Collision Potential of Eiders and Other Birds Near a Proposed Windfarm at St. Lawrence Island, October-November 2002


Title: Collision Potential of Eiders and Other Birds Near a Proposed Windfarm at St. Lawrence Island, October-November 2002
Publication Date:
March 01, 2003
Pages: 37

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Day, R.; Rose, J.; Ritchie, R.; Shook, J.; Cooper, B. (2003). Collision Potential of Eiders and Other Birds Near a Proposed Windfarm at St. Lawrence Island, October-November 2002. Report by ABR Inc. pp 37.
  • During spring and fall, many eiders pass St. Lawrence Island during their passage between breeding and wintering grounds. At those times, they may collide with human-made structures at the village of Gambell, on northwestern St. Lawrence island. Because the Alaska Industrial Development Authority (AIDEA)/Alaska Energy Authority is planning on installing a windfarm at Gambell, we were hired to study bird movements in the vicinity of Gambell and to evaluate the probability of collision with the proposed windfarm, especially the collision of endangered Spectacled (Somateria fischeri) and Steller's (Polysticta stelleri) eiders.
  • The objectives of this study were to: (1) use visual sampling and ornithological radar to observe the migration and movements of eiders and other bird species near Gambell during late fall; (2) measure movement rates, locations of movement, behavior, and flight altitudes of eiders and other bird species near Gambell during late fall; (3) collect information on bird movements that could be used to help site the proposed windfarm in such a manner as to minimize the risk of bird collisions; and (4) to evaluate the collision potential for eiders at Gambell during late fall. To complete these objectives, we conducted surveys for eiders and other species at Gambell in October-November 2002.
  • We recorded 876 groups of birds visually (representing 26,172 birds) and 687 radar targets of birds during this survey.
  • Frequent precipitation (rain) and high winds (causing high swells at sea and extensive sea clutter on the radar display) made radar sampling impossible or difficult much of the time. Consequently, we emphasized the visual sampling but conducted radar sampling when conditions allowed.
  • During visual sampling, movement rates were dominated numerically (in decreasing order) by alcids (almost entirely murres), eiders, unidentified waterbirds, gulls (especially Glaucous Gulls and Black-legged Kittiwakes), other ducks (especially Long-tailed Ducks), and cormorants. Eider movements consisted of Spectacled, King, and Common eiders; Steller's Eider were not recorded.
  • Mean movement rates of total eiders observed visually varied geographically, with all recorded flying only over the ocean and none flying over the mountain, the windfarm, or the town. Almost all non-eider taxa were recorded moving over the ocean, with raptors recorded moving only over the windfarm and the town and with only gulls recorded moving over all four zones.
  • Mean flock sizes varied dramatically among species and species-groups. The mean flock size of eiders was 28.0 birds.
  • Mean flight altitudes also varied dramatically among species and species-groups. The highest mean flight altitude occurred in total gulls, followed (in decreasing order) by cormorants, raptors, unidentified waterbirds, loons, other ducks, eiders, and alcids. Eiders had a mean flight altitude of 1.8 m and a maximal flight altitude of 15 m. Because essentially all birds flew only over the ocean, we were unable to examine whether mean flight altitudes varied geographically.
  • Flight behavior of birds observed visually was dominated overall by contouring flight (i.e., following the shoreline; ~64% of all flocks), followed (in decreasing frequency) by straight-line directional flight (~30% of all flocks), erratic, flying/landing, and circling. Because essentially all birds flew over the ocean, we were unable to examine whether flight behavior varied geographically.
  • The high seas recorded during this study and the low flight altitudes of eiders resulted in an underestimation of movement rates of that group over the ocean with ornithological radar. Although the number of eiders recorded by the radar over the ocean was underestimated, the radar did an excellent job of detecting targets over land, which was an important aspect of this study. The view over land was excellent and was not affected by sea clutter. Therefore, we considered the radar to provide an underestimate of numbers of eiders moving over the ocean but to provide an accurate St. Lawrence Island Eiders ii estimate of numbers of eiders moving over land.
  • "Eiders" exhibited low mean movement rates on radar during most dates and under most weather conditions, with most means averaging 1-3 targets/h. "Non-eiders" exhibited mean movement rates that were ~20 times larger than those for "eiders," with most means averaging ~25 targets/h.
  • Mean movement rates of "eiders" were ~175% higher at night than during the day, whereas mean movement rates of "non-eiders" were ~160% higher during the day than at night (primarily because of all of the daytime gull movements).
  • Mean movement rates of "eiders" on radar varied geographically, with essentially all birds flying only over the ocean and none flying over the mountain and town, similar to what was recorded visually. We believe that the one "eider" target recorded flying over the proposed windfarm was not that of not eiders. Mean movement rates of "non-eiders" also varied geographically, with none recorded over the mountain, moderate numbers moving over the proposed windfarm and town, and much higher numbers moving over the ocean.
  • "Eiders" were recorded on radar exhibiting three of the five standardized behaviors, although ~90% of all "eider" targets flew with straight-line directional characteristics. "Non-eiders" exhibited all five of the standardized behaviors, with ~60% of all "non-eider" targets flying with straight-line characteristics and another 34% flying by contouring (i.e., following the shoreline).
  • We recorded no bird mortality at either the FAA towers or the meteorological tower.
  • Both the radar and visual data indicate that the number of birds moving and wintering in this area is large: we saw a total of >26,000 birds during our visual sampling, with an overall mean daily movement rate of 700 birds/h.
  • The visual data indicate that eiders form a significant proportion of the birds seen near Gambell at this time of the year, representing 24.5-42.9% of all birds.
  • Both the daytime visual and daytime and nighttime radar-movement data indicate that most birds passing Gambell in the fall do so over the ocean, with very little movement over land, including the proposed windfarm (primarily gulls and raptors). Although we saw no eiders or waterfowl of any species flying over land, local villagers informed us that eiders and Long-tailed Ducks fly over the spit on which Gambell occurs after the sea freezes and snow obscures the boundary between sea and land. At those times, these birds "cut the corner" over the spit while moving back and forth as polynyas open and close on the northern and southern sides of the island. Local villagers told us that, when these birds do cross the spit, they occasionally hit the FAA towers.
  • The flight-altitude data indicate that flight altitudes of most species over the ocean are so low that, unless they change altitude as they cross land, they would pass under the rotor blades of the turbines as they are envisioned at this time.
  • The behavioral data indicate that, because most of the birds seen in this study fly by contouring (i.e., following the shoreline), those birds flying over the ocean will have little chance of hitting wind turbines. On the other hand, if a flock of eiders does deviate to cross over the spit, the other members of the flock will follow, resulting in a low probability of collision but a high probability of substantial mortality if a collision does occur.
  • Although summer bird movements were not studied, we suggest that the location of the auklet colony should be a consideration in site selection at this windfarm.
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