679
11E-mail: broberts@bard.edu
Manuscript received 23 August 2011; accepted 30 April 2012.
The Condor, Vol. 114, Number 4, pages 679?688. ISSN 0010-5422, electronic ISSN 1938-5422. ? 2012 by The Cooper Ornithological Society. All rights reserved. Please direct 
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reprintInfo.asp. DOI: 10.1525/cond.2012.110136
ARE AGROFUELS A CONSERVATION THREAT OR OPPORTUNITY FOR GRASSLAND 
BIRDS IN THE UNITED STATES? 
BRUCE A. ROBERTSON1,2,3,11, ROBERT A. RICE1, T. SCOTT SILLETT1, CHRISTINE A. RIBIC4,  
BRUCE A. BABCOCK5, DOUGLAS A. LANDIS2,6, JAMES R. HERKERT7, ROBERT J. FLETCHER JR.8,  
JOSEPH J. FONTAINE9, PATRICK J. DORAN10, AND DOUGLAS W. SCHEMSKE2
1Smithsonian Conservation Biology Institute, Migratory Bird Center, National Zoological Park, Washington, DC 20008
2DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824
3Division of Science, Mathematics, and Computing, Bard College, Annandale-on-Hudson, New York 12504 USA
4U.S. Geological Survey, Wisconsin Cooperative Wildlife Research Unit, University of Wisconsin, Madison, WI 53706
5Center for Agricultural and Rural Development, Iowa State University, Ames, IA 50011
6Department of Entomology, Michigan State University, East Lansing, MI 48824
7Illinois Natural History Survey, University of Illinois at Urbana/Champaign, Champaign, IL 61820
8Department of Wildlife Ecology and Conservation, University of Florida, Gainesville, FL 32611
9U.S. Geological Survey, Nebraska Cooperative Fish and Wildlife Research Unit, University of Nebraska, 
School of Natural Resources, Lincoln, NE 68583-0984
10The Nature Conservancy, 101 East Grand River Avenue, Lansing, MI 48906
Abstract. In the United States, government-mandated growth in the production of crops dedicated to biofuel 
(agrofuels) is predicted to increase the demands on existing agricultural lands, potentially threatening the per-
sistence of populations of grassland birds they support. We review recently published literature and datasets to 
(1) examine the ability of alternative agrofuel crops and their management regimes to provide habitat for grass-
land birds, (2) determine how crop placement in agricultural landscapes and agrofuel-related land-use change 
will affect grassland birds, and (3) identify critical research and policy-development needs associated with agro-
fuel production. We ?nd that native perennial plants proposed as feedstock for agrofuel (switchgrass, Panicum 
virgatum, and mixed grass?forb prairie) have considerable potential to provide new habitat to a wide range of 
grassland birds, including rare and threatened species. However, industrialization of agrofuel production that 
maximizes biomass, homogenizes vegetation structure, and results in the cultivation of small ?elds within largely 
forested landscapes is likely to reduce species richness and/or abundance of grassland-dependent birds. Realiz-
ing the potential bene?ts of agrofuel production for grassland birds? conservation will require the development 
of new policies that encourage agricultural practices speci?cally targeting the needs of grassland specialists. The 
broad array of grower-incentive programs in existence may deliver new agrofuel policies effectively but will re-
quire coordination at a spatial scale broader than currently practiced, preferably within an adaptive-management 
framework.
Key words: biofuels, biodiversity, cellulosic ethanol, Conservation Reserve Program, prairie, switchgrass.
?Son los Agrocombustibles una Amenaza o una Oportunidad para la Conservaci?n de las Aves de 
Pastizal en Estados Unidos?
Resumen. En los Estados Unidos, se predice que el crecimiento impuesto por el gobierno en la producci?n de 
cultivos dedicados a biocombustibles (agrocombustibles) aumentar? las demandas en las tierras de cultivo existentes, 
amenazando potencialmente la persistencia de las poblaciones de aves de pastizal que albergan. Revisamos la litera-
tura publicada recientemente y las bases de datos para (1) examinar la habilidad de los cultivos alternativos de agro-
combustibles y sus reg?menes de manejo para brindar h?bitat a las aves de pastizal, (2) determinar c?mo la ubicaci?n 
de los cultivos en los paisajes agr?colas y los cambios en el uso del suelo relacionados a los agrocombustibles afectar?n 
The Condor 114(4):679?688
? The Cooper Ornithological Society 2012
REVIEW
680 BRUCE A. ROBERTSON ET AL.
las aves de pastizal, e (3) identi?car necesidades de investigaci?n cr?ticas y de desarrollo de pol?ticas asociados con 
la producci?n de agrocombustibles. Encontramos que las plantas nativas perennes propuestas como materia prima 
para los biocombustibles (Panicum virgatum y praderas mixtas de pastos y yuyos) tienen un potencial considerable 
para brindar h?bitat nuevo a una amplia variedad de aves de pastizal, incluyendo especies raras y amenazadas. Sin 
embargo, la industrializaci?n de la producci?n de agrocombustibles que maximiza la biomasa, homogeniza la estruc-
tura de la vegetaci?n y resulta en el cultivo de peque?os campos adentro de paisajes mayormente forestados probable-
mente reduce la riqueza de especies y/o la abundancia de aves que dependen de pastizales. Entender los bene?cios 
potenciales de la producci?n de agrocombustibles para la conservaci?n de las aves de pastizal requerir? el desarrollo 
de nuevas pol?ticas que promuevan pr?cticas agr?colas que apunten a las necesidades de los especialistas de pastizal. 
La amplia gama de programas de incentivo que existe para los productores puede proveer de modo e?ciente nuevas 
pol?ticas de agrocombustibles, pero requerir? coordinaci?n a una escala espacial m?s amplia que la que se practica 
actualmente, preferiblemente dentro de un marco de manejo adaptativo.
North American grassland birds have experienced popu-
lation declines more dramatic and rapid than those of any other 
avian group in North America (Brennan and Kuvleski 2005) and 
represent a particularly sensitive biodiversity component likely to 
be affected by land-use change associated with projected growth 
in biomass production (Fargione et al. 2009, Fletcher et al. 2011). 
Thus evaluating the potential effects of agrofuel expansion on 
grassland birds ranks high as a conservation-research need and 
merits serious attention from policy makers. Compared to that on 
other taxa, the empirical literature on grassland birds also repre-
sents the richest available dataset linking biodiversity responses 
to components of agrofuel production. 
Determining whether the expansion of agrofuels may 
represent a new opportunity for conservation or a potential 
threat to grassland bird populations requires information on the 
ability of particular feedstocks to support diverse and abundant 
bird assemblages and how production of agrofuel crops affects 
the availability of agricultural, semi-natural, and natural habi-
tats and their landscape-scale patterning. 
To understand how an increasing demand for agrofuel 
production will alter the abundance and context of habitats 
available to grassland birds we follow the conceptual frame-
work of Firbank et al. (2008), describing agricultural systems 
according to three scales of intensi?cation: (1) changes in 
the type of crops and their management at the ?eld scale, 
(2) changes in the structure and diversity of agricultural 
landscapes, and (3) changes in large-scale land-use. Next, 
we identify current and future threats and opportunities for 
grassland bird conservation associated with agrofuels and 
identify critical research and policy development needed to 
create sound conservation guidelines for grassland birds. 
We develop a conceptual model useful for understanding 
how these perspectives can be integrated into the production 
of agrofuel crops in the United States (Fig. 1).
UNDERSTANDING AGROFUEL CROPS  
AS HABITAT FOR GRASSLAND BIRDS 
CROP SELECTION
Although grassland birds forage in row crops, ?elds of corn 
grown for ethanol provide limited breeding habitat (Best et al. 
INTRODUCTION
Biofuels, or more accurately, agrofuels, have become a core com-
ponent of sustainable-energy policies worldwide because they 
represent a potential means of increasing energy independence 
while stimulating rural economies and cutting greenhouse-gas 
emissions. In the United States, federal mandates for produc-
tion of agrofuel crops (Energy Independence and Security Act; 
H.R. 6?110th Congress 2007) and associated subsidies (e.g., 
Biomass Crop Assistant Program, H.R. 2419?110th Congress 
2008) are encouraging the cultivation of new biomass crops and 
systems to manage them. Given that at least 206 000 km2 of new 
cultivated land will be needed to meet U.S. energy demand by 
2030 (West et al. 2009), biomass production has the potential 
to reshape landscapes over large scales. The expansion and in-
tensi?cation of agriculture may already pose severe threats to 
biodiversity (Tilman et al. 2001, Green et al. 2005, Firbank et 
al. 2008). Nevertheless, remarkably little information exists 
linking agrofuel crops to biodiversity or economically impor-
tant ecosystem services (e.g., pest control) (Fargione et al. 2009, 
Dauber et al. 2010, Fletcher et al. 2011).
The few studies that have examined the ecological effects 
of increasing agrofuel production have focused on the implica-
tions for biodiversity in general (Groom et al. 2008, Fargione 
et al. 2009, Dauber et al. 2010) or for certain taxonomic groups 
(arthropods: Gardiner et al. 2010; vertebrates: Fletcher et al. 
2011). Not surprisingly, these studies indicate that expansion 
of intensively managed monocultures of annual plants as feed-
stocks (e.g., corn, soybeans) could reduce biodiversity, but the 
development of native and/or perennial plants as feedstocks 
may actually increase species richness at the scales of the 
?eld and landscape (Groom et al. 2008, Fargione et al. 2009, 
Dauber et al. 2010, Fletcher et al. 2011). Such ?ndings suggest 
that well-managed and properly planned agrofuel systems may 
meet future energy needs while simultaneously maintaining 
biodiversity. While these ?ndings are encouraging, it remains 
unclear if these bene?ts will extend to the most rare and sensi-
tive components of biodiversity (i.e., those of highest conserva-
tion priority) because using species richness and abundance as 
measures of a program?s success can fall short in assessing the 
status of specialist species (Filippi-Codaccioni et al. 2010). 
BIOFUEL CROPS AND GRASSLAND BIRDS  681
1995, Brennan and Kuvlesky 2005) as only a few species such 
as the Horned Lark (Eremophila alpestris) and Vesper Sparrow 
(Pooecetes gramineus) regularly nest in corn ?elds, often with 
limited success (Dechant et al. 2002, Dinkins et al. 2002). The 
incorporation of conservation tillage, cover crops, and organic 
farming regimes can increase the diversity and reproductive 
success of grassland birds (Beecher et al. 2002, Hole et al. 
2005), but increasing demand for corn stover as a agrofuel feed-
stock should intensify agricultural practices (Wilhelm et al. 
2007). This will leave less vegetative residue in the ?elds to pro-
tect soil and water resources and act as cover for birds. 
Next-generation cellulosic technology, which produces 
ethanol from lignocellulose rather than from glucose or 
starch-rich components of row crops, is capable of produc-
ing liquid fuel from nonfood crops and is therefore targeted to 
be the leading source of renewable transportation fuel in the 
future (U.S. Renewable Fuels Standard, H.R. 6?110th Con-
gress 2007). However, markets for cellulosic biomass are not 
well established, and research to improve crops, industrial-
ize cellulosic technology, and identify optimal management 
practices is continuing. As a result, research investigating the 
ecological consequences of cultivation of perennial plants for 
cellulose will likely lag behind its implementation. 
Perennial grasses such as Miscanthus ? giganteus and reed 
canary-grass (Phalaris arundinacea) are leading candidates for 
dedicated agrofuel crops in the United States. Both produce high 
biomass when grown in monoculture. Additionally, ?oristically 
diverse grasslands such as restored or reconstructed prairies con-
taining as little as 60% grass can also act as sustainable sources 
of cellulosic biomass (Tilman et al. 2006, Garlock et al. 2012). 
Miscanthus is an exotic and potentially invasive species in 
the United States. But poorly established and weedy stands of 
Miscanthus can support species of high conservation concern 
and a relatively high diversity of breeding birds in the United 
Kingdom (Semere and Slater 2006), though these conditions 
will be atypical of stands managed for biomass. The early 
spring harvest schedule and low requirement for chemicals (re-
viewed in Lewandowski et al. 2000) mean limited disturbance 
for breeding birds, as well as dense habitat for wintering birds 
(King and Savidge 1995, but see Bellamy et al. 2009). To date, 
no information exists on how North American birds might use 
monocultures of Miscanthus. Kirsch et al. (2007) reported that 
reed canary-grass supports a low diversity but high abundance 
of birds, but as for Miscanthus little is known about the costs 
and bene?ts of large monocultures of reed canary-grass for 
grassland birds in the United States.
FIGURE 1. A conceptual model for understanding how grassland bird conservation can be integrated into the production of agrofuel crops in 
the United States. A complex set of socioeconomic and political drivers (top left) will ultimately determine which crops are selected for produc-
tion in various agricultural regions and how they will be managed (bottom left). The direct and indirect effects of these production systems on 
grassland birds at local and landscape scales will need to be studied and monitored, then evaluated for their effectiveness in meeting regional 
conservation targets for grassland birds (bottom center). Conservation strategies must then be designed to mitigate the effects of agrofuel pro-
duction on grassland birds (bottom right). Such strategies may include new intergovernmental cooperation to develop production standards that 
meet conservation targets for grassland birds within a broader strategy for biodiversity conservation, strategic land-use planning within the 
context of producer-incentive programs, and provisions for the conservation of critical habitat for grassland birds. Together with valuation of the 
economic costs and bene?ts (e.g., pest control) of grassland birds to agrofuel production, strategic conservation planning can help inform new 
sustainable agrofuel policy (top) that feeds back within this adaptive-management framework.
682 BRUCE A. ROBERTSON ET AL.
The perennial feedstock best understood from the agrofuel?
grassland-bird-habitat perspective is switchgrass (Panicum vir-
gatum), a native perennial warm-season grass. Switchgrass is a 
model energy crop (McLaughlin and Walsh 1998) capable of pro-
viding habitat for breeding and migrating birds. Annual crops, 
like corn, do not provide useful habitat, in part, because ?elds 
of such crops are largely bare of vegetation during much of the 
year. Several species characteristic of grasslands nest in switch-
grass ?elds, including the Northern Harrier (Circus cyaneus), 
Sedge Wren (Cistothorus platensis), Bobolink (Dolichonyx 
oryzivorus), Dickcissel (Spiza americana), Henslow?s Sparrow 
(Ammodramus henslowii), and Grasshopper Sparrow (A. savan-
narum) (Murray and Best 2003, Roth et al. 2005, Bakker and Hig-
gins 2009, Robertson et al. 2011a). Species using switchgrass as 
stopover habitat include the Northern Harrier, Sedge Wren, Bob-
olink, Eastern Meadowlark (Sturnella magna), Henslow?s Spar-
row, Le Conte?s Sparrow (A. leconteii), and Nelson?s Sparrow (A. 
nelsoni); Robertson et al. 2011b). Nesting success in switchgrass 
of at least one of these species, the Grasshopper Sparrow, is suf-
?cient to sustain stable populations (Murray and Best 2003), but 
demographic information on other species is lacking. 
The overall species richness of grassland birds in switch-
grass monocultures during the breeding season (Bakker and 
Higgins 2009) and migration is lower than in native prairie 
but similar to that of restored mixed grass?forb prairie (Rob-
ertson et al. 2011a,b) and signi?cantly higher than that of 
corn ?elds (Fig. 2). While some common species such as the 
Horned Lark and Brown-headed Cowbird (Molothrus ater) 
can occupy corn ?elds, obligate grassland species such as 
the Sedge Wren, Bobolink, Henslow?s Sparrow, Grasshopper 
Sparrow, and other nongrassland species of conservation in-
terest, such as the Common Yellowthroat (Geothlypis trichas) 
and Clay-colored Sparrow (Spizella pallida), appear to bene?t 
from production of perennials for biomass. Plotting the rela-
tive abundance of breeding bird species in switchgrass or prai-
rie vs. corn against the species? conservation status indicates 
that species of highest conservation concern will bene?t most 
from the expansion of these perennial crops at the expense of 
corn for agrofuel (Fig. 2). Indeed, Fletcher et al. (2011) argued 
that corn-based ethanol production could affect birds of high-
est conservation concern disproportionately more than other 
agricultural, natural, and semi-natural types of land use. 
CROP MANAGEMENT
Although little is known about how grassland bird communities 
will respond to the management associated with the industrial-
ization of switchgrass and other monocultures and polycultures 
based on perennial plants, we can make predictions based on re-
search with row crops (e.g., Rodenhouse et al. 1995). Improve-
ments in feedstock genetics and crop-management techniques 
aim to maximize biomass production by producing dense mono-
cultures of highly productive biomass crops (reviewed in Ben-
ton et al. 2003). While high-density plantings maximize fuel 
production, they tend to favor habitat generalists such as the Song 
Sparrow (Melospiza melodia) and grassland obligates that toler-
ate dense vegetation such as the Sedge Wren (Robertson et al. 
2011a,b). Richness of breeding birds, as well of grassland special-
ists, is highest at intermediate values of vegetation density (Rob-
ertson et al. 2011a). Furthermore, the bene?ts of any monoculture 
as habitat are debatable as ?oral diversity generally begets faunal 
diversity. Applications of the results of previous bird research in 
switchgrass ?elds are likely an optimistic representation of in-
dustrialized monocultural plantations because most switchgrass 
?elds are not currently managed for biomass production and are 
therefore not true monocultures (Roth et al. 2005, Bakker and 
Higgins 2009, Robertson et al. 2011a,b). Therefore, the relative 
value and bene?ts of switchgrass monocultures to grassland 
birds may be lower than those of other grass habitats because of a 
FIGURE 2. Average effect sizes (log response ratios) for abun-
dances of 20 bird species in patches of prairie (open circles) and 
switchgrass (?lled circles) (n = 20 each) and corn ?elds in southern 
Michigan. Using the approach employed by Fletcher et al. (2011), we 
found that species (only those with more extreme values are labeled) 
with higher regional Partners in Flight scores (indicating greater 
regional conservation concern; Carter et al. 2000) were more abun-
dant in prairie or switchgrass ?elds than in corn ?elds (ANCOVA: 
F1,38 = 9.4, P = 0.004). This result suggests that species in greatest 
need of conservation will bene?t most from production of perennial 
agrofuel crops at the expense of corn. The regression line is based on 
response ratios from both types of planting. We found no difference in 
slope between prairie and switchgrass (F1,38 = 0.1, P = 0.76). We used 
the ratio of estimates in prairie and switchgrass ?elds to corn ?elds 
(ln[Xprairie or switch/Xcorn]) as our measure of effect size (Hedges et al. 
1999). Response ratios are based on estimates of the relative abun-
dance of species detected on at least 5% of breeding-season surveys 
by Robertson et al. (2011a). Most ?elds were managed as restored 
prairie or wildlife habitat and not for biomass production. 
BIOFUEL CROPS AND GRASSLAND BIRDS  683
lack of heterogeneity, as has been found for some kinds of plant-
ings under the Conservation Reserve Program (CRP; Millenbah 
et al. 1996, McCoy et al. 2001). 
In addition to differing in structure and plant species diver-
sity, grasslands managed for feedstock based on perennials will 
also differ in the timing and rate of vegetative succession, lead-
ing to corresponding differences in grassland bird assemblages. 
In largely unmanaged switchgrass systems such as those of the 
CRP, vegetation structure is dominated by remnant stalks from 
the previous year?s growth and favors birds that prefer thick 
vegetation structure. However, stands actively managed for 
biomass production will experience the removal of vegetation 
that resets succession and promotes settlement of species that 
prefer open habitats (Murray and Best 2003, Roth et al. 2005, 
Robertson et al. 2011a). Periodic disturbance (e.g., patch-burn 
grazing, Coppedge et al. 2001) is good for grassland systems 
and grassland birds, but, at both the local and landscape scales, 
the intensity and uniformity of cropping results in structural 
and successional homogeneity among the ?elds that may limit 
habitat suitability for some grassland birds. 
Because structural diversity of grassland vegetation, both 
within and between ?elds, promotes richness and abundance of 
breeding and migratory species (Millenbah et al. 1996, McCoy 
et al. 2001, Robertson et al. 2011b), alternative harvest strategies 
may have a role in avian conservation. For example, a staggered 
fall harvest of entire ?elds or portions of ?elds (e.g., strip harvest-
ing) will expand the availability during fall migration of habitat 
for species preferring sites with structural diversity (Robertson 
et al. 2011b). Such novel strategies may also have the secondary 
effect of broadening the habitat?s structural diversity within or 
between ?elds the following spring and summer by increasing 
standing dead vegetation. Coordinated harvesting could thus 
produce a mosaic of grassland habitats that enhances habitat 
value for all subsets of the avian community, not just those that 
prefer the predominant vegetation structure (fall: high biomass/
dense structure; spring: low biomass/sparse structure). Because 
perennial crops require fewer chemicals and are harvested in fall, 
disturbance and the mortality of young associated with annual 
crops would be reduced (Beecher et al. 2002). 
Still, a multitude of open questions remain. The effect of 
harvest and its timing on the availability of arthropods as food 
for breeding, post-breeding, and migrant birds is unknown. Al-
though a fall harvest timing will avoid the direct mortality of 
nesting grassland birds and their young typical of earlier, mid-
summer harvest (e.g., Bollinger et al. 1990), exactly how pat-
terns of cropping in?uence cues for breeding birds? settlement 
remains unknown. Nonetheless, the timing of fall harvest may 
alter the rate and timing of revegetation that shape the attractive-
ness of patches to spring migrants (Robertson et al., in press) and 
summer breeding birds (Robertson et al. 2011a). In warmer re-
gions where multiple annual harvests may be possible and the 
harvest could overlap birds? breeding season, the intensi?cation 
of management could lead to even more severe consequences by 
turning commercial switchgrass ?elds into ecological traps (i.e., 
attractive population sinks; Best 1986, Bollinger et al. 1990). It 
is important to recognize the existing research is generally con-
?ned to the mixed-grass prairie region of the United States. 
Grassland birds adapted to shorter grasses farther west may ?nd 
that biomass plantations rapidly become unsuitable as they in-
crease in height and density during the breeding season.
LANDSCAPE STRUCTURE AND DIVERSITY
The spatial extent and con?guration of agrofuel croplands 
should also shape their suitability as habitat for grassland birds 
(reviewed in Ribic et al. 2009). Switchgrass ?elds and restored 
prairie have more breeding species per area, of both grassland 
obligates and birds in general, with increasing patch size, but 
this pattern is not observed in corn ?elds (Robertson et al. 
2011a). Large patches of habitat with a low edge-to-area ratio 
increase suitability for both edge-avoiding species and those 
that suffer reduced reproductive success near edges (Johnson 
and Temple 1990, Winter and Faaborg 1999). Because some 
grassland bird species are more likely to settle in patches em-
bedded in landscapes with more grassland habitat (e.g., Bakker 
et al. 2002, Renfrew and Ribic 2008), concentrating acreage of 
perennial biomass crops may enhance grassland birds? use of 
smaller patches. Insofar as the economics of ethanol produc-
tion are predicted to cause aggregation of crops near processing 
plants, there is the potential for altering the agricultural 
landscape?s structure with positive consequences for grassland 
birds by creating large unfragmented habitat patches.
Woody biomass crops such as poplar (Populus spp.) may 
also come into production as monocultures. In addition to 
competing for space with crops suitable for grassland birds, 
woody crops could reduce the attractiveness or suitability of 
existing grasslands or grass-based crops if they are grown in 
predominantly agricultural/grassland landscapes (Fletcher 
and Koford 2002, Coppedge et al. 2001, Renfrew and Ribic 
2008, Ribic et al. 2009). Indeed, in contrast to some other taxa 
(e.g., arthropods), increasing landscape diversity does not en-
hance the species richness or abundance of grassland birds on 
a local scale (Robertson et al. 2011a,b). 
AGROFUELS AND LARGE-SCALE  
LAND-USE CHANGE
The possibility that expanded agrofuel production will lead to 
large-scale reductions in habitat for grassland birds is a funda-
mental concern regarding the ecological sustainability of agro-
fuels (Roth et al. 2005, Fargione et al. 2009, Fletcher et al. 2011). 
Indeed, meeting U.S. energy demands is projected to require that 
additional lands equal to the size of the state of Kansas come into 
production (West et al. 2009). Temperate grasslands will be af-
fected more than the other biomes of the U.S. (McDonald et al. 
2009). Federal bioenergy policies in the United States are based 
largely on the assumption that most energy crops will be pro-
duced on land already in use for agriculture, and so far most ex-
pansion in corn production has come from land previously used 
684 BRUCE A. ROBERTSON ET AL.
for other crops, especially soybeans (Secchi and Babcock 2007, 
USDA 2009). Yet mandates for ever-increasing production are 
placing heavier demands on agricultural lands and favoring con-
version of native prairie and semi-natural grasslands associated 
with set-aside programs to corn-ethanol production (Secchi and 
Babcock 2007, Stephens et al. 2008, Fargione et al. 2009). Loss 
of native grasslands is projected to continue if commodity prices 
continue to increase, leading to estimated losses of 121 million ha 
in the prairie pothole region alone (Rashford et al. 2011). Indirect 
land-use consequences of bioenergy production are not unique 
to the United States. Bowyer (2010) reported that the European 
Union?s goal to produce 10% of its transport fuel from renewable 
sources by 2020 will drive farmers to convert 69 000 km2 of wild 
lands into ?elds and plantations. 
The suitability of particular agrofuel feedstocks will vary 
according to geographic region (Evans et al. 2010). Even so, 
the ability of perennial feedstocks such as switchgrass to pro-
duce substantial biomass even on degraded lands or those with 
marginal soils (Fuentes and Taliaferro 2002) places aban-
doned farmland and ?marginal lands? deemed unsuitable for 
corn and other traditional crops at the top of the list to provide 
the acreage required for next-generation fuels (e.g., Hoogwijk 
et al. 2005, Field et al. 2008). Native grasses like switchgrass 
can grow on such lands, further highlighting the capability of 
cellulosic feedstocks to ?ll energy shortfalls.
The distribution of lands that are unpro?table, except when 
crop prices are very high (i.e., ?producer-de?ned marginal lands,? 
Fig. 3), suggests that a number of grassland specialists could be 
affected by future agrofuel production. Perennial biomass crops 
are entering the American landscape most prominently in por-
tions of the Dakotas where some of the largest areas of native 
prairie and rangeland in the United States remain and where cur-
rent and projected losses of grasslands that bene?t birds are most 
serious (Fargione et al. 2009). This region coincides with the 
breeding ranges of several prairie endemics such as Baird?s Spar-
row (Ammodramus bairdii), Chestnut-collared Longspur (Cal-
carius ornatus), and Sprague?s Pipit (Anthus spragueii), all of 
which are of high conservation concern because of severe long-
term population declines associated with loss and fragmentation 
of native grasslands. Additional grassland specialists could also 
be affected in other parts of the United States. Portions of north-
ern Texas, western Oklahoma and Kansas, and eastern New 
Mexico where marginal lands have returned to corn production 
(Fig. 3) correspond closely to the remaining range of the Lesser 
Prairie-Chicken (Tympanuchus pallidicinctus), threatened by 
conversion of native prairie and semi-natural habitats (Rich et al. 
2004, Hagen et al. 2005).
Predicting the effect(s) of agriculturally mediated habitat 
change on grassland birds is dif?cult because changes in land-
use practices associated with agrofuel production are driven by 
interactions among cultural, technological, biophysical, polit-
ical, economic, and demographic forces (Fig. 1; reviewed by 
Dale et al. 2011). Continuing losses of natural and semi-natural 
habitat related to the expansion of corn acreage are unlikely to 
FIGURE 3. Change in average acreage of crops planted following the 2006 legislation to expand agrofuel production and the resulting rise 
in commodity prices. The map shows the difference between 2005?2006 and 2007?2009 in extent of crops by crop-reporting district (Na-
tional Agricultural Statistics Service of the U.S. Department of Agriculture). The difference between these two periods represents, in part, the 
?producer-de?ned marginal lands.? Crops included account for >90% of acreage planted in the U.S. (based on Agricultural Statistics Districts 
2005?2009) and include corn, soybeans, wheat, barley, dry beans, canola, cotton, hay, oats, peanuts, rice, rye, saf?ower, grain sorghum, pota-
toes, saf?ower, sugar beets, sun?ower, and tobacco. Crop prices began to climb in response to agrofuel expansion (along with other reasons) in 
the fall of 2006, so 2007 was the ?rst year of planting in response to higher prices. Thus, for a measure of how higher crop prices have changed 
aggregate planted acreage, average planted acreage in 2005 and 2006 is used as the low-price-regime base. The average planted acreage in 
2007, 2008, and 2009 is taken as a measure of planted acreage in a high-price regime. 
BIOFUEL CROPS AND GRASSLAND BIRDS  685
be reversed if they are simply replaced by perennial crops. In-
creasing agrofuel production can thus be expected to exacer-
bate long-term population declines in grassland birds (Fargione 
et al. 2009), though the effects may vary regionally (Fig. 3). 
Yet, if perennial bioenergy crops can be economically produced 
on marginal lands and replace suf?cient acreage of alternative 
crops or land-cover types less capable of supporting grassland 
birds, the potential for net gains in the availability of grassland 
bird habitat increases (Murray et al. 2003, Meehan et al. 2010), 
at least for species that can tolerate the structural characteristics 
and successional patterns associated with biomass plantations. 
LESSONS AND OPPORTUNITIES FOR POLICY 
DEVELOPMENT
American policies have largely triggered the development of 
agrofuel production through targets (Energy Independence and 
Security Act) and production subsidies (e.g., Biomass Crop As-
sistance Program), but environmental standards have lagged 
behind the rapid development of agrofuels. The United States 
has not adopted bioenergy-related standards to protect biodi-
versity, including grassland birds. Such standards will become 
increasingly critical to the success of biodiversity conservation 
as demand for food, feed, and fuel increases (Tilman et al. 2001, 
Groom et al. 2008). The development of biodiversity standards 
should draw on lessons from Europe, where agrofuel expansion 
and reductions in targets for set-aside programs have already 
reduced populations of grassland birds (Eggers et al. 2009). 
The European Union (EU) addresses bioenergy-production 
issues through the revised Fuel Quality Directive (European 
Commission Environment 2009) and the Renewable Energy 
Sources Directive (EU-RES-D 2009/28/EC). These standards 
prohibit the production of biomass from land with high biodi-
versity value (including native grasslands), promote the use 
of contaminated or marginal lands through an incentive sys-
tem, mandate that biomass be produced in accordance with EU 
standards (e.g., best agricultural practices and environmen-
tal conditions), and require that practices outside of the EU be 
monitored and speci?ed through agreements with producing 
countries. However, these directives do not prevent indirect ef-
fects (Hennenberg et al. 2009) and allow biomass production on 
?set-aside? land (which otherwise cannot be used for production 
under EU agricultural rules), a policy that the U.S. Department 
of Agriculture has considered implementing. This is concern-
ing because the continuing resilience of grassland birds in the 
United States is critically dependent on ?surrogate grasslands? 
(Sample et al. 2003) including agricultural habitats such as pas-
tures, hay?elds, strip crops, small-grain ?elds, and lands set 
aside for conservation (as through the CRP; Herkert et al. 1996, 
Herkert 2009, Seigel and Lockwood 2010). Approximately 0.9 
million ha of the area set aside in the EU has been used in recent 
years for agrofuel production (Eggers et al. 2009). 
In addition, by focusing on species richness and abun-
dance as measures of the programs? success, European 
set-aside programs have largely overlooked the habitat require-
ments and management needs of specialist species (Filippi-
Codaccioni et al. 2010). This suggests that the U.S. will need 
to develop production guidelines speci?c for grassland birds 
within a larger policy targeting the conservation of biodiver-
sity and ecosystem services (Dauber et al. 2010). Finally, the 
EU has not yet set minimum sustainability standards for all 
bioenergy crops nor established a robust and veri?able system 
of certi?cation for agrofuels produced in the EU or imported. 
The EU?s experience suggests that even well-designed 
and enforced standards will not halt declines of grass-
land birds in the United States unless they are broadly 
implemented via incentives to growers and effective land-
use planning (Hennenberg et al. 2009) (Fig. 1). The U.S. Bio-
mass Crop Assistance Program was developed to provide 
?nancial assistance to owners and operators of agricultural 
lands and nonindustrial private forests who wish to estab-
lish, produce, and deliver biomass feedstocks. To date, this 
policy has provided subsidies largely to those already produc-
ing woody biomass as industrial waste and has done little to 
encourage new production of perennial grasses (Stubbs 2011). 
Biodiversity standards could, for example, be incorporated 
into a redesigned Biomass Crop Assistance Program as a 
condition of production subsidies. Uniquely, the U.S. has in 
place a large array of government set-aside programs that typ-
ically target wildlife conservation among other goals (e.g., 
CRP, Environmental Quality Incentives Program, Grassland 
Reserve Program, Conservation Security Program, Wild-
life Habitat Incentives Program). The importance of these 
programs to bird conservation has been documented, even 
though the plant species composition of ?elds associated with 
incentive schemes like the CRP varies substantially from 
native species in mixed stands or monoculture to, in some 
regions, complete monocultures of exotic cool- or warm-
season grasses (Herkert 2009). Therefore, the existing array 
of U.S. programs targeting different natural and agricultural 
habitats and ecological elements has great potential to act as 
an effective mechanism for delivery of bioenergy policy on 
private lands. Indeed, the failure of British ?agri-environmen-
tal? schemes to protect some grassland specialists suggests 
that a wide variety of landowner incentives will be necessary 
to maintain populations of all species (Vickery et al. 2004).
Implementation of wildlife-friendly farming programs 
rarely considers the wider landscape context despite the 
importance of this perspective to conservation of avian 
diversity (Peach et al. 2001, Bradbury et al. 2004). Coor-
dination between agencies managing set-aside programs 
(e.g., U.S. Department of Agriculture?s Farm Service 
Agency, Natural Resources Conservation Service) and 
those managing birds (e.g., U.S. Fish and Wildlife Service, 
state wildlife action plans) has great potential to integrate 
information on the land (e.g., soil productivity), the peo-
ple living on it, and biodiversity priorities. Such coordina-
tion could develop economic incentives that encourage the 
686 BRUCE A. ROBERTSON ET AL.
sowing of crops capable of optimizing habitat availability 
for grassland birds at temporal (e.g., long-term contracts) 
and spatial scales relevant to their population persistence 
(e.g., Rahmig et al. 2008; Fig. 1). For example, changes in 
the CRP to include the landscape-scale priorities of state 
natural-resource managers in the scoring of lands to be set 
aside have been successful in some regions and empha-
size the potential for cooperative landscape conservation 
in agricultural systems. Even simple schemes encouraging 
growers to harvest biomass fuels before or after the region-
ally optimum date may provide biodiversity bene?ts by 
increasing heterogeneity in crop structure. 
Ideally, policies will be implemented with a strategic ap-
proach to land-use planning that incorporates the value of pri-
vate (unprotected) lands (e.g., Wilson et al. 2010) and can provide 
guidance about ef?ciently conserving biodiversity. Effective 
policies will contain provisions for law enforcement (e.g., U.S. 
Migratory Bird Treaty Act, International Convention on Biodi-
versity), delineation of areas dedicated to both production and 
protection (Groom et al. 2008), and evaluation of the effective-
ness of programs in accomplishing conservation goals (Hennen-
berg et al. 2009). Given the large number of economic, political, 
and ecological unknowns, an adaptive-management approach is 
likely to be the best way to continually integrate new knowledge 
into the objectives of state and federal wildlife and agricultural 
programs (Williams et al. 2009) (Fig. 1). Closer integration of 
modeling with ?eld-based monitoring is needed to strengthen the 
evidence available to decision makers, and this information must 
be distilled into clear recommendations digestible by producers, 
land managers, and policy makers. 
New policy frameworks will require a major overhaul and 
integration of existing agricultural legislation in the United 
States and the formal recognition of the inherent tradeoffs 
between crop production and biodiversity and the ecosys-
tem services (e.g., pest control) it provides (Fig. 1). Certainly, 
continuing agrofuel-driven changes in land use in the United 
States will bring the consideration of ecological sustainability 
in bioenergy production to the policy forefront.
CONCLUSIONS
An ever-increasing worldwide demand for fuel makes ex-
panded farming for agrofuels inevitable. Our current state of 
knowledge suggests that perennial crops offer substantial op-
portunities for increasing the area and quality of habitat for 
grassland birds in agricultural landscapes. Yet realizing this 
potential will hinge critically on developments in the techno-
logical and economic feasibility of cellulosic bioenergy and 
on the ability and motivations of decision-makers to consider 
the needs of grassland birds in how they shape future energy 
and agricultural policy. Several conspicuous information gaps 
complicate the development of new policy and programs. For 
example, it remains unclear how agrofuel development is 
linked to other drivers of land-use change, how native and re-
stored prairies will be directly or indirectly affected, and if 
conservation strategies focused on grassland birds may entail 
signi?cant tradeoffs with other important taxa or ecosystem 
services. Agrofuel crops could become a central compo-
nent of a new agricultural landscape of greater economic vi-
ability and ecological sustainability than that dominated by 
row crops (Scherr and McNeely 2008, Fargione et al. 2009, 
Fletcher et al. 2011). Ultimately, preventing growth in agro-
fuels from exacerbating already serious declines in grassland 
bird populations will require continuing investment in re-
search and proactive new national policies targeting the needs 
of grassland birds. 
ACKNOWLEDGMENTS
Financial support for this work was provided by the DOE Of?ce 
of Science (DE-FC02-07ER64494) and Of?ce of Energy Ef?-
ciency and Renewable Energy (DE-AC05-76RL01830), the U.S. 
National Science Foundation LTER program (DEB 1027253), 
MSU AgBioResearch, U.S. Fish and Wildlife Service, Migratory 
Bird Joint Ventures Midwest Region grant 30181AG045. Bruce 
Robertson was supported by a fellowship from the Smithsonian 
Conservation Biology Institute. Patrick Doran was supported by 
The Nature Conservancy?s Great Lakes Fund for Partnership in 
Conservation Science and Economics. 
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