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Abstract Oil production operations produce waste
fluids that may be stored in pits, open tanks, and other
sites accessible to wildlife. Birds visit these fluid-filled
pits and tanks (‘‘oil pits’’), which often resemble water
sources, and may become trapped and die. The US Fish
and Wildlife Service (USFWS) has a program to reduce
these impacts by locating problem pits, documenting
mortality of protected wildlife species, and seeking
cleanup or corrective action at problem pits with the
help of state and federal agencies regulating the oil
industry. Species identification and verification of pro-
tected status for birds recovered from oil pits are per-
formed at the USFWS National Fish and Wildlife
Forensics Laboratory. From 1992 to 2005, a minimum of
2060 individual birds were identified from remains
recovered from oil pits, representing 172 species from 44
families. The taxonomic and ecological diversity of
these birds indicates that oil pits pose a threat to virtually
all species of birds that encounter them. Ninety-two
percent of identified bird remains belonged to protected
species. Most remains identified at the Forensics Labo-
ratory were from passerines, particularly ground-for-
aging species. Based on Forensics Laboratory and
USFWS field data, oil pits currently cause the deaths
of 500,000–1 million birds per year. Although law
enforcement and industry efforts have produced genu-
ine progress on this issue, oil pits remain a significant
source of mortality for birds in the United States.
Keywords Bird mortality Æ Oil Æ Petroleum Æ
Contaminants Æ E&P wastes Æ Pollution Æ Law
enforcement Æ Forensics Æ Migratory Bird Treaty Act Æ
RCRA
Introduction
Petroleum production is accompanied by the produc-
tion of waste fluids. These fluids (often referred to in
the oil industry as ‘‘E&P waste,’’ for exploration and
production waste) are a mixture of water with a variety
of contaminants, comm only including drilling muds,
concentrated salts, hydrocarbons that were not re-
moved in the separation process, and trace amounts of
potentially toxic metals (EPA 2000, 2002). In many oil
production areas, these waste fluids are a major source
of environmental pollution and public health concern
(e.g., San Sebastia
´
n and Hurtig 2004).
Exposure to petroleum waste fluids may also be a
significant source of wildlife mortality. In the United
States, there are more than 500,000 oils wells currently
active (IPAA 2005). When the produced waste fluids
are stored in exposed pits or open-topped tanks
(hereafter, oil pits), they pose a potential hazard to
wildlife. Many U.S. oil production areas are located in
arid regions where open water is scarce, increasing the
attractiveness of oil pits both to waterbirds that land in
the fluid, and to terrestrial birds and other wildlife that
come to drink. Wildlife may also be attracted by food
items that are trapped on the marg ins and surface of oil
pits (Flickinger 1981; Grover 1983; Flickinger and
Bunck 1987).
Beginning in the 1950s, numerous studies have
documented significant wildlife mortality in oil pits:
P. W. Trail (&)
National Fish and Wildlife Forensics Laboratory,
US Fish and Wildlife Service,
1490 E. Main Street,
Ashland, Oregon 97520, USA
E-mail: pepper_trail@fws.gov
Environ Manage (2006) 38:532–544
DOI 10.1007/s00267-005-0201-7
123
PROFILE
Avian Mortality at Oil Pits in the United States: A Review of the
Problem and Efforts for Its Solution
Pepper W. Trail
Springer Science+Business Media, Inc. 2006
914 dead waterfowl in Wyoming (King 1956); 585
vertebrates in Colorado (Tully and Boulter 1970);
more than 1600 birds and mammals in California
(Thomas 1971); 469 birds in New Mexico (Grover
1983); 394 birds in coastal Texas (Flickinger 1981); and
616 birds in Wyoming (Esmoil and Anderson 1995).
Birds are by far the predominant vertebrate remains
recovered from oil pits (Grover 1983), and are the
focus of this report. Documentation of reptile and
mammal mortality in oil pits can be found in Grover
(1983), Flickinger (1981), Thomas (1971), Tully and
Boulter (1970), and Wood and Harrod (2000).
Causes of Mortality in Oil Pits
Exposure to oil causes avian mortality in a variety of
ways (Leighton 1993). Waterbirds that alight in oil pits
may drown or die of exposure after the loss of feather
insulation due to oiling (King 1956; Flickinger and
Bunck 1987). Birds that are trapped in viscous oil pit
fluids may ingest lethal amounts of oil in their struggles
to escape, or die of exposure or starvation (Grover
1983). Although this article concerns only direct mor-
tality at oil pit sites, exposure to toxic fluids in pits likely
causes additional mortality away from pits (Hartung
and Hunt 1966; Snyder and others 1973), as well as
reproductive impairment in birds that survive (Grau
and others 1977; Albers 1978; King and LeFever 1979).
Oil Pits an d U.S. Environmental Laws
Most waste fluids commonly stored in oil pits (E&P
wastes) are exempt from federal regulation as haz-
ardous wastes (EPA 2000). Still, the operators of
facilities with oil pits in the Uni ted States are subject to
regulation under federal wildlife protection and envi-
ronmental pollution laws (Judah 1997; USFWS 1998).
The most comprehensive wildlife law that may be
triggered by avian mortality in oil pits is the Migratory
Bird Treaty Act (MBTA), which prohibits the killing
(or ‘‘taking’’) of native North American migratory
birds. Examples of oil production activities that could
result in ‘‘take’’ are discharges of oil or hazardous
materials, and operation of oil pits that are accessible
to wildlife. Other laws that may be violated by avian
mortality in oil pits include the Endangered Species
Act (ESA), Bald and Golden Eagle Protection Act,
and, for non-migratory upland game birds (Gallifor-
mes), state wildlife management laws.
Enforcement of the MBTA is the responsibility of
the Office of Law Enforcement of U.S. Fish and
Wildlife Service (USFWS). Violations of the MBTA
carry penalties up to a $15,000 fine, or 6 months in jail,
or both, for each count (i.e., each dead bird of a pro-
tected species). There is no ‘‘allowable take’’ under the
MBTA, and, because it is a strict liability statute, the
government is not required to prove that an oil pro-
ducer knew that exposed waste fluids were taking
migratory birds. Although the MBTA provides for
fines and other penalties, it does not give USFWS the
power to compel pit owners to clean up problem sites
or to render them inaccessible to wildlife.
The Environmental Protection Agency (EPA) is
responsible for enforcement of pollution statutes that
apply to oil pits, including the Clean Water Act, the
Resource Conservation and Recovery Act (RCRA),
and the Oil Pollution Act of 1990 (EPA 2000). These
statutes empower EPA to alleviate threats to the
environment or human health caused by waste man-
agement operations, and allow for substantial fines for
violations. Section 7003 of RCRA is triggered if EPA
determines that either solid or hazardous waste is
present in a pit, and that the site poses an actual or
potential threat to human health and/or the environ-
ment (USFWS 1998). Documented avian mortality
demonstrates such an actual environmental threat.
RCRA requir es the violator to complete an EPA-ap-
proved workplan to correct the violations, and to do
the necessary work in the field. If these requirements
are not met, EPA can impose penalties of $6,500 per
day. EPA’s authority to require clean-up of oil pits
makes it a vital partner with USFWS in rendering these
sites safe for both human health and wildlife.
Law Enforcement Related to Wild life Mortality in
Oil Pits
Concerted law enforcement activities aimed at reducing
wildlife mortality in U.S. oil pits began in the late 1970s,
primarily in New Mexico and Texas (Grover 1983; Lee
1990). Much mortality was prevented as a result; for
example, Grover (1983) estimated that 225,000 birds a
year were saved from oil pits due to oil pit clean-ups on
Bureau of Land Management lands in New Mexico. An
early success was the elimination in 1978 of the practice
of pumping waste fluids into dry lake basins (playas) in
Texas, accomplished through negotiations between
USFWS, the U.S. Department of Justice, and Texas
state officials (Lee 1990). USFWS has continued oil pit
enforcement activities in Texas, Oklahoma, and New
Mexico since that time, in collaboration with state
agencies. These efforts have produced considerable
progress. For example, from 1999 to 2002 USFWS
Environ Manage (2006) 38:532–544 533
123
issued letters of noncompliance concerning more than
1800 oil pits and tanks in this three-state area, and
collected more than $194,000 in fines due to Migrator y
Bird Treat Act violations (USFWS 2002). Thes e funds
were all deposited in the North American Wetlands
Conservation Fund, as required by law.
In 1996, the Oil and Gas Environmental Assessment
(OGEA) team was formed in the northern Great
Plains and Rocky Mountain area, including the states
of North and South Dakota, Montana, Wyoming,
Colorado, and Utah (EPA 2003). The team was made
up of representatives from USFWS, EPA, the state oil
and gas agencies, the state environmental agencies,
tribal energy and environmental agencies, the Bureau
of Land Management, and the Bureau of Indian Af-
fairs. By 2002, the OGEA team had coordinated aerial
surveys of approximately 5000 pits (15–20% of the total
in the region), had conducted the ground inspection of
475 potential problem sites, and had completed 365
follow-up action s that corrected the problem identified
(EPA 2003).
In addition to these major coordinated efforts,
USFWS has carried out local oil pit inspection and
enforcement activities in virtually all oil-producing
areas of the United States since the 1990’s (e.g., Wood
and Harrod 2000). These efforts are ongoing.
Collection of Avian Remains from Oil Pits
Exposed oil pits that appear likely to pose a hazard to
wildlife were located by enforcement personnel of -
USFWS and cooperating agencies through aerial and/
or ground-based surveys (USFWS 1998; Wood and
Harrod 2000; EPA 2003). These ‘‘problem oil pits’’
were then visite d and inspection was made for wildlife
remains. Bird remains visible on the surface and
margins of oil pits were recovered and tagged. No
attempt was made to dredge ponds for remains that
might have sunk out of sight into the pit fluids. Most
oil pit inspections were made during the spring and
summer months, and most pits were visited only once.
Analysis and Identification of Remains
The determination that oiled bird remains belong to
protected species is prerequisite to enforcement action
by USFWS. Non-native birds, notably rock pigeon
(Columba livia), European starling (Sturnus vulgaris),
and house sparrow (Passer domesticus), are not
protected, and their death in oil pits does not trig-
ger U.S. federal or state wildlife laws. Successful law
enforcement also requires that bird remains recovered
from oil pits be treated as evidence, with strict chain-of-
custody procedures and analytical protocols for species
identification.
Since 1992, species identification of oiled bird re-
mains has been conducted at the USFWS National Fish
and Wildlife Forensics Laboratory. The laboratory’s
evidence-handling and analytical procedures meet the
strict forensic standards of the American Society of
Crime Lab Directors (ASCLD). Upon receipt at the
laboratory, each set of remains was assigned a tracking
number in the computerized laboratory evidence
inventory system, linked to the ‘‘seizure tags’’ filled out
at the time of collection by USFWS field personnel.
The items remained under seal in the Evidence Unit
freezers until they were transferr ed to the labora tory’s
ornithologist for analysis and identification.
Examination and cleaning were carried out under a
fume hood, using chemical safety precautions. Re-
mains ranged from oil-covered but otherw ise intact
carcasses to single bones or feathers. The most usual
remains were decayed partial carcasses, with heads and
tails often missing. The surrounding matrix varied from
brine with little obvious oil to solid blocks of tar. Oiled
remains sometimes exhibited sufficient species-diag-
nostic characters that they could be identified without
cleaning. In that case, notes were taken documenting
the diagnostic features observed (e.g., plumage pat-
tern), and a confirmatory reference standard from the
laboratory’s bird specimen collection was cited. Usu-
ally, however, cleaning of remains was required for
identification.
Before cleaning began, characteristics were noted
indicating the order or family to which the bird remains
belonged. These included body size and shape, and the
morphology of the beak and feet, if visible. This pre-
liminary evaluation was the basis for selecting parts for
cleaning. For example, if the remains resembled a
dove, a tai l feather was removed, whereas if the re-
mains resembled a duck, a secondary (speculum)
feather was selected, because those are distinctive
feathers for their respective groups.
The selected item was wiped to remove excess oil,
and was then placed in a bath of Stoddards Solvent
(petroleum distillate; Fisher Scientific). In most cases,
this solvent dissolved the oil residue and rendered the
plumage pattern visible. It was sometimes necessary to
gently brush the feather with a soft toothbrush to
loosen solid clumps of oil.
Once the oil residue was removed, the item was
washed in a bath of hot water and detergent. Feathers
typically emerged from this process with little physical
damage, although the concentrated brine found in
534 Environ Manage (2006) 38:532–544
123
some pits could destroy feather structure. Exposure to
oil commonly produced disc oloration of feather vanes,
imparting a yellowish tinge to white areas, but this
usually did not complicate identification. When the
cleaning was complete, the object was dried with
compressed air and was then ready for comparison
with specimen standards.
The Forensics Laboratory maintains a reference
collection of bird specimens, including prepared skins,
skeletons, and loose feathers. This collection includes
more than 6000 specimens and more than 950 bird
species. Species identification was made by detailed
comparison of cleaned feathers and/or bones with
known specimen standards. In addition to specimens,
reference works were consulted during the examina-
tion process, including Pyle (1997) and relevant spe-
cies accounts in the American Ornithologists’ Union
Birds of North America series. The authority for
avian taxonomy was the A.O.U. Checklist of North
American Birds (American Ornithologists Union
2005).
For each set of remains examined, the ornithologist
prepared laboratory bench notes documenting the
observed species-diagnostic characters and the speci-
men reference standards consulted. The cleaned re-
mains were documented with digital photography.
Examination and documentation procedures were
performed in accordance with ASCLD-approved
Forensic Laboratory protocols.
After identification, a forensic report was written for
the USFWS Special Agent in charge of the investiga-
tion. This stated the identity of the bird remains and, if
multiple remains of a given species were recovered
from a single pit, the minimum number of individuals
(MNI) present. MNI was calculated based on dupli-
cated elements recovered from the same pit, such as
skulls or left wings. MNI was used to determine the
number of wildlife law violati ons.
Patterns of Avian Mortality in Oil Pits
From August 1992 to June 2005 (the period covered
by this report), a minimum of 2060 individual bird
remains were recovered from oil pits and identified by
USFWS personnel. One hundred sixty-two of the re-
mains belonged to non-native bird species. All the
rest (1898, or 92% of the total) belonged to native
species protected under the MBTA or managed under
state game laws. These remains represented 172 bird
species from 16 orders and 44 families (Table 1).
Most of these species (154, or 90 %) were identified at
the National Fish and Wildlife Forensics Laboratory;
the remainder was identified by other federal and
state personnel.
Birds were recovered and identified from oil pits
in 21 states, stretching from Ohio to Californi a
(Table 1). Three states—Texas, Oklahoma, and Kan-
sas—accounted for more than 50% of the birds
identified from oil pits at the Forensics Lab (Table 2).
The wide disparity between states reflects both dif-
fering numbers of oil production facilities and differ-
ing intensity of oil pit enforcement efforts.
The threat posed by oil pits was not limited to par-
ticular taxonomic or ecological categories of birds.
Among the victims of oil pits were birds as large as
bald eagle (Haliaeetus leucocephalus) and as small as
kinglets (Regulus species); as insectivorous as yellow-
billed cuckoo ( Coccyzus americanus), as frugivorous as
cedar waxwing (Bombycilla cedrorum), and as grami-
nivorous as pyrrhuloxia (Cardinalis sinuatus); as aerial
as chimney swift (Chaetura pelagica) and as terrestrial
as greater roadrunner (Geococcyx californianus); as
dependent on forests as red-eyed vireo (Vireo olivac-
eus) and on deserts as cactus wren (Campylorhynchus
brunneicapillus). It appears that oil pits pose a hazard
to virtually every bird species that encounters them.
Information on the outcomes of encounters with oil
pits by birds is limited to opportunistic observations
(Flickinger 1981; Grover 1983); no systematic, quanti-
tative studies have been made. Such documentation
would be needed to asses s vulnerability to this hazard
among different ecological categories and species of
birds. Nevertheless, analyses of the identifications
made at the Forensics Lab reveal some broad patterns.
Remains of songbirds and related species (Passerifor-
mes) were the most common (62%) of all birds
recovered from oil pits (Table 3). The next most fre-
quently encountered group, the waterfowl (Anserifor-
mes), accounted for only 10% of remains. Passerines
were represented by 22 different families (Table 4).
The Emberizidae (sparrows and allies) and Icteridae
(blackbirds and allies) accounted for more than 50% of
passerine bird remains recovered (and one third of all
bird remains).
In terms of broad ecological categories, the most
frequent victims of oil pits were ground-feeding birds,
accounting for 63% of all remains (Figure 1). Ecological
categories were defined as follows:
Waterbirds = Pod-
icipediformes + Pelecaniformes + Anseriformes;
Wad-
ing Birds = Ciconiiformes (except Cathartidae) +
Charadriiformes + Gruiformes + Alcedinidae;
Birds of
Prey = Falconiformes + Strigiformes + Cathartidae;
Ground Feeders = Galliformes + Columbiformes +
Geococcyx + Colaptes + Alaudidae + Motacillidae +
Passeridae + Icteridae (except Icterus) + Emberizidae +
Environ Manage (2006) 38:532–544 535
123
Table 1 Bird taxa identified from remains recovered from oil pits
Order Family Species MNI States
Podicipediformes (n = 25)
Podicipedidae (n = 25)
Pied-billed grebe, Podilymbus podiceps 7 MI, IL, NM, TX
Eared grebe, Podiceps nigricollis 12 WY
Eared or Horned grebe (P. nigricollis or P. auritus)5WY
Unidentified grebe (Podicipedidae) 1 KS
Pelicaniformes (n = 3)
Phalacrocoracidae (n = 3)
Double-crested cormorant, Phalacrocorax auritus 3TX
Ciconiiformes (total = 86)
Ardeidae (total = 78)
American bittern, Botaurus lentiginosus 1NE
Great blue heron, Ardea herodias 59 MI, IL, KY, AL, AR, NE,
KS, TX, CO, NM, WY, UT, CA
Great egret, Ardea alba 3TX
Reddish egret, Egretta rufescens 1TX
Snowy egret, Egretta thula
a
n/a NM
Tricolored heron, Egretta tricolor
b
n/a TX
Little blue heron, Egretta caerulea 1AR
Cattle egret, Bubulcus ibis 3 KS, TX
Unidentified egret (Ardeidae) 1 TX
Green heron, Butorides virescens 4 IL, IN, AR
Black-crowned night-heron, Nycticorax nycticorax 4 AL, TX, NM, CA
Yellow-crowned night-heron, Nyctanassa violacea 1TX
Cathartidae (total = 8)
Turkey vulture, Cathartes aura 7 OK, TX
Black vulture, Coragyps atratus 1TX
Anseriformes (total = 213)
Anatidae (total = 213)
Black-bellied whistling-duck, Dendrocygna autumnalis 5TX
Fulvous whistling-duck, Dendrocygna bicolor 1TX
Greater white-fronted goose, Anser albifrons 1NE
Canada goose, Branta canadensis 1OH
Snow goose, Chen caerulescens
a
n/a NM
Wood duck, Aix sponsa 19 OH, IN, KY, AR, NE, KS, TX
Gadwall, Anas strepera 20 IL, MO, KS, OK, TX, CO, WY, UT, NM
American wigeon, Anas americana 5 OK, TX, WY, NM
Mallard, Anas platyrhynchos 13 OH, IL, KS, TX, WY, NM
Mottled duck, Anas fulvigula
b
n/a TX
Blue-winged teal, Anas discors 37 IN, NE, KS, TX, CO, WY
Cinammon teal, Anas cyanoptera
a
n/a NM
Unspecified teal (A. discors or A. cyanoptera) 5 CO, UT
Northern shoveler, Anas clypeata 25 OK, TX, CO, NM, UT
Northern pintail, Anas acuta 4 OK, TX, CO
Green-winged teal, Anas crecca 25 KS, OK, TX, NM, CO, WY, UT
Unspecified dabbling duck (Anas species) 19 OH, IL, MI, TX, KS, NM, CO, WY
Redhead, Aythya americana
c,d
n/a OK, TX
Ring-necked duck, Aythya collaris 6 TX, CO
Greater scaup, Aythya marila 1IL
Lesser scaup, Aythya affinis 11 MI, IL, TX, NM, CO
Unspecified scaup (Aythya species) 4 IL, KS, CO
Canvasback or redhead (Aythya vasilineria or A. americana)2OK
Bufflehead, Bucephala albeola 1MI
Common merganser, Mergus merganser 1CO
Hooded merganser, Lophodytes cucullatus 1CO
Ruddy duck, Oxyura jamaicensis 3 TX, NM
Unidentified waterfowl (Anatidae) 3 WY
536 Environ Manage (2006) 38:532–544
123
Table 1 Continued.
Order Family Species MNI States
Falconiformes (total = 48)
Accipitridae (total = 28)
Mississippi kite, Ictinia mississippiensis
a
n/a NM
Bald eagle, Haliaeetus leucocephalus 1CA
Northern harrier, Circus cyaneus 1WY
Harris’ hawk, Parabuteo unicinctus 1TX
Sharp-shinned hawk, Accipiter striatus 1TX
Cooper’s hawk, Accipiter cooperii 3 KS, OK, NM
Unspecified accipiter (Accipiter species) 2 TX
Swainson’s hawk, Buteo swainsoni 3 KS, OK
Red-tailed hawk, Buteo jamaicensis 16 MI, IL, MO, KS, OK, TX, NM, CO
Golden eagle, Aquila chrysaetos
a
n/a NM
Falconidae (total = 20)
American kestrel, Falco sparverius 18 IN, NE, KS, OK, TX, NM, CA
Peregrine falcon, Falco peregrinus
c
n/a TX
Prairie falcon, Falco mexicanus 2 OK, CO
Galliformes (total = 39)
Phasianidae (total = 5)
Ring-necked pheasant, Phasianus colchicus 4 NE, OK, TX, UT
Lesser prairie-chicken, Tympanuchus pallidicinctus
a
n/a NM
Helmeted guineafowl, Numida meleagris 1OK
Odontophoridae (total = 34)
Scaled quail, Callipepla squamata 2 OK, NM
Gambel’s quail, Callipepla gambelii 3TX
Northern bobwhite, Colinus virginianus 17 IL, KS, OK, TX
Unidentified quail (Odontophoridae) 12 TX, NM
Gruiformes (total = 9)
Rallidae (total = 9)
Virginia rail, Rallus limicola 1IL
Sora, Porzana carolina 1UT
Unidentified rail (Rallidae) 1 CA
Common moorhen, Gallinula chloropus
c
n/a TX
American coot, Fulica americana 6 IL, MO, OK, TX, NM
Charadriiformes (total = 55)
Charadriidae (total = 15)
Killdeer, Charadrius vociferus 15 MI, IL, IN, KS, TX, NM
Recurvirostridae (total = 4)
American avocet, Recurvirostra americana 4 TX, CO, UT
Scolopacidae (total = 22)
Lesser yellowlegs, Tringa flavipes 2 NE, NM
Solitary sandpiper, Tringa solitaria 2 KS, NM
Spotted sandpiper, Actitis macularia 1SD
Least sandpiper, Calidris minutilla
d
n/a OK
Unspecified ‘‘peep’’ sandpiper (Calidris species) 1 KS
Long-billed dowitcher, Limnodromus scolopaceus 1NE
Wilson’s snipe, Gallinago delicata 8 NE, KS, TX, CO, WY, UT
American woodcock, Scolopax minor 4 OH, KY, IL, KS
Unidentified sandpiper (Scolopacidae) 3 NE, WY
Laridae (total = 14)
Laughing gull, Larus atricilla 1TX
Herring gull, Larus argentatus 2AL
Ring-billed gull, Larus delawarensis 2 OH, OK
Unspecified gull (Larus species) 8 MI, CO
Black skimmer, Rynchops niger 1TX
Columbiformes (total = 117)
Columbidae (total = 117)
Rock pigeon, Columba livia 38 OH, MI, IN, IL, MO, KS, OK, TX, NM, CA
Mourning dove, Zenaida macroura 78 OH, IL, MO, NE, KS, OK, TX, CO, NM, CA
Unidentified dove (Columbidae) 1 OH
Environ Manage (2006) 38:532–544 537
123
Table 1 Continued.
Order Family Species MNI States
Cuculiformes (total = 38)
Cuculidae (total = 38)
Yellow-billed cuckoo, Coccyzus americanus 6 KY, KS, TX
Greater roadrunner, Geococcyx californianus 32 OK, TX, NM
Strigiformes (total = 106)
Tytonidae (total = 54)
Barn owl, Tyto alba 54 NE, KS, OK,TX, NM, CA
Strigidae (total = 52)
Eastern screech-owl, Megascops asio 9 KY, IL, KS, TX
Western screech-owl, Megascops kennicottii
d
n/a NM
Unspecified screech-owl (Megascops species) 3 TX, NM
Great horned owl, Bubo virginianus 31 KY, NE, KS, OK, TX, MT, CO
Barred owl, Strix varia 5 KY, AR, KS, OK, TX
Short-eared owl, Asio flammeus 1KS
Burrowing owl, Athene cunicularia 3 TX, NM, CA
Caprimulgiformes (total = 24)
Caprimulgidae (total = 24)
Lesser nighthawk, Chordeiles acutipennis 1TX
Common nighthawk, Chordeiles minor 18 OH, IL, MO, TX, NM
Unspecified nighthawk (Chordeiles species) 3 TX, NM
Whip-poor-will, Caprimulgus vociferus 1IL
Common poorwill, Phalaenoptilus nuttallii 1CA
Apodiformes (total = 4)
Apodidae (total = 4)
Chimney swift, Chaetura pelagica 4 NE, TX
Coraciiformes (total = 2)
Alcedinidae (total = 2)
Belted kingfisher, Ceryle alcyon 2 IL, TX
Piciformes (total = 13)
Picidae (total = 13)
Red-bellied woodpecker, Melanerpes carolinus
c
n/a TX
Golden-fronted woodpecker, Melanerpes aurifrons 3TX
Unspecified woodpecker (Melanerpes species) 3 IL, TX
Northern flicker, Colaptes auratus 7 NE, KS, TX, UT
Passeriformes (total = 1278)
Tyrannidae (total = 67)
Eastern phoebe, Sayornis phoebe 13 OH, IN, IL, KS, OK, TX
Say’s phoebe, Sayornis saya
a
n/a NM
Ash-throated flycatcher, Myiarchus cinerascens
a
n/a NM
Great Crested flycatcher, Myiarchus crinitus 1TX
Western kingbird, Tyrannus verticalis 19 NE, TX, NM
Eastern kingbird, Tyrannus tyrannus 10 IL, ND, NE, KS, TX
Scissor-tailed flycatcher, Tyrannus forficatus 2TX
Unspecified kingbird (Tyrannus species) 19 OK, TX, NM, CO
Unidentified flycatcher (Tyrannidae) 3 IL, KS, NM
Laniidae (total = 11)
Loggerhead shrike, Lanius ludovicianus 8 KS, OK, TX, NM, CA
Northern shrike, Lanius excubitor 2 KS, TX
Unspecified shrike (Lanius species) 1 NM
Vireonidae (total = 1)
Red-eyed vireo, Vireo olivaceus 1IL
Corvidae (total = 15)
Blue jay, Cyanocitta cristata 6KS
Western scrub-jay, Aphelocoma californica 3 NM, CA
Black-billed magpie, Pica hudsonia
e
n/a CO
American crow, Corvus brachyrhynchos 2 KY, TX
Chihuahuan raven, Corvus cryptoleucus 1NM
Unspecified crow (Corvus species) 3 AR, OK, TX
538 Environ Manage (2006) 38:532–544
123
Table 1 Continued.
Order Family Species MNI States
Alaudidae (total = 31)
Horned lark, Eremophila alpestris 31 IL, NE, OK, TX, MT, WY, CO, NM
Hirundinidae (total = 35)
Tree swallow, Tachycineta bicolor 6 IL, ND, NE, KS
Barn swallow, Hirundo rustica 27 IL, KY, KS, OK, TX, WY
No. rough-winged swallow, Stelgidopteryx serripennis 1KS
Unidentified swallow (Hirundinidae) 1 WY
Paridae (total = 3)
Juniper titmouse, Baeolophus griseus 2NM
Carolina chickadee, Poecile carolinensis 1KY
Sittidae (total = 1)
White-breasted nuthatch, Sitta carolinensis 1OK
Troglodytidae (total = 5)
Cactus wren, Campylorhynchus brunneicapillus 2 TX, NM
Carolina wren, Thryothorus ludovicianus 1OK
Bewick’s wren, Thryomanes bewickii 1TX
Rock wren, Salpinctes obsoletus 1KS
Regulidae (total = 1)
Unspecified kinglet (Regulus species) 1 MI
Sylviidae (total = n/a)
Unspecified gnatcatcher (Polioptila species)
c
n/a TX
Turdidae (total = 14)
Eastern bluebird, Sialia sialis 3 OH, TX, KS
Unspecified bluebird (Sialia species) 1 NM
American robin, Turdus migratorius 10 IL, NE, KS
Mimidae (total = 131)
Gray catbird, Dumetella carolinensis 2 NE, KS
Northern mockingbird, Mimus polyglottos 94 AL, KS, OK, TX, NM
Sage thrasher, Oreoscoptes montanus 25 WY, UT
Brown thrasher, Toxostoma rufum 6 IN, KS
Curve-billed thrasher, Toxostoma curvirostre 1TX
Unidentified thrasher (Mimidae) 3 TX, NM
Sturnidae (total = 42)
European starling, Sturnus vulgaris 42 MI, IN, IL, NE, KS, OK, CO, CA
Motacillidae (total = 1)
American pipit, Anthus rubescens 1CA
Bombycillidae (total = 1)
Cedar waxwing, Bombycilla cedrorum 1OK
Parulidae (total = 7)
Yellow warbler, Dendroica petechia 1KS
MacGillivray’s warbler, Oporornis tolmiei 1CA
Common yellowthroat, Geothlypis trichas 1KS
Yellow-breasted chat, Icteria virens 4 KY, CA
Emberizidae (total = 328)
Canyon towhee, Pipilo fuscus 1TX
Cassin’s sparrow, Aimophila cassinii 6 OK, TX, NM
Unspecified sparrow (Spizella species) 27 ND, TX, WY, NM
Tree sparrow, Spizella arborea 1KS
Vesper sparrow, Pooecetes gramineus 13 ND, NE, TX, NM, WY
Lark sparrow, Chondestes grammacus 11 KS, OK, TX, NM
Black-throated sparrow, Amphispiza bilineata 10 TX, NM
Lark bunting, Calamospiza melanocorys 140 NE, KS, OK, TX, CO, NM, WY
Savannah sparrow, Passerculus sandwicensis 11 OH, LA, ND, NE, KS, TX
Grasshopper sparrow, Ammodramus savannarum 2OK
Song sparrow, Melospiza melodia 21 OH, MI, IN, IL, KS, TX, CO, CA
Swamp sparrow, Melospiza georgiana 1IN
Unspecified sparrow (Zonotrichia species) 2 NE
White-crowned sparrow, Zonotrichia leucophrys 2 OK, CA
Dark-eyed junco, Junco hyemalis 2 KS, TX
Environ Manage (2006) 38:532–544 539
123
Table 1 Continued.
Order Family Species MNI States
Lapland longspur, Calcarius lapponicus 3 OK, MT
McCown’s longspur, Calcarius mccownii
a
n/a NM
Smith’s longspur, Calcarius pictus
a
n/a NM
Chestnut-collared longspur, Calcarius ornatus 1KS
Unidentified sparrow (Emberizidae) 74 OH,IL,KY, NE, KS, OK,
TX, WY, CO, NM
Cardinalidae (total = 58)
Northern cardinal, Cardinalis cardinalis 17 KS, OK, TX
Pyrrhuloxia, Cardinalis sinuatus 35 TX, NM
Unspecified bunting (Passerina species) 1 IN
Black-headed grosbeak, Pheucticus melanocephalus 2NM
Dickcissel, Spiza americana 3TX
Icteridae (total = 352)
Red-winged blackbird, Agelaius phoeniceus 44 IL, NE, KS, OK, TX, CO, WY
Unspecified blackbird ( Agelaius species) 6 CA
Unspecified meadowlark (Sturnella species) 179 ND, SD, NE, KS, OK,
TX, WY, CO, NM
Yellow-headed blackbird, X. xanthocephalus 2 NE, KS
Rusty blackbird, Euphagus carolinus 2 IL, ND
Brewer’s blackbird, Euphagus cyanocephalus 4CO
Unspecified blackbird ( Euphagus species) 4 TX
Common grackle, Quicalus quiscula 42 IN, KY, IL, MO, ND, NE,
KS, OK, TX, NM
Great-tailed grackle, Quiscalus mexicanus 2 NE, OK
Unspecified grackle ( Quiscalus species) 4 TX
Brown-headed cowbird, Molothrus ater 39 ND, NE, KS, OK, TX, CO
Unspecified cowbird (Molothrus species) 2 OK, TX
Bullock’s oriole, Icterus bullockii 1NM
‘‘Northern oriole,’’ Icterus galbula or I. bullockii 1NM
Orchard oriole, Icterus spurius 1TX
Unspecified oriole (Icterus species) 16 KS, TX, NM
Unidentified blackbird (Icteridae) 3 KS, NM, CA
Fringillidae (total = 22)
Unspecified rosy-finch (Leucosticte species) 7 WY
House finch, Carpodacus mexicanus 8 NM, CA
Unspecified finch (Carpodacus species) 3 IL
American goldfinch, Carduelis tristis 4 IL, KS
Passeridae (total = 77)
House sparrow, Passer domesticus 77 IN, IL, ND, NE, KS,
OK, TX, CO, CA
Unidentified passerines (not consistent with
Sturnus or Passer) (total = 75)
Grand total = 2060
Identifications were made by staff at the National Fish and Wildlife Forensics Laboratory, unless noted by a superscript. Total = 172
unique taxa (species and taxa that were never identified below the genus level; e.g. meadowlarks, Sturnella sp.). MNI = minimum
number of individuals in oil pit remains analyzed at the National Fish and Wildlife Forensics Laboratory, 1992–2005. n/a = MNI data
not available (analyses not carried out at the Forensics Laboratory)
Data sources for bird taxa identified by authorities other than the National Fish and Wildlife Forensics Laboratory
a
Grover, V. L. 1983. The reduction of wildlife mortality in the sump pits of southeast New Mexico. Report for the Bureau of Land
Management, Carlsbad, New Mexico
b
Flickinger, E. L. 1981. Wildlife mortality at petroleum pits in Texas. Journal of Wildlife Management 45:560–564
c
Lee, R. C. Jr. 1994. Migratory bird kills at petroleum pits in Texas. Report of Investigation No. 120, U.S. Dept. of Interior, U.S. Fish
and Wildlife Service, Division of Law Enforcement, Lubbock, Texas
d
McKay, T. 2002. Environmental contaminants program, off-refuge investigations sub-activity. FY 2002 final report. TX, OK, NM —
oilfield pollution. Project ID: 2F37,9920006.2. U.S. Dept. of Interior, U.S. Fish and Wildlife Service, Division of Law Enforcement,
Oklahoma City, Oklahoma
e
Ramirez, P. Jr., and G. G. Mowad. Personal communication
540 Environ Manage (2006) 38:532–544
123
Cardinalidae (except Pheucticus) + Fringil lidae + Cor-
vidae + Laniidae + Mimidae + Turdidae + Sturnidae;
Arboreal Feeders = Coccyzus + Melanerpes + Bomby-
cillidae + Parulidae + Regulidae + Paridae + Sittidae +
Troglodytidae + Vireonidae + Icterus + Pheucticus; and
Aerial Feeders = Caprimulgiformes + Apodiformes +
Tyrannidae + Hirundinidae. The total number of
identified remains in Figure 1 is 1985 (2060 remains
identified to protected category minus 75 passerines that
were not identified at the family level).
Table 2 Oiled bird remains identified at the National Fish and
Wildlife Forensics Laboratory, summarized by state
State MNI
Alabama 10
Arkansas 10
California 60
Colorado 114
Illinois 123
Indiana 32
Kansas 285
Kentucky 18
Louisiana 1
Michigan 34
Missouri 12
Montana 12
Nebraska 62
New Mexico 159
Ohio 35
Oklahoma 432
North Dakota 19
South Dakota 26
Texas 432
Utah 15
Wyoming 169
Total 2060
MNI = minimum number of individual birds
Table 3 Oiled bird remains identified at the National Fish and
Wildlife Forensics Laboratory, summarized by avian order
Order MNI Percent
Podicipediformes 25 1.2%
Pelecaniformes 3 0.1%
Ciconiiformes 86 4.2%
Anseriformes 212 10.3%
Falconiformes 46 2.2%
Galliformes 39 1.9%
Gruiformes 9 0.4%
Charadriiformes 55 2.7%
Columbiformes 117 5.7%
Cuculiformes 38 1.8%
Strigiformes 106 5.1%
Caprimulgiformes 24 1.2%
Apodiformes 4 0.2%
Coraciiformes 2 0.1%
Piciformes 13 0.6%
Passeriformes 1278 62.0%
Total 2060
MNI = minimum number of individual birds
Table 4 Oiled passerine remains identified at the National Fish
and Wildlife Forensics Laboratory, summarized by family
Family MNI Percent
Alaudidae 31 2.4%
Bombycillidae 1 < 0.1%
Cardinalidae 58 4.5 %
Corvidae 15 1.2%
Emberizidae 328 25.7%
Fringillidae 22 1.7%
Hirundinidae 35 2.7%
Icteridae 352 27.5%
Laniidae 11 0.9%
Mimidae 131 10.3%
Motacillidae 1 < 0.1%
Paridae 3 0.2%
Parulidae 7 0.5%
Passeridae 77 6.0%
Sylviidae n/a n/a
Regulidae 1 < 0.1%
Sittidae 1 < 0.1%
Sturnidae 42 3.3%
Troglodytidae 5 0.4%
Turdidae 14 1.1%
Tyrannidae 67 5.2 %
Vireonidae 1 < 0.1%
Unknown 75 5.9%
Total 1278
MNI = minimum number of individual birds
Fig. 1 Oil pit mortality by general ecological category, for the
bird remains identified at least to the family level at the forensics
lab (n = 1985 remains). See text for description of taxa included
in each ecological category. Sample sizes as follows: water-
birds = 241 remains; wading birds = 144 remains; birds of
prey = 162 remains; ground feeders = 1256 remains; arboreal
feeders = 52 remains; and aerial feeders = 130 remains
Environ Manage (2006) 38:532–544 541
123
Four of the top five species recovered from oil
pits were ground-feeding passerines, na mely, mead-
owlark (Sturnella species), lark bunting (Calamospiza
melanocephala), northern mockingbird (Mimus poly-
glottos), and house sparrow (Passer domesticus); the
fifth was the ground-feeding mourning dove (Zenaida
macroura). The majority of inspected oil pits were
located in open, semiarid habitats with few trees
(USFWS field staff, personal communication). This
likely contributed to the low numbers of arboreal birds
recovered from oil pits (Figure 1).
Birds dependent on water for foraging (waterbirds
and wading birds) made up a small proportion (19%)of
all avian oil pit mortalities (Figure 1). Indeed, the
proportion of waterbirds recovered from oil pits ap-
pears to be decreasing. Between 1992 and 1996, water
and wading birds compr ised 27% of the oiled bird
remains identified at the Forensics Lab. From 1998 to
2005, they comprised only 14% (no oil pit remains were
identified at the laboratory in 1997 due to staff turn-
over). This trend may reflect continuing success in
reducing the size of oil pits.
Avian mortality increases linearly with oil pit sur-
face area (Esmoil and Anderson 1995). Large, lake-
like oil pits formerly attracted large numbers of ducks
(Gregory and Edwards 1991), but the use of such sites
has now been largely eliminated (Lee 1990). The typ-
ical oil pit today is a far smaller, pool-like site. Surveys
of oil pits in Texas in the early 1980s yielded average
pit sizes of 1208 m
2
in coastal areas and 372 m
2
in
northwestern Texas (Flickinger and Bunck 1987). In
contrast, 19 stora ge sites inspected in west Texas from
1999–2002 ranged from 0.56 to 372 m
2
, with a mean of
45.6 m
2
(USFWS 2002). These smaller pits appear to
draw fewer waterfowl, but still attract passerines and
other nonaquatic birds.
Prior Estimates of Avian Mortality in Oil Pits
Several regional and national estimates of direct avian
mortality in oil pits have been made. Grover (1983)
estimated an annual mortality of 450,000 vertebrates at
oil pits in southeastern New Mexico from the 1950s to
1981, when a cleanup effort was launched. Birds rep-
resented more than 90% of this mortality, based on
identified remains. Lee (1990:444) stated that annual
bird mortality from oil pits in Oklahoma, Texas, and
New Mexico ‘‘easily exceeded 300,000 birds, including
100,000 ducks’’ in the late 1980s. Banks (1979:12)
extrapolated from a 1970s annual mortality estimate of
150,000 in California’s San Joaquin valley to make a
‘‘very conservative’’ estimate of 1.5 million birds killed
in oil pits nationwide each year.
For many years, USFWS estimated bird mortality
in oil pits at approximately 2 million per year (e.g.,
Ramirez 1999). Due to progress that has been made on
the oil pit problem through enforcement activities and
industry compliance, that estimate is no longer consid-
ered valid (EPA 2003). Gi ven that enforcement activi-
ties continue to document avian mortality at oil pits, it is
important to estima te the current extent of the problem.
Estimating Current Annual Avian Mortality in Oil Pits
Earlier nationwide estimates of avian oil pit mortality
were based on extrapolations of data from specific areas,
without discussion of underlying assumptions. This
article presents a more explicit process of estimation,
which may spur efforts to address the data gaps that
remain.
There appear to be no published data on the number
of oil pits in the United States. Most drilling sites have
at least one pit for storage of waste fluids, including
produced water and drilling muds, and some wells have
multiple pits for different E&P wastes (EPA 2000,
2002). Therefore, I assumed that each of the nation’s
approximately 500,000 onshore oil wells had one
associated oil pit.
These calculations further assume that 80% of the
nation’s oil pits pose no threat to wildlife. This value is
based on data from aerial surveys in the northern
Great Plains and Rocky Mountains (EPA 2003). This
produces an estimate of approximately 100,000 pits
deserving of inspection nationwide (0.20 · 500,000
wells producing oil). The average rate of avian mor-
tality at inspected pits from 1996 to 2002 across a broad
area of the western United States was 0.30 birds/
inspection (Table 5). Therefore, it is expected that
30,000 dead birds would be recovered if all question-
able oil pits were subjected to a one-time inspection
(100,000 pits · 0.3 birds/pit).
Single inspections reveal only a small fraction of the
annual avian mortality in an oil pit. Many oiled bird
remains are removed by scavengers, and others sink
out of sight over time (Grover 1983). In a study of
Texas oil pits, Flickinger and Bunck (1987) determined
that the average sinking time for passerines in the
warmer months was only 4 days. They recommended
that pits be inspected at least once a week to document
all passerine mortality in summer, with inspections at
least every 3 weeks in winter.
Based on these studies, I propose that the following
inspection schedule would be needed to document
542 Environ Manage (2006) 38:532–544
123
most avian mortality in oil pits: one inspection per
month from November to February; two inspections
per month in March, April, September, and October;
and four inspections per month in May, June, July, and
August. This totals 28 inspections per year. The most
northern states might need no inspections at all from
November through February or March, but the
southern states might need even more than indicated
on this schedule.
One-time inspections of all questionable oil pits in the
United States would yield the remains of approximately
30,000 birds, as calculated above. Thus, a full schedule of
28 inspections per year is predicted to yield a total an-
nual mortality of approximately 840,000 birds (30,000
birds · 28 needed inspections). The toll among pro-
tected birds is estimated at 772, 800 per year, given
Forensics Lab data that 92% of oiled bird remains
belong to protected species.
Clearly, this is a rough calculation. Still, it provides
grounds for concluding that the current annual mor-
tality at oil pits is in the range of 500,000–1 million
birds. That is a considerable decline from the former
mortality estimate of 2 million birds per year, made
prior to concerted enforcement efforts. This is an
encouraging indication that enforcement and proactive
industry compliance have indeed reduced avian mor-
tality in oil pits in the United States. Nevertheless,
even the lower-end estimate of 500,000 birds is a very
high annual toll for a human-caused, preventable
source of mortality on U.S. native birds. It compares,
for example, to an estimate of 250,000 birds killed as a
result of the Exxon Valdez oil spill (Piatt and Ford
1996), which is generally considered to be one of the
greatest environmental disasters of recent times.
Protecting Wildlife from Oil Pits
The goal of USFWS and cooperating agencies is to
render oil production waste fluids inaccessible to wild-
life and humans, and to isolate them from groundwater
supplies. The best permanent solution is the replace-
ment of oil pits with closed tanks or other closed
containment systems. When properly designed and
installed, such systems require little or no maintenance
and eliminate the possibility of soil contamination
(USFWS 2003).
If open pits are retained, they need to be enclosed
with netting to exclude wildlife. Deterrent methods,
including flagging, strobe lights, reflectors, and noise-
makers, do not reduce avian mortality in oil pits
(Esmoil and Anderson 1995). Sturdy, well-installed
netting is highly effective at excluding birds. Such
netting should be suppo rted by a steel frame and
provide complete enclosure. Netting requires mainte-
nance and monitoring to assure that it remains effec-
tive under all conditions. For example, weakly
supported netting may sag into oil pits under the
weight of snow, destroying its ability to exclude wild-
life. Detailed information on effective netting solu-
tions, with photographs, can be found at the website
for the Environmental Contaminants Program of Re-
gion 6 of the Fish and Wildlife Service (USFWS 2003).
Through a combination of law enforcement, educa-
tion, and cooperation with industry, progress continues
to be made in eliminating oil pits that threaten wildlife.
Still, further efforts are needed. The level of noncom-
pliance to wildl ife protection and environmental pol-
lution laws remains too high. Further work by both
government agencies and the oil industry is needed to
Table 5 Results of two recent oil pit inspection efforts by the Fish and Wildlife Service and Environmental Protection Agency
a
Locality No. pits inspected Pits with avian mortality No. of bird mortalities
Colorado 96 20 89
Montana 169 9 47
North Dakota 56 3 7
South Dakota 16 8 38
Utah 115 2 2
Wyoming 347 33 137
Kansas 360 74 183
Nebraska 74 32 140
Subtotals 1233 181 (14.6%) 643
So. New Mexico 280 16 150
Oklahoma 1374 31 81
Texas 537 48 151
Subtotals 2191 95 (4.3%) 382
Grand Totals 3424 276 1025
a
Data from northern Great Plains and Rocky Mountain states from EPA (2003); data from Oklahoma, Texas, and New Mexico from
USFWS (2002)
Environ Manage (2006) 38:532–544 543
123
eliminate this significant, preventable, and illegal
source of avian mortality in the United States.
Acknowledgments This article is based on the work of Special
Agents of the U.S. Fish and Wildlife Service Office of Law
Enforcement, who perform the difficult and essential tasks of
inspecting oil pits and recovering bird remains. In particular, I
wish to thank Special Agents K. Garlick, R. C. Lee, Jr., T.
McKay, M. Medina, S. Middleton, and G. Mowad for their
leadership in this area and for providing unpublished reports.
P. Ramirez, Jr., of the U.S. Fish and Wildlife Service Environ-
mental Contaminants Program and R. Lamdin of the U.S.
Environmental Protection Agency RCRA Program provided
useful information and advice. R. C. Laybourne and B. A. Sabo
developed the feather cleaning methods used at the Forensics
Laboratory and contributed to the identification database re-
ported here. G. Espinoza, L. Saturen, and M. E. Sims assisted
with the cleaning and identification of oiled bird remains.
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