Environmental Engineering Reference
In-Depth Information
Table 2.1
BIRD MORTALITY FROM
ANTHROPOCENTRIC CAUSES
IN THE UNITED STATES
Object
Mortality (Birds Per Year)
Power Grid
130-174 million
Cars and Trucks
60-80 million
Buildings
100-1000 million
Telecom Towers
40-50 million
Pesticides
67 million
Wind Turbines
6400
Source
: Wizelius, Tore. (2007).
Developing Wind Power
Projects: heory and Practice
. Oxford: Earthscan.
2.6.2 The Challenge of Estimating Bird Mortality
One common method for assessing the impact of a wind energy project on
the avian population is to estimate bird mortality, which is often expressed
as the number of birds killed in a given area (i.e., bird kills per square kilo-
meter per year). Separate bird mortality estimates are often calculated for
any endangered species inhabiting an area.
Unfortunately, data can be misleading or altogether inaccurate due to
a number of confounding factors. Many bird mortality estimates use data
from other proxy wind power sites to generate rough estimates of bird kills.
However, species, migration, and scavenging behavior of birds as well as
the characteristics of each wind farm difer. Accordingly, estimates that are
based on proxy data from other sites will never be directly transferrable.
Even studies done post-project construction can be inaccurate due to
enumeration challenges. For example, bird mortality is usually calculated by
counting the number of bird carcasses found within the site area. However,
the number of carcasses found is dependent on the number of birds migrat-
ing through an area. Studies that fail to account for seasonal migration
variations are unrepresentative. Moreover, counting bird carcasses found
within a site boundary produces underestimates of true mortality. Birds
that are injured by wind turbines can ly of to other areas where they per-
ish. Furthermore, bird carcasses that fall to the ground are frequently car-
ried of by scavengers.
Even when bird mortality estimates are relatively representative, abso-
lute mortality numbers tell only part of the story. A thousand birds killed
per year within the boundary of a wind site represents a signiicant mortal-
ity rate if ten thousand birds pass through the site each year. However, if
