setophaga sp., o+= Setophaga petechia, p+= Cardinalis cardinalis. Taxonomic composition (presented by families (left) and orders (right) of birds with collision or electrocution records at sites in Tamaulipas (a, b), Guanajuato (c, d) and Oaxaca (e, f), Mexico. Following each name of families and orders, the number of species that make them up is indicated.
At the site located in the state of Guanajuato, we found evidence of 42 carcasses, of which 33 belonged to 11 species, while we could not identify nine (Table 1). The White-winged Dove was the species with the highest number of records (eight, ∼24% of the total number of records identified to species level; Figure 3b), the family with the most species recorded was Anatidae (four species), and the order with the most recorded species was Anseriformes, with ∼36% of the total (Figure 4c, d, Table 1).
At the site located in the state of Oaxaca, we found 471 carcasses, of which 409 belonged to 48 species. We identified seven carcasses to the genus level (of the genus Icterus—three carcasses, Columbina—three carcasses and Chordeiles—one carcass), seven could be identified only at the family level (Columbidae), and 48 could not be identified (Table 1). Of the total carcasses that we found and could identify to species level, the species we recorded most frequently was the White-winged Dove with 236 carcasses (58%), followed by the Cattle Egret with 40 carcasses, and the Great-tailed Grackle (Quiscalus mexicanus) and Blue-winged Teal (Spatula discors) with 10 carcasses each (∼2%) (Figure 3c). The family with the highest number of recorded species was Icteridae with six species, while the order with the highest number of species identified was Passeriformes (16) equivalent to ∼33% of the total (Figure 4e, f, Table 1).
Discussion
Data on the association between power lines and avian mortality are scarce, particularly in tropical areas where the diversity of this biological group is especially high (Bevanger, 1998; Hyde et al., 2018). We provide novel information on the impact of power lines on Mexican bird diversity. Through an extensive search of the scientific literature, we also demonstrate that further research is urgently needed to explore the effect of these structures on bird populations in Mexico, in order to inform the design and implementation of effective mitigation actions.
In this study, we identified 65 species affected by transmission lines in Mexico, which is the most comprehensive list identified in the country to date. This illustrates the magnitude of the lack of information that exists on this topic in Mexico. For 38 of the 59 species that had not been previously identified as victims of power line associated mortality in Mexico, we only recorded one or two carcasses (24–1, 14–2), which could be related to many factors (e.g., sporadic impact, sampling effort). Therefore, it is essential to generate more information on the mortality rates by species, especially since our results indicate that some of these species affected are in some category of risk (e.g., Northern Bobwhite, Eastern Meadowlark—Near Threatened; IUCN, 2021). In addition, it should be mentioned that sampling effort was less in Guanajuato and Tamaulipas and these states do not have such a great diversity of birds as Oaxaca (Navarro-Sigüenza et al., 2014), which could mean that the number of species affected across the country may, in fact, be much higher. Thus, it is essential to conduct a country-wide survey, with a special focus on states with the greatest bird diversity, as well as in areas of importance for their conservation. Moreover, we could not identify 83 carcasses to species level. Therefore, future studies should incorporate other identification tools (e.g., molecular analysis; Dove et al., 2010) that enable more detailed information to be obtained on the affected species when feather evidence is insufficient for identification.
In this study, the White-winged Dove was by far the most frequently-recorded species affected with 282 records (57% of the identified carcasses). This is a novel finding, as low numbers of carcasses of this species have been identified in other studies (Rogers et al., 2014). The high number of recorded carcasses could be related to the presence of croplands at the study sites where these birds feed (Collins et al., 2010). Likewise, the number of carcasses of Cattle Egret (40) and Mourning Dove (17) could be related to the fact that the characteristics of the surrounding habitats favor their presence, although it may also be influenced by the characteristics intrinsic to the species that make them more susceptible to these hazards, as reported in previous studies (Bernardino et al., 2018; Ferrer et al., 2020). In addition, it is important to mention that the removal rate of carcasses by predators is higher in smaller species, which could have led to a smaller number of carcasses being recorded for these species (Gómez-Catasús et al., 2020).
The number of species that we recorded from the Icteridae family (6 spp.) at the Oaxaca site was double than reported in Bevanger’s review of North America (1998). This highlights the importance of generating more information in countries where data are scarce, as new patterns may be identified due to regional differences in the composition and structure of avian communities. We also identified a large number of Ardeidae species affected at the Oaxaca site. This result could be related to the present network of crop irrigation canals in the area used by these species, since aquatic birds are one of the groups most likely to collide with power lines (Bernardino et al., 2018) because of their morphological characteristics (low loadings; large wings), and flight strategy (thermal soarers) (Bevanger, 1998). The high proportion of Columbidae and Passerelidae (the last previously reported as Emberizidae) recorded at the Tamaulipas site is in agreement with the findings of Ferrer et al. (2020) for southern Spain. The fact that Anatidae species were the most affected at the Guanajuato site may be explained by the presence of water bodies next to power lines. This result also coincides with the findings of Bevanger (1998), who found this family to be the second most affected in terms of the number of species identified. The variation in the most affected families between sites could reflect differences in composition between bird communities at the three sites, as well as differences in the characteristics of the surrounding habitats.
The remarkably high number of species that we recorded in this study of the order Passeriformes is consistent with the findings of Bevanger (1998), where this order was reported to have the second-highest number of affected species. The highest proportion of birds killed being of Passeriformes species at the Tamaulipas and Oaxaca sites also agrees with the findings of previous studies (Demerdzhiev et al., 2009; Pigniczki et al., 2019), while Anseriformes, the group with the highest numbers of carcasses identified at the Guanajuato site, was also identified by Bevanger (1998) as one of three orders most greatly affected by power lines. In the case of Passeriformes, previous studies have found the majority of avian deaths within this order to have been related to the migration period (Demerdzhiev et al., 2009), while the vulnerability of both orders can be attributed to their morphological characteristics.
It is important to note that more than half of the carcasses (56%) that could be identified at the species level belonged to Nearctic-Neotropical migrants, which is consistent with the findings of Bernardino et al. (2018) in their review, where they point out that migratory species are susceptible to being affected by power lines due their movements through unfamiliar terrain, their tendency to group in large numbers, and fly at low altitudes. This result partially coincides with other studies that have evaluated the death of birds related to human structures in Mexico (i.e., building windows), as Uribe-Morfín et al. (2021) reported that 56% of the records belonged to migratory species, while Gómez-Martínez et al. (2019) found this proportion to be 30%, although the families and species identified as the most affected differed from those identified in the present study. In the present study, the White-winged Dove was by far the most-affected species. Although populations of this species are stable (BirdLife International, 2016), the populations of many migratory species have decreased by more than 50% over the last four decades, mainly due to habitat loss (Rosenberg et al., 2016). As a result of this, and because large legal gaps exist in terms of conservation of migratory species in the regions where they spend the different seasons of the year (Runge et al., 2015), it is essential to broaden knowledge of the impact of power lines on this group in order to implement measures to help minimize mortality (Figure 5). Carcasses of birds recorded in the study sites of Tamaulipas: (a) White-winged Dove; Guanajuato: (b) Mexican Duck, (c) Chipping sparrow, (d) Black-crowned Night-Heron, (e) Mourning Dove; and Oaxaca: (f) White-winged Dove, (g) Cattle Egret, (h) Green Heron, (i) Turkey Vulture.
Bird Deaths Associated with Power Lines in Mexico
Through this and previous studies of avian electrocutions and collisions in Mexico (Cartron et al., 2000, 2005, 2006; Ferrer-Sánchez et al., 2017; Manzano-Fischer et al., 2007), a total of 77 different species have been identified as experiencing some level of power line-associated mortality. Fifty-nine of the species identified in this study have not been previously reported as affected by these structures in Mexico. These numbers suggest that power lines represent the cause of mortality affecting the widest range of bird species in the country, even greater than window collisions (71 species; Cupul-Magaña, 2003; Gómez-Martínez et al., 2019; Gómez-Moreno et al., 2018; Uribe-Morfin et al., 2021), and collision with wind turbines (29 species; Cabrera-Cruz et al., 2020; Uribe-Rivera et al., 2018). This does not mean that power lines are the main anthropogenic cause of direct bird deaths in the country, but it does reflect the enormous impact that these structures have on Mexican avifauna. In the United States, predation by cats and window collisions represent the main anthropogenic causes of direct death of birds (Loss et al., 2015), but data on each of these causes of death in Mexico are scarce. It is also important for future studies to evaluate deaths associated with structures related to renewable energy production (e.g., solar facilities), as they are also a major source of mortality, and their cumulative effects could have negative effects on populations (Conklin et al., 2022).
As far as we know, the list of species affected by power lines in Mexico is the most extensive on this topic in Latin America, exceeding the lists recorded for Colombia (46 spp.; De la Zerda & Rosselli, 2003), Venezuela (10 spp.; McNeil, 1985) and isolated records for Brazil and Argentina (Câmara-Gusmão et al., 2020; Sarasola et al., 2020). To our knowledge, no previous association has been identified in the scientific literature between power lines and avian mortality for 38 of the species registered in our study. Therefore, these results represent an important, novel contribution to knowledge about the impact of these structures on bird diversity. Even considering the important contribution of our study, information on the association between power lines and bird mortality in Mexico remains very limited. It is essential to develop systematized studies in the short term that can serve as a starting point to generate estimates of the number of bird deaths at both regional and national levels (Loss et al., 2014; Rioux et al., 2013).
Implications for Conservation
This study adds three species in categories of extinction risk to the list of bird species affected by power lines in Mexico, adding to the nine species in this condition registered in previous studies. We believe that this trend of the impact of power lines on endangered species being under-reported is likely to be repeated in many other Latin American countries, including those with greater bird diversity (e.g., Colombia, Peru, and Brazil), but the available information is very limited. Thus, it is essential to develop studies that consider population parameters to further understand the impact of power lines on populations of vulnerable birds (Marques et al., 2020). Special attention should be paid to species with some threat to their conservation either nationally or internationally (three species recorded in the fieldwork in this study), as well as groups such as raptors (including species of orders Accipitriformes, Falconiformes, and Strigiformes; McClure et al., 2019), previously reported among groups most affected by power lines (Eccleston & Harness, 2018; Lehman et al., 2007). In fact, more than half (8 of 12) of the nationally threatened species affected by power lines in Mexico are raptors (SEMARNAT, 2010). Similarly, another group that should receive special attention in future studies is the Nearctic-Neotropical migrants, since their numbers had been reduced considerably over the last three decades (Rosenberg et al., 2016). Data based on scientific studies are essential as a baseline to implement and propose mitigation measures that reduce the number of deaths caused by power lines (Barrientos et al., 2011; Bernardino et al., 2019; Chevallier et al., 2015; Dwyer et al., 2019; Ferrer et al., 2020; Luzenski et al., 2016). Practices such as conducting studies before the establishment of transmission lines can be useful to identify areas of higher risk for the avifauna (D’Amico et al., 2018; Luzenski et al., 2016).
It is concerning that 15 years have passed since the last study on the impact of power lines on national avifauna in Mexico was published (Manzano-Fischer et al., 2007). Future studies are needed that examine different environments (Costantini et al., 2017), different types of power lines and their characteristics (e.g., height, number of cables, and thickness), using different search methods for carcasses (Borner et al., 2017), and that evaluate the impact of power lines at different stages of the life cycle of birds (e.g., reproduction, migration; Johnson et al., 2002). Finally, there is no legal framework in Mexico that obliges companies to implement preventive actions to avoid or reduce bird deaths caused by the electric grid, unlike other countries such as the United States (Lehman, 2001) or Spain (BOE, 2008), where sentences have been handed down to power companies for failing to implement preventive measures resulting in deaths of threatened species (Aquila chrysaetos, Buteo regalis and Bubo virginianus in USA; Aquila adalberti in Spain) (El País, 2018). Therefore, it is essential to generate evidence-based scientific knowledge that will enable us to understand the magnitude of the problem represented by the power lines for the country’s avifauna, and to be the starting point for society, the government, and private industry to search for strategies that benefit bird diversity, and, where appropriate, to fine companies that do not comply.
Footnotes
Acknowledgments
The authors are grateful to Tereso Hernández Morales, Manuel Cameras Flores, Marlene Soto, Patricia Degante González, William Ramos Arreola, Paola Figueroa Islas and Alex Coronel Jiménez for their technical support during fieldwork. Thanks are expressed to Oscar H. Marín Gómez and Miguel A. Gómez Martínez for their valuable comments on an earlier version of the manuscript and to Paulina García Bañuelos for drawing 
. Two anonymous reviewer provided helpful suggestions that improved this manuscript. Margaret Schroeder and Frances Mcculloch revised the English of the manuscript.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.