Prepared in cooperation with the U.S. Fish and Wildlife Service and U.S. Air Force 

Assessment of Bird Exposure to Lead at Tyndall 

and Beale Air Force Bases, 2016–17

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2018–5164
Cover. Photos of the St. Joe Bay Buffer Preserve near Tyndall Air Force Base, Florida (upper right), and a northern cardinal (upper right, 

inset) caught at the location. Photos of Beale Air Force Base, California (lower left), and a Bullock’s oriole (lower left, inset) caught at this 

location. Photographs by Timothy A. Bargar, U.S. Geological Survey.
Assessment of Bird Exposure to Lead 

at Tyndall and Beale Air Force Bases, 

2016–17

By Timothy A. Bargar

Prepared in cooperation with the 

U.S. Fish and Wildlife Service and U.S. Air Force

Scientific Investigations Report 2018–5164

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DAVID BERNHARDT, Acting Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2019

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Suggested citation:

Bargar, T.A., 2019, Assessment of bird exposure to lead at Tyndall and Beale Air Force Bases, 2016–17: U.S. Geological Survey Scientific Investigations Report 2018–5164, 30 p., https://doi.org/10.3133/sir20185164.

ISSN 2328-0328 (online)
iii

Acknowledgments

This project could not have been completed without the assistance of numerous individuals. 

The authors thank Channing St. Aubin, Lorraine Ketzler, Todd Gerardot, Mark Cantrell, Patricia 

Kelly, Paul Lang, Lydia Ambrose, Peter Maholland, and Melody Ray-Culp of the of the Fish and 

Wildlife Service, Panama City Field Office, and Jennifer Brown of the Sacramento Field Office. 

Personnel of the U.S. Air Force who provided assistance are thanked, including Joe McLernan 

and Alex Bonner of the Tyndall Air Force Base and Darren Rector and Maia Lipschutz of the 

Beale Air Force Base. Thanks also go to U.S. Geological Survey personnel who provided assistance, including Carla Weiser and Tracy Fanara of the Wetland and Aquatic Research Center, 

Barnett Rattner and Sandra Schultz of the Patuxent Wildlife Research Center, and Dylan Shoemaker of the St. Joe Bay Buffer Preserve. This project was supported by U.S. Air Force military 

interdepartmental purchase request number F2MUAA5352GW01 and by funds appropriated to 

the Environmental Health Mission Area of the U.S. Geological Survey.
iv

Contents

Acknowledgments........................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Methods...........................................................................................................................................................3

Sampling Design ...................................................................................................................................3

Capture of Birds and Measurement of their Exposure to Lead ....................................................3

Collection and Analysis of Dietary Items for Lead ..........................................................................7

Soil Sampling.........................................................................................................................................8

Sample Analyses...................................................................................................................................8

Sample Collection Locations ..............................................................................................................8

Statistics.................................................................................................................................................8

Risk Assessment...................................................................................................................................8

Results—Beale Air Force Base.................................................................................................................17

Dietary Items........................................................................................................................................17

Birds......................................................................................................................................................17

Risk Assessment.................................................................................................................................17

Results—Tyndall Air Force Base ..............................................................................................................22

Dietary Items........................................................................................................................................22

Birds......................................................................................................................................................22

Risk Assessment.................................................................................................................................24

Discussion.....................................................................................................................................................26

Beale Air Force Base .........................................................................................................................26

Tyndall Air Force Base.......................................................................................................................27

References Cited..........................................................................................................................................28
v

Figures

1. Map showing location of Beale Air Force Base, California ..................................................3

2. Map showing locations of Tyndall Air Force Base and St. Joe Bay Buffer Preserve, 

Florida .............................................................................................................................................4

3. Map showing location of assessment areas and reference area on Beale Air 

Force Base.....................................................................................................................................5

4. Map showing location of assessment area on Tyndall Air Force Base..............................6

5. Photographs showing, A, a deployed light trap, and B, a pitfall trap along with 

representative samples from each trap....................................................................................7

6. Map showing location of sampling sites witin the assessment area of Tyndall 

Air Force Base for birds, seeds, pitfall traps, and light traps................................................9

7. Maps showing location of sampling sites in the assessment areas of Beale Air 

Force Base: A, DP038, B, SR627 and SR594a, and C, ML586, ML585, and XU643b..........10

8. Maps showing locations of sampling sites in the reference areas of A, Beale 

Air Force Base, and B, St. Joe Bay Buffer Preserve for Tyndall Air Force Base.............13

9. Graphs showing lead concentrations in dietary items collected at Beale Air Force 

Base and its reference area: A, invertebrates and B, seeds ..............................................17

10. Graph showing lead concentrations in blood collected from birds captured 

at Beale Air Force Base, California, and its reference area ...............................................18

11. Graph showing lead concentrations in feathers collected from birds captured 

at Beale Air Force Base, California, and its reference area ...............................................19

12. Graph showing ẟ-aminolevulinic acid dehydratase activity in blood collected from 

birds captured at Beale Air Force Base, California, and its reference area....................19

13. Graph showing lead concentrations in blood of birds captured at Beale Air Force 

Base and its reference area, as well as for birds captured at Tyndall AFB 

and St. Joe Bay Buffer Preserve..............................................................................................20

14. Graph showing lead concentrations in feathers of birds captured at Beale Air Force 

Base and its reference area, as well as for birds captured at Tyndall AFB 

and its reference area, St. Joe Bay Buffer Preserve ...........................................................20

15. Graph showing lead concentrations in soils collected from the Beale Air Force 

Base reference area, California, and from areas A, B, C, and D of D-Street 

of Beale Air Force Base.............................................................................................................21

16. Graph showing lead concentrations in dietary items collected from Tyndall 

Air Force Base and St. Joe Bay Buffer Preserve, Florida....................................................22

17. Graph showing lead concentrations in blood collected from birds captured 

at Tyndall Air Force Base and St. Joe Bay Buffer Preserve, Florida .................................23

18. Graph showing lead concentrations in feathers collected from birds captured 

at Tyndall Air Force Base and St. Joe Bay Buffer Preserve, Florida .................................23

19. Graph showing δ-aminolevulinic acid dehytratase activity in blood collected 

from birds captured at Tyndall Air Force Base and St. Joe Bay Buffer Preserve, 

Florida ...........................................................................................................................................24

20. Graph showing lead concentrations in soils from Tyndall Air Force Base 

and St. Joe Bay Buffer Preserve, Florida ...............................................................................25
vi

Tables

1. Potential guideline levels for lead concentrations in bird feathers and blood ..................2

2. Food ingestion rate, weight, and dietary composition of birds used 

in risk assessment......................................................................................................................15

3. Variables for probabilistic risk assessment for different bird species..............................16

4. Birds captured at Beale Air Force Base and the reference area, California...................18

5. Likelihood that daily exposure of birds to lead at D-Street and Frisky Lake 

at Beale Air Force Base, California, exceeds the lowest observed adverse 

effect level ...................................................................................................................................21

6. Birds captured at Tyndall Air Force Base and St. Joe Bay Buffer Preserve, 

Florida ...........................................................................................................................................22

7. Likelihood that daily exposure of birds to lead at Tyndall Air Force Base 

and St. Joe Bay Buffer Preserve, Florida, exceeds the lowest observed 

adverse effect level....................................................................................................................25
vii

Conversion Factors

International System of Units to U.S. customary units

Multiply By To obtain

Length

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

square kilometer (km2) 0.3861 square mile (mi2)

Volume

liter (L) 2.113 pint (pt)

liter (L) 1.057 quart (qt)

liter (L) 0.2642 gallon (gal)

cubic decimeter (dm3) 0.2642 gallon (gal) 

liter (L) 61.02 cubic inch (in3) 

cubic meter (m3) 35.31 cubic foot (ft3)

cubic meter (m3) 1.308 cubic yard (yd3) 

cubic kilometer (km3) 0.2399 cubic mile (mi3) 

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound avoirdupois (lb)

Datum

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Supplemental Information

Lead concentrations in soil, feathers, and dietary items (invertebrates and seeds) are given in 

parts per million (ppm) dry weight. Lead concentrations in blood are given as micrograms (μg) 

per deciliter (dL) of blood.
viii

Abbreviations

δ-ALAD δ-aminolevulinic acid dehydratase

AFB Air Force Base

bw body weight

oC degrees Celsius

cm centimeters

dL deciliter

dw dry weight

Eco-SSL ecological soil-screening level

FIR food ingestion rate

g grams

h hours

HC hazard concentration

HCl hydrochloric acid

MΩ mega-ohms

mg/kg milligrams per kilogram

NIST National Institute of Standards and Technology

NOEC no observed effect concentration

Pb lead

ppb parts per billion

ppm parts per million

SCP scientific collecting permit

SE standard error

SJB St. Joe Bay Buffer Preserve

TRV toxicity reference value

μg micrograms

μg/dL micrograms per deciliter

μL microliters
Assessment of Bird Exposure to Lead at Tyndall and Beale 

Air Force Bases, 2016–17

By Timothy A. Bargar

Abstract

Soil contamination by lead (Pb) from past small munitions training on Beale Air Force Base, California, and Tyndall 

Air Force Base, Florida, may result in adverse effects for passerine birds that utilize the locations. A study was conducted 

during 2016-17 by the U.S. Geological Survey, in cooperation 

with the U.S. Fish and Wildlife Service and U.S. Air Force, 

at both Air Force Bases (AFBs) to assess the risk of bird 

exposure to Pb. Two different methods were used to estimate 

exposure. The first was analysis of blood and feather samples 

collected from birds captured on both AFBs, and the second 

was food chain modeling using data on Pb concentrations in 

dietary items (invertebrates and seeds) collected from both 

AFBs. Lead concentrations in blood and feathers for birds captured at Beale AFB indicate low exposure and risk; potential 

toxicity is possible based on blood and feather data for birds 

from Tyndall AFB. Food chain modeling utilizing dietary 

contamination indicates a risk likelihood of up to 35 percent 

at Beale AFB and up to 34 percent at Tyndall AFB. Lead exposure from incidental soil ingestion increased risk likelihood at 

both AFBs and is a significant uncertainty in this risk assessment. A companion data release for data collected during this 

project can be found at https://doi.org/10.5066/P92YXMQ2.

Introduction

Lead (Pb) is a widely encountered natural element. It is 

found at a range of concentrations in different components 

of the ecosystem. The average concentration among the soils 

and bedrock of the Earth is 15 parts per million (ppm; Lovering, 1976). In the United States, the statewide average in soils 

ranges from 6.2 (Florida) to 55.0 milligrams per kilogram 

(mg/kg; Pennsylvania) (https://www.epa.gov/superfund/usgsbackground-soil-lead-survey-state-data). Lead concentrations 

in vascular plants can vary depending on the soil Pb levels 

but can range from 15 to 50 ppm in uncontaminated locations 

(Lovering, 1976). Despite being a naturally occurring element, 

Pb is one of a few heavy metals in the environment that has no 

biological role (Goyer, 1986).

Human activities, such as mining (Pavlowsky and others, 

2017), fossil fuel combustion (Kristensen 2015), discharge of 

lead-based ammunition, fishing with lead-based weights, and 

use of lead-based paints (Laidlaw and others, 2017), can result 

in Pb concentrations exceeding background. Manufacture and 

use of some of the lead-based products have decreased or been 

phased out (fuels, ammunition, fishing weights, and paint) to 

reduce environmental contamination. However, contamination from ongoing and past activities has raised concerns for 

biological systems.

Lead toxicity in birds is a well-researched subject. It 

was perhaps first reported in the late 1800s when Hough and 

Grinnel (1894) reported finding Pb shot in gizzards of ducks, 

geese, and swans that exhibited outward signs of what was 

later diagnosed as lead toxicosis. Hough and Grinnel (1894) 

hypothesized that the afflicted waterfowl either incidentally 

or purposely ingested lead shot from wetland sediments and 

later succumbed to lead poisoning. That hypothesis was later 

proven to be true, which led to the ban of Pb-based shot for 

hunting waterfowl. Of course, birds can accumulate Pb from 

routes other than lead pellet ingestion. As a result, numerous 

investigations have focused on Pb toxicity to birds (VallverduColl and others, 2015; Beyer and others, 2014; Kerr and others, 2011; Schulz and others, 2006; Hoffman and others, 2000; 

Beyer and others, 1988; Anders and others, 1982; Dieter and 

Finley, 1979). Health endpoints affected by Pb in those investigations included blood biochemistry (δ-aminolevulinic acid 

dehytratase activity, protoporphyrin level, erythrocyte content, 

and oxidative stress) (Beyer and others, 1988; Dieter and 

Finley, 1979), immunocompetence (Vallverdu-Coll and others, 

2015), histopathology (Beyer and others, 1988), body weight 

(Vallverdu-Coll and others, 2015; Beyer and others, 1988), 

and mortality (Vallverdu-Coll and others, 2015; Hoffman and 

others, 2000; Beyer and others, 1988). 

Concerns for Pb toxicity to wild birds have led to the 

development of guideline exposure levels that can be used 

to estimate risk for birds in areas of known or suspected Pb 

contamination. Non-lethal assessments of avian exposure to 

Pb involve the collection and analysis of feathers and blood. 

Pb concentrations in feathers and blood then are compared 

with concentrations associated with effects. Although field 

studies have found elevated Pb concentrations in feathers 

(Bauerová and others, 2017; Cooper and others, 2017; Burger 

and Gochfeld, 2000; Goede and de Bruin, 1984), few studies 

report an association between Pb concentrations in feathers 

and toxic effects. Burger and Gochfeld (2000) and Tsipoura 
2 Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17

and others (2011) note that 4 ppm of Pb in feathers was associated with adverse effects on behavior and physiology, as well 

as reduced nestling survival. Golden and others (2003) report 

δ-aminolevulinic acid dehytratase (δ-ALAD) depression when 

Pb concentrations in feathers equaled approximately 2 ppm. 

One of the criticisms for using feathers in exposure assessments is the possibility that external contamination (that is, 

soiling of the feathers) could give a false indication of an 

internal exposure level. No regulatory guidelines have been 

identified for Pb concentrations in feathers.

Many researchers have reported on the relation between 

Pb concentrations in blood and toxic effects. Those concentrations are relatively consistent and largely reference a few 

papers (table 1). Buekers and others (2009) did not suggest 

levels of clinical diagnoses, but rather recommended a blood 

Pb concentration of 71 micrograms per deciliter (μg/dL; 

90 percent confidence interval of 26–116 μg/dL) as an HC5

(the 5th percentile of no observed effect concentrations 

reported in the literature) to protect birds from the adverse 

effects of Pb on growth, reproduction, hematology, and physiology. Lastly, Johnson and others (2007) estimated Pb concentrations in blood of 29 and 58 μg/dL as the no observed and 

lowest observed adverse effect levels for birds, respectively. 

These suggested guideline levels enable biologists to infer the 

risk of Pb exposure for birds based on the non-lethal collection 

and analysis of blood. As is the case for feathers, no regulatory 

levels have been recommended for Pb in avian blood.

δ-Aminolevulinic acid dehytratase (δ-ALAD) is an 

enzyme found in blood cells and other tissues involved in porphyrin biosynthesis. Measured levels of δ-ALAD activity in 

avian blood are often used to determine exposure and possible 

Pb toxicity because of its sensitivity to Pb (Sakai and others, 

1983; Dieter and Finley, 1979; Hernberg and others, 1970). 

Disruption of that enzyme is proportional to Pb concentrations 

in blood from approximately 5 μg/dL (Pain, 1989; Hernberg 

and others, 1970) up to 150 μg/dL (Pain 1989). Severe clinical 

or lethal exposures are the diagnoses when the Pb concentration in the blood reaches 150 μg/dL. No further inhibition 

occurs at greater Pb concentrations. Disruption of δ-ALAD 

activity reduces porphyrin biosynthesis leading to porphyria, 

anemia, and lethargy (Eisler, 1988). The combination of Pb 

concentrations in blood and δ-ALAD activity provides a good 

diagnosis of the likelihood of Pb toxicity for birds.

Despite the uncertainties associated with estimating 

bioavailability to birds of soil-associated Pb, regulatory 

guidelines have been suggested for Pb concentrations in soil 

(for example, U.S. Environmental Protection Agency [EPA] 

Ecological Soil Screening Levels [Eco-SSL]; EPA, 2005). The 

guideline values derived for ground-feeding insectivorous, 

herbivorous, and carnivorous birds by the EPA are 11, 46, and 

510 mg/kg dry weight (dw), respectively. These guideline 

values were calculated for a single species representative of 

ground-feeding avian insectivores (Scolopax minor [American 

woodcock]) feeding exclusively on earthworms, a granivore 

(Zenaida macroura [mourning dove]) feeding only on seeds, 

and a carnivore (Buteo jamaicensis [red-tailed hawk]) feeding 

Table 1. Potential guideline levels for lead concentrations in bird 

feathers and blood.

[ppm, parts per million; ALAD, aminolevulinic acid dehytratase; μg/dL, 

microgram per deciliter; HC5, hazardous concentration fifth percentile; 

NOAEL, no observed adverse effect level; LOAEL, lowest observed adverse 

effect level; <, less than; >, greater than]

Lead concentration 

in bird feathers 

(ppm dry weight)

Effect Reference

4 Altered behavior 

and physiology

Burger and Gochfeld, 

2000

2 ALAD depression Golden and others, 2003

Lead concentration 

in bird blood 

(μg/dL)

Diagnosis Reference

71 HC5 Buekers and others, 2009

29 NOAEL Johnson and others, 2007

58 LOAEL Johnson and others, 2007

<20 Background Kramer and Redig, 1997; 

Franson and Pain, 2011

20–60 Subclinical Kramer and Redig, 1997

20–50 Subclinical Franson and Pain, 2011

61–120 Clinical (treatable) Kramer and Redig, 1997

50–100 Clinical (treatable) Franson and Pain, 2011

>100 Severe clinical Franson and Pain, 2011

>120 Lethal Kramer and Redig, 1997

>150 Lethal Pain, 1989

only on small mammals. The values for the herbivores and 

carnivores are greater than the 95th percentile for background 

Pb concentrations in U.S. soils, whereas the value for avian 

insectivores is less than the 50th percentile for background Pb 

concentrations (EPA, 2005). As the term “guideline” implies, 

these values are meant to be screening values and were not 

intended as standards to be used for setting clean-up levels 

(EPA, 1993).

Areas of Tyndall Air Force Base (AFB) near Panama 

City, Florida, have historically been used for small arms training. Soils in those areas are currently contaminated with spent 

ammunition from past training, which resulted in elevated Pb 

concentrations that may present a risk for birds utilizing the 

areas. Small arms training also historically occurred at specific 
Methods 3

locations on Beale AFB near Yuba City, California, but in 

contrast to Pb-contaminated areas at Tyndall AFB, contaminated soils at Beale AFB have been delineated and remediated. 

However, concerns remain that birds utilizing the remediated 

areas may be at risk from remaining Pb contamination. 

This report presents and discusses data from the assessment of Pb risk to passerine birds at Tyndall and Beale Air 

Force Bases conducted in 2016 and 2017 by the U.S. Geological Survey in cooperation with the U.S. Fish and Wildlife 

Service and U.S. Air Force. Concentrations of Pb in the blood 

as well as δ-ALAD activity were measured for birds captured 

at the two AFBs to understand the risk of Pb for the birds. In 

addition, radiographs were generated for the captured birds to 

determine the presence of ingested Pb shot. Because Pb in the 

blood is an indicator of relatively recent contamination (1–2 

months), feathers were collected from each bird for analysis 

of Pb content as an indicator of longer term Pb contamination 

(life span of the feather of up to 1 year). Lastly, dietary items 

(invertebrates and seeds) were collected and analyzed for Pb 

contamination to gain insight into dietary exposure. Lead contamination in birds, δ-ALAD activity, and Pb contamination of 

dietary items were compared between the contaminated areas 

of the AFBs and reference areas. Pb concentrations in feathers 

and blood, and soil and dietary items, are presented in tables 

and figures. Pb concentrations in invertebrates and seeds are 

presented in figures. 

Methods

Sampling Design

This project was conducted at Beale AFB near Yuba City, 

California (fig. 1); Tyndall AFB near Panama City, Florida; 

and St. Joe Bay Buffer Preserve (SJB) near Port St. Joe, 

Florida (fig. 2). Past small arms training on Beale and Tyndall 

AFBs has contaminated soils with Pb from spent munitions. 

The Pb contamination may affect passerine bird species that 

utilize the contaminated habitats.

Areas of the AFBs that were assessed during the project 

are denoted in figures 3 (Beale AFB) and 4 (Tyndall AFB). 

The three areas of Beale AFB that were assessed in this project 

are D-Street (DP038), Frisky Lake (SR627/SR594a), and Warren Shingle Road (ML586/ML585/XU643b). Only a single 

area on Tyndall AFB (SR170/FR038/SR181) was assessed. 

These areas either have (Beale AFB) or have not (Tyndall 

AFB) been remediated for Pb contamination in soils. In both 

cases, the areas are referenced in this report for simplicity as 

suspect areas. Reference areas for each AFB were chosen on 

the basis of similarity of habitat and likelihood of low impact 

from Pb contamination. SJB was chosen as the reference area 

for Tyndall AFB, whereas the southeastern part of Beale AFB 

was chosen as the reference area for the Pb-impacted areas of 

Beale AFB. Hunting activities in both reference areas in the 

past may have resulted in some Pb contamination. However, 

contamination is presumed to be at lower levels than in the 

suspect areas. 

Three goals served as the basis of the sampling design for 

this project—comparing Pb contamination among the suspect 

areas and the reference areas, measuring current avian exposure to Pb, and estimating risk of Pb to birds. Avian exposure 

was measured by collecting blood and feathers and analyzing them for Pb concentrations, and by taking radiographs of 

captured birds to detect the presence of Pb shot pellets in the 

gizzard. Dietary items (seeds and invertebrates) were collected 

and analyzed for Pb concentrations to estimate exposure for 

birds that may forage on the suspect areas and for comparison 

of Pb contamination among the suspect and reference areas.

Capture of Birds and Measurement of their 

Exposure to Lead

Avian exposure to Pb on the AFBs was measured by analysis of blood and feathers non-lethally collected from captured 

birds. Birds were captured (California SCP-13556, Migratory 

Bird permit MB02949C-0) by one of three methods—mist 

netting, baited box traps, or monofilament leg snares. All three 

trap types were placed at multiple locations within the assessment and reference areas. Mist nets were used at Beale and 

Tyndall AFBs in addition to the reference areas. Although box 

traps and leg snares were used at all areas, neither were successful at Beale AFB and its associated reference area. Mist 

Beale 

Air Force 

Base

CALIFORNIA

OREGON

NEVADA

IDAHO

PACIFIC OCEAN

Base modified from U.S. Geological Survey 

National Map Viewer, May 11, 2016 

1:6,443,363-scale digital data

100 200

0 175 350

0 MILES

KILOMETERS

120°

40°

35°

115°

Figure 1. Location of Beale Air Force Base, California.
4 Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17

0 125 250

0 75 150

KILOMETERS

MILES

Base modified from Florida Department of 

Environmental Production, July 1997

1:4,805,948-scale digital data

Tyndall Air Force Base

St. Joe Bay

Buffer Preserve

FLORIDA

87°

87°

30° 30°

29° 29°

28° 28°

27° 27°

26° 26°

25° 25°

86°

86°

85°

85°

84°

84°

83°

83°

82°

82°

81°

81°

80°

80°

Figure 2. Locations of Tyndall Air Force Base and St. Joe Bay Buffer Preserve, Florida. 

nets were placed near structures (shrubs and trees) to capture 

birds attracted to the structure. The nets were erected during 

the pre-dawn hours and were monitored continuously until 4 h 

after sunrise, at which time the nets were closed. Birds trapped 

in the nets, in the box, or by the snares were removed as soon 

as they were discovered, usually within 5 minutes of being 

trapped. The retrieved birds were placed into canvas bags, then 

into cardboard boxes, and taken to the field laboratory (transit 

time of 5–10 minutes). While still in the canvas bags, radiographs (ImageX-1417 paired with PXM-20BT X-Ray source) 

were taken of the birds for later analysis for the presence of Pb 

shot. Afterwards, the birds were weighed to the nearest gram 

(g) to determine the maximum blood volume to be drawn (for 

example, 20-g bird x 0.01 = 0.2 milliliter (mL) maximum 

blood volume assuming 1g blood approximates 1 mL blood). 

After being weighed, the birds were removed from the canvas 

bag and blood was drawn using a heparinized 24-gauge needle 

inserted bevel down into the left jugular vein. Afterwards, 

breast feathers were collected, and the birds were placed back 

into the canvas bag, and then the cardboard box, for return to 

the capture location.

The collected blood samples were transferred to a cryovial from which 50 microliters (μL) was taken for measurement of Pb concentrations. Measurement of Pb concentrations 

is described in section “Sample Analyses.” In addition to the 

sample taken for analysis of Pb, a small portion of blood was 

drawn into a hematocrit tube for determination of sedimentation rate, and then hematocrit, using a capillary micro-hematocrit reader after centrifugation at 12,000 times gravity for 

5 minutes (Unico Model C-MH30 micro-hematocrit centrifuge). Hemoglobin content was also determined (HemoCue 

Hb 201+). Hematocrit was not measured for birds collected at 
Methods 5

Frisky Lake

Warren

Shingle

Road

Bedspring

Lake

D-Street

Reference

area

EXPLANATION

Assessment area—Currently contaminated by, 

or has been remediated 

for, lead contamination

Reference area

Base from U.S. Geological Survey National Map Viewer

October 25, 2016, 1:81,699

4 KILOMETERS

MILES

0 2

0 1 2

121°28' 121°27' 121°25' 121°23' 121°21'

36°11'

36°10'

36°09'

36°08'

36°07'

36°06'

36°05'

36°04'

121°26' 121°24' 121°22' 121°20'

Figure 3. Location of assessment areas and reference area on Beale Air Force Base. 

Tyndall AFB. The remaining blood was placed on dry ice and 

later placed into a freezer at -80 degrees Celsius (oC) until it 

could be analyzed for δ-ALAD activity.

δ-ALAD activity in blood was measured to assess potential toxic response from Pb exposure. The sample preparation 

and analysis procedure followed U.S. Geological Survey 

Patuxent Wildlife Research Center Standard Operating Procedure number TOP 1991. Thawed blood (25 μL) was pipetted 

into double-distilled water (350 μL), vortexed, and incubated 

for 10 minutes at 38 oC. After the addition of aminolevulinic acid (250 μL), the sample was incubated in the dark for 

1 hour at 38 oC. The sample was then vortexed after adding 

10-percent trichloroacetic acid (250 μL) and centrifuged 

for 10 minutes at 1,500 times gravity. Along with 100 μL of 

Ehrlich’s reagent, 100 μL of the sample was added to a well 

on a 96-well plate. After shaking the plate for 20 seconds, 

absorbance at 555 nanometers relative to water was measured 

using an Epoch Microplate Spectrophotometer paired with 

BioTek Gen5 software (Version 2.07). δ-ALAD activity was 

expressed as nanomolar (nM) aminolevulinic acid per minute 

per mL of red blood cells (RBC) and was calculated according 

to Berlin and Schaller (1974) with modifications for the microplate procedure described above. Activity for birds captured at 

Tyndall AFB for which hematocrit was not measured was calculated using preferably the average hematocrit for the same 

species captured elsewhere or the average hematocrit for other 

birds captured in the reference area. For example, the average hematocrit for Cardinalis cardinalis (northern cardinals) 

captured at SJB was used to calculate activity for northern 

cardinals captured at Tyndall AFB, but the average for all birds 

captured at SJB was used for Vireo griseus (white-eyed vireo) 

captured at Tyndall AFB.
6 Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17

1,000 METERS

1,500 3,000 FEET

0 500

0

Base from U.S. Geological Survey National Map Viewer

February 29, 2016, 1:17,348

SR170

FR038

SR181

EXPLANATION

Assessment area

85°37'30"

30°05'30"

30°05'00"

30°04'30"

30°04'00"

85°37'00" 85°36'30"

Figure 4. Location of assessment area on Tyndall Air Force Base. 
Methods 7

Collection and Analysis of Dietary Items for 

Lead

In addition to measurement of Pb concentrations in 

birds and estimation of toxic response in birds by measurement of δ-ALAD activity in blood, potential dietary items 

(invertebrates and seeds) were collected and analyzed for 

Pb to estimate exposure of birds that may exclusively forage 

on the Pb-contaminated areas. Three different methods were 

used to collect invertebrates—light traps, pitfall traps, and 

nets. Light traps (fig. 5) were deployed for a single night at 

multiple locations in Pb-contaminated and reference areas to 

collect night-flying phototaxic invertebrates. The traps were 

battery powered, deployed shortly before dark, and left to 

operate until the battery power was drained (approximately 

8 h). Invertebrates attracted to the light were deflected down 

into a net in the lower chamber of the trap and euthanized by 

a chemical fumigant (Hot ShotTM, active ingredient dichlorvos) placed within the chamber. Pitfall traps (fig. 5) were 

used to capture soil-associated invertebrates. The traps were 

deployed at multiple locations either in triplicate for a 24 h 

period (Beale and Tyndall AFBs, and Beale reference area) or 

singly for 3 consecutive days (St. Joe Bay Buffer Preserve) to 

insure sampling for 3 trap days at each location. Invertebrates 

captured by the light traps were sieved to separate those 

smaller than about 2 millimeters from the remaining invertebrates and composited into an “unsorted” invertebrate sample. 

The larger invertebrates were sorted into orders (for example, 

Coleoptera, Lepidoptera, Orthoptera) to allow assessment of 

the possible role that feeding at different niches and trophic 

levels would have on Pb concentrations in the invertebrates. 

Invertebrates in the pitfall traps were composited to increase 

invertebrate mass for analysis and were not sorted into orders. 

Nets were used to sweep herbaceous vegetation at Beale AFB 

to capture grasshoppers (order Orthoptera), which were highly 

abundant during field sampling. The sorted invertebrates were 

placed into Ziploc bags and sent to the contracted laboratory 

for analysis.

No single plant species was sought for seed collection 

because no assumption was made about seed preference(s) 

by any bird species. Therefore, we collected as many seeds 

as possible from a variety of plants to encompass variation 

among plant species for Pb translocation from roots to seeds. 

Two people each spent 5 minutes collecting seeds from a 

location to standardize the collection effort among locations as 

well as assessment and reference areas. All seeds from a location were composited into a single Ziploc bag and sent to the 

contract laboratory for analysis.

A

B

Figure 5. A, a deployed light trap, and B, a pitfall trap along with representative samples 

from each trap.
8 Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17

Soil Sampling

Soils were collected from 10 randomly selected locations within each of the reference areas for comparison with 

Pb-contaminated soils in the suspect areas. Soil sampling 

in the suspect areas was not part of the present study. It was 

conducted previously by commercial contractors selected 

by the U.S. Air Force. Data for the discussion in this report 

of Pb concentrations in soils in the suspect areas of Tyndall 

and Beale AFBs were provided by employees at Tyndall and 

Beale AFBs.

Sample Analyses

Feather samples were sonicated (Branson 1510 ultrasonic 

bath) and rinsed with deionized water, and then freeze dried 

prior to digestion. All tissue samples (that is, invertebrates 

and seeds) were digested with trace-metals grade nitric and 

hydrochloric acids (EMD Millipore) and hydrogen peroxide 

(J.T. Baker), diluted to volume with ultrapure water (Type 1, 

18.2 Mega ohms per centimeter resistivity), and then analyzed for Pb, and in some cases aluminum, on a Perkin Elmer 

DRC 2 inductively coupled plasma–mass spectrometer. 

External contamination is indicated by elevated aluminum 

concentrations. Laboratory quality control samples accompanied project samples through preparation and analysis steps 

and included method blanks, spiked blanks (laboratory control 

samples), duplicate samples, spiked samples, and certified reference materials. National Institute of Standards and Technology (NIST) standard 955c was the standard reference material 

used for blood, whereas NIST 2976 was used for other tissues. 

The marine sediment reference materials MESS-3 was used 

for soil samples. Analytical accuracy of the methods was 

estimated as 81, 106, and 107 percent for MESS-3, NIST 

2976, and NIST 955c, respectively. Precision (percent relative 

difference between samples and their duplicates) for analyses was estimated to be 1, 4, 1, and 4 percent for soil, seed, 

invertebrate, and blood samples, respectively. Method detection limits (concentration in the matrix) were 291, 47, 49, and 

0.5 parts per billion wet weight for soil, seeds, invertebrates, 

and blood, respectively. The moisture content of samples was 

determined by weight loss through freeze drying using a Labconco Freezone 12L lyophilizer.

Sample Collection Locations

Sampling sites on Tyndall and Beale AFBs are shown in 

figures 6 and 7, respectively, whereas sampling sites in the reference areas are shown in figure 8. Note that pitfall traps were 

not deployed at the Frisky Lake (SR627/SR594a) or Warren 

Shingle Road (ML586/ML585/XU643b) areas of Beale AFB 

because the soil in those areas was too hard. Also note that 

no bird traps were deployed at D-Street (DP038) or Warren 

Shingle Road of Beale AFB. Both of those areas lacked structure that could attract birds and that could conceal mist nets.

Statistics

Lead concentrations in dietary items as well as δ-ALAD 

activity were compared among the suspect and reference areas 

for Tyndall and Beale AFBs. Parametric methods (Analysis of 

Variance) were used for the comparisons if assumptions could 

be satisfied; nonparametric methods (Kruskal-Wallis test) were 

used otherwise. Lead concentrations in blood and feathers 

were compared between Tyndall AFB and St. Joe Bay Buffer 

Preserve only for the same species. All comparisons were at 

a significance level of α=0.05. Significant differences for the 

comparisons were noted in the subsequent discussion when 

p-values were less than the significance level (α=0.05).

Risk Assessment

Two methods were used to estimate risk of Pb to birds 

on the AFBs. In the first method, the risk for birds captured 

on the AFBs was based on guideline levels for Pb concentrations in blood (Buekers and others, 2009; Johnson and others, 

2007) and on Eco-SSL levels for Pb concentrations in soil 

(EPA, 2005). Frequency distributions were generated for Pb 

concentrations in blood, feathers, and soils, and then were 

compared to concentrations considered indicative of varying 

degrees of toxicity (Franson and Pain, 2011; Buekers and others, 2009; Johnson and others, 2007; EPA, 2005; Kramer and 

Redig, 1997).

In the second method, risk for birds that may forage in 

the suspect areas was estimated only on the basis of consumption of Pb-contaminated food and incidental ingestion of Pbcontaminated soil. Exposure from Pb-contaminated respirable 

particulates, water, and passage through the dermis was not 

considered. The focal species chosen for this risk assessment 

are listed in table 2. Risk for passerine and non-passerine 

birds was based on food ingestion rates (FIR) calculated using 

equations 3-4 and 3-5 in the EPA handbook (EPA, 1993), 

published weight data for species commonly observed at the 

AFBs (table 2), Pb-contamination of dietary items collected 

and analyzed during this project, available information on 

dietary preferences, published information on incidental soil 

ingestion rates (Beyer and others, 1994), and toxicity reference 

values (mg/kg body weight per day) compiled by EPA (2005). 

The toxicity reference values were segregated into two broad 

effects categories. The first (Category 1) included biochemical, physiological, pathological, and behavioral effects, and 

the second (Category 2) included reproductive, growth, and 

survival effects. The potential for factors outside of those areas 

to enhance or reduce risk was not considered.

A tiered approach was used in the risk assessment. A 

conservative screening level risk assessment was conducted 

initially. The estimated risk was calculated on the basis of the 

peak measured Pb concentrations for dietary items and soil, 

smallest body weight for birds, highest reported incidental soil 

ingestion proportion for birds (0.3), and the lowest toxicity 

reference value (TRV).
Methods 9

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Base modified from U.S. Geological Survey National Map Viewer

February 29, 2016, 1:11,103

EXPLANATION

Light trap

Pitfall trap

Bird

Seed

85°37'00"

30°05'00"

30°04'30"

85°36'30"

Figure 6. Location of sampling sites witin the assessment area of Tyndall Air Force Base for birds, seeds, pitfall traps, 

and light traps.
10 Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17

Area A

Area B

Area C

Area D

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October 25, 2016, 1:3,404

0 100 200

0 250 500

METERS

FEET

121°24'45"

39°07'30"

39°07'15"

121°24'30"

EXPLANATION

Pitfall trap

Seed

Light trap

A, DP038

Figure 7. Location of sampling sites in the assessment areas of Beale Air Force Base: A, DP038, B, SR627 and SR594a, 

and C, ML586, ML585, and XU643b.
Methods 11

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Bedspring Lake

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Base modified from U.S. Geological Survey National Map Viewer

October 25, 2016, 1:3,404

EXPLANATION

Bird

Seed

Light trap

B, SR627 and SR594a

121°22'40"

39°07'55"

39°07'50"

39°07'45"

39°07'40"

39°07'35"

39°07'30"

121°22'35" 121°22'30" 121°22'25" 121°22'20"

Figure 7. Location of sampling sites in the assessment areas of Beale Air Force Base: A, DP038, B, SR627 and SR594a, 

and C, ML586, ML585, and XU643b.—Continued
12 Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17

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Light trap

200

0 250 500

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Base modified from U.S. Geological Survey National Map Viewer

October 25, 2016, 1:3,404

121°21'35"

39°06'55"

39°06'50"

39°06'45"

121°21'30" 121°21'25" 121°21'20" 121°21'15"

C, ML586, ML585, and XU643b

Figure 7. Location of sampling sites in the assessment areas of Beale Air Force Base: A, DP038, 

B, SR627 and SR594a, and C, ML586, ML585, and XU643b.—Continued
Methods 13

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EXPLANATION

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Seed

121°21'30"

39°06'00"

39°05'30"

121°21'00"

A, Beale Air Force Base

Figure 8. Locations of sampling sites in the reference areas of A, Beale Air Force Base, and B, St. Joe 

Bay Buffer Preserve for Tyndall Air Force Base. Pitfall and light trap locations not shown on this map.
14 Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17

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February 8, 2016, 1:27,893

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EXPLANATION

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Pitfall trap

Bird

Seed

85°18'30"

29°44'00"

29°43'30"

29°43'00"

29°42'30"

29°42'00"

29°41'30"

85°18'00" 85°17'30" 85°17'00" 85°16'30"

B, St. Joe Bay Buffer Preserve

Figure 8. Locations of sampling sites in the reference areas of A, Beale Air Force Base, 

and B, St. Joe Bay Buffer Preserve for Tyndall Air Force Base.—Continued
Methods 15

Table 2. Food ingestion rate, weight, and dietary composition of birds used in risk assessment.

[g/g bw day, gram per gram of body weight per day; g, gram; AFB, Air Force Base; --, no data; FIR, food ingestion rate]

Species Latin name

Applicable 

Air Force 

Base

Food 

ingestion rate 

(g/g bw day)

Weight 

(g)

Dietary composition 

(proportion)1

Minimum Maximum Invertebrates Seeds

Horned lark2 Eremophila alpestris Beale AFB -- 28 48 0.5 0.5

Western meadowlark2 Sturnella neglecta Beale AFB -- 89 115 0.5 0.5

Red-winged blackbird2 Agelaius phoeniceus Beale AFB -- 32 77 0.5 0.5

Savanna sparrow2 Passerculus sandwichensis Beale AFB -- 15 28 0.5 0.5

Lesser scaup3 Aythya affinis Beale AFB 40.162 647 860 0.5 0.5

Canada goose3 Branta canadensis Beale AFB 0.03 1,260 4,960 0 1

Northern cardinal2 Cardinalis cardinalis Tyndall AFB -- 42 48 0.5 0.5

Eastern towhee2 Pipilo erythrophthalmus Tyndall AFB -- 32 52 0.5 0.5

Mourning dove2 Zenaida macroura Tyndall AFB -- 86 156 0.01 0.99

Carolina wren2 Thryothorus ludovicianus Tyndall AFB -- 18 22 0.9 0.1

1

Unless indicated in the source, the proportion for dietary composition was assumed to be 0.5.

2

Weights and dietary information from All About Birds (https://www.allaboutbirds.org/), Cornell Lab of Ornithology.

3

Weights, dietary information, and FIR from U.S. Environmental Protection Agency (1993).

4

Maximum reported FIR.

Equation 1 was the model used to estimate risk.

Risk

FIR P Pb P Pb P              

  invert  invert seeds seeds   soil    Pb

bird weight g

TRV soil

_ ( ) (1)

where

FIR is food ingestion rate;

Pitem is proportion of the diet composed of the dietary item (table 2);

[Pb]item is Pb concentration in the dietary item;

Psoil is proportion of diet composed of soils (incidental soil ingestion rate), which 

based on information reported in Byer and others (1994) ranges from less 

than 0.02 to 0.3; and

TRV is toxicity reference value.

Risk is indicated by a unitless quotient of exposure and the TRV exposure

TRV





 



. Risk is presumed when exposure exceeds the TRV, that is, when the quotient exceeds one.

The FIR was estimated using the following equations, which are from Nagy (1987) as 

cited in EPA (1993):

FIR (passerine birds) = 0.398 × bird_weight(g)0.85 (2)

FIR (nonpasserine birds) = 0.301 × bird_weight(g)0.751 (3)

Food ingestion rates were derived for several passerine species commonly observed at 

Tyndall AFB (northern cardinal, Pipilo erythrophthalmus [rufous-sided towhee], mourning 

dove, and Thryothorus ludovicianus [Carolina wren]) and Beale AFB (Eremophilia alpestris 

[horned lark], Sutnella neglecta [western meadowlark], Agelaius phoeniceus [red-winged 
16 Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17

blackbird], and Passerculus sandwichensis [savanna sparrow]). Ingestion rates for two non-passerine species also 

were used for the risk assessment at Beale AFB because of 

the seasonal use of vernal wetlands by water fowl. However, 

because food ingestion rates for Branta canadensis (Canada 

goose) and Aythya affinis (lesser scaup) were available in the 

EPA handbook (EPA, 1993), they were used for risk estimation rather than an ingestion rate derived on the basis of the 

equations 2 and 3.

On the basis of the “worst case scenario” assumptions, 

a risk quotient less than one would indicate risk is minimal, 

given what is known about exposure at the location and toxicity. However, if the risk quotient is equal to or greater than 

one, a probabilistic risk assessment was conducted.

The probabilistic risk assessment combined the range of 

possible exposures and toxic responses to give a better indication of risk likelihood. This was accomplished through Monte 

Carlo analysis, which repeatedly estimated exposure and 

selected toxicities to generate a set of risk quotients using the 

model described by equation 1. Repeated exposure estimates 

were calculated or toxicities were selected when values for 

each of the variables in the risk model were randomly selected 

(Monte Carlo analysis) from distributions (for example, log 

normal, Weibull, beta) describing the datasets for Pb contamination, bird weight, proportion of dietary items in diet, and 

TRV. Given an adequate dataset (n ≥ 15), the best fit (Chisquare goodness-of-fit) of the data with statistical distributions 

(for example, log normal) was determined. If the dataset was 

insufficient, distributions were assumed. Distributions chosen 

for the variables are shown in table 3. The distribution assumed 

(flat) for incidental soil ingestion is not shown in table 3. The 

incidental ingestion rate (proportion of FIR mass) for birds was 

based on the range (<0.02–0.3) reported by Beyer and others 

(1994). The percentage of risk quotients in the set generated by 

Monte Carlo analysis that exceeds one indicates the risk likelihood given the potential exposures and toxicities. 

Table 3. Variables for probabilistic risk assessment for different bird species.

[N, normal; --, no data; ppm, parts per million; AFB, Air Force Base; L, log normal; Gam, gamma; Tri, triangular. Common name, Latin name: horned lark, 

Ermophilia alpestris; western meadowlark, Sturnella neglecta; red-winged blackbird, Agelaius phoeniceus; savanna sparrow, Passerculus sandwichensis; lesser 

scaup, Aythya affinis; Canada goose, Branta canadensis; northern cardinal, Cardinalis cardinalis; rufous-sided towhee, Pipilo erythrophthalmus; mourning dove, 

Zenaida macroura; carolina wren, Thryothorus ludovicianus]

Bird mass

Distribution type

Triangular

Horned larkWestern meadowlarkRed-winged blackbirdSavanna sparrowLesser scaupCanada gooseNorthern cardinalRufous-sided towheeMourning doveCarolina wren

Dietary proportion

Distribution type

N N N N N -- N N Beta Tri Horned lark Western meadowlark Red-winged blackbird Savanna sparrow Lesser scaup Canada goose Northern cardinal Rufous-sided towhee Mourning dove Carolina wren

Lead concentrations (ppm dry weight)

D-Street Frisky Lake Beale reference Tyndall AFB

InvertebratesSeeds

Soil

InvertebratesSeedsSoilInvertebratesSeedsSoilInvertebratesSeedsSoil

Area

A

Area

B

Area

C

Area

D

Average1 4.77 0.05 101.6 136.7 112.5 20.6 62.7 0.14 -- 13.2 0.06 6.5 16.9 2.1 254.6

Standard deviation1 8.22 0.03 160.2 185.63 166.7 17.36 49.1 0.02 -- 22 0.03 2.1 35.58 5.54 552.79

Distribution type L L Gam Gam L L L L -- L L L L L L

1

Average and standard deviations for the respective distributions were based on collected data.
Results—Beale Air Force Base 17

Results—Beale Air Force Base

All data discussed in this report are available in the companion data release (Bargar, 2019).

Dietary Items

Light traps were deployed at all suspect and reference 

areas. Qualitatively, the largest biomass of invertebrates captured by the light traps was at Frisky Lake, whereas the lowest 

biomass was collected by light traps at Warren Shingle Road. 

Pitfall traps were deployed only at D-Street and in the reference areas; the hard soils at Frisky Lake and Warren Shingle 

prevented deployment of pitfall traps at those areas.

Lead concentrations in invertebrates differed significantly 

among the suspect and reference areas (fig. 9). The lowest Pb 

concentrations in invertebrates were in those captured in the 

suspect area adjacent to Warren Shingle Road, whereas the 

highest concentrations in invertebrates were in those captured 

in the suspect area near Frisky Lake. No significant difference 

in Pb concentrations was evident between D-Street and the 

reference area invertebrates. Although significant differences 

in Pb concentrations among the suspect and reference areas 

were determined for seeds, the nonparametric analysis could 

not make pair-wise comparisons among locations (fig. 9).

Birds

A total of 52 birds were collected in September 2016 

from locations near Frisky Lake, an area potentially affected 

by Pb. No birds were captured from D-Street or from Warren 

Shingle Road. A total of 19 birds were captured from the reference area in June 2017. The list of the birds captured is shown 

in table 4. None of the species found in the suspect areas were 

captured at the reference area.

Pb concentrations in the blood and feathers of the captured birds, and the δ-ALAD activity in blood, are shown in 

figures 10, 11, and 12, respectively. The average Pb concentrations in blood (0.19 μg/dL, standard error (SE) = 0.034) and 

feathers (0.47 ppm dw, 0.115) for birds from the reference area 

were lower than concentrations in blood (0.55 μg/dL, 0.071) 

and feathers (0.60 μg/dL, 0.056) for birds from the suspect 

areas. The δ-ALAD activity for birds from the reference area 

(42.9 nanomoles [nM] of aminolevulinic acid [ALA] per 

minute [min] per milliliter [mL] of red blood cells [RBC], 

SE = 4.06) was significantly greater (p<0.001) than for birds 

from the suspect area (30.1 nM/ALA/min/mL of RBC, 1.09). 

Inspection of the radiographs for captured birds found no 

evidence of Pb particles. Many of the images revealed highdensity areas, but comparison with reference Pb pellets within 

each image indicated those areas were unlikely to be Pb pellets 

or fragments.

Risk Assessment

Lead concentrations in blood were less than the level 

representative of background Pb contamination (20 μg/dL; 

Franson and Pain, 2011; fig. 13), and concentrations in 

feathers were less than the concentration associated with 

decreased nestling survival and effects on avian behavior and 

physiology (4 ppm dry weight; Tsipoura and others, 2011; 

fig. 14). A portion of the soils in all areas (A, B, C, and D) 

of D-Street exceeded the EPA (2005) Eco-SSL for risk to 

B. Seeds

D-Street

Frisky Lake

Warren Shingle Road

Beale reference

0.01

0.1

1

Lead, in parts per million dry weight

Sampling site

A. Invertebrates

D-Street

Warren Shingle Road

Beale reference 1

Beale reference 2Beale reference 3

0.01

0.1

1

10

100

1,000

Lead, in parts per million dry weight

Sampling site

a a, b a a, b

Frisky Lake

b c

Reference samples

Reference

sample

Figure 9. Lead concentrations in dietary items collected at Beale Air Force Base and its reference area: A, invertebrates 

and B, seeds. Letters above sampling sites in A indicate whether lead concentrations for invertebrates from that site are the 

same (same letter) or significantly different (different letter) (α= 0.05) relative to the other sites. Kruskal Wallis analysis of 

seed data in B indicates lead concentrations are significantly different among areas (α= 0.05).
18 Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17

Table 4. Birds captured at Beale Air Force Base and the 

reference area, California.

Species Latin name Number 

captured

Beale Air Force Base

Savanna sparrow Passerculus sandwichensis 22

Song sparrow Melospiza melodia 7

Grasshopper sparrow Ammodramus savannarum 1

White-crowned sparrow Zonotrichia leucophrys 10

Vesper sparrow Pooecetes gramineus 1

Northern mockingbird Mimus polyglottos 2

Mourning dove Zenaida macroura 2

Black phoebe Sayornis nigricans 3

Western meadowlark Sturnella neglecta 1

Brewer's blackbird Euphagus cyanocephalus 3

Reference area

Brown-headed cowbird Molothrus ater 3

Red-winged blackbird Agelaius phoeniceus 1

Ash-throated flycatcher Myiarchus cinerascens 7

Nuttall's woodpecker Dryobates nuttallii 2

Hooded oriole Icterus cucullatus 1

Bullock's oriole Icterus bullockii 3

California scrub jay Aphelocoma californica 1

House finch Haemorhous mexicanus 1

avian insectivores (11 ppm dw) and herbivores (46 ppm dw), 

whereas contamination for portions of the soils in Areas B, 

C, and D exceeded the soil-screening level for risk to avian 

carnivores (510 ppm dw; fig. 15). Geometric means for Pb 

concentrations in the four areas (A = 40.8, B = 48.3, C = 44.8, 

D = 15.1 in ppm dw) exceeded the avian insectivore Eco-SSL, 

whereas the geometric mean for Area B also exceeded the 

avian herbivore Eco-SSL.

Risk quotients from the conservative risk assessment 

exceeded one for both effect categories for all species foraging at D-Street and in the reference area. They also exceeded 

one at Frisky Lake for both effect categories for all species, 

except the Canada Goose. No risk quotients exceeded one 

at Warren Shingle Road. Soil contamination by Pb was not 

incorporated within the conservative risk estimate for Frisky 

Lake or Warren Shingle Road. Sampling of dietary items from 

D-Street was not designed to enable risk assessment for Areas 

A through D individually.

Probabilistic risk was estimated for birds foraging at 

D-Street, Frisky Lake, and the reference areas (table 5). 

Overall, the likelihood of Category 1 effects (lowest observed 

adverse effects) was greater than the likelihood of Category 2 

effects (Pb toxicity to reproduction, growth, and survival), 

which reflects the differing effect-level concentrations for the 

two categories. The likelihood of risk was greater for birds 

foraging at Frisky Lake relative to D-Street and the reference area. Risk likelihood was lower for larger birds (scaup 

and goose) and for the largely herbivorous Canada goose. 

The additional risk from incidental soil ingestion was greater 

for birds foraging at D-Street relative to birds foraging at the 

reference area. Risk likelihood for birds at Frisky Lake did not 

include risk from incidental soil ingestion.

Brewer's blackbird - Beale AFB

Northern mockingbird - Beale AFB

Savanna sparrow - Beale AFB

Song sparrow - Beale AFB

White-crowned sparrow - Beale AFB

Mourning dove - Beale AFB

Vesper sparrow - Beale AFB

Western meadowlark - Beale AFB

Ash-throated flycatcher - reference

Bullock's oriole - reference

Brown-headed cowbird - reference

Nuttall's woodpecker - reference

Red-winged blackbird - reference

California scrub jay - reference

Bird - sampling site

Lead concentration, in micrograms per deciliter

10

1

0.1

0.01

Reference samples

Figure 10. Lead 

concentrations in blood 

collected from birds 

captured at Beale Air Force 

Base (AFB), California, and 

its reference area. (See 

table 4 for Latin names 

of birds)
Results—Beale Air Force Base 19

Savanna sparrow - Beale AFB

Song sparrow - Beale AFB

White-crowned sparrow - Beale AFB

Mourning dove - Beale AFB

Northern mockingbird - Beale AFB

Brewer's blackbird - Beale AFB

Black phoebe - Beale AFB

Vesper sparrow - Beale AFB

Western meadowlark - Beale AFB

Ash-throated flycatcher - reference

Bullock's oriole - reference

Nuttall's woodpecker - reference

Brown-headed cowbird - reference

Hooded oriole - reference

Red-winged blackbird - reference

California scrub jay - reference

House finch - reference

Bird - sampling site

Lead concentration, in parts per million dry weight

2.5

2

1.5

1

0.5

0

Reference samples

Figure 11. Lead 

concentrations in 

feathers collected 

from birds captured at 

Beale Air Force Base 

(AFB), California, and 

its reference area. (See 

table 4 for Latin names 

of birds)

nM ALA/min/mL RBC

100

80

60

40

20

0

Savanna sparrow - Beale AFB

Song sparrow - Beale AFB

White-crowned sparrow - Beale AFB

Mourning dove - Beale AFB

Northern mockingbird - Beale AFB

Brewer's blackbird - Beale AFB

Black phoebe - Beale AFB

Vesper sparrow - Beale AFB

Western meadowlark - Beale AFB

Ash-throated flycatcher - reference

Bullock's oriole - reference

Nuttall's woodpecker - reference

Brown-headed cowbird - reference

Hooded oriole - reference

Red-winged blackbird - reference

California scrub jay - reference

Bird - sampling site

Reference samples

Figure 12. ẟ-aminolevulinic acid 

dehydratase activity 

(ẟALAD) in blood 

collected from birds 

captured at Beale Air 

Force Base (AFB), 

California, and its 

reference area. (nM ALA/

min/mL RBC, nanomoles 

aminolevulinic acid per 

minute per milliliter of red 

blood cells; see table 4 

for Latin names of birds)
20 Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17

Beale Air Force Base

Beale Air Force Base reference area

Tyndall Air Force Base

St. Joe Bay Buffer Preserve

Background (Franson and Pain, 2011)

LOAEL (Johnson and others, 2007)

HC5 (Buekers and others, 2009)

EXPLANATION

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100 1,000

Lead concentration, in micrograms per deciliter

Percentile

Figure 13. Lead concentrations in blood of birds captured at Beale Air Force Base (AFB) and its reference area, as 

well as for birds captured at Tyndall AFB and St. Joe Bay Buffer Preserve. The vertical lines show lead concentrations 

in blood considered to be background (20 micrograms per deciliter [μg/dL]), the lowest observed adverse effect level 

(LOAEL; 58 μg/dL), and the concentration affecting 5 percent of birds (HC5; 71 μg/dL).

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100 1,000

Lead concentration, in parts per million dry weight

Percentile

Beale Air Force Base

Beale Air Force Base reference area

Tyndall Air Force Base

St. Joe Bay Buffer Preserve

Nestling survival, behavior, physiology

EXPLANATION

Figure 14. Lead concentrations in feathers of birds captured at Beale Air Force Base (AFB) and its reference area, as well 

as for birds captured at Tyndall AFB and its reference area, St. Joe Bay Buffer Preserve. The vertical line reflects the lead 

concentration (4 parts per million dry weight) associated with effects in nestling survival, and avian behavior and physiology 

(Tsipoura and others, 2011).
Results—Beale Air Force Base 21

0

10

20

30

40

50

60

70

80

90

100

1 10 100 1,000

Lead concentration, in parts per million dry weight

Percentile

D-Street area A

D-Street area B

D-Street area C

D-Street area D

Beale Air Force Base reference area

Insectivore

Ecological soil screening levels

Assessment areas

Herbivore

Carnivore

EXPLANATION

Figure 15. Lead concentrations in soils collected from the Beale Air Force Base reference area, California, and from areas A, 

B, C, and D of D-Street of Beale Air Force Base. Vertical lines represent the Ecological Soil Screening Levels for lead risk to avian 

insectivores (11 parts per million dry weight [ppm dw]), herbivores (46 ppm dw), and carnivores (510 ppm dw) (From EPA, 2005).

Table 5. Likelihood that daily exposure of birds to lead at D-Street and Frisky Lake at Beale Air Force Base, California, exceeds the 

lowest observed adverse effect level1.

[--, no data; shaded percentages indicate risk likelihood without the assumption of incidental soil ingestion]

Species Latin name

Likelihood that daily exposure exceeds lowest observed adverse effect, in percent

D Street Frisky 

Lake

Reference 

Area A Area B Area C Area D area

Category 1 effect2

Horned lark Eremophila alpestris 23.3 24.9 22.5 15.0 -- 14.8

10.2 23.1 15.0

Western meadowlark Sturnella neglecta 22.2 23.6 21.0 14.4 -- 13.4

9.2 31.6 14.4

Red-winged blackbird Agelaius phoeniceus 23.0 24.3 21.8 14.6 -- 14.8

10.1 23.0 14.7

Savanna sparrow Passerculus sandwichensis 23.9 25.5 22.8 15.4 -- 15.6

10.6 34.6 15.7

Lesser scaup Aythya affinis 20.1 21.3 18.1 12.7 -- 12.0

6.0 28.4 13.0

Canada goose Branta canadensis 16.7 18.5 14.2 7.0 -- 0.0

0.0 0.0 0.0

Category 2 effect2

Horned lark Eremophila alpestris 5.3 5.1 5.6 2.2 -- 1.7

0.3 7.1 1.3

Western meadowlark Sturnella neglecta 4.3 4.8 5.1 2.1 -- 1.4

0.3 6.1 1.2

Red-winged blackbird Agelaius phoeniceus 5.2 4.9 5.3 2.1 -- 1.5

0.3 6.8 1.2

Savanna sparrow Passerculus sandwichensis 6.0 5.2 5.8 2.3 -- 1.6

0.3 7.4 1.4

Lesser scaup Aythya affinis 3.3 3.8 3.9 1.5 -- 1.1

0.2 4.4 0.8

Canada goose Branta canadensis 2.2 3.1 2.8 0.5 -- 0.1

0.0 0.0 0.0

1

Lowest-observed adverse effect levels as compiled in U.S. Environmental Protection Agency (2005).

2

Category 1 effects are lead toxicity to blood biochemistry, physiology, pathology, and behavior; Category 2 effects are lead toxicity to reproduction, growth, 

and survival.
22 Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17

Results—Tyndall Air Force Base

Dietary Items

Lead concentrations in invertebrates captured and seeds 

collected at Tyndall AFB were significantly greater (α = 0.05) 

than in the same matrices from SJB (fig. 16). At Tyndall AFB, 

the average lead concentration was greater in invertebrates 

collected by the pitfall traps (geomean = 39.7 ppm dw) than 

in those collected by the light traps (6.04 ppm dw). At SJB, on 

the other hand, Pb concentrations in invertebrates from pitfall 

traps (1.11 ppm dw) and light traps (0.65 ppm dw) approximated one another.

Birds

Seven different species were captured at Tyndall AFB 

during June and July 2016 and the 33 birds captured at SJB 

in August 2016 (table 6). Four species (northern cardinal, 

mourning dove, rufous-sided towhee, and Carolina wren) were 

captured at both Tyndall AFB and SJB.

Lead concentrations in blood and feathers were significantly greater (α = 0.05) for northern cardinals and mourning doves captured at Tyndall AFB than for those from SJB 

(figs. 17 and 18). Accordingly, δ-ALAD activity in blood was 

significantly lower (p<0.001) at Tyndall AFB (18.3 nM ALA/

min/mL RBC, SE = 3.26) relative to SJB (40.4 nM ALA/min/

mL RBC, SE = 3.68) (fig. 19).

tInspection of the radiographs of captured birds found no 

evidence of Pb particles. Many of the images revealed highdensity areas, but comparison with reference Pb pellets within 

each image indicated those areas were unlikely to be Pb pellets 

or fragments. Those high-density areas may have been grit 

within the digestive tract.

Table 6. Birds captured at Tyndall Air Force Base and St. Joe 

Bay Buffer Preserve, Florida.

Species Latin name Number 

captured

Tyndall Air Force Base

Northern cardinal Cardinalis cardinalis 16

Eastern towhee Pipilo erythrophthalmus 3

Mourning dove Zenaida macroura 14

Brown-headed cowbird Molothrus ater 3

Carolina wren Thryothorus ludovicianus 1

White-eyed vireo Vireo griseus 1

Brown thrasher Toxostoma rufum 2

St. Joe Bay Buffer Preserve

Northern cardinal Cardinalis cardinalis 10

Eastern towhee Pipilo erythrophthalmus 4

Mourning dove Zenaida macroura 12

Ovenbird Seiurus aurocapilla 1

Red-bellied woodpecker Melanerpes carolinus 2

Carolina wren Thryothorus ludovicianus 3

Red-winged blackbird Agelaius phoeniceus 1

Figure 16. Lead 

concentrations in dietary 

items (invertebrates and 

seeds) collected from Tyndall 

Air Force Base and St. Joe 

Bay Buffer Preserve, Florida. 

Lead concentrations in 

seeds and invertebrates from 

Tyndall Air Force Base were 

significantly greater (α = 0.05) 

than lead concentrations in 

invertebrates and seeds from 

St. Joe Bay Buffer Preserve.

Light traps

0.01

0.1

1

10

100

1,000

Lead concentration, 

in parts per million dry weight

Tyndall Air Force Base

St. Joe Bay Buffer Preserve

Pitfall traps

Tyndall Air Force Base

St. Joe Bay Buffer Preserve

Seeds

Tyndall Air Force Base

St. Joe Bay Buffer Preserve
Results—Tyndall Air Force Base 23

0.01

0.1

1

10

100

1,000 Lead concentration, in micrograms per deciliter

Northern cardinal - Tyndall AFB

Northern cardinal - SJB

Mourning dove - Tyndall AFB

Mourning dove - SJB

Eastern towhee - Tyndall AFB

Eastern towhee - SJB

Brown thrasher - Tyndall AFB

Brown-headed cowbird - Tyndall AFB

Carolina wren - SJB

Red-bellied woodpecker - SJB

Red-winged blackbird - SJB

Bird - sampling site

Figure 17. Lead 

concentrations in blood 

collected from birds captured 

at Tyndall Air Force Base 

(AFB) and St. Joe Bay Buffer 

Preserve (SJB), Florida. Lead 

concentrations for northern 

cardinals and mourning doves 

were significantly greater 

(α = 0.05) at Tyndall AFB than 

at SJB. (See table 6 for Latin 

names of birds)

0.01

0.1

1

10

100

1,000

Lead concentration, in parts per million dry weight

Northern cardinal - Tyndall AFB

Northern cardinal - SJB

Mourning dove - Tyndall AFB

Mourning dove - SJB

Eastern towhee - Tyndall AFB

Eastern towhee - SJB

Brown thrasher - Tyndall AFB

Brown-headed cowbird - Tyndall AFB

White-eyed vireo - Tyndall AFB

Carolina wren - Tyndall AFB

Carolina wren - SJB

Red-bellied woodpecker - SJB

Red-winged blackbird - SJB

Ovenbird - SJB

Bird - sampling site

Figure 18. Lead 

concentrations in feathers 

collected from birds 

captured at Tyndall Air 

Force Base (AFB) and St. 

Joe Bay Buffer Preserve 

(SJB), Florida. Lead 

concentrations for northern 

cardinals and mourning 

doves were significantly 

greater (α = 0.05) at Tyndall 

AFB than at SJB. (See 

table 6 for Latin names of 

birds)
24 Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17

0

20

40

60

80

100

Activity, in nanomoles aminolevulinic acid

per minute per milliliter of red blood cells

Northern cardinal - Tyndall AFB

Northern cardinal - SJB

Mourning dove - Tyndall AFB

Mourning dove - SJB

Eastern towhee - Tyndall AFB

Eastern towhee - SJB

Brown thrasher - Tyndall AFB

Brown-headed cowbird - Tyndall AFB

White-eyed vireo - Tyndall AFB

Carolina wren - SJB

Red-bellied woodpecker - SJB

Red-winged blackbird - SJB

Bird sampling site

Figure 19. δ-aminolevulinic acid dehytratase activity in blood collected from birds captured at Tyndall 

Air Force Base (AFB) and St. Joe Bay Buffer Preserve (SJB), Florida. Activity for northern cardinals 

and mourning doves was significantly lower (α = 0.05) at Tyndall AFB than at SJB. (See table 6 for Latin 

names of birds)

Risk Assessment

Lead contamination in blood samples from approximately 

20 percent of the birds captured at Tyndall AFB exceeded 

58 μg/dL, a contamination level suggested as the lowest 

observed adverse effect level for Pb effects in birds (Johnson 

and others, 2007) (fig. 13). Lead contamination in a similar 

proportion of birds exceeded 71 μg/dL, a suggested HC5 for 

effects in birds (Buekers and others, 2009). Lead concentrations in approximately 60 percent of the feathers sampled from 

birds captured at Tyndall AFB exceeded the concentration 

associated with reduced nestling survival and adverse effects 

in physiology and behavior (4 ppm dw; Burger and Gochfeld, 

2000; Tsipoura and others, 2011) (fig. 14). Except for Pb in 

feathers from one bird (Carolina wren), contamination in 

blood and feathers for birds from SJB did not exceed levels 

indicative of adverse effects.

Approximately 90 percent of the discrete soil samples 

from Tyndall AFB had Pb concentrations that exceeded the 

Eco-SSL for avian insectivores, 60 percent exceeded the EcoSSL for herbivorous birds, and 15 percent exceeded the EcoSSL for carnivorous birds (fig. 20). The geometric mean Pb 

concentration in Tyndall AFB soils (58.7 ppm dw) exceeded 

the Eco-SSL for insectivorous and herbivorous birds, but not 

the Eco-SSL for carnivorous birds. Lead concentrations in 

soils from SJB did not exceed any of the Eco-SSLs.

The assumption of maximal exposure for the most sensitive species at Tyndall AFB and SJB resulted in risk quotients 

greater than one. As a result, the likelihood of risk for birds at 

both areas was estimated (table 7). Risk likelihood was greater 

for birds foraging at Tyndall AFB than for birds foraging 

at SJB.
Results—Tyndall Air Force Base 25

0

10

20

30

40

50

60

70

80

90

100

0.1 1 10 100 1,000 10,000

Lead concentration, parts per million dry weight

Percentile

EXPLANATION

Tyndall Air Force Base

St. Joe Bay Buffer Preserve

Insectivore

Ecological Soil Screening Levels

Assessment areas

Herbivore

Carnivore

Figure 20. Lead concentrations in soils from Tyndall Air Force Base and St. Joe Bay Buffer Preserve, Florida. Vertical 

lines represent the Ecological Soil Screening Levels for insectivorous (11 parts per million dry weight [ppm dw]), 

herbivorous (46 ppm dw), and carnivorous (510 ppm dw) birds.

Table 7. Likelihood that daily exposure of birds to lead at Tyndall Air Force Base and St. Joe Bay Buffer Preserve, Florida, exceeds the 

lowest observed adverse effect level1.

Species Latin name

Likelihood that daily exposure to lead exceeds the lowest observed adverse 

effect level, in percent

Tyndall Air Force Base St. Joe Bay Buffer Preserve

Category 1 Category 2 Category 1 Category 2

Soil No soil2 Soil No soil2 Soil No soil2 Soil No soil2

Northern cardinal Cardinalis cardinalis 30.9 18.4 9.4 2.6 5.0 4.7 0.7 0.4

Eastern towhee Pipilo erythrophthalmus 30.9 18.5 9.5 2.7 5.0 4.7 0.6 0.4

Mourning dove Zenaida macroura 25.9 7.6 7.4 0.6 0.4 0.3 0.1 0.1

Carolina wren Thryothorus ludovicianus 34.0 22.4 11.1 4.1 7.5 6.9 1.2 0.7

1

Lowest observed adverse effect levels compiled by the U.S. Environmental Protection Agency (2005).

2

Risk likelihood without assumed incidental soil ingestion.
26 Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17

Discussion

Beale Air Force Base

The average Pb concentration in reference area soil 

(6.5 mg/kg) was lower than the average reported for soils 

in California (19.7 mg/kg; https://www.epa.gov/superfund/

usgs-background-soil-lead-survey-state-data), indicating that 

contamination in the reference area soils likely represents 

background levels. What is not clear, however, is Pb contamination in the suspect areas on a spatial scale larger than the 

remediated areas. The risk for birds estimated in this report 

assumes birds forage exclusively at locations with contamination levels represented by the present study. But it is expected 

that birds forage over a larger area, or multiple areas, where 

Pb contamination may differ from that assessed in the present study. If so, the actual risk for birds would differ from that 

predicted in the present study.

On the basis of the available information for Pb contamination in soils, average Pb concentrations in the dietary items 

did not parallel contamination in the soils. Despite D-Street 

soils being relatively contaminated by Pb, concentrations in 

dietary items were not the highest. The highest contamination of dietary items was found at Frisky Lake. Because Pb 

concentrations in the borrow pit soils were low, many of the 

sampled invertebrates may have been drawn from nearby areas 

where the Pb concentrations are elevated. Given the slope 

of the terrain from SR627/SR594a (Frisky Lake) towards an 

adjacent intermittent stream and seasonal wetland, a portion of 

the past and current Pb contamination may have been transported to the wetland area. Light traps at Frisky Lake drew 

the largest mass of invertebrates relative to traps elsewhere 

on Beale AFB, Beale reference area, Tyndall AFB, and SJB. 

Given the dry, uniform habitat elsewhere around the location where the traps were placed at Frisky Lake, the greater 

biomass likely was due to elevated productivity at the adjacent 

wetland and indicates that the wetland was also the source of 

the elevated Pb concentrations.

Lead contamination and δ-ALAD activity in the captured birds allude to potential differences in Pb availability 

between the reference and suspect areas. Lead concentrations 

in blood and feathers were greater, and δ-ALAD activity 

was lower, for birds from the suspect area. However, there is 

uncertainty in the interpretation of these differences. First, no 

single species was captured from the reference area and from 

the suspect area. Variation among species of dietary preferences (Moorman and others, 2007; EPA, 1993) and physiology 

could confound interpretation of any locational contribution 

to the contamination and enzyme activity levels. Most of the 

species captured in the suspect area (sparrows) in September 

were possible migrants that were not observed in the suspect 

or reference areas in June when reference area was sampled. 

Second, birds captured from the suspect areas were primarily 

from Bedspring Lake (fig. 3), which is part of the wetland area 

adjacent to Frisky Lake. The availability of Pb to birds foraging at D-Street and Warren Shingle Road is not clear from the 

present study.

The risk likelihood estimated for birds at Beale AFB and 

the reference area varied. Generally, the highest risk was estimated for Frisky Lake and the lowest for the reference area, a 

pattern that paralleled Pb concentrations in invertebrates. The 

contribution to risk from contamination in the invertebrates 

was also evident from the lack of risk for the Canada goose, 

for which the assumed dietary preference was 100 percent 

seeds (EPA, 1993). Risk would be minimal for birds that 

consumed primarily seeds and greater for birds that consumed 

a greater proportion of invertebrates. Given the significance of 

dietary preference to the estimated risk, the lack of knowledge 

about the true dietary composition for a focal bird species is a 

significant uncertainty in this risk assessment. Other than for 

the Canada goose, this risk assessment assumed the dietary 

preference of birds for invertebrates and seeds varied normally 

with a central tendency of 50 percent. In addition, the proportion of invertebrates and seeds consumed by the birds was 

assumed to vary inversely; as the proportion of one increased, 

the proportion for the other decreased. Under these assumptions, risk likelihood would increase as the dietary proportion 

made up of invertebrates increased. For several of the species 

for which risk was estimated (for example, western meadowlark, red-winged blackbird), the proportion of the diet made up 

of invertebrates was greater during the late spring and summer 

(that is, nesting season) than in the fall and winter (https://

www.allaboutbirds.org), indicating possible seasonal variation 

of risk. Another significant uncertainty in the risk assessment 

is the true level of incidental soil ingestion. Lead exposure 

owing to incidental soil ingestion resulted in greater than 

50 percent of the risk for birds (100 percent for the Canada 

goose) at the D-Street location and accounted for practically 

all the risk for Category 2 effects at D-Street. The contribution 

of soil ingestion to risk at Frisky Lake was not determined 

owing to the lack of data on overall soil Pb contamination. 

Beyer and others (1994) reported incidental soil ingestion rates 

for birds ranging from less than 2 to 30 percent of diet, which 

served as the basis for the risk estimates in the present study. 

Because most of those data were for ducks and sandpipers 

(none for passerine birds), the level of incidental soil ingestion 

for passerine birds and its contribution to the risk is unknown.

Greater risk likelihood was estimated for Category 1 

effects than for Category 2 effects. Category 1 includes 

effects on behavior, physiology, and biochemistry, whereas 

Category 2 includes effects on survival, reproduction, and 

growth. Therefore, there is a greater likelihood of changes in 

behavior, physiology, or biochemistry than in reproduction, 

growth, or survival. The reduction of δ-ALAD activity in what 

were apparently healthy birds supports this risk estimate. The 

Category 1 endpoints are generally more sensitive to toxicant exposure relative to effects in Category 2, which would 

explain the greater risk likelihood. However, the significance 

to populations or ecosystems of effects in Category 1 relative 

to Category 2 has been debated by regulators and by scientists 
Discussion 27

in the open literature. Organisms have a normal range of 

physiological activity that often is inadequately characterized 

prior to their measurement in environmental assessments, and 

they have compensatory mechanisms that allow them to survive, grow, or reproduce despite alterations of the Category 1 

endpoints (Hagger and others, 2006).

In summary, Pb contamination of dietary items at Beale 

AFB was sufficient to result in estimated risk likelihoods for 

birds of up to 35 percent. The risk likelihood was proportional 

to the consumption of invertebrates and incidental soil ingestion where Pb concentrations in soil are elevated. The paradox 

of low Pb concentrations in dietary items at D-Street despite 

elevated Pb concentrations in co-located soils ideally would be 

investigated further to reduce uncertainty in the risk estimation 

for that location. Lastly, the source of the greater Pb concentrations in invertebrates from Frisky Lake, which led to the 

elevated risk likelihood, also could be investigated.

Tyndall Air Force Base

Lead contamination was greater at Tyndall AFB than at 

SJB. Differences were evident for invertebrates, seeds, and 

soil, and for blood and feathers of bird species captured at the 

AFB and SJB. At the AFB, it is unknown why Pb concentrations in the invertebrates captured by the pitfall traps were 

greater than the concentrations in the invertebrates captured by 

the light traps. Although the internal Pb concentrations could 

be greater for invertebrates collected in the pitfall traps, some 

of the invertebrate species were captured by both the pitfall 

and light traps, indicating the that measured concentrations 

were not strictly internal. In addition, the analytical laboratory 

did not process the invertebrates to remove potential external 

contamination. Therefore, it is likely that the invertebrates 

captured by the pitfall traps were externally contaminated by 

soil-associated particles. Regardless, birds consuming soilassociated invertebrates will be incidentally ingesting soil 

particles and the associated Pb.

The elevated Pb concentrations at the AFB increased 

the exposure of birds to Pb and is likely adversely affecting birds. For the northern cardinal and mourning dove, Pb 

concentrations in blood and feathers were significantly greater 

at the Tyndall AFB than at SJB. Lead concentrations in blood 

and feathers of the rufous-sided towhee also were greater at 

Tyndall AFB, but the statistical significance of the difference 

was not evaluated because too few birds were captured at both 

locations. The elevated exposures to Pb paralleled significant 

depression of δ-ALAD activity for birds from the AFB relative 

to the same species at SJB. In fact, no activity was measured 

in the blood of a few birds captured at the AFB (northern cardinal, mourning dove, Toxostoma rufum [brown thrasher]). 

Foraging behavior, in addition to dietary preference, 

likely plays a significant role in risk for birds on the AFB. 

Greater risk would be expected for invertivorous birds than 

for to granivorous birds, given the greater Pb concentrations 

in invertebrates relative to seeds. The northern cardinal feeds 

predominantly on seeds and fruit but also consumes invertebrates (Halkin and Linville, 1999). The rufous-sided towhee 

is also omnivorous, consuming both seeds and invertebrates 

(Greenlaw, 2015). As a result, relatively elevated Pb concentrations in northern cardinal and rufous-sided towhee would 

be expected compared to a granivore. However, high Pb concentrations were measured in the predominantly granivorous 

mourning dove (Mirarchi, 1993). Because the doves predominantly forage on the ground for seeds, incidental ingestion 

of Pb-contaminated soil is possibly resulting in elevated Pb 

body burdens. Incidental soil ingestion is also possible for the 

northern cardinal and rufous-side towhee because they also 

forage on the ground. The brown thrasher largely consumes 

invertebrates and forages for them on the ground by probing 

the soils and leaf litter with its bill (Bent 1948). This foraging habit could lead to greater incidental soil ingestion rates 

relative to the other species, which may be the reason Pb 

concentrations in their feathers and blood are relatively high 

and δ-ALAD activity is relatively low. As a result, greater risk 

would be estimated for birds that forage on the ground for 

invertebrates.

Elevated risk likelihood was estimated for Tyndall AFB 

relative to SJB. The highest likelihood was for the Carolina 

wren (34.0 percent), whereas the lowest risk was for the 

mourning dove (25.9 percent). As was the case for risk estimates for birds at Beale AFB, removal of the assumption of 

incidental soil ingestion reveals its considerable significance 

to the risk estimation. Dietary preference also had a significant 

effect on the risk estimation. Risk was lowest for the predominantly granivorous mourning dove and highest for the largely 

invertivorous wren. Although lower risk likelihood was estimated for birds at SJB relative to the AFB, the likelihood of 

approximately 5 percent for Category 1 effects is ironic given 

the overall low Pb concentrations in the dietary items and 

soils. Two factors are likely responsible for the greater than 

expected risk. First, the Pb concentration in one of the pitfall 

trap samples was 459 mg/kg dw, which was the highest measured at any of the locations (SJB, Tyndall AFB, Beale AFB, 

and the Beale reference area). Second, the assumption for the 

distribution (log normal) of possible contamination levels in 

invertebrates at SJB along with the high Pb concentration in 

the one pitfall trap sample results in a skew towards greater 

Pb concentrations than those measured. As a result, a small 

proportion of the risk quotients estimated during Monte Carlo 

sampling of the distribution exceeded one.

In summary, Pb contamination of soils at the AFB is 

sufficient to raise Pb exposure for birds to the point that they 

might be adversely affected. This was supported by depressed 

δ-ALAD activity and predicted by the probabilistic risk 

assessment. However, risk is not likely to be uniform for all 

bird species as it will depend upon the dietary preferences and 

foraging behavior of the species.
28 Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17

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Bargar—Assessment of Bird Exposure to Lead at Tyndall and Beale Air Force Bases, 2016–17—Scientific Investigations Report 2018–5164

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20185164