Predicting the Weather-Dependent Collision Risk for Birds at Wind Farms - Wind and Wildlife - page 15

Fig. 6 Response curves of the GAMM for the common scoter displaying the relationship between
the flight altitude and predictor variables. The values of the environmental predictors are shown on the
X-axis and the probability on the Y-axis in logit scale. The degree of smoothing is indicated in
the title of the Y-axis. The shaded areas and the dotted lines show the 95 % Bayesian confidence
intervals
to bird migration, and they offered a statistical basis for assessing changes in
migration altitude in response to topographical and meteorological parameters.
For the species for which the number of rangefinder tracks was sufficient to undertake
GAMM models a general characteristic was the tendency for a decreasing flight
altitude during head wind, increasing wind speed and high levels of humidity, and
increasing flight altitude during tail winds, decreasing wind speed and low levels of
humidity. Humidity was considered to be a proxy for visibility. Accordingly, the
models indicate increasing collision risks for landbird species during weather
conditions which influence the birds to fly at altitudes lower than they would other-
wise use and that coincide with rotor-swept height, whereas a wide range of seabird
species seem to face a higher collision risk during weather conditions which
influence the birds to fly at altitudes higher than they would otherwise use and that
coincide with rotor-swept height. With a few exceptions, seabirds generally showed
a high degree of avoidance of marine wind farms during migration, and hence
collision risk for these species was low. Thus, the weather-dependent collision risk
for birds at wind farms seems to be a general phenomenon, rather than a risk related
to certain species of birds.