May 24 2011
Collisions: Wave Power
Wave-energy-generating devices may indirectly impact marine birds by altering oceanographic processes and food availability (with implications for trophic cascades). These same devices could also enhance habitats by directly providing roosting habitats, but also causing prey aggregation due to suitable substrates for sessile organisms. Wave energy devices could also improve and protect foraging opportunities for marine birds. (Grecian, Inger, and Attrill 2010).
Figure 1: Wave-energy Generating Device (Power Buoy: Point Absorber)
However, wave-energy-generating devices also pose a huge risk for diving birds. The energy convertors, anchor chains, and cabling are all highly mobile and hard to navigate around for these birds. The risk of birds colliding with these structures is highest when diving for prey, but can vary with the type of diving technique. Surface divers have slow and controlled dives but plunge-diving species have a lower margin for voidance, which is more threatening. However, no experiments have calculated potential collision risks to marine birds. These devices will also increase turbidity around moving parts, reducing visibility and increasing potential collision risk. (Grecian, Inger, and Attrill 2010).
Figure 2: Diving Bird
Wave-energy-generating devices can create the risk of entrapment for both fish and diving birds. The devices that use pressure differentials to drive internal turbines (oscillating water columns of overtopping devices) have enclosed chamber sections that are partially exposed to open ocean. This can be a risk for marine birds that are capable of entering the chamber and could be killed by the turbines or propulsion of water from within the device. One solution suggested is covering the openings with protective mesh. (Grecian, Inger, and Attrill 2010).
Figure 3: Wave Energy: Overtopping Device
Collisions: Wind Turbines
Wind turbines have many impacts and hazards to coastal and inland birds, fish, marine mammals, and bats. Avoidance ability and vulnerability to collision with wind turbines varies with species, size, nocturnal or crepuscular, age, reproductive stage, weather, and amount of light. During bad weather marine birds are at greater risk due to reduced visibility and maneuverability. Flight pattern is also an important factor. For example, raptors drift on wind currents and practice contour flying, making them more likely to collide with turbines. (Wilson, Elliott, Cutts, Mander, and Mendao 2010)
Figure 4: Offshore Wind Farm in UK
Different species are also affected differently. Gull species are frequent victims because they are so abundant and widespread. Raptors however, have low collision rates but increase when large numbers of them occur in areas with high densities of turbines. Passerine migrants collide with turbines at a low rate given the large amount passing through. Large birds tend to be less maneuverable and have a greater risk of colliding with a turbine structure. Geese have been proven to be adept at avoiding collision. But, for migrant birds, turbines on land only cause problems when they are situated on exposed sites with high migration densities such as passes, straits, and peninsulas.
Indirect impacts of wind turbines to birds are the disruption of foraging behavior, breeding activities, and the change in migratory patterns. Direct impacts of wind turbines are increased mortality overall, alterations in availability of food, a change in roost and nesting resources, and increased predation risks. Birds avoid areas around turbines as a response to visual or audio cue because the turbines act as a barrier to movement. Birds also respond to destruction, modification, and creation of habitat associated with wind turbines construction and operation. There are also direct population changes because birds collide with turbine structures. However, habituation can be important with regard to avian mortalities by wind turbines. When other anthropogenic structures exist such as chimneys, birds are used to avoiding large structures and collision is reduced. Birds may also learn with time to avoid the turbines. (Wilson, Elliott, Cutts, Mander, and Mendao 2010).
Figure 5: Birds colliding with wind turbine
Bats are much different than birds, because they are attracted to the wind turbines and will actively investigate the turbines. There are several possible reasons for so many bat fatalities near wind turbines. Some bats may think the turbines are potential roosts. There are many insects present around the turbines, and bats will chase their food into the turbines. Bats are also attracted to the audible and ultrasonic sound produced by the turbines. Although, the bats may not be able to detect the turbines and rotor movements, and complex electromagnetic fields can confuse and disorient the bats. Finally, bats are very susceptible to depressurization injuries such as barotrauma. Barotrauma is a sudden decrease in air pressure near moving blades, which causes tissue damage to air-containing structures in the bats. (Wilson, Elliott, Cutts, Mander, and Mendao 2010).
Figure 6: Bats
Marine mammals have the lowest collision rate of the three types of animals. There are several possible causes for mortality and collision between wind turbines and marine mammals. Mortality through collision with increased boat traffic is unlikely during operation because collisions with boats are rare. Marine mammals will leave the area due to disturbance depending on the type of species. Noise damage to the marine mammals is possible during operation with low levels. Finally, construction can cause a disruption of normal behavior, but becomes less common when the marine mammals have become accustomed to the operational levels of noise and activity. (Wilson, Elliott, Cutts, Mander, and Mendao 2010).
The impact of offshore wind farms may still not be completely clear. Further research is needed to assess the affects of weather and light on animal collisions with the turbines. Little data has been collected offshore due to the expense of at-sea surveys, which leaves a lack of habitat utilization of potential developmental areas.
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