4.8 IMPACT OF AGRICULTURAL PESTICIDES ON BIRDS OF PREY IN THE LOWER FRASER VALLEY
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4.8 IMPACT OF AGRICULTURAL PESTICIDES ON BIRDS OF PREY IN THE LOWER FRASER VALLEY
4.8
IMPACT OF AGRICULTURAL PESTICIDES
ON BIRDS OF PREY
IN THE LOWER FRASER VALLEY
by Laurie Wilson, Megan Harris
and John Elliott
Pacific Wildlife Research Centre
Environment Canada, Delta, B.C.
Bald eagles and other birds of prey are often observed during the winter months in the Lower Fraser
Valley. Millions of migratory birds (raptors, waterfowl, shorebirds) flock to the Fraser estuary during
the winter to join the already abundant resident populations. Farmland is critical habitat for both.
Agriculture is also an important economic sector in B.C. In order for the agricultural industry to
remain competitive with other markets, farmers depend on pesticides to ensure crop success. These
pesticides can have adverse impacts on wildlife populations.
Birds of prey, particularly bald eagles, are good indicator species to monitor the impact of agricultural
pesticides on local wildlife populations. (They can also be used to indicate levels of other contaminants,
such as dioxins and furans, in food chains; see Wilson et al. [1999]). Raptors are good indicators because
they often hunt for injured or sick prey in farm fields, where poisoning incidents may have occurred. They
are large, majestic birds that are more easily identified than smaller, less visible species. Raptors, particularly
eagles, are also favourites of many citizens who may be more likely to notify authorities about dead or
injured eagles than other birds.
The most common type of insecticides applied on agricultural crops today in B.C. are anticholinesterase
pesticides. These insecticides act by blocking synaptic transmission in the nervous system. In general, these
chemicals break down quickly in the environment, but while they are present, they can be extremely
poisonous. Although these chemicals are intended to control agricultural pests, non-target species present
in the area, such as birds, are frequently exposed. Between 1960 and 1994, more than 100 avian mortality
incidents involving at least 3,700 songbirds, waterfowl and birds of prey were attributed to agricultural
pesticides in the Lower Fraser Valley and southeastern Vancouver Island (Wilson et al. 1995).
1014.8 IMPACT OF AGRICULTURAL PESTICIDES ON BIRDS OF PREY IN THE LOWER FRASER VALLEY
INCIDENCE OF RAPTOR POISONINGS BY PESTICIDES
In 1990, a study to determine causes of raptor mortality in the Lower Fraser Valley and southeast Vancouver
Island was initiated, paying particular attention to the extent of exposure to lead shot and anticholinesterase
pesticides. A request for sick, injured and deceased raptors was published in local periodicals and circulated
to wildlife agencies. Dead or debilitated birds were obtained from government sources, local wildlife
rehabilitators and the public. Plasma and/or brain cholinesterase activity was measured and those with
inhibited levels (indicative of exposure to these types of pesticides) had ingesta analyzed for pesticide residues.
Postmortem examinations were completed on all carcasses to determine the most probable cause of death.
From 1990 to 1997, a total of 754 raptors were collected, the majority (61%) of which were bald eagles.
Many of these raptors were gathered from the Fraser delta. Overall, the most common causes of death of
bald eagles were electrocution, trauma (a term for generic injuries caused by violent means such as vehicle
collision, fighting and drowning) and pesticide poisoning. However, the primary causes of mortality/injury
of eagles collected in the Fraser delta were electrocution and pesticide poisoning (Fig. 1).
Figure 1. Causes of mortality of bald eagles collected in British Columbia and the Fraser delta: 199197
(N=458).
A total of 57 cases of raptor poisonings were recorded, 34 (60%) of which occurred in the Fraser delta.
Poisoning events also occurred in agricultural areas further up the valley (Langley, Chilliwack) and on
Vancouver Island around Courtenay. A few poisoned raptors were reported in urban environments. Most
poisonings involved bald eagles, although occasionally red-tailed hawks, rough-legged hawks and great
horned owls were afflicted. Specific chemicals were identified in 31 cases involving seven different anti-
cholinesterase insecticides (Fig. 2): carbofuran, fensulfothion, phorate, fonofos, terbufos, parathion and
fenthion. Most of these chemicals were registered for use in B.C. as granular formulations at the time the
incidents occurred. Details of several poisoning incidents are discussed in Elliott et al. 1995; 1996a; 1997.
Confirmation of poisoning by anticholinesterase pesticides is extremely difficult as enzymes inhibited by
these chemicals recover quickly and pesticide residues break down rapidly in the body, thereby allowing
only a very small window of opportunity for confirmation of exposure. In addition, poisoned raptors are not
necessarily found near pesticide sources. This may be because they remove their contaminated prey from
the source prior to consumption, or alternatively, raptors may not be as sensitive to the chemical or not
1024.8 IMPACT OF AGRICULTURAL PESTICIDES ON BIRDS OF PREY IN THE LOWER FRASER VALLEY
receive as large a dose, and therefore are able
to move away from the field prior to suffer-
ing severe debilitation and death. Pre-1990
incidents of dead eagles and hawks were of-
ten associated with roost locales, but were
not tested for pesticides (Elliott et al. 1997).
ROUTES OF PESTICIDE EXPOSURE
Historically, large numbers of songbirds and
waterfowl were poisoned when flocks would
land in a field which had recently been
treated with pesticides. The route of their
exposure was quite clear: acute toxicity from
a lethal dose of a toxic chemical acquired
when they foraged in the treated area. Some
die-off events have also been attributed to Figure 2. Number of raptor poisoning incidents where specific
misuse of pesticides. Occasionally, individu- anticholinesterase pesticides have been identified, by year (N=31).
als have intentionally applied more chemi-
cal to a field than has been registered for a specific crop. Alternatively, there have been cases of illegal
baiting, where pesticides have been added to carcasses that have been left out for vermin to scavenge.
Sometimes there were accidental spills. However, the majority of raptor poisonings have not been associated
with these sorts of activities. They have occurred during the fall and winter months, long after spring and
summer pesticide applications. Based on published degradation rates of anticholinesterase pesticides in soil,
concentrations in the treated fields at that time of year should have been very low, certainly below levels
associated with acute toxicity.
Most raptors were poisoned by consuming contaminated waterfowl, as duck remains were usually identi-
fied in their gut contents. Therefore, the following scenario was hypothesized. Wintering ducks and other
waterfowl foraging in flooded agricultural fields would inadvertently ingest granular formulations of pesti-
cides while searching for seeds and grit. Although the active ingredient on the granular formulations should
be broken down within several months of application, the high acidity and frequent flooding of valley soils
slow degradation rates (Elliott et al. 1997). The waterfowl are therefore poisoned by the still potent active
ingredient which is concentrated in sufficient quantity on the granules to result in acute toxicity. As a result,
raptors are poisoned secondarily as they scavenge on dead or debilitated waterfowl.
To test our hypotheses, a study was conducted in 1995 with Agriculture and Agri-Food Canada (AAFC)
to determine if granular formulations of four anticholinesterase insecticides (carbofuran, phorate, fonofos
and terbufos) initially placed in soil in the spring would retain sufficient active ingredient during the
fall and winter months to result in waterfowl mortality. Results indicated that active ingredients of all
chemicals were detected after the end of the growing season and sufficient concentrations of phorate and
fonofos were present to kill ducks foraging in treated fields up to nine months post-application (Fig. 3)
(Wilson et al. 1996).
This study showed that, theoretically, waterfowl could ingest a lethal dose of pesticides when foraging in
agricultural fields during the winter months. However, we had not yet found conclusive evidence in the
field. Therefore, a subsequent study was conducted during the winters of 1996 and 1997 where we searched
for waterfowl carcasses in potato fields which had been treated with and without granular fonofos. Evidence
of 174 bird remains were found, with 50 per cent in treated fields. Most remains were scavenged, with only
1034.8 IMPACT OF AGRICULTURAL PESTICIDES ON BIRDS OF PREY IN THE LOWER FRASER VALLEY
31 intact carcasses suitable for post-mortem
examination and/or toxicology. Twenty-six
brains were analyzed for cholinesterase activ-
ity levels, and five ducks had severely de-
pressed levels indicative of lethal exposure.
All of the poisoned ducks were found in fields
which had been treated with granular
fonofos. As these ducks were found in differ-
ent fields at separate times during the study,
their deaths were not a result of an acciden-
tal spill or misuse of fonofos in a single hot
spot. This study shows that ducks can ac-
quire a lethal dose of anticholinesterase pes-
ticides in farm fields in the lower mainland Figure 3. Persistence of active ingredient of select granular
even when the chemicals are applied at the pesticides in Fraser Valley soils.
recommended rates. Higher risk fields may
be identified based on soil type, the extent
of flooding, the amount of chemical used
and the intensity of waterfowl foraging. Cli-
matic conditions in a particular year may
also play a role.
WINTER EXPOSURE FACTORS FOR
BALD EAGLES
In order to quantify and mitigate the risk of
pesticide poisoning, several projects were ini-
tiated to better understand raptor feeding be-
haviour, particularly bald eagles, during win-
ter when most poisonings occurred. During
the winters of 1994, 95, 96, average num- Figure 4. Average number of bald eagles counted at
bers of bald eagles rose steeply through De- winter roosts in Delta, B.C., 1994, 95, 96.
cember and January at two roost sites, to peak
at an average of 140 at the end of February (Fig. 4). These high February numbers coincided with peaks in
incidents of poisoning; thus, the degree of scavenging pressure may be an important variable influencing
the frequency of poisonings within a given year.
Scavenging behaviour of raptors in agricultural areas was investigated by placing 30 duck carcasses in fields
and monitoring them using still and time-lapse video technology. Most carcasses were found by raptors
within 72 hours, and 78 per cent were rapidly scavenged within 24 hours (Peterson et al., in prep). Of
the species identified by this technique, bald eagles were the first species to find carcasses, about 22 per
cent of the time. Other scavengers were also observed including northern harriers, red-tailed hawks and
northwestern crows.
While our studies on the persistence of granular anticholinesterase pesticides in lower Fraser agricultural
soils suggest a sound explanation for many of the poisoning incidents reported, there was the potential that
eagles were poisoned at the Vancouver Municipal Landfill, located in the midst of the Fraser delta in Burns
Bog. Surveys were conducted during the winters of 1994, 95 and 96 in order to assess the dependence of
1044.8 IMPACT OF AGRICULTURAL PESTICIDES ON BIRDS OF PREY IN THE LOWER FRASER VALLEY eagles on the landfill as a foraging area and to determine the likelihood of poisoning incidences (Lee et al., in prep.). During the day, while regular landfill activities were underway, bald eagles mostly perched or loafed around the landfill, although occasionally they scavenged or pirated garbage. Further observation during the winter of 1998 showed that large numbers of adult and juvenile eagles (up to 100) foraged at the landfill at dusk and dawn (outside of normal active periods at the landfill). Some birds may obtain sufficient food exclusively at the landfill; in which case they would have reduced the risk of poisoning by pesticides used in agricultural activities. However, as little of the identified food consumed at the landfill was of high nutritional value (
4.8 IMPACT OF AGRICULTURAL PESTICIDES ON BIRDS OF PREY IN THE LOWER FRASER VALLEY
such as wireworm in potato crops. The efficacy of several alternative pest control strategies are currently
under investigation by AAFC.
This study of raptor health has also revealed other anthropogenic causes of death, some of which are being
addressed. For example, hunting of waterfowl using lead shot has been banned in B.C., primarily due to the
lead-poisoning of bald eagles after scavenging on waterfowl carrying high numbers of shot in their gizzards
(Elliott et al. 1992). Other toxic agents have also been identified, such as rodenticides, which poison raptors
after ingestion of rodents poisoned by bait. On the habitat side, BC Hydro is trying to reduce the incidence
of electrocutions by investigating various types of structural changes to utility poles and lines.
IMPACTS OF PESTICIDES ON RAPTOR POPULATIONS
Christmas bird counts indicate that winter bald eagle populations in the Fraser Valley have increased sig-
nificantly during the 1980s, and now the number of bald eagles is close to 300. This increase probably
reflects a general recovery of North American bald eagle populations in response to the cessation of DDT
use in the 1970s (Elliott et al. 1996b). Prior to the winter of 1989-90 in the Fraser delta, despite many
documented incidents of waterfowl poisonings, a few of which were accompanied by poisonings of other
raptors, there were no documented pesticide poisonings of bald eagles (Wilson et al. 1995). During the
early 1990s, the number of wintering eagles in the delta increased significantly over the populations re-
corded in the previous decade. The first incidents of bald eagle poisonings by anticholinesterase pesticides
were reported in the winter of 1989-90. Thus, the incidence of poisonings may reflect a larger number of
wintering birds and increased scavenging pressure. During the 1990s, increased eagle densities in February
coincided with timing of peak poisoning incidents, further suggesting that the number of eagles present
likely increases the probability of finding eagle carcasses. Another contributing factor may have been that a
systematic surveillance to document pesticide poisoning incidents had not been established until 1990.
From 1991 to 1997, an average of five to 10 bald eagles per year were diagnosed as anticholinesterase
poisoned in the delta. This constitutes at most five per cent of the estimated wintering population. While it
is difficult to determine whether the dead eagles retrieved represented the total mortality due to pesticides,
the number of eagles wintering on the delta has remained stable.
Bald eagle productivity surveys have been conducted along coastal B.C. since 1990. The reproductive
success of eagles breeding in the Fraser delta is quite high compared to other locations along the west coast
(Fig. 6) (Elliott et al. 1998a). Poor eagle productivity in other west coast areas has been attributed to limited
and/or nutritionally poor food supplies as well as geographic topography (such as deep fjords) making
foraging difficult (Elliott et al. 1998a). Historically, chlorinated contaminants such as dioxins and furans
found in bleached-kraft pulp mill effluent have adversely affected eagles and other wildlife breeding in some
areas (Elliott and Norstrom 1998b). Therefore, even though the incidence of pesticide poisoning is com-
paratively high for eagles breeding in the delta, the abundance of high nutritional prey items (salmon,
waterfowl, gulls) and easy foraging (in foreshore and agricultural areas and from fishery by-catch) leads to
high reproductive success. Based on the estimation by Stahlmaster (1987) that 1.0 eaglet/occupied terri-
tory constitutes a healthy population, the Fraser delta eagle breeding population is stable. Because poisonings
happen during the winter months when numerous migrant eagles are present, many of the poisoned eagles
are likely migrants. The impact of these deaths on populations in their breeding areas is unknown.
CONCLUSIONS AND RECOMMENDATIONS
A total of 34 cases of raptor poisonings by anticholinesterase pesticides were documented between 1990
97 in the Lower Fraser Valley. Most reported poisonings involved bald eagles, although other raptors were
also afflicted.
1064.8 IMPACT OF AGRICULTURAL PESTICIDES ON BIRDS OF PREY IN THE LOWER FRASER VALLEY
Figure 6. Reproductive success of bald eagles nesting along coastal British Columbia: 199096.
Seven anticholinesterase chemicals were identified in the poisoned raptors and most of these chemicals were
registered for use in B.C. as granular formulations at the time of the incidents. It is believed that most
poisoning incidents were from pesticides which were applied at recommended rates (e.g. poisonings were
not from misuse of pesticide products). Raptors were exposed by consuming contaminated waterfowl which
inadvertently ingested granular pesticides while foraging in flooded agricultural fields. Granular formula-
tions of certain pesticides persist longer than anticipated in acidic, flooded soils common in the Fraser delta.
Five of the seven pesticides implicated in poisonings have been removed from B.C. markets. A sixth granular
formulation is scheduled to be removed in 1999 after existing stocks have been exhausted. The cooperation
of farmers and pesticide manufacturers has been instrumental in ensuring a quick resolution to this poten-
tial conflict between agricultural production and the need for clean, toxin-free wintering habitat for raptors.
Productivity of bald eagle populations in the Fraser Valley was higher than in other areas monitored along
coastal B.C. Key factors affecting reproductive success here include the abundance and high nutritional
value of prey items and the low foraging effort required. Even though there have been poisoning episodes,
1074.8 IMPACT OF AGRICULTURAL PESTICIDES ON BIRDS OF PREY IN THE LOWER FRASER VALLEY
bald eagle populations in the Fraser Valley have been steadily increasing since the late 1980s, likely reflect-
ing a general recovery of North American populations.
The monitoring and investigation of suspicious mortalities in raptors is a very effective method for identify-
ing pesticide or other contaminant problems in the environment and should be maintained. Eagles are a
useful indicator species for tracking contamination in both terrestrial and aquatic ecosystems because indi-
viduals forage on a number of different prey items in a variety of habitats throughout the delta and the
appearance of sick or dying eagles is not likely to go unnoticed. This enhanced likelihood of detection
provides protection for populations of less noticeable wildlife in the Lower Fraser Valley.
REFERENCES
Elliott, J. E., K. M. Langelier, A. M. Scheuhammer, P. H. Sinclair and P. E. Whitehead. 1992. Incidence of Lead Poisoning in
Bald Eagles and Lead Shot in Waterfowl Gizzards from British Columbia, 198891. Canadian Wildlife Service
Progress Note No. 200. Pacific and Yukon Region, Environment Canada, Vancouver, B.C.
Elliott, J. E., L. K. Wilson, K. M. Langelier and P. Mineau. 1995. Secondary Poisoning of Birds of Prey by
Anticholinesterase Insecticides. Presented at the 16th Annual SETAC (Society of Environmental Toxicology and
Chemistry) Meeting, 59 November 1995, Vancouver, B.C. Poster Abstract No. 449.
Elliott, J. E., K. M. Langelier, P. Mineau and L. K. Wilson. 1996a. Poisoning of bald eagles and red-tailed hawks by
carbofuran and fensulfothion in the Fraser delta of British Columbia, Canada. Journal of Wildlife Disease 32(3):
486491.
Elliott, J. E., R. J. Norstrom, G. E. J. Smith. 1996b. Patterns, trends and toxicological significance of chlorinated
hydrocarbon and mercury contaminants in Bald Eagle eggs from the Pacific Coast of Canada, 19901994. Archives
of Environmental Contamination and Toxicology 31: 354367.
Elliott, J. E., L. K. Wilson, K. M. Langelier, P. Mineau and P. H. Sinclair. 1997. Secondary poisoning of birds of prey by the
organophosphorus insecticide, phorate. Ecotoxicology 6: 219231.
Elliott, J. E., I. E. Moul and K. Cheng. 1998a. Variable reproductive success of bald eagles on the British Columbia coast.
Journal of Wildlife Management. 62(2): 518529.
Elliott, J. E. and R. J. Norstrom. In press 1998b. Chlorinated hydrocarbon contaminants and productivity of bald eagle
populations on the Pacific coast of Canada. Environmental Toxicology and Chemistry.
Lee, S. L., M. Porter, J. E. Elliott. In prep. Bald Eagle Winter Use of a Landfill, Delta, British Columbia.
Peterson, C. A., S. L. Lee and J.E. Elliott. In prep. Scavenging of Waterfowl Carcasses by Avian Predators in the Fraser
River Delta of British Columbia.
Stahlmaster, M. 1987. The Bald Eagle. Universe Books, New York. 227 pp.
Wilson, L. K., I. E. Moul, K. M. Langelier and J. E. Elliott. 1995. Summary of Bird Mortalities in British Columbia and
Yukon, 19631994. Canadian Wildlife Service Technical Report Series No. 249. Environment Canada, Pacific and
Yukon Region, Delta, B.C.
Wilson, L., J. E. Elliott, S. Szeto and B. Vernon. 1996. Retention of Insecticide in the Granule and Its Potential Hazard to
Wildlife. Presented at the 17th Annual SETAC (Society of Environmental Toxicology and Chemistry) Meeting,
1721 November 1996, Washington, D.C. Poster Abstract No. P0526.
Wilson, L., M. Harris and J. Elliott. 1999. Contaminants in wildlife indicator species from the Fraser Basin. In: C. Gray
and T. Tuominen, eds. Health of the Fraser River Aquatic Ecosystem: A Synthesis of Research Conducted Under the
Fraser River Action Plan. Environment Canada, Vancouver, B.C. DOE FRAP 1998-11.
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