General Comparative Analysis of Bird-Bat Collisions at a Wind Power Plant in the Department of Rivas, Nicaragua, between 2014 and 2022

From 2014 to 2022, eight monitoring campaigns have been carried out, documenting 119 collisions of birds belonging to 25 species corresponding to 14 families. Of the total collisions, 35 individuals could not be identified because only remains of the animal’s body (feathers) were found, due to the presence of day and night predators. Of the bird species identified, 17 are resident, three are migratory species, two are transient species, one species with transient populations that migrate south, and two species with both resident and migratory populations. During these years, no species with an important conservation category according to the IUCN were reported. Three species are on Nicaragua’s Red List, the migratory species Blackburnian Warbler (Setophaga fusca) and the resident species Mangrove Cuckoo (Coccyzus minor), both with the Near Threatened category; and the only migratory hummingbird for Nicaragua, the Ruby-throated Hummingbird (Archilochus colubris) with the Vulnerable category. The family with the highest frequency of collided bird species is the pigeons (Columbidae), these being very significant (X² = 345.20, p < 0.01). The species with the highest frequency of collisions is the Common Ground-Dove (Columbina passerina) species, with these collisions being very significant (X² = 72.05, p < 0.01). Collisions per month and year show very significant differences, especially for April 2016 (X² = 41.60, p < 0.01). Tower T13 shows significant collisions in these eight monitoring campaigns (X² = 36.48, p < 0.05). Bird collision distances show very significant collisions between 0 and 5 m away from the turbines (X² = 268.96, p < 0.01). No differences were found regarding collisions between large and small birds (X2 = 2.09, p > 0.05). The granivore group presented a very significant frequency of collisions (X² = 84.00, p < 0.01), as well as a very significant frequency of collisions in the non-passerines birds (X² = 42.26, p < 0.01). Very significantly higher fatality frequencies were observed in 2016 (X² = 60.16, p < 0.01). For the period 2014 to 2022 in bats, 134 collisions of bats belonging to 18 species corresponding to four families were observed. Of the total number of collisions, 24 individuals could not be identified because they were in poor condition. No species with important conservation criteria have been recorded according to the IUCN or the Nicaraguan Red List. The Molossidae family is the group with the highest number of very significant collisions (X² = 53.61, p < 0.01), with the Pallas’s Mastiff Bat (Molossus molossus) being the one that presented very significant collisions (X² = 199.69, p < 0.01). Very significant collisions occur, with a peak in November 2015 (X² = 75.19, p < 0.01). Tower T15 presents the highest frequency of collisions, which is very significant (X² = 39.04, p < 0.01). The frequency of collisions remains very significantly higher in the three distance categories closest to the towers, from 0 to 14.9 m (X² = 43.64, p < 0.01). The highest frequency for very significant collisions of bats is that of insectivores (X² = 222.10, p < 0.01). A very significant frequency of collisions was observed in 2015 (X² = 68.75, p < 0.01). Key periods like fall and spring bird migration should be prioritized when planning collision monitoring plans. Standardized monitoring protocols and implementation of estimated mortality formulas that compensate for the search effectiveness of observers, the search area, and the removal of collisions are also important for not underestimating bird and bat collisions.

Introduction

Wind energy is positioned as an alternative in the search for cleaner and more sustainable energy sources to combat climate change and reduce dependence on fossil fuels.

However, as the wind industry expands, a crucial environmental dilemma arises bird and bat collisions with wind turbines. Although these technologies have a low impact in terms of greenhouse gas emissions, their interaction with local fauna poses challenges for the conservation of biodiversity in the region (Gasparatoset al., 2017).

As wind power plants are installed in various landscapes in the region, there is a risk of collisions with migratory birds, which travel long distances between their breeding and feeding areas. However, the resident birds in these projects are the most exposed because they spend the entire year living with this technology. Bats are another taxonomic group that is affected by this infrastructure. It is not clear why they collide; some hypotheses suggest that they are attracted by insects, which in turn are attracted to the tower, confusing these structures as perching sites or not being able to detect the structure because they are cylindrical, among others (Cryan & Barclay, 2009; Marquéset al., 2014).

Mitigation of bird-bat collisions in wind power plants requires multidisciplinary approaches that consider both technical and ecological aspects. Strategies such as appropriate placement of turbines based on the flight patterns of local wildlife, use of acoustic detection and repellent technologies, and collaboration between industry, governments, and conservation organizations are crucial to minimizing negative impacts (Arnettet al., 2011; Ledecet al., 2011; Hayeset al., 2019; Weaveret al., 2020).

However, challenges remain in the effective implementation of these measures due to the lack of long-term data and the need to consider the particularities of each species and habitat. According to Agudeloet al. (2021), most of the collision information is concentrated in the scientific literature for North America and Europe, with few studies in Latin America, and of the little that exists, the information available varies in quantity and detail of the information presented.

The objectives of this work have been the following: to determine the total number of deaths of birds and bats that impact wind towers, to know the spatial and temporal distribution of collisions of birds and bats, to relate aspects of the ecology of birds and bats with collisions with wind towers from 2014 to 2022.

Materials and Methods

Study Site

The study was carried out in a project in the Department of Rivas on the southern Pan-American Highway with central coordinates 11° 22′ 19.84″ N and 85° 45′ 27.27″ W. The project includes the installation of 22 wind turbines with a total capacity of 40 MW.

Data Collection

The study was based on the bird and bat collision protocol proposed by the authors of this document for wind power plants in Nicaragua, which includes the methodology for determining the observed mortality and estimated mortality with its formula and experiments to compensate for efficiency of observers to find carcasses, search area, and removal of carcasses by predators. For this article, only the observed mortality from collisions in the field will be taken, which consists, among other aspects, of monitoring twice a week, starting in the early hours of the morning, varying in each monitoring the start by location, concentrating only on the area of road and platform of the tower within a radius of 61 m to the center of the wind tower.

Data Analysis

All datasets were analyzed using an X² Goodness of Fit Test (Perez, 2021). Statistical analyses were conducted using Microsoft Excel and an extension of it.

Results and Discussion

Comparative Analysis between 2014 and 2022

Since bird-bat collision monitoring began in 2014 to 2022, eight non-consecutive monitoring campaigns have been carried out for a total of 30 months over eight years.

Birds between 2014 and 2022

119 collisions have been documented observed in these eight campaigns, belonging to 25 species corresponding to 14 families. Of the total collisions, 35 individuals could not be identified because only remains of the animal’s body were found, being able to identify even gender, family or any type of information depending on the state of the body. An important observation is the presence of feather remains in a good part of the bird collisions found, which indicates the presence of diurnal and nocturnal predators, so we think that bird collisions remain unrecorded due to this removal. Of the bird species identified, 17 species are resident, three are migratory species, two are transient species, one species with transient populations that migrate south, and two species with both resident and migratory populations.

During these eight monitoring campaigns, no species with an important conservation category were reported according to the IUCN (2021). Three species are on the Manzanarezet al.(2018), the migratory species Blackburnian Warbler (Setophaga fusca), and the resident species Mangrove Cuckoo (Coccyzus minor), both with the Near Threatened category; and the only migratory hummingbird for Nicaragua, the Ruby-throated Hummingbird (Archilochus colubris) with the category of Vulnerable.

The family with the highest frequency of collided species is that of pigeons (Columbidae) (Fig. 1), these being very significant (X² = 345.20, p < 0.01). This group differs from what was reported by American Wind Wildlife Institute (AWWI) (2021) regarding bird collisions in the United States, where, according to the report, it is the group of small passerines that tend to collide with wind towers.

Fig. 1. Frequency of collided bird families, 2014–2022 (N = 111).

The species with the highest frequency of collisions is the Common Ground Dove (Columbina passerina) species, with these collisions being very significant (X² = 72.05, p < 0.01) (Fig. 2).

Fig. 2. Frequency of bird species collided, 2014–2022 (N = 84).

Throughout this time, collisions per month and per year show very significant differences, especially for April 2016 (X² = 41.60, p < 0.01) (Fig. 3) unlike the previous period 2020 in which there were no differences, which once again highlights the importance of monitoring replicas over time, since by increasing the number of samples the differences are smoothed out. March and April continue to be important months since it is the spring migration season (South to North) and/or with the beginning of reproductive activity where there are greater movements of resident birds, as well as the beginning of the migration season starting in September.

Fig. 3. Bird collisions observed per month per year in eight monitoring campaigns, 2014–2022 (N = 119).

The analyses of collisions per tower in these eight campaigns show significant differences, especially in the tower where tower 13 is historically mentioned (X² = 36.48, p < 0.05). The hypothesis is maintained that it is surrounded by a wall of soil serving as a “corral” where pigeon species gather, these being the most collided, as well as the presence of crops and houses near the tower (Fig. 4).

Fig. 4. Bird collisions per tower in eight monitoring campaigns, 2014–2022 (N = 119).

Between the periods from 2014 to 2022, bird collision distances continue to show very significant collisions between 0 and 5 m away from the turbines (X² = 268.96, p < 0.01) (Fig. 5).

Fig. 5. Distance from bird collisions to towers in eight monitoring campaigns, 2014–2022 (N = 119).

Categorizing the size of collisions as small and large, it was found that there are no differences (X² = 2.09, p > 0.05); however, a greater number of fatalities was found in small birds. In the monitoring protocol, a large bird is considered based on the weight and size of a White-tipped Dove (Leptotila verreauxi) (Fig. 6).

Fig. 6. Collisions observed by bird size during eight monitoring campaigns, 2014–2022 (N = 94). G = big bird, P = small bird.

When analyzing bird collisions according to the food guild, we see that the granivore group had a very significant collision frequency (X² = 84.00, p < 0.01). This is consistent with the most collided family and species in this period being that of pigeons (Fig. 7).

Fig. 7. Collisions observed by food guild during eight monitoring campaigns, 2014 to 2022 (N = 96). C = Carnivore,F = Frugivore, G = Granivore, I = Insectivore,N = Nectarivore, O = Omnivore.

A very significant frequency of collisions is observed in non-passerines birds (X² = 42.26^**, p < 0.01) (Fig. 8).

Fig. 8. Collisions observed by type of bird during eight monitoring campaigns, 2014 to 2022 (N = 100). NP = No Passerine, P = Passerine, R = bird of prey.

A new analysis is carried out comparing the different monitoring periods per year. Very significantly higher fatality frequencies were observed in 2016 (X² = 60.16, p < 0.01). It is important to clarify for this analysis that not all years have the same monitoring intensity (Fig. 9).

Fig. 9. Bird collisions observed per year in eight monitoring campaigns, 2014 to 2022 (N = 119).

Bats between 2014 and 2022

134 collisions of bats belonging to 18 species corresponding to four families were observed in these eight monitoring campaigns. Twenty-four individuals could not be identified because only remains of the animal’s body were found, being able to identify even gender, family, or any type of information depending on the state of the body.

During this period, no species with important conservation criteria have been recorded according to the IUCN or Nicaraguan Red List (Manzanarezet al., 2018).

The Molossidae family continues to be the group with the most highly significant collisions (X² = 53.61, p < 0.01) (Fig. 10). The species of this family are characterized by flying high and eating insects. According to American Wind Wildlife Institute (AWWI) (2021), of the more than 25 species of bats that collide in North America, the families Vespertilionidae and Molossidae correspond to the highest collision percentages.

Fig. 10. Frequency of collided bat families in eight monitoring campaigns, 2014 to 2022 (N = 124).

The species with the highest number of collisions was the Pallas’s Mastiff Bat (Molossus molossus), being very significant (X² = 199.69^**, p < 0.01) (Fig. 11).

Fig. 11. Frequency of bat species collided, 2014–2022 (N = 110).

There are very significant collisions with a peak in November 2015 (X² = 75.19^**, p < 0.01) (Fig. 12).

Fig 12. Observed bat collisions by month and year in eight monitoring campaigns, 2014–2022 (N = 134).

Tower 15 continues to be the tower with the highest frequency of collisions, this being very significant (X² = 39.04, p < 0.01) (Fig. 13). The hypothesis remains that this tower is surrounded by forest cover, these being shelters for bats, however, more observation is needed.

Fig. 13. Observed bat collisions per tower in eight monitoring campaigns, 2014–2022 (N = 134).

The frequency of collisions remains very significantly higher in the three distance categories closest to the towers, that is, from 0 to 14.9 m (X² = 43.64, p < 0.05) (Fig. 14).

Fig. 14. Distance from bat collisions to towers in eight monitoring campaigns, 2014–2022 (N = 134).

Fig. 15 shows that the highest frequency of very significant collisions of bats continues to be that of insectivores (X²= 222.10, p < 0.01).

Fig. 15. Frequency of bat collisions by the food industry in eight monitoring campaigns, 2014–2022 (N = 115).

A new analysis is carried out comparing the different monitoring campaigns over the years. Fig. 16 shows a frequency of very significant collisions in 2015 (X²= 68.75, p < 0.01).

Fig. 16. Bat collisions observed by year, 2014–2022 (N = 134).

Knowledge about the reproductive activity of bats is limited. This period is possibly one of the phases with the greatest physical activity, where a possible hypothesis is that this is when the number of collisions could increase, such is the case of pregnant or lactating females, which will have to increase their resource foraging activity to maintain the energy charge for their offspring. Another aspect to consider during the year and about which little is known in Nicaragua as well, is the availability of insects in the study area. As mentioned above, the Molossidae family is the one that has had the most collisions and is made up of insectivorous species. According to Torres-Floreset al. (2012), in Mexico, during a study on bat ecology, a greater number and biomass of arthropods were recorded in the rainy season.

According to Medina (2014), the reproductive cycle of bats varies among species in Nicaragua. Generally, only one pup is born after approximately three months of gestation, with one or two births throughout the year. The calves are generally born at the end of the dry season, or the beginning of the rainy season and a second period may occur with births in the middle or end of the rainy season. In the case of bats in Costa Rica, pregnant females can be found from January to March and again between June and July (LaVal & Rodríguez, 2002).

Hypotheses remain about why bats collide with wind towers, among them, bats could use the turbines as perching sites, bats are attracted by the sounds of the engines, because they cannot detect the cylinder of the turbine or the turbine blades in motion, rapid changes in pressure produced by the blades can cause internal injuries or disorientation among others (Cryan & Barclay, 2009; Kunzet al., 2007; Sélem & Meléndez, 2015).

The collisions of birds and bats by month, by towers, and between years can vary from one period to another between dry and rainy seasons, due to reproductive aspects of the species, atmospheric conditions, lunar phase, and availability of insects in the case of bats, surrounding vegetation among others, which is why it is necessary to monitor consecutive periods and for several years to determine trends between these variables according to the degree of knowledge.

Conclusions

In these eight periods between 2014 and 2022, the monitoring has been carried out for short intervals between several years. The numbers of bird-bat collisions differ between the months of the year and between the dry and rainy seasons, so it is advisable to maintain the monitoring scheme that has been carried out since the park began operating. In this context, collision studies have been prioritized in key periods of migration, starting from September (the month in which the first migratory movements from North America begin), fall migration (north to south), until December (when the season of strong winds begins, so there will be less collision of birds and bats), or from March to May during the spring migration (south to north) and the beginning of the breeding season of resident birds.

There have been months in which collisions are important for both birds and bats, these being the months of September to November, months that should be prioritized. However, for birds, the months of March to April are also important because of the beginning of spring migration (south-to-north migration) and an increase in activity because it is the breeding season for resident birds. In the case of bats, there is not much information available about the causes of why they collide with wind towers; one of the possible hypotheses is their reproductive activity, whose periods in Nicaragua are at the end of the dry season and possibly in the middle or at the end of the rainy season; all of the above justifies maintaining the monitoring scheme that has been carried out over the last few years.

It is extremely important to standardize collision monitoring protocols and to implement estimated mortality formulas that compensate for the search effectiveness of observers, the search area, and the removal of collisions by day and night predators, all to be able to compare the collisions found within a country and between countries. At the same time, it is essential to access information and publish publications to promote a proactive approach to the conservation of biodiversity in the context of wind energy.

By providing recommendations based on solid data and access to information on collisions, companies will not only be able to take preventive and corrective measures that reduce impacts on local fauna, such as those indicated in the Guidelines on Environment, Health, and Safety in a wind energy project published by the World Bank (World Bank Group, 2015), ensuring the operational efficiency of these projects but will also contribute to achieving the Sustainable Development Goals (SDGs) established by the United Nations.