Reproductive success of birds in relation to wind turbine proximity in Iowa

Molly K. Gillespie and Stephen J. Dinsmore

Dept. of Natural Resource Ecology and Management, Iowa State University, Ames, IA 50011

Corresponding author email: mollyg@iastate.edu

As concerns continue to rise over the costs and environmental impacts of traditional fuel sources such as

fossil fuels and nuclear energy, wind energy is becoming an increasingly important factor in future energy

development. Previous studies have assessed the impact of direct mortality for birds from wind turbines, but few

have looked at indirect effects. Our objective was to model avian nest survival in relation to proximity to turbines

to determine if turbine proximity altered the productivity of a site. We hypothesized that nest survival might be

lower at the turbine sites versus the control sites, perhaps due to changes in stress levels or predator

communities, both of which could be altered by the changes in land use, fragmentation of the landscape, or

increased human traffic that is related with wind farms. We modeled the daily survival of > 400 Red-winged

Blackbird nests at wind farms and paired control sites in three Iowa counties (Story, Osceola, and Hancock) from

May through July of 2011 and 2012. We used Program MARK to model the survival of nests as a function of

site- and nest-specific covariates during both incubation and nestling stages. Patterns in the daily survival of

nests illustrate a possible consequence of wind turbines on a nesting songbird and should be considered when

creating wind turbine placement guidelines.

Abstract

We monitored 418 Red-winged Blackbird nests during the incubation stage (Figure 3) and 356 nests

during the nestling stage (Figure 4) from 14 May through 17 July of 2011 and 2012. Nests were located by

systematically searching roadside ditches around wind farms (Figure 1) in central, north central, and

northwestern Iowa where there are concentrations of wind farms due to the high average wind speeds. We also

searched at control sites within 2 to 5 km of each wind farm, a distance that is beyond the influence of the wind

farm (U.S. Fish and Wildlife Service 2003) while still being close enough to minimize differences in topography,

land use, or other factors.

When nests were found during the incubation stage, they were aged via egg floatation (Loekemoen and

Koford 1996). Nestlings were aged based upon feather development patterns. Nests were monitored every 3-4

days after discovery until they either failed or succeeded. A nest was considered successful if one or more young

hatched (for the incubation stage) or fledged (for the nestling stage) (Mayfield 1961). We ran nest survival

models in program MARK that included the effect of individual nest covariates (Table1) as well as year and site

effects. A best model was chosen using Akaike’s Information Criterion (AIC) for both incubation and nestling

stages.

Methods

Our best model for both stages included a site by treatment by year effect, so that each county had

different survival rates between years, and also between the treatment and control sites. There was a linear trend

of season, with survival generally decreasing as the season progressed. The distance to an edge was a

significant effect on the nestling stage. None of the other covariates had a significant effect on nest survival.

Across our study, we found no significant difference between any of the control and turbine sites (Figure 2,

Figure 3). The wind farm sites trended towards higher survival at three out of the six sites for the incubation

stage, and at four out of the six sites for the nestling stage. However, our best model for the incubation stage did

contain a non-significant effect of turbine proximity, with survival increasing as distance to turbine increased.

Results

Lokemoen, J.T., R.R. Koford. 1996. Using candlers to determine the incubation stage of passerine eggs.

Journal of Field Ornithology 67.4:660-668.

Mayfield, H.R. 1961. Nesting success calculated from exposure. Wilson Bulletin 73:255-261.

U.S. Fish and Wildlife Service 2003. Interim guidelines to avoid and minimize wildlife impacts from wind turbines

[online] http://www.fws.gov/habitatconservation/wind.pdf.

Literature Cited

• Funding provided by the Iowa Department of Natural Resources/USFWS through a State Wildlife Grant

(Project Number T-51-R-1)

• Nextera Energy; specifically Skelly Holmbeck and the staff at Story I Wind Farm

• Iowa Department of Natural Resources Staff

• Landowners and managers for their cooperation

• Field Technicians: Joe Lambert, Trang Nguyen, Matt Peterson, Scott Buckallew, and Corey Lange

Acknowledgements

Iowa currently ranks second in the nation for installed wind energy capacity and 75% of the state is

currently considered suitable for wind energy development. Much of this area is likely to be developed in coming

years, as the U.S. Department of Energy’s goal is to have 20% of the domestic energy needs met by wind energy

by 2030. Previous studies in Iowa have focused on the direct mortality of birds from wind turbine collisions rather

than any potential indirect effects. Our goal was to model avian nest survival in relation to proximity to turbines in

order to determine whether certain species exhibit any avoidance behavior that may lead to population declines.

Introduction

As concerns continue to rise over the costs and environmental impacts of traditional fuel sources such as

fossil fuels and nuclear energy, wind energy is becoming an increasingly important factor in future energy

development. Nest survival can be a good indicator of the productivity of a site, as density can be misleading in

situations where nest survival is low (sink populations). For a generalist species like the Red-winged Blackbird,

the presence of turbines does not appear to have an impact on nest survival. We recommend that future studies

look at nest survival of more specialized species, including species of concern. More sensitive species may be

impacted differently by turbine proximity, and this information should be taken into account when determining

turbine siting guidelines with relation to those species’ habitat requirements.

Discussion

Figure 2: Predicted daily survival (95% confidence intervals) for A) Hancock County 2011,

B) Hancock County 2012, C) Osceola County 2011, D) Osceola County 2012, E) Story

County 2011, and F) Story County 2012 for sites with wind turbines (red) and for paired

control sites (black) for the incubation stage of Red-winged Blackbirds. .

Figure 3: Red-winged Blackbird nest

containing two parasitic Brown-headed

Cowbird eggs.

Covariate Measurement

Height height of nest from ground (cm)

Veg height of vegetation above nest (cm)

Edge distance from nest to a road or fencerow (m)

Woodlot distance from nest to nearest woodlot (m)

Turbine distance from nest to nearest turbine (m)

RobelVarvariance of robel pole readings at nest and in

each of the four cardinal directions

RobelMeanmean of robel pole readings at nest and in each

of the four cardinal directions

Cowbirdpresence of cowbird parasitism at nest (0=none,

1=parasitized)

Table 1: Individual nest covariates measured at nests

and used in modeling predicted daily survival in

MARK.

A B

C D

E F

Figure 5: Predicted daily survival (95% confidence intervals) for A) Hancock County 2011,

B) Hancock County 2012, C) Osceola County 2011, D) Osceola County 2012, E) Story

County 2011, and F) Story County 2012 for sites with wind turbines (red) and for paired

control sites (black) for the nestling stage of Red-winged Blackbirds.

A B

C D

E F

Table 2: Covariates from the top ranked model using AIC in program MARK for each nest stage. A

single symbol (+ or -) indicates a non-significant trend in either the positive (+) or negative (-)

direction, a double symbol (++ or --) indicates a significant trend (α=0.05).

Nest Stage Covariates effecting daily survival

Incubation Site*Year, Day (--), Height (+), Turbine(+)

Nestling Site*Year, Day (--), Edge (--), Veg (-)

Figure 1: Typical nesting habitat from

our study.

Figure 4: Red-winged Blackbird nest containing

Red-winged Blackbird and Brown-headed

Cowbird nestlings, approximately 7-8 days of

age