Human Health and Ecological Risk Assessment

for the Use of Wildlife Damage Management Methods

by USDA-APHIS-Wildlife Services

Chapter XVII

The Use of DRC-1339 in

Wildlife Damage Management

June 2019 

Peer Reviewed Final

September 2022
i

THE USE OF DRC-1339 IN WILDLIFE DAMAGE MANAGEMENT

EXECUTIVE SUMMARY

DRC-1339 is a toxicant registered to control various pest bird species under a variety of 

agricultural and nonagricultural uses. The USDA-APHIS-Wildlife Services (WS) Program uses 

DRC-1339 to control damage caused by specific species of blackbirds, grackles, cowbirds, 

starlings, pigeons, collared-doves, crows, ravens, magpies, and gulls. WS took an annual average 

of 2.8 million birds with DRC-1339 lethally from fiscal year (FY) 2011 to FY 2015 and 52% of 

these were European starlings, an invasive species. Of all WS take nationally for all species and 

with all methods, DRC-1339 represented 71% of the lethal take. WS annually averaged the use 

of 77.4 pounds of technical product for FY11-FY15 and took a total of 15 species in this time. 

APHIS is the registrant for DRC-1339 Technical and its end use products. DRC-1339 is a 

restricted use pesticide and only USDA APHIS certified applicators or by persons under their 

direct supervision trained in bird control use the product. Updated tables 

USDA APHIS evaluated the potential human health and ecological risks from the proposed use 

of DRC-1339 to control bird damage. DRC-1339 is corrosive to eyes and skin and the acute 

inhalation toxicity is unknown but assumed to be Category I (most hazardous) by EPA. Although 

the hazard potential could be high, the anticipated minimal exposure to this pesticide will be low 

risk due to the limited use of the product. Exposure is greatest for workers who mix the product 

with a bait material; however, required personnel protective equipment results in a low potential 

for exposure and risk when factoring in available health effects. The potential exposure and risk 

to the general public is low due to the use pattern and label restrictions, as well as lack of dietary 

exposure through food or drinking water. 

Ecological risks to aquatic nontarget organisms are low based on the use pattern, available 

toxicity data and labeled mitigation measures designed to reduce exposure to aquatic habitats.

Risks to terrestrial invertebrates and plants are also low based on available effects data and the 

method of application. Risk is greatest for sensitive terrestrial nontarget vertebrates, in particular 

birds, but these risks can be reduced with label requirements and other measures that are 

designed to reduce exposure.
ii

Table of Contents

1 INTRODUCTION........................................................................................................................................1

1.1 Use Pattern.......................................................................................................................................1

2 PROBLEM FORMULATION ......................................................................................................................4

2.1 Chemical Description and Product Use............................................................................................5

2.2 Physical and Chemical Properties....................................................................................................9

2.3 Environmental Fate ..........................................................................................................................9

2.4 Hazard Identification.......................................................................................................................10

2.4.1 Mode of Action ......................................................................................................................10

2.4.2 Acute Toxicity........................................................................................................................10

2.4.3 Subchronic and Chronic Toxicities........................................................................................11

2.4.4 Developmental and Reproductive Effects.............................................................................11

2.4.5 Neurotoxicity Effects .............................................................................................................11

2.4.6 Carcinogenicity and Mutagenicity .........................................................................................12

2.4.7 Immunotoxicty Effects...........................................................................................................12

2.4.8 Endocrine Effects..................................................................................................................12

3 DOSE-RESPONSE ASSESSMENT........................................................................................................13

3.1 Human Health Dose-Response Assessment.................................................................................13

3.2 Ecological Effects Analysis.............................................................................................................13

3.2.1 Aquatic Effects Analysis........................................................................................................13

3.2.2 Terrestrial Effects Analysis ...................................................................................................13

3.2.3 Toxicity of Formulations and Metabolites to Nontarget Wildlife and Domestic Animals.......16

3.2.4 Indirect Effects of Carcasses from Control Actions on Wildlife and the Environment ..........16

4 EXPOSURE ASSESSMENT....................................................................................................................17

4.1 Human Health Exposure Assessment............................................................................................17

4.1.1 Potentially Exposed Human Populations and Complete Exposure Pathways .....................17

4.1.2 Exposure Evaluation .............................................................................................................18

4.2 Ecological Exposure Assessment ..................................................................................................19

4.2.1 Aquatic Exposure Assessment .............................................................................................19

4.2.2 Terrestrial Wildlife and Domestice Animals Exposure Assessment .....................................20

4.2.3 Terrestrial Invertebrates and Terrestrial Plants Exposure Assessment ...............................20

4.2.4 Assessment of Indirect Effects of Carcasses from Control Actions......................................21

5 RISK CHARACTERIZATION ...................................................................................................................24

5.1 Human Health Risks.......................................................................................................................24

5.2 Ecological Risks .............................................................................................................................25

5.2.1 Aquatic Risks ........................................................................................................................25

5.2.2 Terrestrial Wildlife and Domestic Animals Risks...................................................................25

5.2.3 Terrestrial Invertebrates and Plants Risks ............................................................................29

5.2.4 Indirect Effects of Carcasses from Control Actions on the Environment..............................30

6 UNCERTAINTIES AND CUMULATIVE IMPACTS ..................................................................................30

7 SUMMARY...............................................................................................................................................31

8 LITERATURE CITED...............................................................................................................................31

9 PREPARERS: WRITERS, EDITORS, REVIEWERS ..............................................................................38

9.1 APHIS WS Methods Risk Assessment Committee........................................................................38

9.2 Internal Reviewers..........................................................................................................................40

9.3 Peer Review ...................................................................................................................................41

9.3.1 Peer Reviewer Agencies Selected by the Association of Fish and Wildlife Agencies..........41

9.3.2 Comments.............................................................................................................................41

Appendix 1. Estimating DRC-1339 Take ....................................................................................................47

Appendix 2. Update on DRC-1339 Usage from FY16-FY20 ......................................................................52
1

1 INTRODUCTION

DRC-1339, or 3-chloro-p-toluidine hydrochloride, is an avicide (toxicant for birds) used by the U.S. 

Department of Agriculture (USDA), Animal and Plant Health Inspection Service (APHIS), Wildlife 

Services (WS) Program to reduce bird conflicts at livestock facilities and airports, and to reduce 

damage to crops, livestock, property, and natural resources, including threatened and 

endangered species, per label allowances. The primary target species include European 

starlings1, rock pigeons, Eurasian collared-doves, and specific species of blackbirds2, corvids3, 

and gulls. DRC-1339 is a very pale yellow, crystalline powder that is highly soluble in water and 

other polar solvents. It was named from a code it received at the Denver Research Center4(DRC),

as the 1,339th chemical tested at the Center, which became its common name. It has also been 

known by the tradename Starlicide®, which was originally registered as a pelleted bait for starlings 

under a label from Purina Mills in 1967. 

This human health and ecological risk assessment provides a qualitative and quantitative 

evaluation of potential risks and hazards to human health and the environment, including 

nontarget fish and wildlife, as a result of exposure to DRC-1339 from proposed WS uses, which 

are limited and targeted in scope (USDA 2012). The methods used to assess potential human 

health effects follow standard regulatory guidance and methodologies (National Research Council

1983), and generally conform to other Federal agencies such as the U.S. Environmental 

Protection Agency (USEPA 2017c). The methods used to assess potential ecological risk to 

nontarget fish and wildlife generally follow USEPA (2017c) methodologies.

The risk assessment is divided into four sections: problem formulation (identifying hazard), toxicity 

assessment (dose-response assessment), and exposure assessment (identifying potentially 

exposed populations and determining potential exposure pathways for these populations). Lastly, 

the information from the toxicity and exposure assessments is combined to characterize risk 

(determining whether there is adverse human health or ecological risk). A discussion of the 

uncertainties associated with the risk assessment and cumulative effects is also included in this 

risk assessment. 

1.1 Use Pattern 

For more than 50 years, DRC-1339 has proven to be an effective tool for starling, pigeon, 

blackbird, corvid, and gull damage management (West et al. 1967, West and Besser 1976, Besser 

et al. 1967, and DeCino et al. 1966). DRC-1339 is a slow acting avicide that kills target birds 

between 3 and 80 hours after ingestion of a lethal dose (Dawes 2006). The slow action of the 

avicide allows the chemical to be partially or mostly metabolized prior to the birds succumbing to 

the chemical (Schafer 1984, Goldade 2017). DRC-1339 appears to pose little risk of secondary 

poisoning to nontarget animals, including avian scavengers (Cunningham et al. 1979, Schafer 

1984, Knittle et al. 1990). The technical grade5 of the active ingredient is very highly acutely toxic 

to many pest birds, but generally less acutely toxic to raptors, waterfowl, finches, and other birds,

and most mammals (DeCino et al. 1966, Palmore 1978, Schafer 1981). For example, an 89-gram

(g) starling, a highly sensitive species, requires a dose of only 0.3 milligrams (mg)/bird on average 

to cause death (Royall et al. 1967) while many other bird species such as raptors, house 

1 Scientific names are given in the Risk Assessment Introduction Chapter I, unless first time used.

2 Generic use of blackbirds for this risk assessment includes specific species of blackbirds, cowbirds, and grackles on labels.

3 Corvids refers to the family Corvidae, which includes ravens, crows, magpies, and jays, but jays are not on any DRC-1339 label.

4 Later was renamed the WS-National Wildlife Research Center when it moved from Denver to Fort Collins, CO.

5 Technical grade DRC-1339 is ≥97% pure and contains no added inert ingredients. The end-use products consist of 100% of the technical grade 

DRC-1339.
2

sparrows, and finches are classified as non-sensitive, requiring a much higher dose (Eisemann 

et al. 2003). A 29 g house sparrow would require a dose of 9 mg, while a 22 g house finch and 

118 g American kestrel would require more than 5 mg and 38 mg (DeCino et al. 1966, Schafer et 

al. 1983). It should be noted that larger birds and pigeons require more product (more toxicant) 

to be ingested to be lethal. Secondary hazards of DRC-1339 are likely very low unless toxic bait 

is still largely intact in the carcass. DRC-1339 acts in a relatively humane manner producing 

minimal outward clinical signs (Timm 1994, Dawes 2006). Prior to the application of DRC-1339, 

prebaiting is often required to monitor for nontarget species that may consume the bait. If 

nontarget species are observed, then the use of DRC-1339 would be postponed or not applied at 

that particular location. The application method such as the use of prebaiting to assess palatability 

of the bait and prevent overbaiting, and the low risk of secondary hazards reduce the potential

exposure to sensitive threatened and endangered species as well as preclude hazards to most 

other nontarget species.

Some people have stated that DRC-1339 is an inhumane toxicant and should not be used. WS 

recognizes that any use of lethal methods, toxicants in particular, is considered by many 

individuals to be inhumane even if time until death and symptoms exhibited appear to be minimal.

DRC-1339 causes renal failure in treated birds (Timm 1994). Renal failure in birds causes weight 

loss, depression, lethargy, increased thirst (polydipsia) and urination (polyuria), dehydration, 

articular gout, and eventually death (Merck 2018a). Death in birds occurs typically within a few 

days following ingestion of a lethal dose (Timm 1994). Mammals can succumb rather quickly with 

those ingesting a lethal dose dying in 3 to 12 hours (Timm 1994). Higher doses do not increase 

the speed of mortality (Timm 1994). Research is not available on pain experienced by birds 

treated with DRC-1339, just observational reports (DeCino et al. 1966, Timm 1994, Dawes 2006); 

convulsions, spasms or distress calls have not been observed in birds receiving a lethal dose, 

rather the birds die a seemingly quiet death. Birds that get a lethal dose may show no outward 

clinical signs for many hours and go about normal activities. About four hours before death, the 

birds cease to eat or drink and become listless and inactive, and possibly comatose (Timm 1994, 

Dawes 2006). They perch with their feathers puffed up (piloerection) and appear to doze. The 

product has been assessed as relatively humane and suitable for further investigation for potential 

use in Australia (Dawes 2006, Bentz et al. 2007) and is registered in New Zealand.

The current end use products, named Compound DRC-1339 Concentrate – Bird Control and 

Compound DRC-1339 Concentrate – Livestock, Nest & Fodder Depredations (both are 100% 

DRC-1339 Technical, which is ≥97% purity DRC-1339), are used to control various bird species 

under various agricultural and non-agricultural uses in the U.S. Labels have varied over the last 

50 years when the first formulation was registered, changing species that can be targeted, 

allowing additional bait substrates, restricting amounts that can be used over a given area, and 

types of areas that can be treated. For FY116to FY15, the data used for this risk assessment, the 

federal DRC-1339 labels included new labeling updates for various uses during this time (Table 

1). 

In late 2017, the Bird Control label (USDA 2017a) was approved by EPA, and replaced the 

Feedlots, Gulls, Pigeons, and Staging Areas labels as of January 2019; this Bird Control label 

also fully or partially incorporated uses from 20 state Special Local Needs (SLN) labels. The 

labeling lists the bait substrates, target species, and sites where DRC-1339 can be used. Mixing 

directions depend on the bait substrate (e.g., rice, cracked and whole corn, French fries, and 

livestock pellets) that can be used to mix with DRC-1339 and how much untreated bait to cut with 

the treated bait. Prebaiting is required for all applications. DRC-1339 prepared baits deteriorate 

6 FY11 equals the federal Fiscal Year 2011, which is October 1, 2010-September 30, 2011 (the year is denoted by FY11, FY12, and so on).
3

rapidly and need to be used relatively soon after preparation or disposed according to label 

directions.

Table 1. DRC-1339 labels and significant dates when use restrictions on the label changed, to provide a 

comparison to take (Table 2) and label usage (Table 3) for the labels used from FY11 to FY15.

WS took an annual estimated average of 2,810,095 target birds of 15 species using an annual 

average 35,122 grams (1,239 oz. or 77 lbs.) of DRC-1339 in 38 states from FY11 to FY15 (Table 

2). During this time, WS applied DRC-1339 under 18 Section 3 and SLN (Section 24(c)) labels

operationally (Table 3). The most common resources protected by WS were livestock and feed, 

aircraft, other wildlife, and crops. The species groups taken were starlings and blackbirds (99.1%), 

pigeons (0.5%), corvids (0.4%), and gulls (0.004%). The most common target species lethally 

taken were European starlings (52%), brown-headed cowbirds (27%), red-winged blackbirds

(16%), and common grackles (4%) (Table 2). Weight-wise, the majority of DRC-1339 used

targeted starlings (89%), common ravens (2.9%), feral pigeons (2.5%), American crows (1.8%), 

and brown-headed cowbirds (1.6%); it should be noted that some DRC-1339 targeting a specific 

species may have had minimal take for various reasons like birds did not show up to feed or bait 

was ruined by weather.

Table 2. The annual average number of birds WS killed with DRC-1339 treated baits in bird damage 

management from FY11 through FY15. Take was estimated for WS projects that did not determine take. 

ANNUAL AVERAGE DRC-1339 USE AND SPECIES TAKEN

Species* Take DRC-1339 (g) States That Used DRC-1339

Target

European Starling* 1,449,656 31,222.8 AZ CA CO CT IA ID IL IN KS MA MD ME MI MN MO MT NE NJ 

NM NV NY OH OK OR PA SD TX UT VA VT WA WI WV WY

Yellow-headed Blackbird 80 4.6 OK

Red-winged Blackbird 452,014 450.8 AZ CA CO LA NM NV OR TX WV WY

Brown-headed Cowbird 744,988 549.5 AZ CA LA NV OH OK TX

Brewer's Blackbird 6,062 41.1 AZ CA NM NV OR

Common Grackle 123,624 255.6 LA OK TX WV

Boat-tailed Grackle 60 0.2 LA

Great-tailed Grackle 7,897 34.9 AZ NM OK TX

Rock Pigeon* 13,112 896.0 AZ CA CO IA ID IL KS KY ME MI MN MO MT ND NE NM NV OK 

OR PA TN TX UT VT WA WV WY

Great Black-backed Gull 6 0.5 ME

California Gull 6 1.2 ID

American Herring Gull 90 7.9 ME

Black-billed Magpie 321 18.4 ID OR WY

American Crow 3,385 631.8 CA ID MA NE OK OR TX WA WY

Common Raven 8,794 1,006.5 AZ CA ID MT NM NV OR TX UT WA WY

TOTAL (15 sp.) 2,810,095 35,121.8 38 States

Nontarget

Brown-headed Cowbird 12 0.1 WI

Rock Pigeon* 152 3.0 NM WV WY

American Crow 80 3.0 NM

Common Raven 0.4 0.1 NM

TOTAL (4 sp.) 244 6 5 States

GRAND TOTAL (15 sp.) 2,810,339 35,128 38 States

* Introduced species

DRC-1339 LABEL CHANGES FOR FY11 TO FY15

Product (Parent Label) EPA Registration No. Significant Label Change Dates

Feedlots 56228-10 10/26/2009 02/01/2011 01/30/2014 03/05/2014

Gulls 56228-17 05/19/2010 12/11/2013

Pigeons 56228-28 10/26/2009 12/11/2013

Livestock, Nest & Fodder Depredations 56228-29 10/26/2009 12/11/2013

Staging Areas 56228-30 10/26/2009 03/29/2011 12/11/2013
4

WS personnel took an annual average of 244 nontarget birds of four species (Table 2); of these, 

164 were being targeted at feedlots, but accidentally taken while targeting other species with a 

particular DRC-1339 formulation. The annual average of American crows (80) and common 

ravens (0.4) were not target species at the sites where they were accidentally taken. All of the 

nontarget species taken are species WS would take with DRC-1339 under different 

circumstances. WS did not take other nontarget species unintentionally, including threatened, 

endangered, or sensitive species, or species not listed on the label.

The number of target and nontarget birds estimated to be taken is determined by monitoring the 

bait site to see the composition and number of bird species feeding on baits and collecting 

carcasses post application as required by the label for the various use sites. This especially true 

for nontargets that may not be seen when thousands of birds such as starlings are being treated.

WS personnel estimate take using the WS Unified Model for Estimating DRC-1339 Bait 

Applications developed by the WS National Wildlife Research Center, which takes into account 

species composition and number, weather, bait type, bioenergetics, dose-response, and other 

relevant factors. The take estimator is always being refined. It results in the maximum number of 

birds that could be taken, which is generally higher than the number actually taken. Without these 

factors, take can be estimated using species responsible for damage and grams of DRC-1339 

used based on a less conservative method (Appendix 1). This has been used to estimate take 

where a WS specialist forgot to estimate take, did not want to estimate take (some specialists are 

very uncomfortable making estimates of how birds are present), how effective the bait was (e.g., 

precipitation), and so on and decline to make an estimate, or an estimate was not required (it has 

been policy since about 2013 to estimate take). From FY11 to FY15, an annual average of about 

70 projects had to be estimated, but this declined to 4 from FY16-FY20 after a requirement was 

made to ensure take was estimated. For the analysis in this document, take was estimated for 

any project without the take except for small numbers of eggs put out for ravens and crows to 

protect sensitive species because they often have no take and it was usually denoted in 

comments.

Historically, APHIS registered five DRC-1339 Section 3 labels, but only two Section 3 labels are 

currently registered as of 2019 (Table 3). Four Section 3 labels (Feedlots, Gulls, Pigeons, and 

Staging Areas) were incorporated into the Bird Control label, while the Livestock, Nest & Fodder 

Depredations (LNFD) label remains a separate Section 3 label and registration. Additionally, 

states have since registered additional state-limited uses for DRC-1339 under SLN registrations.

In addition to the cancelation of the four Section 3 labels, 25 SLN registrations were cancelled in 

late 2018 to early 2019 after their uses were incorporated under the Bird Control label or were 

determined to no longer be needed. As of 2022, WS has 9 active DRC-1339 SLN registrations (4 

under the LNFD parent label and 5 under the Bird Control label (Table 3). Of the 36 labels active 

within FY11 to FY15, only half were used in those five years (Table 3). The majority of DRC-1339 

product used by WS was used under the now cancelled APHIS Feedlots label or SLN labels under

the Feedlots parent label (83.5%). The APHIS Staging Areas label or SLN labels under the 

Staging Areas parent label were used next most (11.3%). The others were used minimally.

2 PROBLEM FORMULATION

DRC-1339 is used by APHIS WS for various projects on specific species of birds. The various 

use sites, depending on target species, include commercial animal operations such as livestock 

and poultry feedlots, buildings and fenced non-crop areas, airports, industrial sites, dumps and

landfills, federal and state wildlife refuges and protected areas, gull colonies in coastal areas, and 

bird staging areas and roost sites. The following sections discuss the chemical description and 
5

product use; physical and chemical properties; environmental fate; and hazard identification for 

DRC-1339.

Table 3. The annual average number of grams of DRC-1339 applied by APHIS-WS in WDM from FY11 

thru FY15 by all labels with the annual average number of projects and Work Task (WT) applications.

Lightly shaded lines - registrations with no use from FY11-FY15.

* USEPA Registration No. 56228-63 - Bird Control label fully replaced these labels by January 2019.

** Labels not fully incorporated in Bird Control label, cancelled, and re-registered by the state under the Bird Control parent label, or

no longer used and cancelled by January 2019.

^ SLN labels are still registered under the LNFD parent label.

2.1 Chemical Description and Product Use

DRC-1339 (C7H9Cl2N, CAS No. 7745-89-3) is 3-chloro-p-toluidine hydrochloride (synonyms: 3-

chloro-4-methylbenzenamine hydrochloride, or 3-chloro-4-methylaniline hydrochloride). 

Technical DRC-1339 (DRC-1339 Technical, USEPA Reg. No. 56228-59) was first registered 

with USEPA in 1967 (USEPA 1995). PM [Purina Mills] Resources, Inc., which was acquired by 

Virbac Corporation, was previously the registrant for Starlicide Technical (USEPA registration 

No. 67517-7); however, the company transferred the registration to APHIS (USEPA registration 

No. 56228-59) in September 2013 (USEPA 2013b). When the registration was transferred, 

APHIS changed the name of the product to DRC-1339 Technical. All APHIS end-use 

Compound DRC-1339 Concentrate products are prepared from and identical in composition to 

ANNUAL AVERAGE DRC-1339 USE BY PODUCT FOR FY11 TO FY15

Abbr. Product Name or State Registered SLN (Parent Label) EPA Registr. No. Applied (g) Projects WTs

Feedlots* Cancelled 56228-10 28,065.0 302 350

Gulls* Cancelled 56228-17 9.6 0.4 0.4

Pigeons* Cancelled 56228-28 837.6 36 60

Livestock, Nest & Fodder Depredations (LNFD) 56228-29 471.6 118 394

Staging Areas* Cancelled 56228-30 3,252.4 53 143

SLN ID (Feedlots)** Cancelled ID-050014 122.4 4 7

SLN ID (LNFD)^ ID-140005 0.8 0.2 0.2

SLN ID (Staging Areas)* Cancelled ID-050013 - - -

SLN IL (Feedlots)

Cancelled IL-120002 155.9 7 7

SLN IN (Feedlots)* Cancelled IN-080003 - - -

SLN IN (Staging Areas)* Cancelled IN-040001 - - -

SLN KS (Staging Areas)* Cancelled KS-120003 - - -

SLN KY (Feedlots)* Cancelled KY-020003 - - -

SLN KY (Staging Areas)

Cancelled KY-020002 - - -

SLN MD (Staging Areas)* Cancelled MD-080005 - - -

SLN MS (Staging Areas)* Cancelled MS-050008 - - -

SLN ND (Feedlots)** Cancelled ND-920001 - - -

SLN NE (Staging Areas & Feedlots)* Cancelled NE-100003 - - -

SLN NM (Staging Areas)** Cancelled NM-110004 - - -

SLN NV (LNFD)^ NV-150001 395.7 38 139

SLN NV (LNFD)

Cancelled NV-040004 40.1 3 14

SLN NV (Staging Areas)* Cancelled NV-020005 - - -

SLN OK (Staging Areas)**(Replaced by OK-180002 in 2018) OK-990001 567.6 50 117

SLN OR (Staging Areas)** (Replaced by OR-190004 in 2019) OR-010024 - - -

SLN TN (Feedlots)* Cancelled TN-080003 - - -

SLN TN (Staging Areas)* Cancelled TN-080004 - - -

SLN TX (Feedlots)** Cancelled TX-890001 7.1 0.6 0.8

SLN TX (SA)** (Replaced by TX-190006 in 2019) TX-020003 9.2 1 1

SLN TX (Feedlots)

Cancelled TX-090010 975.2 1 1

SLN TX (LNFD)

Cancelled TX-060016 - - -

SLN UT (LNFD)

Cancelled UT-130005 7.7 0.2 0.2

SLN WV (Staging Areas)* Cancelled WV-110001 - - -

SLN WV (Staging Areas)* Cancelled WV-010002 - - -

SLN WV (Staging Areas)* Cancelled WV-040001 46.7 6 7

SLN WY (LNFD)^ WY-110002 58.5 11 16

SLN WY (Staging Areas)**(Replaced by WY-180003 in 2018) WY-070002 98.9 12 31

TOTAL 5 FEDERAL 31

SLN 35,122.0 643 1,289
6

DRC-1339 Technical, which is comprised of ≥97% purity DRC-1339 (USDA 2019), the active 

ingredient (a.i.). APHIS currently has just two Compound DRC-1339 Concentrate Section 3 enduse products registered with USEPA, but four Section 3 labels were replaced by the Bird 

Control label at the end of 2018 and are included below as these labels were used for the data 

included in this risk assessment.

• Compound DRC-1339 Concentrate – Bird Control (USEPA Reg. No. 566228-63), a 

combined label designed to replace the Feedlots, Gulls, Pigeons, and Staging Areas 

labels and incorporate most of the associated SLN uses. The label, approved by USEPA 

in December 2017, fully replaced the following Section 3 labels by January 2019 (USDA

2017a), which were:

• Compound DRC-1339 Concentrate – Feedlots (USEPA Reg. No. 56228-10) for bird 

control in feedlots (cancelled in 2018) (USDA 2017b);

• Compound DRC-1339 Concentrate – Gulls (USEPA Reg. No. 56228-17) for control of 

gulls at landfills and to protect colonial nesting seabirds (cancelled in 2018) (USDA

2016a); 

• Compound DRC-1339 Concentrate – Pigeons (USEPA Reg. No. 56228-28) for control 

of pigeons causing health, nuisance, or economic problems in and around structures 

or in non-crop areas (cancelled in 2018) (USDA 2016c); and

• Compound DRC-1339 Concentrate – Staging Areas (USEPA Reg. No. 56228-30) for 

bird control in non-crop staging areas associated with roosts (cancelled in 2018)

(USDA 2016d); 

• Compound DRC-1339 Concentrate – Livestock, Nest & Fodder Depredations

(USEPA Reg. No. 56228-29) for control of crows, ravens, and magpies that damage and 

feed on the contents of silage/fodder bags, prey on newborn livestock, eggs or the young 

of federally-designated Threatened or Endangered species, or of other species 

designated to need of special protection (USDA 2016b).

For the purpose of this risk assessment, the new Bird Control label will be used when assessing 

risk related to the Feedlots, Gulls, Pigeons and Staging Areas use sites, because the separate 

Section 3 labels were cancelled at the end of December 2018. The four older Section 3 labels are 

discussed when describing prior projects conducted under these labels for the data used in this 

risk assessment. The Bird Control label also incorporated many of the State SLN registrations 

(Table 3).

In cases where an active SLN use was not incorporated into the Bird Control label and was still 

needed, a new SLN was submitted for that specific use under the Bird Control parent label.

However, a summary of information for the old SLN labels regarding each use pattern as well as 

species controlled is given below and in Table 4, as well as referenced because these are the 

labels that WS used to apply DRC-1339 from FY11 to FY15.

• Feedlots (Commercial Animal Operations): Various bait materials can be used such as 

rolled barley, cracked corn, and rolled whole corn, but baits can only be used in feedlots 

to control target bird species identified on the label such as European starlings, rock 

pigeons, and specific species of blackbirds, crows, and ravens, as well as bronzed 

cowbirds (Molothrus aeneus) when in mixed flocks (Table 4). Feedlots are defined on the 
7

label as areas around commercial animal operations where beef cattle, dairy cattle, swine, 

sheep, goats, mink, poultry, or game birds are confined primarily for the purpose of 

production and eventual sale in agricultural and commercial markets. From FY11 to FY15, 

WS applied an annual average of 39,326 g of DRC-1339 under the Feedlots label and two 

SLN labels under the parent Feedlots label for 315 unique properties in 364 work tasks, 

primarily for European starlings (Table 3).

• Gulls: Bread cubes are mixed with DRC-1339 and can be used to control targeted species 

of gulls in coastal or inland gull colonies, within predation radii of important colonial nesting 

sites of terns, puffins, or other colonially nesting birds that will be protected; or close to 

areas where target gull species damage property or crops during the breeding season 

(Table 4). It may also be used at feeding sites located at airports, industrial sites, dumps 

or landfills, or other noncrop areas throughout the year. From FY11 to FY15, WS applied 

an annual average of 10 g of DRC-1339 under the Gulls label for gull damage on 0.4 

unique properties in 0.4 work tasks (Table 3).

• Pigeons: Whole-kernel corn is mixed with DRC-1339, which then can be used to control 

feral pigeons in roosting or loafing areas on flat rooftops, or within fenced areas (Table 4). 

From FY11 to FY15, WS applied an annual average of 838 g of DRC-1339 under the 

Pigeons label for feral rock pigeon damage on 36 unique properties in 60 work tasks 

(Table 3).

• Staging Areas: Baits prepared with one of the grain components (cracked corn, rolled 

barley, brown rice, or poultry pellets) may only be used in noncrop, staging areas 

associated with nighttime roosting sites of blackbirds, cowbirds, grackles, and starlings 

(Table 4) and crows under the various SLNs. From FY11 to FY15, WS applied an annual 

average of 3,975 g of DRC-1339 under the Staging Areas label and four SLN labels under 

the parent Staging Areas label for 122 unique properties in 286 work tasks, primarily for 

starlings, brown-headed cowbirds, red-winged blackbirds, common grackles, and crows 

(Table 3).

• Livestock, Nest & Fodder Depredations: Hard boiled eggs or meat-cube baits are 

treated with DRC-1339, which can be used to control species such as common raven, 

Chihuahuan raven (Corvus cryptoleucus), American crow, black-billed magpie, and fish 

crow (Table 4). Baits (eggs or meat cubes) can be used in rangeland or pastureland where 

ravens, crows, or magpies prey on newborn livestock, or refuges or other areas where 

they prey upon the eggs or young of federally designated threatened or endangered 

Species, or federal or state protected wildlife. From FY11 to FY15, WS applied an annual 

average of 974 g of DRC-1339 under the LNFD label and five SLN labels under the parent 

LNFD label for 170 unique properties in 552 work tasks, primarily for common ravens 

(Table 3).

USEPA has been reevaluating the data supporting DRC-1339 and the registered products under 

Registration Review since September 2011. The final work plan for registration review stated that 

USEPA (2012a) would require human health data for conducting a revised occupational risk 

assessment. The work plan also listed data needs for performing a comprehensive ecological risk 

assessment including an endangered species assessment for all uses. USEPA (2013a) issued a 

Data Call-In (DCI) formally listing the studies that would be required for continued registration of 

products containing DRC-1339. After reviewing submissions to address many of the initial data 

requirements in the DCI, USEPA reduced the number of required studies. 
8

Table 4. Summary of use patterns for DRC-1339 (USDA 2017b, 2016a, b, c, d, USEPA 2017b).

Product

Use

Target Species Application Site Application Method Application Rate

Feedlots Brewer’s, Red-winged &

Yellow-headed Blackbirds, 

Common, Boat-tailed &

Great-tailed Grackles, 

Brown-headed Cowbird,

European Starling, 

Common & Chihuahuan 

Ravens, American & Fish 

Crows, Black-billed 

Magpie, Rock Pigeon, and 

Eurasian Collared-Dove, 

and Bronzed Cowbird when 

in mixed flocks with one or 

more of the above sp.

Feedlots with beef or dairy 

cattle, swine, sheep or

goats, and poultry or game 

bird farms

Manual baiting – bait 

stations/trays using a 

scoop or other 

appropriate utensil

Mechanical baiting –

hopper of truck-mounted 

or trailer-type feeder and 

apply with mechanical 

applicator

Maximum single: 0.1 lbs.

a.i./treated acre (2% a.i. - 1:10

dilution of untreated bait: 50 

lbs. of diluted bait/acre, or 1 lb.

of diluted bait/1000 ft2)

Gulls Gull spp. - Herring, Great 

Black-backed, Ring-billed,

Laughing (non-protected 

areas), Western & 

California Gulls

Target gull’s nesting 

colonies and gull feeding 

areas at airports, industrial 

sites, dumps, landfills, and 

non-crop areas

Manual broadcast or 

place treated bread 

cubes wearing rubber 

gloves and using a scoop 

or other utensil

Maximum: 0.1 lb. a.i./per 

treated acre/treatment (bait 

densities of 5 treated 

cubes/100 ft2 and 2200 treated 

cubes/ treated acre)

Pigeons Feral pigeons Roosting or loafing areas 

on flat rooftops, or within 

fenced areas from which 

the public, pets, domestic 

animals, and most nonavian wildlife can be 

excluded during bait 

application

Manual dispense or 

broadcast treated wholekernel corn wearing 

rubber gloves and using 

a scoop or other utensil

Maximum: 0.05 lb. a.i./ treated 

acre (25 lbs./acres of a 1:1 

dilution of properly treated 

whole-kernel corn with 

untreated whole-kernel corn)

Livestock, 

Nest &

Fodder 

Depredations

Common & Chihuahuan 

Ravens, American & Fish 

Crows, and Black-billed 

Magpie

Rangeland and pasture 

areas where ravens, 

magpies, or crows prey 

upon newborn livestock; 

Refuges or other areas 

where ravens, magpies, or 

crows prey upon the eggs 

or young of federally 

designated Threatened or 

Endangered Species, or 

Federal or State protected 

wildlife; and within 25 feet 

of silage/fodder bags 

damaged or likely to be 

damaged by crows, ravens, 

or magpies

Manually place (wearing 

rubber-gloves) <75 meat 

cube baits at each baited 

site (5 to 10 baits in 

clusters over an area not 

to exceed 1000 ft2)

Maximum: 0.083 lbs. of 

a.i./treated acre (18 treatedegg baits in at least 5 bait sets 

applied over an area of 400 ft2 

surrounding an animal carcass 

draw station). For meat baits,

<0.01 a.i./treated acre, 5-10 

baits per 1000 ft2, no more 

than 75/baited site, and baits 

must be observed. Assuming a 

maximum used per acre, max 

of 0.003 lb. a.i./acre for meat 

baits.

Staging 

Areas

Red-winged Blackbird, 

Common, Boat-tailed &

Great-tailed Grackle, 

Brown-headed Cowbird

and European Starling, and

Brewer’s, Tricolored &

Yellow-headed Blackbirds, 

American Crow, and Blackbilled Magpie when in 

mixed flocks with one or 

more of the above species

Stubble fields, harvested 

dormant hay fields, open 

grassy or bare ground

noncrop areas, roads, 

roadsides, rooftops, 

industrial and commercial 

structures, and secured 

parking areas

Feeding stations;

Mechanical broadcasting 

with ground-based 

equipment; and Manual 

broadcasting – wearing 

rubber gloves and using 

a scoop or other utensil

Maximum: 0.1 lb. a.i./ treated 

acre/ treatment or 

Maximum yearly: 0.5 lb. a.i./

acre (<58 lbs./treated acre of 

cracked corn or rolled barley 

baits, 110 lbs./treated acre of 

diluted poultry pellet bait, or 

137 lbs./treated acre of diluted 

brown rice bait. Do not make 

more than 5 treatments per 

year to any one treated site)

Bird Control Combined bird species Commercial animal 

operations; staging areas; 

gull colonies; and gull 

feeding or loafing sites at 

airports, industrial sites, 

dumps, landfills, and noncrop areas

Retrievable feeding 

stations, bait stations, or 

trays; manual or 

mechanical baiting; and 

hand or mechanical 

broadcast. 

For broadcast applications: do

not exceed a maximum single 

application rate of 0.1 lbs.

a.i./acre (1.12 g a.i./100 m2) or 

a maximum yearly application 

rate of 0.5 lb. a.i./acre (5.61 g 

a.i./100 m2). 

For manual baiting: 1 lb./ 1000 

ft2(0.49 kg/100 m2) over dry or 

frozen areas

a.i. = Active Ingredient
9

In 2014, USEPA (2014a) further agreed to waive some of the remaining studies by including 

additional mitigation language on product labels to reduce the likelihood of DRC-1339’s 

movement to water and improve the success of leftover bait cleanup. Waived studies included 

photodegradation in soil, aerobic aquatic metabolism, anaerobic aquatic metabolism, terrestrial 

field dissipation, estuarine/marine fish acute toxicity, freshwater invertebrate lifecycle, terrestrial 

plant toxicity, and aquatic plant and algal toxicity studies (USEPA 2014a). With the approval of 

the amended DRC-1339 labels on October 20, 2015, USEPA (2015) officially waived the abovementioned studies.

For the environmental study requirements that remained, APHIS agreed to conduct the studies 

using a phased approach as funds became available. These studies include honeybee (Apis 

mellifera) acute oral toxicity, adsorption/desorption or soil column leaching, aerobic soil 

metabolism, and environmental chemistry analytical methods and independent laboratory 

validation in soil and water. APHIS has completed the acute oral honeybee toxicity study, the 

aerobic soil metabolism study, and the analytical methods and independent laboratory validation 

study in water. Results from the honeybee acute oral toxicity study (Section 3.2.2) and aerobic 

soil metabolism (Section 2.3) are summarized in this risk assessment. The two remaining 

environmental fate studies have not been completed.

2.2 Physical and Chemical Properties

DRC-1339 is an off-white to yellow powder with a moth ball odor (USDA 2019). DRC-1339’s 

parent compound, 3-chloro-p-toluidine, has a melting point ranging from 21 to 24oC and a boiling 

point ranging 220 to 230oC at 760 mm Hg. DRC-1339, on the other hand, has a melting point of 

260 ̊, at which point it vaporizes. DRC-1339 has a reported vapor pressure of 1.06 x 10-4torr at 

25o C and calculated Henry’s Law Constant of 1.47 x 10-8 atm/m3/mol (USEPA 2011a). DRC-1339

has a bulk density of 0.44 g/ml. The water solubility for DRC-1339 ranges from 53 to 91 g/L 

(USEPA 1995, 2011a).

2.3 Environmental Fate

The environmental fate describes the processes by which DRC-1339 moves and degrades in the 

environment. The environmental fate processes include: 1) persistence, degradation, and mobility

in soil; 2) movement to air; 3) migration potential to groundwater and surface water; 4) degradation 

in water; and 5) plant uptake.

In general, DRC-1339 is unstable and does not persist in soil. It degrades rapidly in soil when 

exposed to sunlight, heat, or ultraviolet radiation (USDA 2001). DRC-1339 has an average 

degradation half-life in soil of 0.17 days based on results from four different soil types (Batelle 

2018). Dissipation half-life values ranged from 0.02 days in a Texas loam to 2.0 days in a clay 

soil. DRC-1339 has low mobility in high organic matter soils because it strongly binds to organic 

matter. DRC-1339 binds rapidly and irreversibly to soil organic matter suggesting that

volatilization from soil into the atmosphere is not a significant pathway for exposure. DRC-1339 

has moderate vapor pressure (1.06 X 10-4torr at 250C) and a high Henry’s Law constant value

(estimated - 1.47 x 10-8 atm-m3-mol-1), suggesting a low potential for volatilization into the 

atmosphere from aqueous solutions (USEPA 2018a). DRC-1339 has low migration potential to 

groundwater and surface water due to its high affinity to soil organic matter.

DRC-1339 is resistant to hydrolysis but sensitive to light with a photodegradation half-life in water 

ranging from 6.5 to 41 hours depending on the season, as it is faster in summer than winter 

(USDA 2001, USEPA 2011a). DRC-1339 is not expected to bioconcentrate in aquatic 
10

environments. DRC-1339 slightly accumulates in bluegill with average bioconcentration factors of 

33x (edible tissues), 150x (nonedible tissues), and 88x (whole fish) (Spanggord et al. 1996, 

USEPA 2018a).

Uptake by plants is unlikely since DRC-1339 is mixed with a bait that is used on bare soil, fallow 

ground, or in trays. Any DRC-1339 that would leach from the bait material would degrade quickly 

in soil or bind to soil organic matter reducing bioavailability to plants. In addition, most of the bait 

is removed by the target species reducing the amount of DRC-1339 available for any potential 

plant uptake. 

2.4 Hazard Identification

DRC-1339 is hazardous to human health because of its acute inhalation toxicity and eye and skin 

corrosiveness. Pesticide label statements regarding the health effects based on toxicity studies 

include “Fatal if inhaled. Corrosive. Causes irreversible eye damage and skin burns. May be fatal 

if swallowed. Harmful if absorbed through skin. Prolonged or frequently repeated skin contact may 

cause allergic reactions in some people.” (USDA 2016b, 2017a, b).

USEPA evaluated human incident reports for DRC-1339 during product reregistration and did not 

identify any human incident cases from their Office of Pesticide Program Incident Data Systems 

(IDS) between 2006 and 2011 (USEPA 2011b). The aggregate IDS module includes less severe 

human incidents with minor, unknown, or no effect outcomes. WS has no "Adverse Incidence 

Reports" (6(a)2) from FY87 to FY21 for DRC-1339 for WS personnel or the public. An additional 

literature review did not identify any human exposure cases related to DRC-1339.

2.4.1 Mode of Action

The biochemical mechanism of action for DRC-1339 is not well understood. Previous studies 

suggest that ingested DRC-1339 is rapidly hydrolyzed to 3-chloro-p-toluidine, which is the toxic 

compound (Eisemann et al. 2003). In sensitive birds, DRC-1339 causes irreversible kidney and 

heart damage resulting in death normally within 1 to 3 days of ingestion. In mammals, DRC-1339 

depresses the central nervous system at 10-100 times higher the dose that can cause effects in 

birds. Central nervous system depression can cause cardiac or respiratory arrest resulting in 

death 2 to 10 hours after ingestion. The effects to the central nervous system in non-sensitive 

mammals can be successfully treated symptomatically (USDA 2001, Eisemann et al. 2003). The 

kidney mitochondrial enzyme, deacetylase, may be responsible for the difference in susceptibility 

to 3-chloro-p-toluidine (Eisemann et al. 2003). The enzyme is present in chickens, starlings, 

pheasants, and rock pigeon, which are sensitive to 3-chloro-p-toluidine. The enzyme is not 

present in red-tailed hawks and mammals resulting in lower sensitivity to 3-chloro-p-toluidine (Mull 

and Giri 1972).

2.4.2 Acute Toxicity

The acute oral median lethality values (LD50), and ocular and dermal irritation scores in rats 

indicates that DRC-1339 is moderately toxic (Category II) via the oral route and highly toxic 

(corrosive, Category I) when in contact with skin and eyes (Table 5). USEPA (1995) concluded 

during registration review that DRC-1339 is highly toxic (Category I) in acute inhalation exposures 

based on its oral toxicity and the moderate to severe irritation and corrosivity observed in ocular 

and dermal irritation studies, although an acute inhalation study was not performed. The dermal 

sensitization study shows that DRC-1339 is a mild to moderate skin sensitizer in guinea pigs. The 

DRC-1339 Safety Data Sheet (USDA 2019) states that contact exposure to the eye causes
11

severe damage. Dermal contact can result in severe skin burns or an allergic reaction. Table 5

summarizes the acute toxicity values of DRC-1339 used by USEPA to assess acute toxicity risk 

to human health.

Table 5. Acute technical DRC-1339 toxicity data for mammals (USEPA 1995, USDA 2019). 

Test Species Test DRC-1339 Conc.*

97% a.i. USEPA Category

Laboratory Brown Rat Oral LD50 302-350 mg/kg II

Domestic New Zealand Rabbit Dermal LD50 > 2,000 mg/kg III

Laboratory Brown Rat Inhalation LC50 Not Required I

Domestic New Zealand Rabbit Eye Irritation Corrosive I

Domestic New Zealand Rabbit Dermal Irritation Corrosive I

Domestic Guinea Pig (Cavia porcellus) Dermal Sensitization Mild/Moderate -

a.i. = active ingredient M = male, F = female, - = Does not apply

2.4.3 Subchronic and Chronic Toxicity

USEPA (2018b) waived the DRC-1339 subchronic toxicity study, as well as other chronic toxicity 

studies, based on a weight of evidence approach that considered use pattern, toxicology and 

exposure. However, two subchronic toxicity studies were performed in rats using 3-chloro-ptoluidine, the toxic non-protonated parent compound of DRC-1339. A 5-day study in male and 

female Wistar albino laboratory brown rats exposed to 3-chloro-p-toluidine administered through 

inhalation at doses of 0.027, 0.105, 0.382, or 1.284 milligrams per liter (mg/L) for 6 hours/day

showed no signs of toxicity up to 0.105 mg/L (No Observable Adverse Effects Level (NOAEL)).

Clinical signs of toxicity at higher doses included neglected skin and ruffled fur, cyanosis, apathy, 

and decreased motility (Hazardous Substance Data Bank 2019). Rats in another study were orally 

dosed for two weeks with 3-chloro-p-toluidine at 300 milligrams per kilogram (mg/kg) body weight 

(bw)/day (10% solution in peanut oil), for 5 days/week. The rats were ill and cyanotic after the 

third and fourth treatments (Hazardous Substance Data Bank 2019).

Long-term exposure to DRC-1339 concentrate may cause an allergic skin reaction (USDA 2019).

2.4.4 Developmental and Reproductive Effects

A literature review did not identify mammalian toxicity studies on reproductive or developmental 

effects. USEPA (2018b) waived a developmental toxicity study due to the low potential for repeat 

oral, dermal or inhalation exposure to workers or applicators. 

2.4.5 Neurotoxicity Effects

A literature review shows depression of the central nervous system in mammals from exposure 

to DRC-1339 (Eisemann et al. 2003, Felsenstein et al. 1974, Borison et al. 1975). Although the 

direct effects on neurological function are unknown, 3-chloro-p-toluidine has been detected in 

brain tissue and the observed central nervous system effects include intense weakness, dyspnea, 

and complete paralysis following intraperitoneal administration (Eisemann et al. 2003). Other

observed central nervous system effects include centrally induced skeletal muscle relaxation or 

paralysis, such as loss of the righting reflex in mice and rats (Felsenstein et al. 1974, Borison et 

al. 1975). USEPA (2013a) initially requested a neurotoxicity screening battery test in its DCI notice

during registration review. However, the USEPA Office of Pesticide Programs subsequently 

waived the neurotoxicity study in a Hazard and Science Policy Council meeting on August 30, 

2012 (USEPA 2014b) and still considers it waived (USEPA 2018b).
12

2.4.6 Carcinogenicity and Mutagenicity

The USEPA (1995) human health assessment concluded that DRC-1339 is not a carcinogen 

based on two 78-week exposure studies of the free base (3-chloro-p-toluidine) in rats and mice 

performed by the National Cancer Institute (1978). The study results found body weight 

depression without inducing tumors at the highest dose administered (3,269 ppm).

USEPA (1995) also concluded that DRC-1339 is not a mutagen based on the negative results of 

three mutagenicity assays performed in Salmonella spp. strains and Chinese hamster (Cricetulus 

griseus) ovary cells (Stankowski et al. 1997). In the Ames assay with Salmonella strains TA1535, 

TA1537, TA1538, TA98, and TA100, DRC-1339 was negative for inducing reverse gene mutation 

at the histidine locus at levels up to 2,500 μg/plate with and without metabolic activation. In the 

Chinese hamster ovary mammalian cell forward gene mutation assay, DRC-1339 was also 

negative for inducing forward mutation at the hypoxanthine-guanine phosphoribosyltransferase 

locus with and without metabolic activation to cytotoxic/precipitating doses up to 600 μg/mL. In 

the chromosomal aberration assay in Chinese hamster ovary cells, DRC-1339 was positive in a 

dose-related manner for structural aberrations in S9-activated cultures at moderately cytotoxic 

doses of 250 or 350 μg/mL. However, DRC-1339 was negative without metabolic activation at 

cytotoxic doses up to 350 μg/mL.

2.4.7 Immunotoxicity Effects

A literature review did not identify any DRC-1339 mammalian immunotoxicity studies. USEPA 

(2013a) requested an immunotoxicity test (870.7800) in its DCI notice during registration review, 

but waived the study based on the weight of evidence approach considering all the available 

hazard and exposure information provided by USDA APHIS in a Hazard and Science Policy 

Council meeting on December 27, 2014 (USEPA 2014b). The low volume/minor use waiver 

justification included: 1) the limited time period a mixer, handler, or applicator would be exposed 

while using DRC-1339; (2) the current worker protection requirements on the DRC-1339 labels; 

(3) the limited annual use of DRC-1339; and 4) data from 3-chloro-p-toluidine that can be used to

bridge to 3-chloro-p-toluidine hydrochloride.

2.4.8 Endocrine Effects

A literature search did not identify any studies indicating the potential of DRC-1339 to affect the

endocrine system. DRC-1339 is not among the group of 99 pesticide active ingredients on the 

initial and second lists to be screened under the USEPA (2014c) Endocrine Disruptor Screening 

Program. However, both lists were generated based on exposure potential and not whether the 

pesticide is a known or likely chemical to disrupt the endocrine system (USEPA 2014c). DRC1339 is not among the EU (European Union) list of chemicals with the potential to impact the 

endocrine system (Danish Centre on Endocrine Disrupters 2018). The EU list includes three 

categories: Category 1 – endocrinal effect recorded at least on one type of animal; Category 2 –

a record of biological activity in vitro leading to disruption; and Category 3 – not enough evidence 

or no evidence data to confirm or disconfirm endocrinal effect of tested chemicals (Hrouzková

and Matisova 2012).
13

3 DOSE-RESPONSE ASSESSMENT

3.1 Human Health Dose-Response Assessment

A dose-response assessment evaluates the dose levels (toxicity criteria) for potential human 

health effects including acute and chronic toxicity. USEPA did not establish an oral reference 

dose for DRC-1339 because USEPA does not believe that the potential exists for significant 

exposure to occupational workers. USEPA did not establish a tolerance for DRC-1339 because 

there are no registered food or feed uses. The maximum contaminant level has not been

established for drinking water.

3.2 Ecological Effects Analysis

This section of the risk assessment discusses available ecological effects data for terrestrial and 

aquatic biota. Available acute and chronic toxicity data are summarized for all major taxa and will 

be integrated with the exposure analysis section to characterize the risk of DRC-1339 to nontarget

wildlife and domestic animals. Information in this section was gathered from on-line databases 

and searches for relevant peer reviewed and other published literature.

3.2.1 Aquatic Effects Analysis

DRC-1339 is moderately toxic to fish. The 96-hour median lethality concentration (LC50) for 

bluegill is 11 mg/L (Bowman 1991a). The 96-hour LC50 for the rainbow trout is 9.7 mg/L (Bowman

1991b). The 96-hour LC50 for southern leopard frog (Rana sphenocephala) tadpoles is 44 mg/L 

(Marking and Chandler 1981).

DRC-1339 has moderate to high toxicity to aquatic invertebrates depending on the test species

(Table 6). The 48-hour median effective concentration (EC50) for the freshwater cladoceran is 

0.079 mg/L (USEPA 2011a; Blasberg and Herzog 1991) while marine species appear to be more 

tolerant with 96-hour LC50 values of 10.8 and 16.0 mg/L for the penaeid shrimp and blue crab, 

respectively (Walker et al. 1979) (Table 6).

Table 6. Acute aquatic invertebrate toxicity for DRC-1339 technical.

Test species Test Results Reference

Cladoceran (Daphnia magna)

EC50 0.08 mg/L USEPA 2011a; Blasberg and Herzog 1991

LC50 1.6 mg/L Marking and Chandler 1981

Caddisfly (Isonychia sp.) LC50 6.5 mg/L Marking and Chandler 1981

Mayfly (Hydropscyche sp.) LC50 12 mg/L Marking and Chandler 1981

White River Crayfish (Procambarus acutus 

acutus)

LC50 15 mg/L Marking and Chandler 1981

River Horn Snail (Oxytrema catenaria) LC50 6.7 mg/L Marking and Chandler 1981

Glass Shrimp (Palaemetus kadiakensis) LC50 6.1 mg/L Marking and Chandler 1981

Panaeid Shrimp (Panaeus sp.) LC50 10.8 mg/L Walker et al. 1979

Blue Crab (Callinectes sapidus) LC50 16.0 mg/L Walker et al. 1979

Asiatic Clam (Corbicula manilensis) LC50 18.0 mg/L Marking and Chandler 1981

3.2.2 Terrestrial Effects Analysis

Mammals

DRC-1339 appears to have moderate acute toxicity to rats with acute oral LD50 values of 302-350

mg/kg (Table 5). Additional mammalian toxicity data indicate low to moderate acute toxicity for 

various mammals (Table 7), although DRC-1339 may be more toxic to cats (Felsenstein et al. 
14

1974). In a swine gavage study with DRC-1339, none died, and no adverse clinical or 

histopathological effects were reported when dosed with 50 mg/kg of DRC-1339. Swine were also 

fed poisoned birds with no reported mortalities or any external clinical effects (Caslick et al. 1972).

Birds

A large amount of toxicity data is available for acute exposures to a range of bird species (Table 

7). Eisemann et al. (2003) summarized DRC-1339 avian toxicity data for more than 55 species 

available from published and unpublished sources. Available acute oral dosing studies show high 

toxicity to corvids, red-winged blackbirds, starlings, gallinaceous birds, doves, herring gulls, and 

barn owls with LD50 values ranging from 1.33 to 42.1 mg/kg (Table 7). DRC-1339 ranges from 

slightly to moderately toxic for mallards, house sparrows, and cooper’s hawks with LD50 values 

ranging from 105 to 562 mg/kg (Table 7). 

Available acute dermal toxicity testing using birds report an LD50 of 14 and 80 mg/kg for the breast 

and foot respectively, using the European starling (Schafer et al. 1969).

Table 7. Acute oral median lethality and subacute dietary DRC-1339 toxicity studies for mammals and birds.

Test species Test Results Reference

Mammals

Brown Rat (Laboratory) LD50 302 mg/kg USEPA 2018a

North American Deermouse ALD* 1,800 mg/kg Schafer and Bowles 1985

Brown Rat (white lab) LD50 1,170-1,770 mg/kg Ford 1967

Domestic Dog ^ LD50 >100 mg/kg Ford 1967

Domestic Sheep LD50 >200 mg/kg Ford 1967

Birds

Mallard LD50 105 mg/kg USEPA 1995

LC50 322 mg/kg (98% a.i.)

Chachalaca (Ortalis sp.) LD50 42.1 mg/kg Eisemann et al. 2003

Northern Bobwhite LD50 2.9 mg/kg USEPA 1995

LC50 14.1 mg/kg (98% a.i.)

Ring-necked Pheasant LD50 10 mg/kg Eisemann et al. 2003

Domestic Turkey LD50 10.26 mg/kg Eisemann et al. 2003

Rock pigeon LD50 17.7 mg/kg Eisemann et al. 2003

Mourning Dove LD50 3.2 mg/kg Eisemann et al. 2003

Herring Gull LD50 4.6 mg/kg Eisemann et al. 2003

Cooper's Hawk LD50 562 mg/kg Eisemann et al. 2003

Barn Owl LD50 4.2 mg/kg Eisemann et al. 2003

Scrub-Jay (Aphelocoma sp.)** LD50 1.8 mg/kg Eisemann et al. 2003

American Crow LD50 1.33 mg/kg Eisemann et al. 2003

Common Raven LD50 2.9 mg/kg Eisemann et al. 2003

European Starling LD50 3.2 mg/kg Eisemann et al. 2003

House Sparrow LD50 375 mg/kg Eisemann et al. 2003

Red-winged Blackbird LD50 2.4 mg/kg Eisemann et al. 2003

*ALD – Acute Lethal Dose estimated LD50 when unable to calculate 

^ Emetic at doses of 10, 50 and 100 mg/kg a.i. = active ingredient

** Species split into 4 species (Island (Aphelocoma insularis), California, Florida (A. coerulescens), and Woodhouse's (A. 

woodhouseii) Scrub-Jays) since Schafer et al. (1983), the data used in Eisemann et al. 2003 (likely California or Woodhouse's, or 

both, knowing where birds captured).

Subacute dietary testing using the northern bobwhite and mallard (Table 7) demonstrated that 

DRC-1339 is moderately to highly toxic to surrogate bird species representing upland game birds 

and waterfowl. Both studies were five-day exposures and are part of the USEPA standardized 

protocols for conducting avian subacute dietary toxicity studies.
15

Additional dietary toxicity studies have also been conducted with other species and different 

durations. Eisemann et al. (2003) summarized the available published and unpublished dietary 

toxicity data for various bird species with similar sensitivities to those reported in acute oral 

exposures. Schafer et al. (1977) reported 30 and 90-day LC50 values of 4.7 and 1.0 mg/kg-diet, 

respectively, for European starlings. The same study also reported a 28-day LC50 of 18 mg/kgdiet for the northern bobwhite and a 30-day LC50 of less than 100 ppm for rock pigeon. Cummings 

et al. (2003) exposed savannah sparrows, Canada geese, snow geese, western meadowlarks, 

mourning doves, and American tree sparrows for five days to dietary DRC-1339 concentrations 

of 769 mg/kg-diet. No significant mortalities occurred in Canada geese, snow geese and 

savannah sparrows, but 80% mortality was observed in American tree sparrows and 90% 

mortality was observed for mourning doves and western meadowlarks. Cummings et al. (2002) 

reported no mortalities of wild-caught savannah sparrows, white crowned sparrows, field 

sparrows, song sparrows, and chipping sparrows offered 2% treated brown rice (714 mg/kg-diet) 

over a five-day period. 

Additional non-standardized studies evaluating chronic and reproductive effects are also available 

for various bird species. Schafer et al. (1977) conducted chronic reproduction studies using 

Japanese quail (Coturnix japonica) and domestic pigeons. Reproductive effects were seen at 10 

mg/kg-diet and above for quail including decreased egg and live-chick production, and increased 

incidence of egg breakage and at 25 mg/kg-diet for pigeons including increased proportion of 

infertile eggs; no effects were observed in the first-generation offspring for either of these species.

Hubbard and Neiger (2003), in a 5-day reproduction study using ring-necked pheasants, dosed 

females and males three times each with a dose of 2 or 4 mg DRC-1339 and compared 

reproductive endpoints to a control group found a statistically significant effect on brood size and 

a non-statistical negative correlation on clutch and brood size with increasing dose. 

Reptiles and Terrestrial Phase of Amphibians

DRC-1339 toxicity data for reptiles and the terrestrial phase of amphibians do not appear to be 

available. In cases where data is lacking, USEPA assumes that avian toxicity data is 

representative of reptiles. There are uncertainties in this assumption related to differences 

between the two taxa, but for this risk assessment DRC-1339 is considered moderately to highly 

toxic to reptiles when considering the range of sensitivities to surrogate avian species. In the case 

of terrestrial phase amphibians, DRC-1339 is considered moderately toxic based on the aquatic 

phase LC50 value for the southern leopard frog. 

Terrestrial Invertebrates

The acute oral toxicity study of DRC-1339 to the honeybee demonstrates very low toxicity with a 

48-hr LD50 greater than the nominal dose of 72 micrograms (μg)/bee, and a no observable effect 

concentration (NOEC) of 72 μg/bee, the highest concentration tested (USEPA 2018a).

Terrestrial Plants

DRC-1339 phytotoxicity is low based on available limited data with foliar applications to the pinto 

bean (Phaseolus vulgaris) and Douglas fir (Pseudotsuga menziessi) reporting no observed effects 

when treated with a 6% solution of DRC-1339 (Schafer and Bowles 2004).
16

3.2.3 Toxicity of Formulations and Metabolites to Nontarget Wildlife and Domestic Animals

Available toxicity data for nontarget mammals and birds to the technical DRC-1339 would be

similar to the formulations since they are composed primarily of the technical active ingredient

(97% a.i.) (Tables 5 and 7). The toxicity of DRC-1339 degradates and metabolites to nontarget 

species is unknown but is assumed to be similar to the parent for this risk assessment for two of 

the three metabolites. The three major degradates identified from environmental fate studies 

include carbon dioxide, 3-hydroxy-p-toluidine, and N-acetyl-3-chloro-p-toluidine. Carbon dioxide 

and N-acetyl-3-chloro-p-toluidine were measured in the aerobic soil metabolism study and 3-

hyroxy-p-toluidine was the primary degradate identified in the aqueous photolysis study (USEPA 

2011a).

Peoples (1965) found that starlings primarily excreted one metabolite, 4-amino-3-chlorobenzoic 

acid, categorized as an irritant and otherwise nontoxic, along with DRC-1339. The majority of 

excreta (89%) came within the first 2 hours following ingestion, which consisted of 82% 4-amino3-chlorobenzoic acid and 18% DRC-1339; no DRC-1339 was excreted in four birds after 4 hours 

following ingestion. Thus, the majority of DRC-1339 is converted to nontoxic metabolites in 

excreta. The total weight of all excreta prior to death for 8 birds given 1 mg of DRC-1339 orally

was the same percentage at 82% 4-amino-3-chlorobenzoic acid (0.64 mg) and 18% DRC-1339 

(0.15 mg). Starling digestive systems change seasonally, primarily as the diet changes from 

invertebrates to plant material, which is typically the beginning of WDM targeting starlings (they 

really begin flocking as well as consume livestock food). Starling intestines and villi becoming 

longer and the gizzard gets larger when they change diets (Feare 1984); starlings consume more 

and thus the rate of food passage though the gut increases (Levey and Karasov 1989). Therefore, 

it would be expected that DRC-1339 passes with greater potential during this time.

Issues have been raised concerning the risk from birds killed with DRC-1339, exposure of 

carcasses to people and pets, and the impact of their carcasses on the environment. Birds often 

die in their nighttime roost. One issue is that birds could die near people’s residences, which could 

be a nuisance to the property owner and pets. WS personnel try to determine the whereabouts of 

a roost associated with a project and try to pick up all birds that expire at these roosts. It is possible 

for birds, though, to leave a treated site and roost at a site not known to WS personnel. This could 

be at a residence or an area where the public may or may not have access. The primary concern 

has been the potentially large number of birds that could die from a treatment on a property and 

their potential to be a risk to pets and people from the birds or their excrement. Mammals and 

birds metabolize or excrete DRC-1339 within a matter of hours, and known metabolites are 

nontoxic to birds and mammals (Peoples 1965, Cunningham et al. 1979, Timm 1994). However, 

some DRC-1339 remains in the excreta from starlings. Species sensitive to DRC-1339 such as 

crows may be able to get a toxic dose of DRC-1339 from undigested gut contents, but this has

only been anecdotally reported for crows (Knittle et al. 1990). Raptors (e.g., Cooper’s hawk and 

American kestrel) fed a diet of birds killed with DRC-1339 for over 100 days were not found to 

suffer any ill effects and all gained weight (DeCino et al. 1966). WS personnel attempt to find all 

carcasses associated with a project, especially those associated with public areas. Some 

projects, especially treatment of ravens, occurs in areas where it is unlikely the public would be 

exposed and where WS personnel have the lowest potential for knowing where birds are roosting.

3.2.4 Indirect Effects of Carcasses from Control Actions on Wildlife and the Environment

Concerns have been voiced that the birds that die in a nighttime roost over water, such as in a 

cattail (Typha spp.) marsh, could increase the risk of communicable diseases or quicken

eutrophication of the wetland. Birds may die and fall into the waters. The risks of these issues are
17

analyzed but are an indirect effect of the use of DRC-1339 on the environment and not directly 

related to the chemical analysis. The disease risk or quickened eutrophication would not likely 

occur from such a possibility, especially as compared to the excrement that would be deposited 

in those same waters should the birds continue to roost at that location.

4 EXPOSURE ASSESSMENT

4.1 Human Health Exposure Assessment

The exposure analysis evaluates the potential for exposure of humans to DRC-1339. The 

exposure assessment begins with the use pattern for DRC-1339. An exposure pathway for DRC1339 includes (1) a release from a DRC-1339 source, (2) an exposure point where human contact 

can occur, and (3) an exposure route such as ingestion, inhalation, or dermal contact by which 

contact can occur. Exposures for the identified human populations are evaluated qualitatively for 

each identified exposure pathway.

4.1.1 Potentially Exposed Human Populations and Complete Exposure Pathways

DRC-1339 is a “restricted use pesticide” (RUP), which currently is limited to use by USDA APHIS 

certified applicators trained in bird control, or by persons under their direct supervision (USDA

2016a, b, c, d, 2017a, b). DRC-1339 applications are typically conducted on small acreage (~1 

acre), and typically occur once or twice before the project is completed (USDA 2011). Prebaiting 

is required for most uses to ensure that the bait is well accepted and nontarget species are not 

foraging on the baits. The treated baits are applied via manual or mechanical broadcast

applications, manually by placing or dispensing baits into feeding stations or other application 

sites. The treated bait cannot be applied by air. All DRC-1339 labels are for non-food use only.

Based on the expected use patterns for DRC-1339, WS handlers and applicators (occupational 

workers) in the program who are mixing and applying the pesticide in the field are the most likely 

subgroup of the human population to be exposed to DRC-1339. A potential complete direct 

contact exposure pathway is identified for handlers and applicators with the potential for exposure 

evaluated in Section 4.1.2.

Exposure by the general public to DRC-1339 is unlikely when applicators follow label 

requirements concerning application sites, entry restrictions, prebaiting, and post-treatment 

cleanup requirements. Entry restrictions only allow protected applicators in the area during 

application. Persons other than authorized handlers must stay away from the treated area at all 

times, and pets and livestock kept away from the treated area. Each DRC-1339 use has

restrictions on storage, application, and temporary placement of treated bait to locations that are 

not accessible by children, pets, or domestic animals. Residential use is prohibited and 

unauthorized persons are restricted from entering application sites during application. Signage 

may be posted near treatment sites to warn people against handling bait, especially where it 

would be easily seen, or make owners of pets and possibly livestock from being exposed. During 

the prebaiting assessment, WS personnel determine which bait is most readily accepted by the 

target birds and assess the risk to children, livestock, and nontarget species for each potential 

use site. The prebaiting assessment also ensures that the proper amount of bait is used 

minimizing potential exposure to humans, domestic animals, and nontarget species. Labels also 

require observation of bait sites throughout the day when practical. The post-treatment cleanup 

requirement after application, especially broadcast applications, minimizes the potential for 

human exposure to uneaten baits. For several days after the baits are applied, applicators are 

required to search for and remove poisoned bird carcasses from the area to minimize exposure
18

to the general public and nontarget wildlife. For example, the Pigeons, Gulls, and Staging Areas 

label uses (now Bird Control label uses) require burial of uneaten bait mechanically or manually 

covering baits to a minimum depth of 2 inches when the application is made to bare ground (USDA

2016c), to areas such as landfills or other non-crop lands (USDA 2016b), or to areas such as 

stubble fields, harvested dormant hay fields, open grass or bare-ground non-crop areas and 

roadsides (USDA 2016d, 2017a). The LNFD label (USDA 2016b) requires collecting unconsumed 

and leftover meat daily, and unconsumed and leftover egg baits, and carcasses within 7 days of 

treatment.

A complete exposure pathway is not identified for dietary exposure. DRC-1339 labels have no 

registered food or feed uses. All DRC-1339 uses have restrictions on using the treated baits as 

food, feed, or in any way used such that they could contaminate food commodities or animal feed. 

The labels have entry restrictions to keep livestock away from the bait at all times. The Staging 

Areas label use (now Bird Control label) also includes a restriction against grazing animals or 

growing most crops for 365 days after areas are treated with DRC-1339 (USDA 2016d, 2017a).

Other plant back restrictions are 15 days for rice, wheat, corn and barley and 30 days for sunflower 

and soybeans. The 365-day restriction is USEPA’s default value in the absence of specific 

environmental fate/residue information. To address USEPA’s (2011b) consideration of the 

registered use of DRC-1339 in livestock and poultry feedlots constituting a food use, the Feedlots 

label use (now Bird Control label) prohibits placing treated bait in pens that are occupied by 

livestock (USDA 2017b). The label use restrictions are sufficient to preclude exposure to livestock

and poultry.

A complete exposure pathway is not identified for drinking water because of the limited use pattern 

of DRC-1339, and label restrictions that prohibit placing treated baits near water bodies (within 

50 feet of permanent manmade or natural bodies of water). Depending upon the use site, DRC1339 can be applied by targeted broadcast application techniques, in open bait stations, or in 

individual meat or egg baits. Bait stations and meat and egg baits significantly reduce the risk of 

environmental contamination. Broadcast applications occur infrequently to limited areas and are 

designed so that bait remains on the ground for just a short duration. Bait removal by the target 

pest further reduces the chance of offsite transport via runoff. In addition, current labeling requires 

the applicator to retrieve unconsumed toxic bait. Any toxic bait that may be left on the ground after 

cleaning up would be minor and expected to degrade quickly in the environment based on the 

reported short half-lives in soil. The use patterns and environmental fate of DRC-1339 preclude 

contamination of surface and ground water that could be used for drinking water.

4.1.2 Exposure Evaluation

This section qualitatively evaluates worker exposure from direct contact while mixing DRC-1339 

with baits and applying them in the field, as well as re-entering treated sites for post treatment 

cleanup activities. The Bird Control and LNFD labels are RUPs and are handled by certified 

applicators or persons under their direct supervision. As discussed in Section 2.4, DRC-1339 is 

an acute inhalation toxicant and corrosive to eye and skin. Exposure from inhalation and other 

direct contact to DRC-1339 for a handler (mixing the concentrate formulations) or an applicator 

(applying diluted baits) are minimized under normal conditions with proper worker hygiene and 

the use of personal protective equipment (PPE).

PPE requirements for handlers who mix packages containing 1 lb. or more of the product include:

• Coveralls over long-sleeved shirt and long pants;

• Chemical-resistant gloves;
19

• Chemical-resistant footwear plus socks;

• Protective eyewear (goggles and face shield); and

• NIOSH-approved elastomeric half mask respirator with organic vapor (OV) cartridges and 

combination R or P filter OR a NIOSH-approved gas mask with OV canisters; OR a NIOSHapproved powered air purifying respirator with OV cartridges and combination HE filters. 

PPE requirements for handlers who mix packages containing less than 1 lb. include:

• Long-sleeved shirt and long pants;

• Chemical resistant gloves; and

• Protective eyewear (goggles or face shield).

PPE requirements for applicators who handle treated bait and for workers who collect carcasses 

or uneaten bait during post-treatment cleanup include:

• Long-sleeve shirt and long pants;

• Chemical-resistant gloves; and

• Protective eyewear (goggles or face shield). 

Other safety requirements for users on the labels include:

• Properly cleaning and maintaining PPE following manufacturer’s instructions or using detergent 

and hot water if no such instructions are provided,

• Washing hands before eating, drinking, chewing gum, using tobacco, or using the toilet;

• Removing clothing immediately if pesticide gets inside, then washing thoroughly and put on clean 

clothing; and

• Removing PPE immediately after handling the product.

Accidental exposure may occur during mixing and application of baits, but the chance of this type 

of exposure is low since DRC-1339 use is only allowed by USDA APHIS personnel that are 

certified applicators or persons under their supervision. The limited use of DRC-1339 reduces the 

potential for accidental exposure.

4.2 Ecological Exposure Assessment

Various application methods are allowed on the Bird Control label depending on the use site and 

the bird species being targeted. All applications are made by mixing DRC-1339 with a bait that 

can be applied to the target area. For the purpose of this ecological exposure assessment and 

the associated risk characterization section, the broadcast application staging area use was used 

to estimate aquatic and terrestrial residues. Use rates for staging area applications are higher and 

allow for broadcast applications over larger areas, and therefore, increase potential for exposure 

to nontarget aquatic and terrestrial wildlife.

4.2.1 Aquatic Exposure Assessment

Aquatic exposure from proposed DRC-1339 applications is expected to be low based on the 

method of application, proposed use pattern and mitigation measures to protect aquatic 

resources. The current use restrictions for the Bird Control and LNFD labels require a 50-feet “Notreatment” application buffer from manmade and natural water bodies that will reduce the potential 

for DRC-1339 to enter water bodies from runoff. Drift is not a potential pathway for exposure since 

applications are made as a bait and only broadcast in limited applications. No applications are 
20

allowed on either label using aerial application equipment, further reducing the potential for any 

off-site transport.

A maximum estimate of aquatic residues was made using the maximum application rate from the 

Bird Control label (0.1 lb. a.i./acre) and assuming that all the material would be deposited into a 

static water body. This scenario is not expected to occur under field conditions and would only 

occur from an accidental spill into a small waterbody. The maximum application rate for the LNFD

label is 0.083 lb. a.i. per acre. The water body dimensions evaluated in this assessment were one 

acre in area and one to six feet deep. The maximum instantaneous DRC-1339 residues from this 

estimate ranged from 0.006 to 0.035 mg a.i./L. These are conservative estimates of exposure 

since it assumes all material from a treatment area would be deposited into a water body, 

assumes no DRC-1339 degradation and does not account for the mitigating effects of the “No 

treatment” application buffer. The aquatic residue values can be compared to the aquatic effects 

data for DRC-1339 to determine whether any potential for risk under the proposed exposure 

scenario would occur. The results of this comparison are discussed in more detail in Section 5.2.1, 

the aquatic risk characterization.

4.2.2 Terrestrial Wildlife and Domestic Animals Exposure Assessment

Exposure estimates for nontarget birds and mammals were made using the USEPA (2012b) 

terrestrial exposure model, T-REX (Terrestrial Residue Exposure Model). The model allows the 

user to input pesticide use and environmental fate data as well as effects data for birds and 

mammals that can be used as a deterministic estimator of risk by deriving risk quotients. The 

model can be used for liquid pesticide applications as well as granular and treated seed

applications. The LD50 per square foot method was used in this assessment to determine potential 

risk to nontarget birds and mammals since it is applicable for broadcast uses of treated seeds, or 

baits such as DRC-1339. The use of the LD50 per square foot does not have any ecological 

relevance since nontarget animals may forage over larger areas but it does provide a means to 

quantify risk with the assumption that risk increases as the number of LD50s per square foot 

increases. This method is commonly used for granular pesticide applications. The staging areas

maximum labeled broadcast treatment (0.1 lb. a.i./acre) was used to develop exposure residues 

that could be compared to mammal and bird effects data for DRC-1339 and then used to 

extrapolate the risk for various sized birds and mammals. USEPA (2018a) estimated DRC-1339 

residues for various bait types that may be applied using trays, bait stations, or feeding stations 

and can result in the concentration of treated bait to smaller areas than what would occur using 

broadcast applications. DRC-1339 exposure residues were estimated for various-sized birds and 

mammals similar to those used in estimating DRC-1339 exposures using broadcast treatments. 

Concentrations of DRC-1339 in the final diluted bait mixture ranged from 0.05% w/w for whole 

raisin, culled French fries, waste potato, crouton, and small bread cube baits, to 0.2% w/w for high 

nutrition animal feed, dry pet food, and dry processed grain and seed baits. These estimates were 

used to estimate doses for various sized mammals and birds that could then be compared to 

weight-adjusted median lethality values.

4.2.3 Terrestrial Invertebrates and Terrestrial Plants Exposure Assessment

The methods of application for DRC-1339 preclude significant exposure to terrestrial invertebrates 

and plants. Some terrestrial invertebrates may be attracted to baits containing DRC-1339 but

exposure would be reduced since baits are consumed by the target species during the baiting 

period or removed from the application site per label requirements. Applicators are required to 

remove any unconsumed, regurgitated, or spilled bait at the conclusion of the baiting period. Any 

bait that may be left after the baiting period and is not removed would degrade quickly in the 
21

environment once exposed to sunlight. DRC-1339 would also bind to organic matter reducing 

bioavailability to most terrestrial invertebrates and plants. 

4.2.4 Assessment of Indirect Effects of Carcasses from Control Actions

A few potential issues could arise from the bird carcasses resulting from a control action using 

DRC-1339. In particular, it has been postulated that outbreaks of two avian diseases, botulism 

and cholera, could increase where birds fall into wetlands. There is also the potential for 

accelerated eutrophication of wetlands to result from the bird carcasses adding to nutrient 

deposits. 

Disease

Avian Botulism. Avian botulism is a paralytic disease of birds that occurs when toxins produced 

by the bacterium Clostridium botulinum are ingested (Locke and Friend 1987, Rocke and Bollinger 

2007). Seven distinct types of botulism toxins, designated by the letters A through G, have been 

identified. Type C and E toxins usually cause waterfowl die-offs from botulism (Locke and Friend 

1987). Many species of birds and some mammals are affected by Type C and E botulism in the 

wild. Waterfowl, shorebirds, and gulls are commonly affected, and songbirds are only infrequently 

affected (Locke and Friend 1987). 

Botulism bacteria are common in the soil of both terrestrial and aquatic environments. However, 

the bacteria only produce toxin under certain environmental conditions that favor bacterial growth, 

which include times when ambient temperatures are above 77 ̊F, water levels are low, and rotting 

vegetation, and invertebrate and vertebrate carcasses are present. High fly7 numbers (e.g., Order 

Diptera family Muscidae (housefly and allies)) and environments with no oxygen (Rosen 1971, 

Locke and Friend 1987) also favor the production of botulism bacteria. Most botulism outbreaks 

occur during late summer from July through September. Aquatic invertebrates ingest C. botulinum

when feeding on sediment, and many die during the summer because of high water temperatures 

and low water levels. The bacteria within the invertebrates produce a toxin as the invertebrates 

decay, and fish, waterfowl, and other birds become intoxicated when they consume the dead 

invertebrates (Reed and Rocke 1992). The affected fish and birds then die and maggots feeding 

on the carcasses pick up the toxin. These maggots are then eaten by other birds, which become 

sick, and the cycle continues. Large-scale bird die-offs occur as a result of this toxin amplification. 

This mode of transmission is common with type C botulism in the western United States, but the 

maggot-carcass cycle also occurs with type E botulism outbreaks in the Great Lakes. C. botulinum

bacterium persists in wetlands in a spore form that can persist for many seasons since it is 

resistant to heat and drying (Locke and Friend 1987).

Management of the environmental conditions in wetlands, especially water levels, and early and 

continuous clean-up and incineration of botulism-killed waterfowl carcasses, is recommended to 

prevent or control avian botulism outbreaks (Locke and Friend 1987). In addition, the occurrence 

of carcass-maggot cycles of botulism is dependent on a number of factors in addition to the 

presence of carcasses with botulism spores. These factors include fly density, and environmental 

conditions that facilitate fly egg-laying, maggot development, and maggot dispersal from 

carcasses (Reed and Rocke 1992).

7

Insects in the Order Diptera including the families Muscidae – houseflies and allies such as the housefly (Musca domestica) and Tabanidae –

predatory flies like deer fly (Chrysops spp.).
22

Control of birds with DRC-1339 is unlikely to cause or enhance a botulism outbreak. First, control 

operations would occur when botulism infected material is not present (late fall to early spring), 

but possibly could be exposed to some in drinking water. Thus, it is unlikely most birds would 

contribute to the maggot-bird transmission cycle since maggots should be unaffected. Secondly, 

most projects, especially projects that involve hundreds of birds, are conducted by WS from late 

fall through spring (December to March) when birds congregate. The carcasses would 

decompose by early summer, prior to when an outbreak would likely occur. Therefore, no 

evidence exists to suggest that the bird carcasses themselves could initiate rapid bacterial growth 

and amplification of bird-maggot transmission. Thus, it is unlikely that increased risk of avian 

botulism would result from bird carcasses killed by DRC-1339 that fell into a wetland.

Avian Cholera. Avian cholera, Pasteurella multocida, is a contagious, bacterial disease that most 

species of birds and mammals worldwide can contract, and particularly virulent strains are usually 

fatal (Friend 1999, Samuel et al. 2007, Merck 2018b). Avian cholera commonly occurs in 

waterfowl, with major die-offs occurring almost annually, whereas it occurs less frequently with 

only occasional die-offs in coots and scavenging gulls and crows. There are only a small number 

of reports in shorebirds, cranes, and songbirds as well as domestic fowl, and these are usually 

not associated with wild waterfowl outbreaks. Die-offs from avian cholera can occur any time of 

year, but predictable seasonal patterns exist, primarily in fall and winter, in areas where avian 

cholera has become well established in wild waterfowl, such as waterfowl movement corridors 

west of the Mississippi River. Transmission occurs from direct bird-to-bird contact, by ingestion of 

contaminated food or water, and possibly by aerosols. Transmission is enhanced by the 

gregarious nature of most waterfowl species and by dense concentrations of migratory water 

birds. The bacteria can persist in water for several weeks, in soil for up to 4 months, and in 

decaying bird carcasses for at least 3 months. Acute infections in birds can result in rapid death 

6 to 12 hours after exposure, and birds have been known to fall from the sky due to the rapid 

onset. Therefore, early detection of outbreaks is crucial in stopping the disease. Rigorous and 

careful collection, removal, and incineration of waterfowl carcasses is recommended to control 

the outbreaks and to reduce exposure of scavenging birds. 

Studies found that while P. multocida bacteria can be detected in water and soil samples from 

wetlands immediately after an outbreak (Moore et al. 1998), wetlands are probably not an 

important reservoir for maintaining the bacteria (Lehr et al. 1998). Starlings and blackbirds are 

susceptible to P. multocida, but little evidence has been found to suggest they are involved in 

many avian cholera outbreaks. The primary concern is blackbirds that roost in cattail marshes, 

especially during migration. The risk of exposing waterfowl to avian cholera from blackbird 

carcasses in the dense cattail marsh habitat where most are likely to occur is considered low.

Potential to Cause Accelerated Eutrophication of Wetland Areas

A concern has been raised that the carcasses of birds killed by DRC-1339 might significantly 

increase nutrients in cattail marsh roosting areas, resulting in accelerated eutrophication. 

Eutrophication is an ecosystem's response to the addition of artificial or natural nutrients, mainly 

phosphates, to an aquatic system. The increased key nutrients, phosphorous (P), potassium (K), 

nitrogen (N), and carbon (C), increase plant production, which leads to increased decomposition 

of organic material that often reduces or depletes oxygen content in the water (Cole 1975). Less 

oxygen can reduce or eliminate certain species and the increased biomass can reduce the size 

of wetlands. The delayed mode of action of DRC-1339 is such that most birds would not become 

lethargic and die until they were in their nighttime roosts. If birds died in nighttime roosts, they 

would be an additional source of nutrients introduced into an aquatic system. To make a 

comparison, blackbirds and starlings deposit large quantities of fecal material into nighttime roost 
23

sites and would continue to roost and deposit fecal material into cattail marsh roosts for the entire 

winter roosting period. Therefore, this analysis looks at a comparison between the amount of 

nutrients that would be deposited by bird carcasses and the amount of nutrients from the bird 

droppings that would continue to be deposited into the winter wetland roost. 

Most DRC-1339 blackbird projects are conducted from October to March. From FY11 to FY15, 

the most starlings taken in a single project was an estimated 152,000 in FY12 in Washington. The 

most red-winged blackbirds and brown-headed cowbirds taken in one project, respectively, was 

67,000 in Texas and 65,000 in Louisiana, both in FY11. Of these species, red-winged blackbirds 

are the most likely species to be found roosting above wetlands, typically cattail marshes 

(Yasukawa and Searcy 1995), whereas starlings (Cabe 1993) and brown-headed cowbirds 

(Lowther 1993) prefer evergreen thickets and trees but can sometimes be found in cattails. 

However, in order to assess the risk of wetland eutrophication from bird carcasses, we assumed 

all birds die and fall into a wetland.

The average weight of starlings, red-winged blackbirds, and brown-headed cowbirds (assuming 

equal male/female ratios) is 87 g (Blem 1981), 49 g (Hayes and Caslick 1984), and 42 g (Lowther 

1993), respectively (Table 8). The lean dry weight (excluding the weight of water and fat) of 

starlings is about 38% of the whole weight (calculated from data in Blem 19818). No lean dry 

weight values were found for red-winged blackbirds or brown-headed cowbirds. Using the 38%

value for all three species, gives a lean dry weight of 33 g for starlings, 19 g for red-winged 

blackbirds, and 16 g for brown-headed cowbirds (Table 8). The amount of P, K, and N was 

estimated to be 1.3%, 0.7%, and 14%, respectively, of the lean dry mass. With these assumptions, 

Table 8 estimates the weights for birds and nutrients of concern added to a wetland.

On the other hand, nightly droppings into the wetland would continue if birds were not taken with 

DRC-1339. Fecal output, feces, urates, and urine are highly variable depending on the species 

and the extent of wetland water conservation needed by that species (e.g., arid vs. wet habitats). 

Daily fecal output varied significantly for starlings depending on the type of food eaten (animal vs

plant matter (poultry pellets) or 3.5 g/day vs 14.7 g/day) (Taitt 1973); animal matter is typically 

selected if available, but starlings commonly feed on the pelletized grain at confined animal 

feeding operations. For this analysis, we will assume a starling’s fecal output is an average from 

these two food sources, about 9 g/day, which would be appropriate for the winter months when 

most control actions occur. Starlings tend to rely more on plant matter intake than animal matter 

(fewer invertebrates are available in frozen ground and snow) during the winter months when 

most control actions occur. Additionally, we will consider the nightly fecal output to be half the 

daily output, about 4.5 g/starling, since that is the portion that would go into the wetland and use 

the same percentages for red-winged blackbirds and brown-headed cowbirds (Table 8). The dry 

matter of excreta was found to be an average of 0.73 g for females and male red-winged 

blackbirds (Hayes and Caslick 1985). This would be about 29% of their nightly output. Using this 

same percentage for dry fecal matter nightly output, starlings and cowbirds would excrete 1.31 g 

and 0.64 g. The amount of P, K, and N was estimated to be 1.3%, 0.7%, and 14% of the lean dry 

mass (Hayes and Caslick 1984, Chilgren 1977, 1985). Table 8 provides estimates of weights of 

carcasses and nutrients added to wetlands. Considering the estimated weights provided in Table 

8, it would take less than a month of roosting for droppings to surpass the weights from bird 

carcasses in all categories except N, which would take about 39 days. Assuming that birds are 

on their nightly winter roosts for close to six months of the year (mid-October to mid-April) and 

that control actions, which occur mostly from mid-November to mid-March (Sept.-April), likely 

prevent about half the droppings or 3 months (90 nights) accumulation, the dry waste from 

8 The lean dry weight divided by the overall weight minus weight of lipids (weight without water and fat)
24

carcasses would be less than the dry weight of droppings added to the wetland had the control 

action not occurred. This means that accelerated eutrophication would not be expected to occur 

from bird damage management activities. 

Table 8. Amount of nutrients from bird carcasses and nightly fecal output potentially deposited into wetlands 

from birds controlled with DRC-1339.

Test Species European Starling Red-winged Blackbird Brown-headed Cowbird

Nutrient

Bird Feces Bird Feces Bird Feces

Statistics for Individual Birds or Nightly Fecal Output (grams)

Avg Wt. (♂ & ♀)/50% for feces/night 87 4.51 49 2.5 42 2.2

Total Dry Weight (50% for feces/night) 332 1.31 19 0.733 16 0.64

Dry Wt. P (1.3% bird - 1.5% feces) 0.4294 0.020 0.247 0.0113 0.208 0.010

Dry Wt. K (0.7% bird - 1.4% feces) 0.2314 0.018 0.133 0.0103 0.133 0.009

Dry Wt. N (14% bird - 9.2% feces) 4.62 0.121 2.66 0.0673 2.24 0.059

Nutrient Statistics for Maximum Single Project Take FY11-FY15 (kilograms)

Highest WS Project Take (FY11-FY15) 152,000 67,000 65,000

Project Weight of Birds/Wet Excreta 13,224 686 3,283 168 2,730 143

Project Dry Weight of Birds/Excreta 5,016 199 1,273 49 1,040 42

Total Dry Weight Phosphorous 65 3.0 16 0.75 13 0.65

Total Dry Weight Potassium 35 2.7 8.9 0.68 8.6 0.59

Total Dry Weight Nitrogen 702 18 178 4.5 146 3.8

1

from Taitt 1973 2from Blem 1981 3from Hayes and Caslick 1984 4from Chilgren 1977, 1985/Murphy and King 1982

5 RISK CHARACTERIZATION

5.1 Human Health Risks

Risks associated with adverse human health are characterized qualitatively in this section. Under 

the existing WS uses, DRC-1339 baits to control bird populations should pose minimal risks to 

human health. 

Adherence to label requirements regarding PPE minimizes risk to WS workers who mix and apply 

DRC-1339. Although DRC-1339 is a hazard to humans due to its acute toxicity via the inhalation, 

ingestion, ocular, and dermal routes, the low potential for exposure to DRC-1339 when following 

label requirements during mixing and application suggests adverse health risks to workers are 

not expected. Any exposure and risk would be short term based on the methods for baiting and 

the low frequency of use for DRC-1339 by WS. Since 1987 when USDA APHIS started to record 

worker chemical exposures, there has been one minor incident of a worker exposure to DRC1339. This incident occurred in January 2022 and was reported to USEPA under FIFRA 6(a)2 

adverse effect reporting. The incident involved a worker who was mixing DRC-1339 Concentrate 

(EPA Reg. No 56228-63) outdoors under windy conditions. Some of the material was blown into 

his face and inhaled resulting in lung irritation. No other adverse effects were reported from the 

exposure. Exposure of the general public to DRC-1339 is not anticipated based on the limited use 

pattern (e.g., entry restriction, non-residential use, prebaiting assessment, and often observing 

baits throughout the day), and the post-treatment cleanup requirements (e.g., remove 

unconsumed or spilled baits and collect dying or dead birds for proper disposal). Therefore, 

adverse health risk to the general public is not expected which is supported by the lack of adverse 

incidents that have been reported to date. 

WS personnel pick up and dispose of carcasses found. WS personnel attempt to find roosts prior 

to baiting but these can change. Since carcasses can sometimes be found elsewhere, WS 

personnel notify relevant agencies such as local law enforcement, state wildlife, agriculture, and 

health agencies, and local veterinarians that may receive calls that people have found dead bird 
25

carcasses. Carcasses can be a nuisance or disturbance to people that find them. Carcasses 

found are disposed at a landfill, deep burial, or incinerations. Part of the decision is the potential 

presence of disease and what method of disposal is best.

5.2 Ecological Risks

5.2.1 Aquatic Risks

The risk to aquatic organisms from the use of DRC-1339 is minimal (Table 6) with Daphnia 

magna, a cladoceran, having the lowest 48-hr EC50 value at 0.079 mg/L and LC50 value at 1.6 

mg/L. The method of application, label requirements for removal of unused bait and carcasses, 

and “No treatment” buffers adjacent to aquatic habitats (50 feet) results in a low potential for 

exposure and risk. Additional restrictions on the label that prohibit applications directly to water,

to areas where surface water is present or runoff is likely to occur, or to intertidal areas below the 

mean highwater mark reduce exposure and risk to aquatic organisms. A comparison of the 

available effects data for aquatic vertebrates and invertebrates summarized in Section 3.2.1 to 

the estimated maximum acute aquatic residues in static waterbodies that were estimated in the 

aquatic exposure assessment show wide margins of safety for aquatic organisms (Figure 1).

These risks were estimated based on an accidental spill into a small static waterbody. Actual risk 

would be significantly less based on the use pattern and environmental fate for DRC-1339, and 

label restrictions that reduce exposure to aquatic organisms. The maximum amount of a.i. would 

be 0.036 mg/L if all a.i. was dropped into a small waterbody accidentally, which is just above the 

estimated 48-hr No Observed Effect Level for Daphnia magna at 0.32 mg/L (Blasberg and Herzog 

1991).

Figure 1. Acute aquatic risk characterization for DRC-1339.

Chronic effects data for aquatic invertebrates and vertebrates are not available, but the method 

of application for DRC-1339, collecting unused bait, and label restrictions to protect aquatic 

resources, in addition to a short half-life in the environment would suggest that chronic risk would 

be negligible.

5.2.2 Terrestrial Wildlife and Domestic Animals Risks

The risk of DRC-1339 use to domestic animals such as pets and livestock will likely be low. DRC1339 has moderate toxicity to most mammals, but in the case of pets and livestock, the label 

provides use restrictions on storing, temporarily placing, and entry into treated areas to preclude 

0.001 0.01 0.1 1 10 100

Log DRC-1339 Concentrations (mg/L)

Acute Aquatic Invertebrate Effects

Estimated Acute Aquatic Concentrations

Acute Aquatic Vertebrate Effects
26

harm to most domestic animals. Even under the highest precautions, free-roaming domestic pets 

and feral animals such as dogs and cats may access treated areas but monitoring sites during 

prebaiting and baiting with DRC-1339 should reduce exposure.

The LD50 per square foot method was used to determine whether food consumption rates for 

various sized nontarget wild mammals would exceed median lethality values for DRC-1339 using 

broadcast applications. Risk quotient values for various sized mammals ranged from less than 

0.01 for a 1000 g mammal to 0.10 for a 15 g mammal. Eisemann et al. (2001) reported risk 

quotient values of 0.01 and <0.01 for 30 and 300 g mammals, respectively, using the LD50 per 

square foot method. USEPA (2004, 2017c) has established levels of concern (LOC) above which 

there is a presumption of risk for nontarget organisms when a risk quotient is exceeded. The acute 

high-risk LOC is 0.50, thus the acute risk of DRC-1339 exposure to wild mammals is presumed 

to be low for broadcast applications. DRC-1339 is more typically applied using various bait 

matrices in bait stations and trays. Risks may be higher for mammals under conditions where 

highly palatable baits are applied in small piles in bait trays concentrating the quantity of DRC1339 that could be rapidly consumed by nontarget animals. USEPA (2018a) estimated risk 

quotient values exceeded the acute high risk LOC for small (15g) and medium-sized (35g)

mammals exposed to DRC-1339 baits using dried processed grains or whole seeds (corn, barley, 

distillers grain, milo, lentils and peas), dry pet food, culled French fries, waste potatoes, and high 

nutrition animal feed. Risk quotient values ranged from 0.10 for large mammals (1000 g)

consuming DRC-1339-treated whole raisins to 0.63 for small mammals consuming the above 

mentioned baits. Risks from these types of applications are higher than those estimated using the 

LD50 per square foot method but provide a more representative estimate of risk since bait 

applications typically employ non-broadcast methods of application, concentrating DRC-1339-

treated bait to smaller areas using bait stations or trays.

The risk to nontarget birds in broadcast applications is higher compared to mammals due to the 

higher toxicity of DRC-1339 to most bird species. Using the LD50 per square foot approach risk 

quotient values exceed the LOC of 0.50 for different sized birds using the USEPA T-REX model

under broadcast applications. Risk quotient values for a 20, 100, and 1000 g bird were 24.92, 

3.92, and 0.28, respectively. These values exceed the LOC for acute high risk suggesting acute 

risk to nontarget birds. Similar risk quotient values have been estimated for various bird species 

using the LD50 per square foot method (Eisemann et al. 2001). Risk quotient values ranged from 

70.3 for the red-winged blackbird to 0.39 for the mallard suggesting acute risk to avian species.

USEPA (2018a) estimated risk quotient values that exceeded the acute high-risk LOC for all bird 

sizes (10, 100, and 1000 g), and for all bait types, suggesting acute high risk for all birds that 

consume treated bait regardless of the type of bait used. Risk quotient values ranged from 12 for 

large birds (1000 g) consuming DRC-1339-treated raisins to 240 for small birds (10 g) consuming 

DRC-1339-treated seeds, dry pet food, and high nutrition animal feed. Similar to mammals, risks 

quotient values are higher for birds under use conditions where highly palatable baits are applied 

using bait trays or stations that result in high concentrations of DRC-1339 in small areas. Linder 

et al. (2004) estimated risk quotient values for various bird species using bird toxicity data and 

food ingestion rates to demonstrate acute risk was higher for smaller sized granivorous birds 

when compared to larger bodied nontarget birds such as the bobwhite and mallard. These 

estimates assume birds will consume only toxic bait and does not account for dilution of bait with 

nontoxic bait, which is how most bait formulations are made. Nontarget birds that feed on treated 

bait used in bait stations, trays, or broadcast applications are at risk of acute lethal and sublethal

effects due to their sensitivity to DRC-1339 and methods of application that can concentrate DRC1339 in small areas.
27

The acute risk to nontarget birds and mammals under field use can be reduced depending on the

application method, removal of bait by the target species, and other measures, some of which are 

stated on the DRC-1339 labels. Broadcast label applications allow for individual rates up to 0.1 

lb. a.i./acre and a seasonal maximum of 0.5 lb. a.i./acre, but typical application rates are lower. 

An assessment of use rates in Louisiana rice fields reported typical single application rates of 

0.04 lb. a.i./acre with a seasonal maximum of 0.24 lb. a.i./acre. In addition, applications are not 

made to an entire field but are made to a small area within a field. The area where bait applications 

are made typically range from 0.5 to 1.0 acre in size with a swath width of no greater than 50 feet.

Prebaiting reduces the risk to nontarget wildlife by increasing target species acceptance of the 

bait and ensures that nontarget species are not feeding on the bait. O’Hare (2013) reported that 

within the first 12 hours of application greater than 90% of the treated bait was removed in 75-

95% of the baiting projects in rice fields in Texas and Louisiana. In addition, the average number 

of days spent prebaiting was 5.4 to 11 days compared to 1 to 3.5 days for toxic bait suggesting 

risk to nontarget birds and mammals is short term. The lower application rate, area of treatment,

and bait removal efficiency by the target species lowers the risk to nontarget mammals and birds.

Additionally, several label requirements reduce the risk of DRC-1339 to nontarget terrestrial 

vertebrates and include:

• DO NOT apply toxic baits in locations where nontoxic prebait has not been accepted well by target 

species or where nontarget wildlife have been observed to feed on prebait.

• DO NOT store toxic baits in locations accessible to children, pets, domestic animals, or nontarget 

wildlife.

• DO NOT apply in areas where toxic baits may be consumed by Threatened or Endangered 

Species. 

• DO NOT apply toxic baits made from this product by air.

• The applicator must remove all unconsumed, regurgitated, or spilled toxic bait, and as much of the 

broadcast toxic bait as possible at the conclusion of the treatment period.

• For broadcast applications made to areas such as stubble fields, harvested dormant hay fields, 

open grassy or bare ground noncrop areas and roadsides, bury uneaten toxic bait via mechanical 

(e.g., discing under) methods or to a minimum depth of 2 inches (5.08 cm) if manual (e.g., shoveling 

under) methods are used, as appropriate.

• Change prebaiting locations and nontoxic bait material if necessary to achieve good acceptance 

by target species or if nontarget species have been observed eating the prebait. 

The Bird Control and LNFD labels also contain additional use specific information designed to 

reduce the exposure of DRC-1339 to nontarget wildlife. These label requirements and other 

measures collectively reduce the risk to nontarget wildlife, in particular, mammals and birds that

may forage on treated seed, pet food, culled French fries, meat, and egg baits. Measures such 

as prebaiting small plots that are placed away from field edges where other bird species frequent 

can reduce nontarget effects in broadcast applications of DRC-1339 (Knittle et al 1980, Linz et al 

2002). Prebaiting also allows observation of nontarget use where locations can be changed in the 

event of unacceptable nontarget use. Additionally, diluting bait with nontoxic rice or other nontoxic 

bait materials will reduce risk to nontarget birds that are less sensitive to the effects of DRC-1339 

compared to the target species (Avery et al. 1998, Boyd and Hall 1987, Eisemann et al. 2001,

Linz et al. 2002, Linz et al. 2004). Cummings et al. (2002) observed nontarget avian species in 

Louisiana DRC-1339 treated fields, but the number of species was low and was related to the 

location of the bait sites, feeding activity of blackbirds, and bait availability that was designed to 

maximize blackbird use. Similar results have been observed in other applications (Knittle et al. 

1980). The target bird species dominated the treatment areas reducing the potential for exposure 

to nontarget birds. In cases where applications are made in the spring, baiting can be made prior 

to the arrival of spring migrants reducing risk to nontarget bird species (Eisemann et al. 2001).
28

Nontarget species anticipated for a DRC-1339 treatment are dependent on the bait type used and 

location. Grain baits attract many granivorous birds such as finches, house sparrows, field 

sparrows, doves, blackbirds, and gallinaceous birds (quail, pheasants, and turkeys). They also 

attract rodents such as deermice, house mice, and brown rats. Most grain baits are used in 

feedlots or staging areas where the birds that are present are almost exclusively the target 

species. For treated rice applications, risk is greatest to those nontarget bird species that have 

been observed at feeding sites, are granivorous, and are sensitive to DRC-1339 broadcast treated 

rice baits. Ringed-necked pheasants, mourning doves, and northern bobwhite are examples of 

granivorous bird species that have been observed at baiting sites and are sensitive to DRC-1339

(Pipas et al. 2003). Various sparrow species have also been observed at baiting sites, but most 

appear to have moderate sensitivity to DRC-1339 based on acute oral toxicity data (LD50 = 100-

400 mg/kg) (Eisemann et al. 2001) and would have to consume larger quantities of the diluted 

toxic bait than the more sensitive target species. Measures such as those discussed above will 

reduce the potential impacts to these nontarget species. Avery et al. (1998) suggested that risk 

will be reduced for ringed-necked pheasants in field applications of DRC-1339 to control 

blackbirds in sunflower fields when bait dilution is implemented. Acute risk is minimized, but

chronic risk may occur in areas where pheasants receive sublethal doses and access other fields.

Processed potatoes such as peels and culled french fries and tater tots are used in areas where 

these are fed to livestock, mostly in a feedlot or dairy situation. Potatoes mostly attract corvids, 

starlings, blackbirds, house sparrows, and periodic gulls. Cull potatoes are used almost 

exclusively for feedlots and starlings, a few blackbirds, and magpies. Cubed bread “sandwiches” 

are used almost entirely for gulls, but periodically ravens as well. Generally, other than corvids, 

few nontarget species are present during applications. The primary concern is raptors and meat 

cubes. These are monitored while they are out to ensure that no nontargets attempt to take the 

baits. Spencer (2002) gives standard procedures for making egg baits and baiting ravens with 

them. These may be used at landfills, electrical infrastructure, livestock bedding grounds, and 

sensitive species nesting sites. While not many eggs may be used protecting sensitive species 

like the western snowy plover and piping plover nest sites, the most work tasks are associated 

with them. Few nontargets are typically associated with these projects but most nontargets would 

include badgers, skunks, foxes, coyotes, and ground squirrels; these species are generally 

unaffected by taking baits and ground squirrels typically only get into eggs because the eggs are 

punctured to put in DRC-1339 with a syringe or are cracked (this often prevents caching eggs by 

corvids).

For corvids (ravens, crows, and magpies) the primary bait substrates are eggs, dog food, and 

meat cubes. Dog food is generally used for magpies and sometimes crows and ravens at feedlots 

where the potential for nontargets are too high. Bread cubes are used for gulls and periodically 

ravens. Sites where these are used are to protect sensitive species especially nesting shorebirds 

and grouse, feedlots, livestock lambing and calving areas. Livestock predation by corvids can be 

significant and mostly caused by nonbreeding juveniles and adults in “floating flocks” that can 

number in the hundreds.

Other methods to reduce nontarget bird impacts include the use of traps that are specific to the 

target species that contain treated bait. Glahn et al. (1997) reported no nontarget impacts when 

using DRC-1339 to control boat-tailed grackles in citrus orchards. DRC-1339 treated watermelon 

was placed in cage traps that resulted in the control of grackles with no observed nontarget 

impacts.

The low risk to most nontarget species has been validated by field data where little to no nontarget 

carcasses have been observed or collected during and after baiting (Smith 1999, Cummings et 
29

al. 2002). There is some uncertainty with these results since time to death can be multiple days 

and locating poisoned carcasses or observing sick birds and mammals can be impacted by 

several factors (Vyas 1999). Acute risks to birds have been demonstrated in field applications 

with nine avian incidents reported to USEPA (USEPA 2018a). This is a relatively low number but 

supports the potential for effects to sensitive avian species. WS field personnel record nontarget 

species take and collect this information during and after baiting operations. From FY11-FY15, 

WS took an annual average of 244 nontarget birds including feral pigeons and brown-headed 

cowbirds, which were being targeted with other methods where they were taken, and American 

crows and common ravens (Table 2). This was minimal in comparison to take (see Section 1.1).

Secondary poisoning risks are expected to be low based on the rapid metabolism of DRC-1339 

in birds and low residues that have been observed post treatment. Approximately 90% or more 

of DRC-1339 is metabolized and excreted in animals within 2 hours after ingestion (USDA 2001,

Cunningham et al. 1979). Goldade et al. (2004) reported that a rapid elimination phase occurred 

between 0 to 4 hours with an average half-life of 0.16 hours for juncos and 0.62 hours for 

blackbirds. A slower elimination phase followed with an average of 3.4 hours for juncos and 5.4 

hours for blackbirds. At four hours post dosing approximately 91 and 85% of the parent compound 

had been excreted in juncos and blackbirds, respectively. Residues in various organs for both 

birds were measured over a 24-hour period with residues highest in the kidneys. Residues as a 

percentage of the initial dose were low for all organs and tissues 24 hours post-dosing with values 

ranging from less than 0.01 to 2.20%. These values suggest that any secondary poisoning risks 

would be short term due to the lack of significant residues in any carcasses. Johnston et al. (1999) 

demonstrated the low potential for secondary poisoning in various avian and mammalian

scavengers and predators based on measured residues in boat-tailed grackles. Residues were 

compared to available acute oral toxicity data and daily food consumption rates for various 

species with resulting risk quotients ranging from 0.034 for the barn owl to 0.00057 for the 

domestic dog. Kostecke et al. (2001) documented potential avian and mammalian scavengers of 

bird carcasses in South Dakota and determined that secondary poisoning risks for most 

scavengers and predators is low based on the species identified and their low sensitivity to the 

effects of DRC-1339. Cunningham et al. (1979) estimated that most scavengers and predators 

would have to consume two to three times their daily food consumption rates to exceed a lethal 

dose based on DRC-1339 residues measured in starlings. This type of risk would be low due to 

the method of application and label requirements to collect and remove bird carcasses during and 

after the baiting operation. There is the possibility of exposure from feeding on target bird species 

that receive a sublethal dose of DRC-1339. This type of risk could occur for species that are 

sensitive to DRC-1339 and feed solely on DRC-1339 exposed birds for greater than 30 days

(Cunningham et al. 1979). The use pattern and metabolism of DRC-1339 makes this type of risk 

negligible.

5.2.3 Terrestrial Invertebrates and Plants Risks

The risk of DRC-1339 use to terrestrial invertebrates and plants is negligible. The available data 

shows low toxicity to the honeybee and terrestrial plants that have been tested at concentrations 

above those expected from applications in the field (USEPA 2018a). In addition, the methods of 

application for DRC-1339 suggest that potential exposure to terrestrial invertebrates and plants 

would also be low, resulting in a low probability of risk to either group. Some invertebrates may 

be attracted to the various baits that can be used with DRC-1339, but any impact to sensitive 

invertebrates would be localized to bait that is not readily consumed by the target species.
30

5.2.4 Indirect Effects of Carcasses from a Control Action on the Environment

Our risk assessment indicated that even if all bird carcasses from the largest control actions 

between FY11 and FY15 were to fall into a single wetland, an increased risk of avian botulism 

and cholera would not be expected, and the rate of eutrophication would not change.

6 UNCERTAINTIES AND CUMULATIVE IMPACTS

The uncertainties associated with this risk assessment arise primarily from lack of information 

about the effects of DRC-1339, its formulations, metabolites, and potential mixtures to nontarget 

organisms that can occur in the environment. These uncertainties are not unique to this 

assessment but are consistent with uncertainties in human health and ecological risk 

assessments with any environmental stressor.

Another area of potential uncertainty in this risk assessment is the potential for cumulative impacts 

to human health and the environment from the proposed use of DRC-1339. The potential for 

cumulative impacts is expected to be low based on the low volume and minor use of DRC-1339 

in the various APHIS uses. WS used an annual average of 77.4 pounds of DRC-1339 from FY11 

to FY15 nationwide in 38 states, which is very minimal. Areas where cumulative impacts may

occur include: 1) repeated worker and environmental exposures to DRC-1339 from program 

activities, and other sources; 2) exposure to other chemicals with a similar mode of action; and 3) 

exposure to other chemicals affecting the toxicity of DRC-1339.

Repeated exposures that could lead to significant risk from DRC-1339 are not expected due to 

label requirements that prevent significant exposure. An accidental exposure may occur from 

improper use of PPE but the potential for this to happen is low and would not occur with repeat 

applications. The potential for accidental exposure is reduced since DRC-1339 products are 

restricted-use and for use only by USDA APHIS certified applicators or those under their direct 

supervision.

Cumulative impacts may occur from DRC-1339 use in relation to other chemicals that have a 

similar mode of action, as well as others that have a different mode of action but could result in 

synergistic, additive, or antagonistic effects. This is an area of uncertainty since its unknown what 

other stressors, including chemicals, humans and nontarget wildlife may be exposed to during a 

DRC-1339 application. 

From a human health perspective, the WS low volume and minor use of DRC-1339 is expected 

to result in negligible cumulative impacts, as well as the potential for cumulative impacts from 

exposure to other chemicals. DRC-1339 is not registered for food use and is unlikely to impact 

surface or ground water so risks are negligible for the public. The lack of exposure and risk to the 

public suggests that cumulative impacts would also be incrementally negligible when factoring in 

other stressors.

Cumulative impacts to ecological resources are also expected to be incrementally negligible.

Risks to aquatic resources and most terrestrial nontarget wildlife is low due to lack of toxicity and 

significant exposure. There is risk to some sensitive terrestrial vertebrates, including the target 

species; however, the potential cumulative impacts are expected to be minor for most species.

The potential for cumulative impacts from the effects of DRC-1339 to terrestrial vertebrates will 

be greatest for those species that have low numbers, small home ranges, are sensitive to DRC1339, and attracted to treated bait. Sensitive terrestrial vertebrates that may be impacted by the 

use of DRC-1339 and observed at baiting sites typically have wide geographic distributions and 
31

home ranges suggesting any potential cumulative impacts from the use of DRC-1339 relative to 

other stressors would be negligible.

7 SUMMARY

WS uses DRC-1339 to manage several bird species that damage a variety of agricultural and 

non-agricultural resources. For more than 50 years, DRC-1339 has proven to be an effective 

method of starling, pigeon, blackbird, corvid, and gull damage management. DRC-1339 is a slow 

acting avicide that is metabolized or excreted in birds and mammals within a matter of hours. 

DRC-1339 poses little risk of secondary poisoning to nontarget animals, including avian 

scavengers. DRC-1339 poses no risk to aquatic nontarget wildlife. Nontarget birds and mammals 

that are sensitive to DRC-1339 may be at risk to DRC-1339, but this risk can be reduced through 

label language designed to reduce exposure. Risks to pollinators and terrestrial plants is 

negligible based on the use pattern of DRC-1339 and available limited effects data. The WS use 

pattern, application rates that are mostly on private lands, results in negligible risk for the public. 

Dietary risk from DRC-1339 exposure to the public is low since the avicide has no registered food 

uses and does not pose a threat to drinking water. The risk to WS applicators is also low because 

they receive training in the product’s use, are certified by the State to use restricted use pesticides, 

and follow label instructions, including the use of appropriate PPE. The release of DRC-1339 into 

the environment is expected to have no or negligible cumulative impacts to nontarget species, 

the public, and the environment.

8 LITERATURE CITED

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Batelle U.K. 2018. [

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Cole, G. A. 1975. Textbook of Limnology. C.V. Mosby Company, Saint Louis, Mo. 283 pp.

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starlings: Preliminary evaluation of their effects on secondary hazard potential. Bird Control Seminars 

Proc. 6:31-37.

Cummings, J.L., J.F. Glahn, E.A. Wilson, and J.E. Davis, Jr. 2002. Potential hazards of DRC-1339 treated 

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9 PREPARERS: WRITERS, EDITORS, AND REVIEWERS

9.1 APHIS WS Methods Risk Assessment Committee

Writers for “Use of DRC-1339 in Wildlife Damage Management Risk Assessment”:

Primary Writer: Fan Wang-Cahill 

Position: USDA-APHIS-Policy and Program Development (PPD), Environmental and Risk Analysis 

Services (ERAS), Environmental Health Specialist, Riverdale, MD

Education: B.S. Biology and M.S. Hydrobiology - Jinan University, Guangzhou, China; Ph.D. Botany 

(Ultrastructure/Cell Biology) – Miami University

Experience: Joined APHIS in 2012, preparing human health risk assessments and providing assistance 

on environmental compliance. Prior experience before joining APHIS includes 18 years environmental 

consulting experience specializing in human health risk assessments for environmental contaminants 

at Superfund, Resource Conservation and Recovery Act (RCRA), and state-regulated contaminated 

facilities.

Primary Writer: Jim Warren 

Position: USDA-APHIS-Policy and Program Development (PPD), Environmental and Risk Analysis 

Services (ERAS), Environmental Toxicologist, Little Rock, AR 

Education: B.S. Forest Ecology and M.S. Entomology – University of Missouri; Ph.D. Environmental 

Toxicology – Clemson University

Experience: Sixteen years of experience working for APHIS preparing ecological risk assessments and 

providing assistance on environmental compliance. Prior experience before joining APHIS includes 

other government and private sector work regarding ecological risk assessments related to various 

environmental regulations.

Writer: Thomas C. Hall

Position: USDA-APHIS-WS, Operational Support Staff, Staff Wildlife Biologist, Fort Collins, CO

Education: BS Biology (Natural History) and BA Psychology – Fort Lewis College; MS Wildlife Ecology –

Oklahoma State University

Experience: Special expertise in wildlife biology, identification, ecology, and damage management. Thirtyfour years of service in APHIS Wildlife Services including operations and research in CO for research 

and OR, GU, CA, OK, and NV for operations conducting a wide variety of programs including bird 

damage research and management, livestock protection (predators and birds), invasive species 

management, wildlife hazard management at airports, property and natural resource protection 

including waterfowl, brown tree snake, feral swine, rodent, and beaver damage management. Applied 

and supervised the use of DRC-1339. 
39

Editors/Contributors for “Use of DRC-1339 in Wildlife Damage Management Risk Assessment”:

Editor: Michelle Gray 

Position: USDA-APHIS-Policy and Program Development (PPD), Environmental and Risk Analysis 

Services (ERAS), Environmental Protection Specialist, Raleigh, NC

Education: BS Biology – University of Illinois; MS Zoology with an emphasis in wildlife toxicology –

Southern Illinois University

Experience: Eight years of experience in preparing environmental analyses in compliance with the National 

Environmental Policy Act. Three years of service in APHIS conducting risk analysis.

Editor: Andrea Lemay 

Position: USDA-APHIS-Policy and Program Development (PPD), Environmental and Risk Analysis 

Services (ERAS), Biological Scientist, Raleigh, NC

Education: BS Plant and Soil Science (Biotechnology) - University of Massachusetts; MS Plant Pathology 

-North Carolina State University 

Experience: Thirteen years of service in APHIS conducting risk analysis. Four years of experience in 

preparing environmental analyses in compliance with the National Environmental Policy Act.

Editor/Contributor: Jeanette O’Hare (retired)

Position: USDA-APHIS-Wildlife Services (WS), National Wildlife Research Center (NWRC), Registration 

manger, Fort Collins, CO 

Education: B.S. Biology – College of Saint Mary; M.A. Biology – University of Nebraska - Omaha

Experience: Thirteen years of experience working for WS NWRC providing regulatory compliance support 

for the development of wildlife damage management tools. Prior experience before joining APHIS 

includes assessing the environmental fate of pesticides and providing the agency guidance on water 

quality issues at the state government level, and laboratory experience in the fields of pharmacology 

and toxicology, and immunology.

Editor/Contributor: Emily Ruell 

Position: USDA-APHIS-WS, NWRC, Registration Manager, Fort Collins, CO

Education: B.S. Zoology and Biological Aspects of Conservation – University of Wisconsin - Madison; M.S. 

Ecology – Colorado State University (CSU); M.A. Political Science – CSU

Experience: Eight years of experience with WS NWRC preparing and reviewing vertebrate pesticide 

registration data submissions and other registration materials, and providing pesticide regulatory 

guidance to WS, WS NWRC, and collaborators. Prior experience before joining APHIS includes seven 

years of conducting field and laboratory wildlife research at CSU, and environmental policy research 

for the U.S. Geological Survey.

Editor: Ryan Wimberly 

Position: USDA-APHIS-WS, Operational Support Staff, Staff Wildlife Biologist, Madison, TN

Education: BS Wildlife Management and Ecology – Northwest Missouri State University

Experience: Special expertise in wildlife biology, ecology, and damage management. Seventeen years of 

service with APHIS Wildlife Services, including operations and research, conducting a wide variety of 

programs, including bird damage research and management, livestock protection, invasive species 

management, wildlife hazard management at airports, property, and natural resource protection. Expert 

in preparing environmental documents for WS programs to comply with the National Environmental 

Policy Act and the Endangered Species Act.

Data Contributor: Joey Millison

Position: USDA-APHIS-WS Information and Technology (IT), Junior Applications Developer

Education: Information and Technology coursework from various sources

Experience: Eleven years of experience in APHIS, WS Management Information System (MIS) Group. 

Retrieves WS field data from the MIS for writers, reviewers, and editors.
40

9.2 Internal Reviewers

USDA APHIS Wildlife Services

Reviewer: Anthony G. Duffiney

Position: USDA-APHIS-WS, State Director, Okemos, MI

Education: BS Fisheries and Wildlife Biology, Michigan State University

Experience: Twenty-two years of service with APHIS Wildlife Services in Michigan, Florida and West 

Virginia. Specialized experience in all levels of WS Operations including pesticide use, National 

Environmental Policy Act, Freedom of Information Act, Endangered Species Act, predator control, feral 

swine damage management, wildlife hazards at airports, wildlife disease sampling, invasive reptiles, 

urban wildlife damage. Worked with NWRC and a private livestock feed company in developing new 

baiting strategy for use of DRC-1339 in cattle feedlots and dairy farms. Conducted bait trials with 

traditional baits to prove efficacy of new bait material, CU Bird Carrier. Trained WS personnel from 10 

State programs in use of new bait. Experience with DRC-1339 to control damage caused by European 

starlings, common and boat-tailed grackles, rock pigeons, American crows, common ravens, and ringbilled gulls.

Reviewer: Jack W. Sengl

Position: USDA-APHIS-WS, Staff Biologist, Reno, NV

Education: BS Fisheries and Wildlife Biology, Utah State University

Experience: Special expertise in wildlife damage management and oversight. Twenty years of service in 

APHIS Wildlife Services in the Aleutian islands, AK, IL, NY, OH, VT, and NV with an array of experience 

including field experience (livestock, dairy, feedlot, property, natural resource, aquaculture, urban-deer 

management, human health and safety and managing wildlife hazards at airports and disease 

sampling/reporting) involving predators, birds and rodents and 11 years of program oversight (National 

Environmental Policy Act, policy, pesticide registration, monitoring and training, safety, firearms 

training, controlled material inventory tracking, and coordination of multi-agency meeting). Applied, 

supervised and provided annual training for the use of DRC-1339; created a 24c label for DRC-1339.

Reviewer: Randal S. Stahl (retired)

Position: USDA-APHIS-WS, Chemist, Fort Collins, CO

Education: BS Plant & Soil Science, University of Tennessee; MS Plant Physiology, Texas A&M University; 

PhD Soil Chemistry, University of Maryland

Experience: Special expertise in developing analytical methods to quantify DRC-1339 in baits and tissue 

matrices. Eighteen years of service in APHIS Wildlife Services supporting research activities conducted 

at the National Wildlife Research Center. Developed and support the DRC-1339 Unified Take estimate 

model used by Wildlife Services to report take estimates for select species following baiting operations 

under the Bird Control and Livestock, Nest & Fodder Depredations labels.

Reviewer: Keith Wehner

Position: USDA-APHIS-WS, Regional Director, Fort Collins, CO

Education: BS in Biology, Michigan Technological University

Experience: Nineteen years of service in APHIS Wildlife Services with experience in a wide variety of 

programs (livestock, dairy, property, natural resources, and human health and safety protection) 

including predator, bird, beaver, feral swine, and disease management activities.

Reviewer: Michael Yeary

Position: USDA-APHIS-WS, Asst. Regional Director, Fort Collins, CO

Education: BS in Wildlife Ecology, Texas A&M University

Experience: Special expertise in wildlife damage management including supervising an aerial operation 

program. Thirty-seven years of service in APHIS Wildlife Services in TX, KS, and CO with experience 

in a wide variety of programs (livestock, aquaculture, dairy, property, natural resources, and human 

health and safety protection) including predator, bird, beaver, feral swine, and rodent damage 

management activities.
41

9.3 Peer Review

The Office of Management and Budget requires agencies to have peer review guidelines for 

scientific documents. The APHIS guidelines were followed to have “Use of DRC-1339 in Wildlife 

Damage Management” peer reviewed. WS worked with the Association of Fish and Wildlife 

Agencies to have experts review the documents.

9.3.1 Peer Reviewer Agencies Selected by the Association of Fish and Wildlife Agencies

California Department of Fish and Wildlife

Montana Fish, Wildlife, and Parks

Oklahoma Department of Wildlife Conservation

Wyoming Game and Fish Department

9.3.2 Comments

Peer reviewers provided editorial comments on the manuscript. These were appreciated and 

incorporated into the final document. Following are the comments regarding concerns with the 

risk assessment and a response:

1. Comments: Convert all ppm values to mg/L values to describe LC50 values in section 3.2.1

Response: These were converted. Ppm and mg/L are the same concentration, but the change 

specifies whether solid or liquid, respectively. 

2. Comment: Section 5.2.3 does not reference the honeybee toxicity study that Wildlife Services 

conducted. A summary of that study should be included in Section 5.2.3 and it would be helpful if 

some references or examples were included to support the statement made in the second sentence 

that “Available data show low toxicity to both taxa ....”

Response: The reference was added and statement amended.

3. Comment: This risk assessment lacks the procedures that are followed in order to use this 

chemical safely and effectively in the field, and the best practices that should be followed during 

site selection, pre-baiting, monitoring during the application phase, and clean-up procedures postapplication. Some of these topics are touched upon in scattered parts of the document, but they 

are never collated into a set of procedures or multiple sets of procedures that follow each of the 

four primary applications of the product (feedlots, gull control, pigeon control, and blackbird staging 

areas). 

Response: The risk assessment discusses the label requirements for using DRC-1339. This 

includes site selection, pre-baiting, monitoring, and post treatment measures designed to reduce 

risk to human health and the environment. The measures are not listed in one place in the 

document but are discussed where relevant to characterize exposure and risk to human health and 

the environment. Users should rely on the label for the list of procedures followed instead of those 

given in this risk assessment. Additionally, a reference (Spencer 2002) was added to in Section 

5.2.2 that describes standard operating procedures for making egg baits and placing them out for 

common ravens, which is somewhat similar to other procedures.

4. Comment: A criticism sometimes voiced by those that oppose the use of DRC 1339 is that egg 

bait sites are inadequately monitored following implementation. It would be useful in this document 

to demonstrate that it has been monitored in some (not all) instances, and how nontarget take is 

determined.
42

Response: DRC-1339 egg bait sites targeting corvids, especially ravens, are typically monitored 

prior to and sometimes during or after treatment (Spencer 2002). Research conducted on egg baits 

in Nevada using videography indicated that the traditional 1:2 ratio (ravens to missing eggs) used 

by managers to estimate raven take may result in substantial overestimation of raven numbers, 

especially if ground squirrels begin consuming egg baits (Coates et al 2007). WS monitors many

DRC-1339 treated bait sites for nontarget species. For egg baits specifically, the primary nontarget 

species found taking baits are ground squirrels and striped skunks, mammalian nontargets that 

mostly go unaffected by taking baits. Many of these projects are done to protect nesting sensitive 

species such as the greater sage-grouse and sharp-tailed grouse. Mammals would need to eat 

over 50 eggs to get a lethal dose of DRC-1339, which could not physically occur and is precluded 

by label bait restrictions. Basically, in the areas where baits are placed, few nontarget species that 

could be affected by DRC-1339, are present. For the most part, the site locations dictate the species 

that will likely be present. In general, feedlots and staging areas have few birds other than the target 

species where baits are placed.

5. Comment: Early on, the document stresses that few nontarget animals, primarily birds, are taken 

and some of those are a target species but not during implementation. The document 

acknowledges that detecting all nontarget take is difficult if not impossible.

Response: The nontarget species taken from FY11-FY15 were species being targeted at 

treatment sites but were not being targeted by the treatment. The labels specify the species that 

can be targeted under each label. While these species may be targeted with a given label, they 

cannot be with some labels. Hence, if species are not on the label being used, they are not target 

species generally. The new Bird Control label combined several labels and allowed taking several 

species, which will reduce the number of nontargets taken. Appendix 2 has take from FY16-FY20 

and no nontargets were taken. This may be partially due to being able to target a broader number 

of species under a single label. Additionally, if nontarget species that would likely feed on the bait 

are noticed prior to baiting or during prebaiting, a site may not be treated or the nontargets hazed 

out of the area prior to baiting. It should be noted that nontarget species seen eating baits are 

considered nontarget species taken.

6. Comment: Section 2.3 has two seemingly contradictory sentences that need further explanation.

The last sentence of the first paragraph states that DRC-1339 has a low migration potential to 

ground and surface waters as a result of its high affinity to soil organic matter. But the first sentence 

in the next paragraph states that the DRC-1339 is highly soluble in water. Many of the sites on 

which this chemical is applied, are bare-soil sites with no guarantee of high organic content. If this 

chemical is highly soluble in water, then it seems likely that there would be some potential for it to 

move into groundwater or surface waters following storm events. If the chemical readily binds to 

organic material, then it would seem prudent to incorporate an organic compound into the posttreatment clean up procedure as a way of controlling off-site movement via stormwater.

Response: The statements are not necessarily contradictory. Most all soil, whether bare on top or 

not, has organic matter and DRC-1339 is not likely to escape in groundwater. Clarification was 

added to that section. The primary note is that it would be highly unlikely for DRC-1339 to get to 

groundwater and an analysis was given if DRC-1339 were accidentally spilled directly into water, 

which showed low potential for any adverse events as a result. That, along with buffers to surface 

water for placement, makes it unlikely that DRC-1339 would have an effect on water organisms.

7. Comment: In Section 6 it suggests in the third paragraph that exposure to DRC-1339 will not occur 

because PPE will never be used improperly by WS Certified Applicators or persons under their 

direct supervision. This could happen to anyone including WS personnel and should be a changed.

Response: We agree. This paragraph was changed to reflect the possibility that exposure could 

occur.
43

8. Comment: How were the take numbers shown in Table 2 calculated. Section 1.1 describes the 

typical use patterns for DRC-1339 and assesses how widespread its use is and how many birds

are killed annually, but the section leaves a few unanswered questions. According to the report, 

avian mortalities typically occur off-site several days after the poison is ingested (page 2); therefore. 

it would seem difficult to accurately quantify the level of take achieved. This needs greater 

clarification.

Response: A paragraph on estimates was added in Section 1.1. However, formulas are now 

available to field personnel to use to calculate the number of birds taken. Field personnel input the 

number of species at bait site, their composition, temperature, precipitation, bait type, and grams 

of DRC-1339 used and that gives the calculations for take. For the few where the field personnel 

did not enter any take (average 42 annually), it was calculated using formulas developed for 

National Environmental Policy Act documents (Appendix 1). Prior to FY13, take in several states 

was the number of carcasses found, which does not always represent the number taken. It should 

be noted that almost all birds die within two days after ingesting the bait.

9. Comment: There appeared to be little information pertaining to storage and disposal of 

unconsumed DRC-1339 bait mixtures and the associated risks.

Response: Section 5, the Summary, has been amended to include this statement. Thank you for 

the comment.

10. Comment: Rock Pigeons were taken unintentionally in the state of West Virginia where the only 

control measures that were implemented for other species were for European Starlings, Redwinged Blackbirds, and Common Grackles (Table 2, page 3). The lethal dose for Rock Pigeons 

appears to be five to six times greater than it is for European Starlings and Red-winged Blackbirds 

(Table 7, page 13), so it is surprising that Rock Pigeons could be killed incidentally during control 

work for starlings and blackbirds. Do you have a hypothesis for how they acquired a dose that was 

5 to 6 times greater than designed for the target species? Large crops?

Response: If the WS Specialist sees a bird feeding on the bait, even if it is unlikely to die, they are 

included in nontarget take. We agree that it takes more treated bait to kill feral rock pigeons and 

believe these may not have been taken. This is done to err on the side of being conservative (it is 

possible if it got enough treated baits). Actual rock pigeon bait is mixed with higher levels of DRC1339. It should be noted that at all feedlots where these were actually taken, rock pigeons were 

being targeted too. But the label used was the label for feedlots which would be less toxic bait for 

rock pigeons unless they consumed larger quantities.

11. Comment: One aspect of a procedure that is not addressed in the document is whether and how 

the state and federal wildlife agencies are notified of these control actions. Is there a protocol to 

notify the U.S. Fish and Wildlife Service and the jurisdictional state wildlife agency before specific 

control actions are implemented, or is there a procedure for notifying these agencies after-the-fact 

that a control action was taken and a quantified number of birds were taken? It would be helpful if 

agencies could be notified of these actions ahead of time in case there are calls from the public, 

and it would be helpful if an annual report of the birds taken was provided. One or both of these 

measures could be incorporated into the standard procedure for the application of DRC-1339.

12. Comment: We are not aware of any toxicosis in nontarget wildlife but acknowledge that DRC-1339 

is not routinely tested in vertebrate tissues.

Response: WS generally monitors projects to determine if nontarget species could be impacted.

If a bird consumes bait, it is considered taken, even if it does not get a toxic dose. Fortunately, few 

nontarget species are seen feeding on baits. WS responds to any dead birds found in the vicinity 

of a DRC-1339 project, usually within 20 miles, to ensure that they are picked up and disposed 

appropriately. Since birds can feed, leave, and not die for many hours, they may show up in places 

we did not anticipate. Generally, most projects involving flocking birds are conducted during winter 
44

months when birds are roosting in massive flocks. WS typically finds the roost and collects birds 

from the site. Occasionally, birds may change roosts, and these may not be found or found from 

the public notifying an agency. These too then are retrieved and disposed appropriately. Some 

roosts are in areas where the public will not see and WS has no potential to retrieve them; as 

discussed, the toxicant is metabolized and excreted in animals within 2 hours after ingestion.

13. Comments: Potential exists for the unintentional take of other birds with large crops such as

mourning doves, white-winged doves, northern bobwhite, scaled quail, and waterfowl, and it 

suggests that the pre-baiting and monitoring protocol should be particularly sensitive for the 

presence of these non-target species.

The calculation of take of non-target species needs to be more completely described. It seems 

unlikely that only four species of non-target birds were taken when you consider that the chemical 

was applied at over 3,000 project sites (see Table 3 – 643 projects per year over five years). I have 

no doubt that Wildlife Services is very cautious and efficient in their use of this chemical but given 

the wide range of projects on which this chemical was applied over the 34-state area, is seems 

unlikely that there weren’t incidental takes of Horned Larks, native sparrows, and meadowlarks –

the latter of which is closely related to blackbirds and should have a very similar susceptibility to 

DRC-1339.

Response: We added further language in Section 1.1 on nontarget take. Prebaiting helps identify 

if nontarget birds are feeding at a site or monitoring treated sites for their presence. WS monitors 

sites for nontarget birds to include these species. Doves have been species with most potential 

and have been taken in the past 20 years. Nontarget birds can be missed, especially at sites where 

thousands of birds are feeding on bait. If a nontarget bird is seen feeding on the bait, it is assumed 

to be taken. However, at these projects none were seen as no nontarget species were noted to be 

taken. We believe that some may have been taken as they can be easily missed in big flocks, but 

none were documented. 

14. Comment: When used properly, DRC-1339 appears to be effective at killing targeted species with 

minimal take of nontarget species when compared to other methods (e.g., Table 2).

Response: We agree. It is a very target-specific method when used appropriately.

15. Comment: The layout from one section to the next (i.e., Sections 3, 4, and 5) should have 

corresponding section in each.

Response: Sections were added to correspond. In the original version, short sections had been 

combined, but they have been parsed out again. Thank you for the comment.

16. Comment: Currently, DRC 1339 is limited to the take of about 5,000 common ravens in Nevada

annually (between agriculture and wildlife uses). A currently developing environmental 

assessment being undertaken by USDA WS could provide reasoning and rationale that may be 

used to increased permitted take through the Migratory Bird office with USFWS. That increased 

take could become as high as 12,500 common ravens annually within the state of Nevada alone.

If the maximum increased take were pursued, could you anticipate if that level of increased use of 

DRC 1339 would have any additional adverse environmental effects? Is it worth addressing that 

potential in this document?

Response: Take of species in a given state is analyzed in National Environmental Policy Act 

documents for that state such as Nevada (WS 2020). WS analyzed the take for 10,000 common 

ravens in Nevada and total take in the state by all permittees was set by USFWS at 19,000 

without harm to the population. 

The risk assessment was prepared based on the current labeling for DRC-1339. Exposure and 

risk in the risk assessment were based on maximum use rates for each use site. Any potential 

future changes to labeling that could occur were not addressed since they have not been 
45

approved for use by USEPA. Any changes to the label for DRC-1339 resulting in increased use 

would require an update to this risk assessment. In the example provided by the commenter it 

appears that frequency of use would increase with proposed usage under current labeling. 

Increased usage of any pesticide may result in additional risk but adherence to label 

requirements will minimize risk to human health and the environment.

17. Comment: In the Aquatic Exposure Assessment, Section 4.2.1, second paragraph, the document 

states that maximum DRC-1339 residues are estimated to range from 0.006 to 0.035 mg/L and 

that this is characterized as a “conservative estimate” of exposure. I’m not sure that this is a 

conservative estimate; instead, it appears to be a maximum estimate. The conservative approach 

in this type of analysis would be to use maximum estimates, but the estimates themselves are not 

conservative estimates and probably shouldn’t be characterized that way.

Response: Conservative, in this sense, is to convey that if the maximum amount of DRC-1339 

from a treatment occurred, we would anticipate that the effects would be less than the maximum 

because it is not likely this would ever occur. DRC-1339 cannot be applied within 50 feet of any 

waterbody, which reduces risks considerably.

18. Comment: It is obvious why this chemical is used to control European Starlings and various

species of blackbirds; however, it’s not clear why this product is used for pigeon and gull control.

Pigeons and gulls require a much larger effective dose in order to obtain lethal control, and the 

document is not clear why DRC-1339 is used for this purpose rather than potentially more lethal 

chemical control for these larger birds.

Response: DRC-1339 is an effective toxicant for gulls and feral pigeons. Table 4 in the risk 

assessment discusses maximum use rates for various use sites and pest species. Pigeon and gull 

control rates are the same or less than other species that are listed on the label. Other WDM 

methods may be easier to implement for these species compared to DRC-1339 treatments, so they 

are not often targeted with DRC-1339 in comparison to starlings mostly due to the sheer numbers 

in a flock.

To illustrate efficacy for pigeons, an analysis of feral pigeon take with DRC-1339 can be calculated. 

The standard average number of whole corn kernels in a pound is about 1,300, but variable 

depending on variety of corn. However, lower or higher weights for kernels would not change the 

outcome. If 1,300 kernels weigh one pound and are treated, each kernel would have about 3.5 mg 

DRC-1339 (prior to being cut with untreated baits). The oral LD50 for pigeons is 18 mg/kg (Timm 

1994, Eisemann et al. 2003). Thus, it probably takes more for 100% efficacy (acute doses for all) 

with pigeons, and a minimum of about 30 mg/kg; for pigeons at an estimated average weight of 

360 g, this would require 10.5 mg treated bait necessary to kill them or at least 3 baits. Pigeons eat 

about 36 gm of feed per day or, with whole corn, about 100 kernels (depending on weight of 

kernels). It is likely that when feed is put out, pigeons will consume a quarter to half their daily intake 

(depending on the number of pigeons feeding, the distribution of baits, and the length of time the 

pigeons are exposed to the baits), or about 25 to 50 kernels. This would be enough to get a lethal 

dose for most birds, averaging about 4 to 8 treated baits for cut baits (1:5 ratio of treated:untreated).

Similarly, the same results occur for gulls, but the substrate is usually bread.

19. Comment: The aquatic risk characterization, Section 5.2.1, is noticeably short and provides no 

analysis. It could be improved upon by referencing Table 6 and explaining how/why the toxicity 

values shown in that table are much greater than the concentrations that are expected to occur in 

the aquatic environment.

Response: Section 4.2.1 gave the exposure assessment and the analysis there was shown to be 

minimal precluding a robust discussion in Section 5.2.1. However, further information was added 

to the discussion. We believe that the risk is very minimal from potential toxicity levels and use 

restrictions from the label. Additionally, no known occurrence of an aquatic system has been 

reported.
46

Comments received not requiring a response. We appreciate these comments.

1. Comment: Overall the method risk assessment was complete and thorough in describing methods, 

consequences, and successes.

2. Comment: All uncertainties and assumptions were adequately considered and described.

3. Comment: The list of references presented in the methods risk assessment seemed appropriate.

4. Comments: The Terrestrial Wildlife Risk Assessment, section 5.2.2, is especially important and 

I’m pleased to see that it was thorough. I especially appreciated the section discussing the take of 

nontarget birds because of the risk that DRC-1339 poses to meadowlarks, mourning doves, and 

potentially other birds that co-occur with blackbirds.

5. Comments: This is a comprehensive review of DRC-1339. This review provides information about 

target take, nontarget risks, secondary toxicity, and environmental fate for DRC-1339.

6. Comments: My experience and knowledge supports the use of DRC 1339 as a safe and 

effective toxicant that is narrowly targeted without substantive nontarget effects. 

7. Comment: We appreciate Wildlife Services reporting on the take of target and nontarget species, 

including their fates (killed, freed, dispersed) in the Introduction Chapter. 

8. Comments: This technical report addressing the use of the chemical DRC-1339 for avian damage 

management is very thorough in terms of why Wildlife Services uses this compound, how this 

chemical works and the risks posed by this chemical.
47

Appendix 1. Estimating DRC-1339 Take

WS estimated take for DRC-1339 in many outdated National Environmental Policy Act 

Environmental Assessments prior to estimating this take became mandatory. The following is a 

synopsis of data used to estimate take from some of the documents (e.g., Texas, Colorado, and 

Arizona). About 42 projects were estimated annually from FY11 to FY15, data for this document, 

which included European starling, brown-headed cowbird, great-tailed grackle, feral pigeon, and

black-billed magpie projects. Common raven, American crow, and fish crow projects were 

estimated only for projects other than those involving the protection of sensitive species where 

only a few eggs are placed at a time and take is only made when a few individuals were recorded 

From FY16 to FY20, about 4 projects per year were estimated, which included pigeons and 

starlings, and a few ravens and American crows.

Precise information on bird mortality due to WS control operations involving toxicants is not available.

Prior to FY14, the MIS required WS Specialists record the dead birds found following a control 

operation, which may only be a small percentage of the birds actually taken. However, some WS State 

Directors or District Supervisors required Specialists to estimate the number of birds such as starlings 

and blackbirds taken during a control operation. Since recording data in the MIS has been variable from 

one operation to another and one state to the next, MIS data for birds taken with DRC-1339 were used 

for determining total take, unless take has been estimated for all projects; if it was in a state that counted 

carcasses, it was not used because this was often not all. However, potential take can be estimated 

with a basic knowledge of DRC-1339, bait type (e.g., cracked corn), and basic bird species biology for 

those birds targeted. This appendix provides estimates of birds taken with DRC-1339 by WS for species 

that had estimates determined from the number of grams DRC-`339 used and the species targeted.

Most bird mortality by WS operations involves DRC-1339 treated baits. Glahn and Avery (2001) 

described methods to estimate bird mortality from using assessments of bait consumption and 

calculations. Homan et al. (2005) developed an empirical model based on bioenergetics for starlings at 

feedlots and the model predicted that 93 starlings would be killed for every pound of treated cattle ration 

pellet baits used (116 starlings/g DRC-1339). However, field studies testing the model found that the 

baits only killed an average of 67 starlings per pound used (72.5% of the “ideal” model). This would 

equate to 84 starlings taken for every gram of DRC-1339 used. Packham (1965) found that an average 

of 57 starlings were killed per pound of DRC-1339 treated French fries (a larger bait size) used at 

feedlots or 71 starlings taken per gram of DRC-1339. Thus, a difference exists between what models 

predict for results to that which actually occurs under field conditions and take with different baits. Most 

models predict the maximum number of target species that can be taken or the “ideal.” However, ideal 

conditions rarely exist in the field and take is typically only a fraction of the expected results (Glahn and 

Avery 2001).

Part of the problem with predicting take with DRC-1339 treated baits is that breakdown of the chemical 

starts relatively quickly once baits are prepared. Within hours to several days after baits are prepared 

and once the baits are exposed to environmental conditions (e.g., precipitation, heat, and sunlight), 

baits degrade, lose potency, and discolor turning dark gray which are often not selected by the target 

species. Thus, baits may be consumed and not be toxic (degraded) or discolored and not selected 

making them less effective. Additionally, baits may be made for a set number of birds seen during 

prebaiting operations and this number may not return when baits are placed out. Thus, baits may 

remain following treatments which then are disposed according to the label. The MIS system does not 

capture this “wastage” (bait placed in the field and not consumed, and, hence, disposed), but only the 

amount placed in the field. These factors (degradation, discoloration, and wastage) inherently would 

increase the estimated target species take using WS MIS data because all DRC-1339 used in 

operations is recorded whether or not it was successful. Homan’s et al. (2005) field trials, compared to 

the empirical model, accounted for most problems with discoloration and degradation (did not likely 

include precipitation because all trials had an estimated take) problems (72.5% efficacy from predicted 

to actual field trial take), but did not account for wastage because the amount of bait consumed was 

recorded for each field trial (baits placed less baits picked up after treatment). For WS projects using 
48

DRC-1339, wastage likely averages between 10% and 25% of the baits placed. Thus, realistically the 

baits used that are successful in typical field conditions (from preparation to take of the target species) 

are probably closer to 60% of the estimated “ideal” or modeled take for the grams of DRC-1339 used, 

instead of the 72.5%. To conservatively estimate the number of target starlings taken for a given project, 

the Homan et al. (2005) field trial data multiplied by a factor of 90% to account for wastage, thus 

assuming wastage of 10%, or 76 starlings taken per gram of DRC-1339 used.

WS also targets blackbirds in the family Icteridae at feedlots and other damage sites. Take would be 

different for each species of blackbird, as well as sex with most males weighing much more than 

females, based on the target species weight and daily feed consumption. Average weights for a species 

including females and males are 54 grams for Red-winged Blackbirds, 76 grams for Yellow-headed 

Blackbirds, 66 grams for Brewer’s and Rusty Blackbirds, 107 for Common Grackles, 169 for Greattailed Grackles, 40 grams for Brown-head Cowbirds, and 63 grams for Bronzed Cowbirds. It is expected 

that these species, respectively, would consume an average of 11g, 13g, 12g, 12g, 18g, 24g, 23 g, 9g, 

and 12 g of baits when feeding. DRC-1339 treated baits for feedlots are not broadcast but put in feeding 

lanes and so birds have easier access to large quantities of baits whereas more searching is required 

for baits that are broadcast. It is estimated that blackbirds will get 12.5% of their daily intake needs from 

baited sites. Take for each species is estimated for feedlot baits in Table 1.1. For blackbirds, because 

of varying weights, Table 1.1 estimates the number taken with the different baits and formulations based 

on their daily consumption. Blackbirds move around in feedlots and fallow fields and, thus, could get 

much of their diet from non-baited areas. It is assumed that blackbirds get an eighth of their daily dietary 

needs from treated areas whereas starlings and pigeons, which are much more sedentary in feedlots 

than blackbirds, would probably get at least 25% (likely much higher for these species). These are likely 

conservative estimates, but adequate for determining impacts.

WS also targets blackbirds in the family Icteridae at feedlots, rice fields, and for other resources.

Estimated take is very different depending on the bait substrate used and method of baiting (piles or 

broadcast). Take is different for each species, as well as sex with most males weighing much more 

than females, based on the target species weight and daily feed consumption. Average weights for a 

species, the average of the mean weight for males and females (Table 1.1) and assuming a 1:1 sex 

ratio, are 54 grams for Red-winged Blackbirds, 76 grams for Yellow-headed Blackbirds, 66 grams for 

Brewer’s and Rusty Blackbirds, 107 for Common Grackles, 169 for Great-tailed Grackles, 157 grams 

for Boat-tailed Grackles, 40 grams for Brown-head Cowbirds, and 63 grams for Bronzed Cowbirds. It 

is expected that these species, respectively, consume 11g, 13g, 12g, 12g, 18g, 24g, 23 g, 9g, and 12 

g of bait. DRC-1339 treated rice baits are broadcast at 10 to 20 pounds/acre. DRC-1339 treated baits 

for feedlots are not broadcast but put in feeding lanes and so birds have easier access to large 

quantities of baits whereas more searching is required for rice baits. It is estimated that blackbirds get 

12.5% of their daily intake needs from baited sites, but it is likely that less would be obtained from areas 

treated with rice baits as compared to feedlots and other sites. However, wastage would be much 

greater in rice treated fields, probably a third or up to half, because baits are broadcast requiring 

searching by birds which becomes more tedious as the number of baits decline. The percentage of 

birds obtaining a lethal dose in rice fields is much less, about 50% mortality (Johnston et al. 2005, 

2006).

Field studies with rice found that birds ingested an average of about 25 rice kernels (0.5g) or about 2% 

to 6% of their daily intake requirements with red-winged blackbirds and brown-headed cowbirds, the 

species most targeted with treatments to protect rice, between 5% and 6% of their daily intake. Thus, 

using the current assumptions of 12.5% of the daily intake would be similar to take with rice baits (for 

red-winged blackbirds, the assumptions 100% mortality with 12.5% intake and 10% wastage results in 

840 birds taken per gram of DRC-1339 vs. 50% mortality with 5% intake and 42% wastage results in 

820 taken per gram of DRC-1339) and used for estimating take for each species in Table 1.1. The take 

for each species of blackbird is estimated for feedlot baits and rice baits in Table 1.1. For blackbirds, 

because of varying weights, Table 1.1 estimates the number taken with the different baits and 

formulations based on their daily consumption. Blackbirds move around in feedlots and fallow fields 

and thus get much more of their diet from non-baited areas. It is assumed that blackbirds get an eighth 

of their daily dietary needs from treated areas whereas starlings, and pigeons, also discussed herein, 
49

which are much more sedentary in feedlots than blackbirds, would probably get at least 25% (likely 

much higher for these species). These are conservative estimates, especially because the efficacy of 

baits in the field compared to the “ideal” take is not used for blackbirds which would reduce take 

estimates by at least 25% (Homan et al. 2005), but adequate for determining impacts.

Cummings et al. (unpubl data, NWRC, pers. comm. 2006) found that treated baits at feedlots “ideally” 

would take an estimated 400 blackbirds per gram of DRC-1339 used. Table 1.1 found that take would 

range from 163 per gram of DRC 1339 used for “other” baits for Great-tailed Grackles to 434 for Brownheaded Cowbirds. Cummings et al. (unpubl data, NWRC, pers. comm. 2006) also found that for each 

pound of treated cut (1 treated: 26 untreated) rice baits placed in fields, 374 blackbirds were killed.

Johnston et al. (2005) predicted that 324 Red-winged Blackbirds from a pound of rice baits would be 

killed (this number declined with the days of baiting to 285 for 5 days). These estimates would equate 

to 1,057 and 913 blackbirds killed per gram of DRC-1339 used. It should be noted that the first estimate 

included primarily Red-winged Blackbirds and Brown-headed Cowbirds and the second only Redwinged Blackbirds. Table 1.1 estimates that take will range from 385 for Great-tailed Grackles to 1,027 

for Brown-headed Cowbirds. It also should be noted that birds were captured following feeding in 

treated fields and not all birds died from the dose they received. Several birds were collected and the 

number of rice grains in all birds was not enough to kill them (about 50% mortality rate for birds feeding 

in treated rice fields). However, their take estimates were similar to those determined in Table 1.1. It 

should also be noted that efficacy, similar to what Homan et al. (2005) found for starlings (the “ideal” 

take vs. actual take), was not calculated into these estimates. This would reduce take estimates by a 

fourth. However, our estimates in Table 1.1 include an assumed 10% wastage loss which would make 

the estimates very close to those found by researchers.

The MIS allowed WS Specialists to use a code, “Mixed Blackbirds,” for sites where several species of 

blackbirds (starlings, blackbirds, cowbirds, and grackles) were present. Thus, species composition at 

operational sites was estimated using Audubon Christmas Bird Count data or USGS Breeding Bird 

Survey data (Christmas Bird Count data for winter projects (December 1 to March 31) or an average of 

the two for migration time frames (April 1 to November 30). Most projects are conducted when species 

are flocking, which excludes breeding and summertime months. Additionally, the habitat preference of 

a species was also considered. For example, starlings are the most prevalent species at feedlots in the 

United States. Starlings require a high protein, high calorie diet, and livestock feed such as cattle ration, 

pelleted feed are a great source. Unlike most blackbirds, starlings eat little grain due to their poor 

assimilation efficiency (turning feed into energy) for grain (Twedt 1985). Starlings prefer insects and eat 

them as available. As insects wane in cold weather, starlings turn to feedlots to acquire the necessary 

energy to survive. Thus, starlings can be found in abundance at feedlots during winter. On the other 

hand, blackbirds efficiently assimilate grains into energy and have more opportunity to find them in 

harvested and fallow fields (spillage) and rangeland (weed seeds), and, therefore, may forage more in 

these areas rather than in feedlots (Twedt 1985). It should be noted that rusty blackbirds, a species of 

concern, typically prefer bottomlands and wetlands and do not often feed with other blackbirds even 

though they will roost with them. 

WS also targets feral pigeons with DRC-1339. Per label directions, WS uses whole kernel corn for 

these projects with 1.7 g DRC-1339 treating 1 pound of bait which is then cut at 1 treated: 5 untreated.

Baits can be cut at 1 treated: 1 untreated depending on the needs of the project and the length of time 

birds are observed feeding during prebaiting. The standard average number of whole corn kernels in a 

pound is 1,300 (Ontario Corn Producer Association 2007), but this is variable depending on variety of 

corn. However, lower or higher weights for kernels would not change the outcome. Assuming that 1,300 

kernels equals one pound and are treated, each kernel (350 mg) would have about 1.3 mg DRC-1339 

(prior to being cut with untreated baits). The oral LD50 for pigeons is 18 mg/kg (Timm 1994, Eisemann 

et al. 2003). Thus, it likely takes more than 18 mg for 100% efficacy (acute doses for all) because only 

50% of the pigeons would be killed at this level. At an estimated average weight of 310 g (270 g (Sibley 

2000) or 350 g (Johnston 1992) equals 4.9 mg to 6.3 mg – website searches came up with similar 

weights)) it would take 5.6 treated baits to kill 50% or 6 baits (rounded up). Pigeons eat about 36 gm. 

of feed per day (British Columbia Ministry of Environment 2001) or, with whole corn, about 103 kernels 

at 1,300/pound. It is likely that when feed is put out, pigeons will consume between a quarter to half 
50

their daily consumption (depending on the number of pigeons feeding, the distribution of baits, and the 

length of time the pigeons are exposed to the baits), or about 26 to 52 kernels. This would be enough 

for about half of the birds to get a lethal dose averaging about 4 to 9 treated baits for cut baits (1:5 ratio 

of treated:untreated). Assuming pigeons feed on whole kernel corn baits that have 1,300 kernels per 

pound and consume a third of their daily intake (34 kernels) while baits are placed out, one pound of 

cut bait would take 19 pigeons (each pigeon would get an average of 5.7 treated baits – the level for 

50% to be killed). This would equate to taking 67 pigeons per gram of DRC-1339. Using a similar factor 

to account for wastage in field use (10%) as above, would result in a conservatively estimated 60 

pigeons taken with each gram of DRC-1339 used. It should be noted that baits can be cut at 1:1 to 1:5 

for pigeons depending on how much bait is required at a site for the number of pigeons present; WS 

Specialists use the 1:1 treated to untreated baits for projects with very few pigeons or when there are 

a lot of pigeons present to ensure they get enough toxicant. A lower ratio of treated to untreated would 

reduce the number of birds that could be taken. It is assumed that all baits are cut at the 1:5 rate which 

would increase the number of birds taken but be a more conservative estimate for the purposes of 

analysis. Additionally, baits are often left out for pigeons as long as they are feeding. It is likely that 

pigeons would consume at least half their dietary needs, if not 100%. If pigeons consumed 100% of 

their daily consumption requirements and this reached a level of LD100, then 13 pigeons would be 

killed per pound of bait or 40 per gram of DRC-1339 (taking wastage into account). It is likely that the 

latter is closer to the estimate.

WS Specialists also target American Crows under a Special Local Need labels to protect pecans and 

other crops with whole kernel corn and pecan baits. Take would be similar to pigeons, except that crows 

would likely take fewer baits when they feed. The average crow weighs about 515 grams (Verbeek and 

Caffrey 2002) and consumes about 52 grams of feed per day. The oral LD50 for crows is 1.33-1.78 

mg/kg and they are likely to get a lethal dose consuming low quantities of bait (1 kernel would likely be 

enough to kill a crow). If crows consume a fourth of their daily diet at a treated site (similar to pigeons 

because would tend to remain at a feeding station longer), they would consume 13 grams of prepared 

baits. Assuming that baits are made with whole kernel corn (about 1300 kernels/pound), crows would 

consume about 37 kernels or about 6 treated baits. At this consumption rate, a pound of prepared bait 

would take 35 crows. This would equate to taking 45 crows per gram of DRC-1339. Using the same 

wastage percentage (10%) as discussed, WS expects that it could take 40 crows per gram of DRC1339 used.

Table 1.1. Estimated blackbird take for DRC-1339 treated baits. The estimated numbers taken 

per gram of DRC-1339 were used for projects that did not estimate take.

Species* RWBL YHBL BRBL RUBL COGR GTGK BTGK BHCO BROC

Spp. Aver. Weight (g) 54 76 66 66 107 169 157 40 63

Daily Aver. Consumpt. (g) 11 13 12 12 18 24 23 9 12

% Daily Aver. Cons. Eaten 12.5% 12.5% 12.5% 12.5% 12.5% 12.5% 12.5% 12.5% 12.5%

Wastage 10% 10% 10% 10% 10% 10% 10% 10% 10%

 DRC-1339 Rice Baits

Std g DRC Used for Bait 92

Pounds bait made 260

Lbs. bait/1 g DRC 2.83

# birds/g DRC 840 711 770 770 513 385 402 1,027 770

 DRC-1339 Other Baits

Std g DRC Used for Bait 92

Pounds bait made 110

Lbs. bait/1 g DRC 1.20

# birds/g DRC 355 300 325 325 217 163 170 434 325

RWBL = Red-winged Blackbird, YHBL = Yellow-headed Blackbird, BRBL = Brewer’s Blackbird, RUBL = Rusty Blackbird, COGR = 

Common Grackle, GTGK = Great-tailed Grackle, BTGK = Boat-tailed Grackle, BHCO = Brown-headed Cowbird, BROC = Bronzed 

Cowbird
51

Literature Cited

British Columbia Ministry of Environment. 2001. Animal weights and their food and water requirements.

BC Gov. @http://www.env.gov.bc.ca/wat/wq/reference/foodandwater.html. Last visited 4/6/12.

Eisemann, J. D., J. L. Cummings, and P. A. Pipas. 2003. Acute and chronic toxicity of compound DRC1339 (3-chloro-4-methylaniline hydrochloride) to birds. Pp. 49-63. In Management of North 

American Blackbirds. G. M. Linz, ed. NWRC, Ft. Collins, CO.

Glahn, J. F., and M. L. Avery. 2001. Estimation of Red-winged Blackbird mortality from toxic bait 

application. Pp. 109-118. In J. J. Johnston, ed. Pesticides and Wildlife. Amer. Chem. Soc. Symp. 

Series 771. Wash., D. C.

Homan, H. J., R. S. Stahl, J. J. Johnston, and G. M. Linz. 2005. Estimating DRC-1339 mortality using 

bioenergetics: A case study of European Starlings. Proc. Wildl. Damage. Manage. Conf. 11:202-

208.

Johnston, J. J., M. J. Holmes, A. Hart, D. J. Kohler, and R. Stahl. 2005. Probabilistic model for 

estimating field mortality of target and non-target bird populations when simultaneously exposed to 

avicide bait. Pest Mange. Sci. 61:649-659.

Johnston, J. J., J. Cummings, D. K. Kohler, R. Stahl, M. J. Holmes, and A. Hart. 2006. Probabilistic 

model to optimize formulation and baiting strategies for the pesticide CPTH (3-chloro-4-

methylaniline hydrochloride). Vertebr. Pest Conf. 22:440-446.

Johnston, R. F. 1992. Rock Dove (Columba livia). No. 576. In The Birds of North America Online. A. 

Poole, ed. Acad. Nat. Sci., Phil., Penn. and Amer. Ornithol. Union, Wash., DC.

Ontario Corn Producer Association. 2007. From one bushel of corn. Ont. Corn Prod. Assoc. @ 

http://www.ontariocorn.org/classroom/bushel022405.htm. Last visited 07/11/07.

Packham, C. J. 1965. Starling control with DRC-1339 at cattle feedlots in Idaho winter of 1964-1965.

Unpubl. Rep. WS State Office, Boise, ID. 22 pp.

Sibley, D. A. 2000. The Sibley Guide to Birds. National Audubon Society, Alfred A. Knopf, New York. 

Timm, R. M. 1994. Description of active ingredients. Pp. G23-G60. In Prevention and Control of Wildlife 

Damage. S. Hygnstrom, R. Timm, and G. Larson, eds. Univ. Nebr., Coop. Ext., Instit. Ag. & Nat. 

Res., Univ. Nebr., USDA-APHIS-WS, & Great Plains Ag. Council Wildl. Committee.

Twedt, D. J. 1985. The effect of dietary protein and feed size on the assimilation efficiency of starlings 

and blackbirds. Proc. Great Plains Wildl. Damage Contr. Workshop. 7:40-48.

Verbeek, N. A. and C. Caffrey. 2002. American Crow (Corvus brachyrhynchos). No. 647. In The Birds 

of North America Online. A. Poole, ed. Acad. Nat. Sci., Phil., Penn. and Amer. Ornithol. Union, 

Wash., DC.
52

Appendix 2. Update on DRC-1339 usage from FY16-FY20.

WS took an annual estimated average of 1,507,858 target birds of 14 species using an annual 

average 16,233 grams (572 oz. or 36 lbs.) of DRC-1339 in 30 states (total 36 states in the 5 years) 

from FY16 to FY20 (Table 2.1). This was less use of DRC-1339 and take for all species; this 

decrease was likely due to a combination of the COVID 19 pandemic and shortage of chemical; 

the company that manufactured DRC-1339 stopped and it took a while for another company to 

start producing it. During this time, WS applied DRC-1339 under 18 Section 3 and SLN (Section 

24(c)) labels operationally (Table 2.2). The most common resources protected by WS were 

livestock and feed, aircraft, other wildlife, and crops. The species groups taken were starlings and 

blackbirds (99.0%), corvids (0.7%), and pigeons (0.3%), and minimal gulls (>0.1%). The most 

common target species lethally taken were European starlings (45%), red-winged blackbirds

(30%), brown-headed cowbirds (19%), and common grackles (5%) (Table 2.2), similar to FY11-

FY15. Weight-wise by grams used, the majority of DRC-1339 targeted starlings (84%), common 

ravens (7.3%), red-winged blackbirds (2.6%). feral pigeons (1.8%), brown-headed cowbirds 

(1.6%), and American crows (0.9%); it should be noted that some DRC-1339 targeting a specific 

species may have had minimal take for various reasons like birds did not show up to feed or bait 

was ruined by weather and baits were picked up. Most all projects had the take estimated using 

a WS estimator. The few that did not, if it did not say anything like “rained on bait, so picked up” 

or picked up bait because birds did not come” on the work task, then take was estimated at 

standard rates (e.g., 76 starlings/g) based on prior discussion of numbers taken, copied below.

During this time, no nontarget species were documented to be taken.

Table 2.1. The annual average number of birds WS killed with DRC-1339 treated baits in bird damage 

management from FY16 through FY20. Take was estimated for WS projects that did not determine take. 

ANNUAL AVERAGE DRC-1339 USE AND SPECIES TAKEN

Species* Take DRC-1339 (g) States That Used DRC-1339

Target

European Starling* 674,166 13,630.0 CA CO CT IA ID IL KS MA ME MI MN MO MT ND NE NM NV 

NY OH OK OR PA SD UT VA VT WA WI WV WY

Yellow-headed Blackbird 420 3.1 NM

Red-winged Blackbird 451,337 414.6 CO LA NH OR TX WA

Brown-headed Cowbird 289,844 248.8 LA NM OK OR TX WA

Brewer's Blackbird 300 1.8 CA OR

Common Grackle 76,707 203.2 LA OK TX

Great-tailed Grackle 236 3.2 AZ NM TX

Rock Pigeon* 3,701 294.2 CO IA ID KS MD ME MI MO MT ND NE NM OK SD TN UT VT 

WV WY

Eurasian Collared-Dove 520 34.6 ID NM WA

California Gull 10 3.2 ID

Black-billed Magpie 449 67.8 MT OR UT WY

American Crow 2,133 150.8 CA MA NM OK OR TX WY

Fish Crow 1 0.2 MA

Common Raven 8,034 1,178.0 CA ID MA MT NM NV OR TX UT WA WY

GRAND TOTAL (14 sp.) 1,507,858 16,233.5 36 States (Ave. 30/year)

* Introduced species

As of 2022, WS has 9 active labels and DRC-1339 SLN registrations (the Bird Control label and 

4 SLNs under it and the LNFD label and 3 SLNs under it) (Table 2.2). While 20 labels were used 

between FY16 and FY20, most were cancelled and not used following the registration of the Bird 

Control label since it included most uses (Table 2.2). Many of the cancelled labels and a few other 

labels had very few work tasks (WTs) associated with them, which correlates to minimal DRC1339 use. The Feedlots, Staging Areas, and Bird Control labels had the greatest use of DRC1339, but the Livestock, Nest & Fodder Depredations had the most WTs. Most of these WTs were 

associated with setting out a minimal number of eggs to take common ravens and American crows 

depredating threatened and endangered species.
53

Table 2.2. The annual average number of grams of DRC-1339 applied by APHIS-WS in WDM from FY16

thru FY20 by all labels with the annual average number of Work Task (WT) or applications.

Lightly shaded lines - registrations with no use from FY11-FY15.

* USEPA Registration No. 56228-63 - Bird Control label fully replaced these labels by January 2019. 

** Labels not fully incorporated in Bird Control label, cancelled, and re-registered by the state under the Bird Control parent label, or 

no longer used and cancelled by January 2019.

^ SLN labels are still registered under the LNFD parent label.

ANNUAL AVERAGE DRC-1339 USE BY PRODUCT FOR FY16 TO FY20

Shortened Product Name or SLNs’ State Registered (SLN 

Parent Label) EPA Registration No. Applied (g) WTs

Feedlots* Cancelled 56228-10 8,130.5 122

Gulls* Cancelled 56228-17 3.2 0.6

Pigeons* Cancelled 56228-28 110.3 8

Livestock, Nest & Fodder Depredations (LNFD) 56228-29 315.0 330

Staging Areas* Cancelled 56228-30 1,433.9 73

Bird Control 56228-63 5,309.4 103

SLN ID (Feedlots)** Cancelled ID-050014 10.8 0.2

SLN ID (LNFD)^ ID-140005 12.2 4

SLN ID (Staging Areas)* Cancelled ID-050013 0.4 0.2

SLN IL (Feedlots) Cancelled IL-120002 13.8 1

SLN NV (LNFD)^ NV-150001 163.3 50

SLN NV (LNFD) Cancelled NV-040004 319.9 89

SLN NV (Staging Areas)* Cancelled NV-020005 15.1 2

SLN OK (Staging Areas)**(Replaced by OK-180002 in 2018) OK-990001 85.1 16

SLN OR (Staging Areas)** (Replaced by OR-190004 in 2019) OR-010024 44.2 0.6

SLN TX (SA)** (Replaced by TX-190006 in 2019) TX-020003 2.8 0.4

SLN UT (LNFD) Cancelled UT-130005 62.8 3

SLN WV (Staging Areas)* Cancelled WV-040001 7.2 3

SLN WY (LNFD)^ WY-110002 246.5 61

SLN WY (Staging Areas)**(Replaced by WY-180003 in 2018) WY-070002 54.9 2

TOTAL 6 FEDERAL

13 SLN

16,341.3 869