Study finds wind farms impact breeding bird distribution

Hen harrier in flight. Image credit, Andreas Trepte.If you follow this site, you may have seen that we've already reviewed studies on the impacts of wind turbines to: 1) birds, 2) bats, and 3) marine habitat. Wind farms are being developed across the world at a rapid pace to provide clean energy and (hopefully) fight global warming.  But we need to give careful consideration to their impacts on habitat so that we can find a way to provide clean energy while minimizing harm to species.

Now an interesting study enters the fray looking at the effects of wind farms on the overall occurrence of birds in an area. This study takes a unique approach. Most attention on this issue has focused on whether turbines kill birds through direct strikes. This new study is one of the first to look at whether wind turbines and associated infrastructure influence distribution of breeding birds in general.

Study findings...
The researchers conducted bird surveys at 12 upland wind farms in the UK.  They found:

• Seven of the 12 species studied exhibited significantly lower frequencies of occurrence close to the turbines.

• The reduction in bird occurrence ranged from 100 to 800 meters depending on the species.

• Based on these results, the study predicts a 15–53%, reduction in breeding density within 500 meters of the wind farm depending on the species.

• The study found buzzards (Buteo buteo), hen harriers (Circus cyaneus), golden plovers (Pluvialis apricaria), snipes (Gallinago gallinago), curlews (Numenius arquata) and wheatears (Oenanthe oenanthe) to be most affected.

One confounding aspect of the study is that wind farms are not randomly located. To avoid a type 1 error in the study, the researchers incorporated measures to to control for a variety of environmental factors (e.g. vegetation composition, proximity to roads, wind conditions, etc) that might otherwise affect both bird distribution and wind farm placement.

Implications for Conservation
The implications of this study really depend on the reason why wind farms are causing the reduced bird distribution. Unfortunately, the study wasn't able to distinguish the reason. It could be any of the following:

• Birds may be modifying their behavior in response to wind turbines and simply avoiding the area.

• Wind turbines might be killing birds leading to reduced local population.

• It's possible wind farms are leading to reduced avian productivity in the area.

• A combination of the above factors could be at work.

The researchers affirm that finding the cause is important. They state,

"If there is high mortality of birds breeding close to the turbines associated with collision, then a wind farm may become a population sink if repeatedly colonized by naive birds. If, however, the birds simply avoid breeding close to the turbines, then depending upon the strength of density dependence displaced birds may settle elsewhere with little cost or ultimately be lost to the population. Research to disentangle these mechanisms should be a high priority.

However, they argue that in the absence of such an explanation, we should use their calculations of reductions in habitat usage to estimate potential losses to avian populations and likely reductions in breeding bird densities from wind farm projects.

--Reviewed by Rob Goldstein

Pearce-Higgins, J., Stephen, L., Langston, R., Bainbridge, I., & Bullman, R. (2009). The distribution of breeding birds around upland wind farms Journal of Applied Ecology DOI: 10.1111/j.1365-2664.2009.01715.x