Attractiveness of brown rice baits to non-target birds in harvested corn and soybean fields.

Abstract

Brown rice is used as a bait-carrier for the avicide DRC-1339 (3-chloro-4-methylaniline) when baiting blackbirds (Icteridae). In March and April 1996 and 1997, we assessed non-target granivorous bird use of rice-baited plots placed in harvested corn and soybean fields in eastern South Dakota for 168 observation hours. In both years combined, we identified 10 and 14 granivorous species in corn and soybean fields, respectively. In 1996 (X = 0.2, SE = 0.04) and 1997 (X = 1.2, SE = 0.38), total numbers of granivores min(-1) were similar between crops (P > or = 0.322). In 1996, bird numbers were higher (P = 0.069) in rice-baited fields (X = 0.3, SE = 0.07) than in unbaited reference fields (X = 0.1, SE = 0.04). In 1997, bird numbers (X = 1.2, SE = 0.38) did not differ between treatments (P = 0.456). Our data show that small numbers of non-target birds visited the rice-baited plots. However, total number of different individual birds using the plots was unknown.

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Pest Management SciencePest Manag Sci 60:1143–1148 (online: 2004)
DOI: 10.1002/ps.913
Attractiveness of brown rice baits
to non-target birds in harvested
corn and soybean fields
George M Linz,1∗Gregory A Knutsen,2†H Jeffrey Homan1and William J Bleier2
1US Department of Agriculture, Wildlife Services, National Wildlife Research Center, Great Plains Field Station, 2110 Miriam Circle,
Bismarck, ND 58501, USA
2Department of Biological Sciences, Stevens Hall, North Dakota State University, Fargo, ND 58105, USA
Abstract: Brown rice is used as a bait-carrier for the avicide DRC-1339 (3-chloro-4-methylaniline) when
baiting blackbirds (Icteridae). In March and April 1996 and 1997, we assessed non-target granivorous
bird use of rice-baited plots placed in harvested corn and soybean fields in eastern South Dakota for
168 observation hours. In both years combined, we identified 10 and 14 granivorous species in corn and
soybean fields, respectively. In 1996 (X = 0.2, SE = 0.04) and 1997 (X = 1.2, SE = 0.38), total numbers of
granivores min−1were similar between crops (P ≥ 0.322). In 1996, bird numbers were higher (P = 0.069)
in rice-baited fields (X = 0.3, SE = 0.07) than in unbaited reference fields (X = 0.1, SE = 0.04). In 1997,
bird numbers (X = 1.2, SE = 0.38) did not differ between treatments (P = 0.456). Our data show that small
numbers of non-target birds visited the rice-baited plots. However, total number of different individual
birds using the plots was unknown.
 2004 Society of Chemical Industry
Keywords: DRC-1339; granivorous birds; Icteridae; non-target risk; spring migration
1
Sunflower is a valuable crop in North Dakota and
South Dakota where collectively about 1.1billion
kg, valued at US$243million, were harvested in
2001.1,2Expansion of production has been ham-
pered, however, by the inability of wildlife biologists
to keep blackbird (Icteridae) damage below econom-
ically acceptable levels.3Estimates of annual direct
economic losses from blackbird damage consistently
exceed $5million.4
In response, the US Department of Agriculture
is investigating the compound DRC-1339 (3-chloro-
4-methylaniline, 3-chloro-p-toluidine hydrochloride)
as a potential tool for managing spring-migrating
blackbird populations. This research is concen-
trated south of the main sunflower-growing areas
ofNorthDakota and
where large concentrations of blackbirds are found
prior to breaking up into progressively smaller
groups as they migrate to breeding areas.5Reduc-
ing the size of this regional population during
spring, prior to the breeding effort, might be an
INTRODUCTION
northernSouth Dakota
effective solution for reducing blackbird damage to
sunflower.5
DRC-1339 was first developed to control European
starlings (Sturnus vulgaris L) at feedlots.6In the 1960s,
DRC-1339-baited cracked corn was tested for baiting
spring-migrating blackbird populations in South
Dakota, but was determined to be ineffective.7During
the 1980s, DRC-1339-baited rice was successfully
developed for baiting blackbirds in Louisiana to
protect sprouting rice.8In the following decade,
DRC-1339-baited rice was used to develop baiting
strategies for reducing the number of spring-migrating
blackbirds in North Dakota and South Dakota.5
The only two quantitative studies conducted in our
study area showed that non-blackbird (non-target)
use of rice-baited plots in harvested corn fields was
low.9,10Despite intensive searches by humans and
trained dogs, no non-target birds were found that had
succumbed to DRC-1339.9,10However, non-target
bird use of rice-baited plots in soybean fields was
not studied, and questions have persisted about the
potential risks of using rice baits in harvested corn in
eastern South Dakota.11
∗Correspondence to: George M Linz, USDA, Wildlife Services, National Wildlife Research Center, 2110 Miriam Circle, Suite B, Bismarck,
ND 58501, USA
E-mail: george.m.linz@usda.gov
†Present address: US Fish and Wildlife Service, Long Lake National Wildlife Refuge & Wetland Management District, 12000—353rd St SE,
Moffit, ND 58560, USA
Contract/grant sponsor: Wildlife Services Program of the US Department of Agriculture, Animal and Plant Health Inspection Service
Contract/grant sponsor: Department of Biological Sciences, North Dakota State University
(Received 27 June 2003; revised version received 11 March 2004; accepted 6 April 2004)
Published online 15 June 2004
 2004 Society of Chemical Industry. Pest Manag Sci 1526–498X/2004/$30.00
1143

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GM Linz et al
Acute oral toxicity tests show that there are dif-
ferential toxicities of DRC-1339 dosages among
bird species.12In the more susceptible (LD50<
20mgkg−1) birds (blackbirds, doves, pheasants),
DRC-1339 causes irreversible kidney and heart dam-
age leading to death 24–72h following ingestion.12
DRC-1339 is highly (LD50= 10–50mgkg−1) to
moderately toxic (LD50= 51–500mgkg−1) to most
sparrows, finches and waterfowl. However, repeated
exposure to sublethal doses of DRC-1339 can result
in death for resistant birds as well.13DRC-1339 does
not appear to affect reproduction except at levels very
close to those where toxicity is expressed.13,14A single
DRC-1339-baited rice grain is sufficient to kill smaller
susceptible birds, but larger birds, such as pheasants,
might need to eat 25 treated seeds to obtain a lethal
dose.15With data showing that DRC-1339 is toxic to
some non-target species of birds, it seems prudent to
determine which susceptible species might be exposed
to treated baits.
In the springs of 1996 and 1997, we compared
non-target granivorous bird use of rice-baited plots
and unbaited reference plots placed in harvested fields
of corn and soybean in eastern South Dakota. Our
objectives were to identify granivorous birds using
the plots and quantify bird-use of rice-baited and
unbaited reference plots placed in harvested corn
and soybean fields. This information may be used to
design blackbird baiting programs while minimizing
non-target bird impacts.
2
The study area was in Brookings, Miner and Lake
counties in eastern South Dakota. This area was
chosenbecauseitisconsideredtobethemostnorthern
region where migrating flocks of blackbirds are large
enough to warrant a baiting program.5Eastern South
Dakota lies in the Coteau Des Prairies physiographic
region in the Central Lowland province.16The
landscape is characterized by low, rolling hills and
a variety of glacial till deposits; undrained lakes
and small wetland basins abound. Formerly tall-
grass prairie, the land now consists mainly of pasture
and row crops. Shelterbelts and windbreaks divide
expansive field crops and surround farmsteads and
residential areas. Corn and soybean are the principal
crops in eastern South Dakota, comprising 92% of the
planted crops.
The long-term average temperature and precipita-
tion during March and April in eastern South Dakota
are 3.3◦C and 4.6cm, respectively.2During our 2-
year study, temperatures and precipitation were below
average for March and April. In 1996, the temper-
ature averaged 0.2◦C and precipitation was 1.3cm.
In 1997, the average temperature was 0.9◦C and
precipitation was 3.8cm.2An intense early spring
storm entered the study area on 5–6 April 1997 and
was followed by record cold (−15◦C) from April 8
to 12.
STUDY AREA
3
In mid-March 1996, we selected three fields each of
harvested soybean and corn located within 1.6km of
blackbird roosts. We placed one pair of plots of equal
size (∼1.1ha) in each field about 50m apart. One
member of each pair was baited with brown rice; the
other served as an unbaited reference. In mid-March
1997, we selected four harvested fields of each crop
and standardized the size of the plots at 0.8ha.
We applied 22.7kg of brown rice once or twice
per week using a seed broadcaster mounted on an
all-terrain vehicle. The frequency of baiting mimics
a potential operational program.5We marked the
corners of each plot with colored stakes to assist the
observers in delineating plot boundaries. We scanned
thepairedplotsfromablindsituated3maboveground
level and mounted on a pickup truck parked about
25m from the plots. After a 30-min period of quiet,
a single observer recorded the species and numbers of
birds using the plots. Observation periods lasted 1h
with 1-min counts alternating on each plot every 5min
(12 observations h−1). All observations were made by
a pool of four trained observers. In both years, the
study started after the snow had melted and ended
when spring cultivation was initiated. Observations
were not conducted during periods of snow, rain or
wind >32kmh−1.
In 1996, we observed the paired plots in random
order from 21 March to 26 April during four equal
time strata. In 1997, we observed paired plots in
random order from 29 March to 29 April during two
equal time strata. We eliminated the two mid-day
time strata in 1997 because bird activity had been
comparatively low in these strata during 1996.
METHODS
4
We used mean number of birds per minute of
observation during the 168 1-h periods as the
measurement unit for analyzing bird activity in
the plots. We analyzed count data for individual
species occurring in
>10%
observations. The majority of species were seen
infrequently and thus were grouped into the general
category of granivorous species. Prior to statistical
analysis, the count data for individual species and
all granivorous species combined were transformed
using the square root to increase normality.17Our
study was designed as a three-factor (ie Date, Crop,
Treatment) experiment with two repeated measures
factors (ie Date, Treatment). We used the Proc GLM
procedure to examine null hypotheses that the mean
numbers of birds were similar between harvested corn
and soybean fields, between rice-baited and unbaited
plots, and among dates within year.18Interactions
among treatments (unbaited and baited) date within
year (1996 and 1997) and between crops (soybean
and corn) also were tested to examine for differences
in trends in bird numbers. We set the significance
level at 0.10 because (1) resources were not sufficient
STATISTICAL ANALYSES
of the 1-h timed
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Avian use of harvested grain fields
to increase sample sizes and (2) the consequences of
accepting false null hypotheses (Type II errors) on
populations of birds using DRC-1339-baited plots are
much greater than if Type I errors (rejecting true null
hypotheses) were made.19
5
5.1
We identified 16 species of granivorous non-target
birds(Tables 1, 2) in 1996 and
both study years, western meadowlarks (17.3%)
occurred most often, followed by horned larks
(10.4%), American tree sparrows (7.7%), song
sparrows (6.0%), vesper sparrows (5.0%), Lapland
longspurs (4.8%), mourning doves (2.4%), mallard
RESULTS
Bird species
1997. Across
ducks (1.8%), ring-necked pheasants (1.8%), Canada
geese (1.5%) and American coots (1.5%). The
remaining five birds, dark-eyed junco, chipping
sparrow, savannah sparrow, gray partridge and snow
buntingwererecordedduring<1%oftheobservations
hours. Dark-eyed junco, chipping sparrow, and snow
bunting were recorded in 1996 but not in 1997.
Lapland longspur, American coot, Canada goose,
vesper sparrow, gray partridge and savannah sparrow
were observed in 1997 but not in 1996.
In 1996, we counted 349 granivorous birds during
71 observation hours. Western meadowlarks and
American tree sparrows were observed during >10%
of the hour observations. In 1997, we recorded 3,326
non-blackbird granivorous birds during 97h. Western
meadowlarks and horned larks were observed during
Table 1. Mean numbers of granivorous birds, excluding blackbirds, present in harvested corn and soybean fields in eastern South Dakota from 21
March to 26 April 1996 and from 29 March to 29 April 1997
1996 1997
CornSoybeanCorn Soybean
Name
Mean number
of birds min−1
(n = 28h)a(SE)
Mean number
of birds min−1
(n = 43h)a(SE)
Mean number
of birds min−1
(n = 46h)a(SE)
Mean number
of birds min−1
(n = 51h)a(SE)
Lapland longspur
Calcarius lapponicus L
American tree sparrow
Spizella arborea (Wilson)
American coot
Fulica americana Gmelin
Western meadowlark
Sturnella neglecta Audubon
Song sparrow
Melospiza melodia (Wilson)
Canada goose
Branta canadensis (L)
Mallard
Anas platyrhynchos L
Horned lark
Eremophilia alpestris (L)
Snow bunting
Plectrophenax nivalis (L)
Dark-eyed junco
Junco hyemalis (L)
Chipping sparrow
Spizella passerina (Bechstein)
Vesper sparrow
Pooecetes gramineus (Gmelin)
Savannah sparrow
Passerculus sandwichensis (Gmelin)
Ring-necked pheasant
Phasianus colchicus L
Gray partridge
Perdix perdix L
Mourning dove
Zenaida macroura (L)
Unidentified sparrow
Emberizidae
All granivores
0.00 0.0000.000.000 0.00 0.000 1.650.955
0.080.072 0.110.064 0.01 0.0090.030.030
0.000.000 0.000.0000.50 0.4390.00 0.000
0.030.0150.05 0.0250.020.006 0.03 0.010
0.040.036
<0.01 0.005
<0.010.005 0.030.019
0.00 0.0000.00 0.0000.03 0.0190.00 0.000
0.000.0000.04 0.034
<0.01 0.007 0.00 0.000
0.00 0.000
<0.01 0.006
<0.010.005 0.06 0.020
0.000.000
<0.01 0.0040.000.000 0.00 0.000
0.000.000
<0.010.004 0.000.000 0.000.000
0.01 0.000
<0.010.004 0.000.000 0.000.000
0.00 0.0000.000.000
<0.01 0.0040.040.021
0.000.0000.00 0.0000.00 0.000
<0.010.002
0.010.007 0.000.000
<0.01 0.006
<0.01 0.006
0.000.0000.00 0.0000.000.000
<0.010.001
0.000.000
<0.010.004 0.010.012
<0.01 0.001
0.00
0.15
0.000
0.080
0.00
0.24
0.000
0.082
0.00
0.60
0.000
0.445
<0.01
1.85
0.001
0.952
aPlots were observed for 1min at 12 consecutive 5-min intervals and averaged over the 1-h observation period.
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GM Linz et al
Table 2. Mean numbers of granivorous birds, excluding blackbirds, present in rice-baited and unbaited reference plots placed in fields of soybean
in eastern South Dakota from 21 March to 26 April 1996 and from 29 March to 29 April 1997
1996 1997
Unbaited referenceRice baited Unbaited referenceRice baited
Name
Mean number
of birds min−
(n = 71h)a(SE)
0.00
0.03
0.00
0.00
0.02
<0.01
0.04
<0.01
0.00
0.01
<0.01
0.00
<0.01
0.00
0.00
0.00
0.00
0.12
Mean number
of birds min−1
(n = 71h)a(SE)
0.00
0.19
0.00
0.00
0.06
0.01
0.01
<0.01
0.00
0.00
0.00
<0.01
0.00
<0.01
0.00
<0.01
0.02
0.29
Mean number
of birds min−1
(n = 97h)a(SE)
0.10
0.02
0.10
0.02
0.01
0.01
<0.01
0.03
0.02
<0.01
0.01
0.00
0.00
0.00
0.00
0.00
<0.01
0.34
Mean number
of birds min−1
(n = 97h)a(SE)
1.64
0.02
0.38
<0.01
0.04
0.03
0.00
0.03
0.02
<0.01
<0.01
0.00
0.00
0.00
<0.01
<0.01
0.00
2.17
Lapland longspur
American tree sparrow
American coot
Canada goose
Western meadowlark
Song sparrow
Mallard
Horned lark
Vesper sparrow
Ring-necked pheasant
Mourning dove
Dark-eyed junco
Chipping sparrow
Snow bunting
Savannah sparrow
Gray partridge
Unidentified sparrow
Total
0.000
0.020
0.000
0.000
0.010
0.004
0.027
0.004
0.000
0.007
0.004
0.000
0.004
0.000
0.000
0.000
0.000
0.043
0.000
0.160
0.000
0.000
0.021
0.007
0.012
0.003
0.000
0.000
0.000
0.003
0.000
0.004
0.000
<0.001
0.017
0.071
0.060
0.017
0.080
0.012
0.004
0.006
0.000
0.013
0.011
0.004
0.008
0.000
0.000
0.000
0.000
0.000
<0.001
0.110
0.709
0.015
0.285
0.009
0.008
0.014
0.000
0.009
0.012
0.004
0.002
0.000
0.000
0.000
0.002
<0.001
0.000
0.754
aPlots were observed for 1min at 12 consecutive 5-min intervals and averaged over the 1-h observation period.
>10% of the observation hours. The increase in bird
numbers between 1996 and 1997 was largely due
to lingering migratory flocks of Lapland longspurs
feeding in soybean fields (Table 2).
5.2
We recorded 11 and 14 granivorous bird species
in corn and soybean fields, respectively. Of these
species, 9 were common to both crops (Table 1). In
1996 (X = 0.20, SE = 0.042) and 1997 (X = 1.24,
SE = 0.382), average granivore numbers min−1were
not significantly different among observation dates
(P range = 0.120–0.899).
In 1996, numbers of American tree sparrow, west-
ern meadowlark and total granivorous birds were
similar between harvested fields of corn and soy-
bean (P range = 0.322–0.914), averaging 0.10 birds
min−1(SE = 0.034), 0.04 birds min−1(SE = 0.012)
and 0.20 birds min−1(SE = 0.042), respectively.
There was a marginally significant crop and date inter-
action for western meadowlarks (P = 0.092) because
the birds tended to use corn fields in early April and
soybean fields in late April.
In 1997, horned larks (X = 0.03, SE = 0.008),
western meadowlarks (X = 0.02, SE = 0.004), and
total granivorous bird (X = 1.24, SE = 0.382) abun-
dances did not differ between corn and soybean
fields (P range = 0.122–0.473). The crop type and
date interaction was significant for horned larks
(P < 0.001) due to high numbers of birds using rice-
baited soybean fields in early April, while few used
corn fields throughout the study.
Corn vs soybean
5.3
In 1996, total numbers of American tree sparrows,
western meadowlarks, and total granivorous birds
were significantly different (P range = 0.069–0.087)
between rice-baited and unbaited reference plots
(Table 2). In 1997, total numbers of horned larks,
westernmeadowlarks,and
not differ between rice-baited and untreated plots
(P range = 0.299–0.494). Interactions between treat-
ment and date were not significant in 1996 (P range =
0.529–0.826) or 1997 (P range = 0.185–0.458).
Rice-baited vs unbaited reference
totalgranivores did
6
We observed 16 granivorous bird species in study plots
placed in fields of harvested corn and soybean. Earlier
studies found 13 bird species in similarly placed and
sized plots in corn fields during 1995,91998 and
1999.10These researchers recorded four species that
we did not record: green-winged teal (Anas crecca L),
American widgeon (A americana Gmelin), wood duck
(Aix sponsa (L)) and house sparrow (Passer domesticus
L). Thus, across five consecutive springs and three
separate studies, 20 granivorous bird species were
recorded in plots in eastern South Dakota. These
species probably represent nearly all birds that would
frequent roadside plots from late March to late April.
Our data showed that horned larks preferred
harvested soybean fields over harvested corn fields.
Castrale20also found that horned larks selected
soybean over corn fields in southeastern Indiana.
These results were not surprising because horned
DISCUSSION
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Avian use of harvested grain fields
larks are considered open land birds.16The gregarious
nature, small size and granivorous food habits of
horned larks might be reasons for concern. However,
the LD50acute toxicity test for the horned lark showed
that these birds are less susceptible to DRC-1339 than
are blackbirds.12
Western meadowlarks and American tree sparrows
seem at greatest risk from spring baiting in eastern
South Dakota. A single rice kernel, treated with
0.4mg DRC-1339, is fatal for both species. Western
meadowlarks are at risk because they eat rice21and
were seen in our bait plots singly and in pairs
throughout the study period. In 1997, American tree
sparrows were present in the bait plots in flocks up
to 20 birds for about 3 days in early April. However,
these birds prefer to eat small weed seeds and waste
grains,22and might select against rice when alternative
food is available. Other sparrow species are believed
to be less sensitive to DRC-1339.12,23
In our study, granivorous birds generally preferred
rice-baitedplots tounbaited referenceplots, indicating
an attraction to rice baits as a food source. Similarly,
Smith10also found that granivorous birds were
attracted to rice. On the other hand, Linz et al.9
reported comparable numbers of birds in rice-baited
and reference plots in corn stubble fields in the same
study area that we used in eastern South Dakota. We
cannot explain the difference in results among studies.
It seems reasonable, however, that some seed-eating
birds could be attracted to rice.
7
IMPLICATIONS
Our data support the contention of Smith10and
Linz et al9that a spring blackbird baiting program
with DRC-1339-treated rice bait presents a potential
hazard to granivorous birds. However, both exposure
and susceptibility of non-target birds to DRC-1339
must be considered prior to a complete assessment
of risk. Exposure depends on feeding ecology, habitat
use,abundance,andavailabilityofDRC-1339,putting
some avian species more at risk than others. Western
meadowlarks and American tree sparrows are the
species mostatrisk ineasternSouth Dakotabecauseof
theirfoodhabits,relativenumbersandsusceptibilityto
DRC-1339.Otherbirdscouldbeatrisk,ifconditioned
to visit baited plots. Any planned baiting program
would involve using a diluted bait ratio of one treated
to 25 untreated ricekernels or greater and <25–0.8-ha
plots,5which might reduce non-target exposure.
CONCLUSIONS AND MANAGEMENT
ACKNOWLEDGEMENTS
WethankBCheck,JTharman,JWendel,BBonesteel,
and T Slowik for field assistance. This research
was cooperatively funded by the National Wildlife
Research Center, a unit within the Wildlife Services
Program of the US Department of Agriculture,
Animal and Plant Health Inspection Service, and the
Department of Biological Sciences at North Dakota
State University. This study was conducted under
National Wildlife Research Center Study Protocol
QA-437, as amended.
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