Vertebrate Pest Conference Proceedings collection

Proceedings of the Fourteenth Vertebrate Pest

Conference 1990

University of Nebraska - Lincoln Year 

EFFECTS OF FIELD VERTEBRATE

PEST CONTROL ON NONTARGET

WILDLIFE (with emphasis on bird and

rodent control)

E.E. Littrell

California Department of Fish and Game, Pesticide Investigations

Unit

This paper is posted at DigitalCommons@University of Nebraska - Lincoln.

http://digitalcommons.unl.edu/vpc14/55
EFFECTS OF FIELD VERTEBRATE PEST CONTROL ON NONTARGET WILDLIFE (with 

emphasis on bird and rodent control)

E. E. LITTRELL, California Department of Fish and Game, Pesticide Investigations Unit, 1701 Nimbus Road, Suite F, 

Rancho Cordova, California 95670.

ABSTRACT: Vertebrate pest control measures may have an impact on nontarget wildlife. Bird and rodent control programs 

using avicides and rodenticides in California have been, and are currently being, examined by the California Department of Fish

and Game on a routine basis. Each pesticide used has its deleterious side effects. This paper reviews these side effects and 

suggests possible future impacts which could be expected.

Proc. 14th Vertebr. Pest Conf. (L.R. Davis and R.E. Marsh, Eds.) 

Published at Univ. of Calif., Davis. 1990.

The California Department of Fish and Game is 

responsible for protecting the fish and wildlife of our state. 

It is the objective of the Department of Fish and Game to 

prevent the loss of wildlife from the effects of pesticides and 

to see that the habitat upon which fish and wildlife depend is 

not adversely affected. The Department does not endorse the 

use of any pesticide. However, we know that pesticides in 

various forms are generally acceptable and are being used for 

many purposes. Recognizing that pesticides are going to be 

used, we recommend that materials least hazardous to fish 

and wildlife are employed.

The California Department of Fish and Game (CDFG) 

organized our present investigatory unit in 1956 by 

establishing an Economic Poisons Section in its Game 

Management Branch. The Pesticide Investigations Unit is 

now located organizationally in the Environmental Services 

Division of the Department. The major duties of the unit are 

to prevent pesticide-caused adverse fish and wildlife effects by 

assessment of new pesticides or formulations, review of 

current pesticide uses for adverse effects, and by investigation 

of pesticide-caused fish and wildlife losses. As part of this we 

review all uses of pesticides, including bird and rodent control 

activities, especially since these use vertebrate pest control 

materials potentially hazardous to nontarget wildlife.

The mid-Seventies saw an increased awareness of "the 

environment." Because of this, legislation was introduced in 

1975 at the state level to prohibit the use of avicides and 

rodenticides that could kill or injure threatened or endangered 

animals. This bill was vetoed by the Governor. However, he 

did ask the Departments of Food and Agriculture and Fish 

and Game to develop a workable legislative proposal on this 

issue. The directors of the two departments appointed a 

committee to comply with the Governor's request to seek a 

practical solution. A joint policy statement between the two 

departments and the California Agricultural Commissioners' 

Association was the result. The CDFG entered into this 

agreement in 1977 with the California Department of Food 

and Agriculture and the California Agricultural 

Commissioners’ Association to review the counties' vertebrate 

pest control programs for impacts to threatened or 

endangered vertebrates. This is the basis for our current 

relationship, including review of materials and methods for 

impacts to all species of fish and wildlife.

Prior to this, the concern for protection of nontarget 

wildlife goes back quite a ways. A paper published in our 

scientific quarterly, "California Fish and Game" (Pierce and 

Clegg 1916), describes tests to determine if strychnine sulfate

was hazardous to California quail (Callipepla californica). It 

was determined that field applications would not be 

hazardous. This was in 1916. This type of issue is still being 

debated in the strychnine reregistration proceedings. In 1952, 

a short time after sodium monofluoroacetate (compound 

1080) was developed for field use, tests were run by the 

CDFG to determine clinical signs in California quail exposed 

by gavage to solutions of 1080 (Sayama and Brunetti 1952). 

Clinical signs were not definitive, but, again, it was found not 

to be hazardous to this species when used on a grain bait.

A more recent history of CDFG tests done with 

rodenticides would include telemetry of San Joaquin kit fox 

(Vulpes macrotis mutica) in areas where 1080 was being used 

for California ground squirrels (Spermophilus beecheyi), 

monetary support of tests conducted by the University of 

California on the effects of 1080 on turkey vultures (Cathartes

aura) as a surrogate for California condors (Gymnogvps 

californianus). incident monitoring to determine the cause of 

death of animals reported dead during pest control programs, 

and many field trips to review actual routine applications of 

rodenticides and avicides, especially in the 1970s when 

endangered species were first so classified.

RANKING OF THE HAZARD OF VARIOUS 

PESTICIDES USED AS CONTROL METHODS

Based on my experience in 10 years of review of 

vertebrate pest control methods using pesticides, I suggest the 

following ranking of the hazards of methods currently used, 

from least to most hazardous.

10, 9, 8. Starlicide, Avitrol, and poison perches. These 

have a small possibility of a secondary hazard to scavengers or 

predators such as peregrine falcons (Falco peregrinus) 

(Schafer 1984). We occasionally receive calls about this 

potential hazard in areas where the falcon has been 

reintroduced, such as in the bigger cities or high rises. We 

have no documentation of secondary poisoning with these 

materials. We usually recommend against the use of avicides 

in areas peregrine falcons are foraging so that a wide margin 

of safety is provided for this endangered species.

7, 6. Gas cartridges and aluminum phosphide. These 

are obviously hazardous to commensal animals such as 

Alameda whipsnakes (Masticophis lateralis euryxanthus), 

possibly giant garter snakes (Thamnophis couchi gigas), and 

burrowing owls (Athene cunicularia). Burrows should be 

checked for signs of owl or snake activity before using any 

kind of burrow fumigant. We have no documentation of 

adverse effects in our files.

59
5. Zinc phosphide. This can be hazardous for 

gallinaceous birds such as quail and pheasants (Phasianus 

colchicus). The U.S. Fish and Wildlife Service allows its use 

as an alternative to 1080 in areas inhabited by endangered 

mammals since it is not secondarily hazardous. We do have 

documentation in our files of adverse effects some years ago 

where quail were impacted. There have been no records in 

recent years of problems. We did become concerned a 

couple of years ago when a proposal was made to use zinc on 

a nonstandard seed bait for commensal rats in rice. The 

program did not develop to any degree and no adverse 

impacts were reported.

4. M-44 sodium cyanide ejector device. This has killed 

a California condor in field use. The U.S. Fish and Wildlife 

Service has developed modifications of its use to prevent any 

future similar losses. The ejectors are now hidden under 

some kind of available cover to exclude them from the view 

of sight-feeding condors in anticipation of the return of 

condors to the wild.

3. Sodium monofluoroacetate (compound 1080). As you 

might imagine, the unit has quite a bit of file material on this 

rodenticide. We have conducted many field surveys over the 

years to investigate this subject. An especially large effort was 

forwarded in the Sixties and Seventies when an interest in 

what are now classified as endangered species developed. In 

over two dozen field trips and related investigations only four 

or five relatively minor incidents with nontarget wildlife such 

as corvids and blackbirds have been seen to date. Magpies 

(Pica sp.) seem especially sensitive. There are no records in 

our files of significant mammalian kills except for obvious 

misuses for illegal predator control. Some researchers have 

expressed an opinion that compound 1080 may have an 

impact in reduction of the food supply (ground squirrels) for 

predators. Ten-eighty seems to be relatively nonhazardous for 

scavenging raptorial birds based on our records and laboratory 

studies such as those conducted by UCD on vultures. We do 

not see losses of raptors with legal uses. Both bird and 

mammal losses will occur if it's used illegally for predator 

control. Illegal applications are likely to be at much higher 

dosages than those normally used for rodent control.

2. Diphacinone/chlorophacinone. Both mammals and 

birds have been affected by primary and secondary exposure 

in laboratory tests (Evans and Ward 1967; Mendenhall and 

Pank 1980). These and other laboratory experiments indicate 

a potential field hazard is present when using anticoagulants. 

We are starting to now receive animal submissions at our 

laboratory which show physical signs suggestive of 

anticoagulant poisoning. The circumstances of the losses as 

described by the field investigators are also suggestive. The 

signs we look for and have seen include the finding of 

different species of animals found dead together, such as 

carnivores and herbivores, their presence near water (a sign 

of dehydration typical of anticoagulant poisoning), and 

hemorrhage seen at necropsy. Residue analyses are difficult 

to perform using current technology. The finding of signs and 

residues together is rare but a cooperating laboratory did 

recover residues of diphacinone in one case we examined 

(Littrell 1988). The difficulty of performing residue analyses 

seems to be common throughout the U.S. as confirmed by 

personal communication with other researchers in the field. 

This seems to be at least partially attributable to the 

metabolism of the anticoagulants. They may be metabolized 

over time so that death occurs after the parent compound is

gone. Instances of misuse by inappropriate placement or the 

use of a material not registered for field use are starting to 

come to our attention. I ask those of you using these 

materials to exercise great care in their placement to avoid 

exposure to nontarget wildlife.

1. Strychnine. This material is probably the worst 

because of its toxicity to a variety of species and because of 

its secondary persistence. We have no firm records of 

secondary or nontarget effects from small bird control, 

however. The problems have been due to exposure to 

strychnine used for rodent control, either ground squirrels or 

gophers (Thomomys sp.). Exposures have been both primary 

and secondary. There have been problems with secondary 

poisoning of predatory and scavenging birds. For instance, we 

have a documented case of Canada geese (Branta Canadensis) 

being killed by spillage of a gopher (Thomomys sp.) bait 

formulation used at a park, and of at least one golden eagle 

(Aguila chrysaetos) killed by consumption of poisoned 

Belding's ground squirrels (Spermophilus beldingi). A bald 

eagle (Haliaeetus leucocephalus) was killed by ingestion of a 

Belding's ground squirrel in an area strychnine was being used 

for gopher control. We have also had cases of misuse when 

strychnine was being used illegally to kill or repel black bears 

(Ursus americanus) attacking bee hives.

As strychnine and 1080 are phased out and become 

unavailable, the anticoagulants will take their places as the 

most hazardous vertebrate pest control agents. We will see 

problems with their use and I am sure nontarget wildlife will 

be affected. Please follow labels very closely to avoid killing 

nontarget wildlife. We especially anticipate nontarget wildlife 

will be killed by improper placement of baits. This might 

happen by not using a bait box or by piling material in a 

mound. Illegal use for predator control will also be a 

problem. Even normal application methods are potentially 

hazardous because of residues found in carcasses. I expect to 

see more raptors come in with circumstantial signs of this type 

poisoning. We already have received a few.

As a sort of postscript of concluding remarks I would like 

to add the following. In researching our files for this 

presentation I came across an Administrative Report which 

was titled "A Review of the Use of Toxic Materials for 

Mammalian Animal Control in California" (Hagen 1972). 

This report was written in 1972, almost 20 years ago. I 

almost could have used it for my presentation today. I would 

like to leave you with two thoughts from the report. The first 

was the statement that federal registration for the use of 

compound 1080 for rodent control will be withdrawn within 

5 years and that restrictions on the use of strychnine for 

rodent control may soon follow. This was in 1972, remember. 

The second was the thought that if compound 1080 becomes 

unavailable, rodent control may revert back to the ranchers 

and they will use strychnine and zinc phosphide. (I will add 

parenthetically here that now it probably will be anticoagulants 

that are used.) Paraphrasing again: lack of training in 

control methods or handling of hazardous materials by 

ranchers and farmers will result in far greater hazard to 

nontarget species.

Have times changed in 20 years?

LITERATURE CITED

EVANS, J., and A. L. WARD. 1967. Secondary poisoning

associated with anti-coagulant-killed nutria. Amer. Vet.

Med. Assn. J. 151(7):856-861.

60
HAGEN, H. 1972. A review of the use of toxic materials 

for mammalian animal control in California. California 

Department of Fish and Game, Wildlife Management 

Administrative Report No. 72-5. 

LITTRELL, E. E. 1988. Wild carnivore deaths due to 

anticoagulant intoxication. California Fish and Game 

74(3):172-185. 

MENDENHALL, V. M., and L. F. PANK. 1980. Secondary 

poisoning of owls by anti-coagulant rodenticides. Wildlife 

Soc. Bull., 8(4):311-315.

PIERCE, C. C, and M. T. CLEGG. 1916. The effect of 

strychnine sulfate on California valley quail. California 

Fish and Game 2(1):11-13. 

SAYAMA, K., and O. BRUNETTI. 1952. The effects of 

sodium fluoroacetate (1080) on California quail. 

California Fish and Game 38(3):295-300. 

SCHAFER, E. W. 1984. Potential primary and secondary 

hazards of avicides. Vertebr. Pest Conf. 11:217-222. 

Univ. Calif., Davis.

61