Causes of Mortality in Bald Eagles (Haliaeetus leucocephalus) in The Canadian Maritime Provinces, 1991-2016 - Canadian Wildlife Biology ...
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CWBM 2020: Volume 9, Number 2 ISSN: 1929–3100
Original Research
Causes of Mortality in Bald Eagles (Haliaeetus
leucocephalus) in The Canadian Maritime
Provinces, 1991-2016
Amélie MATHIEU1, E. Jane PARMLEY2,3, Scott MCBURNEY4, Colin ROBERTSON5,
Helene VAN DONINCK6, and Pierre-Yves DAOUST4
1
British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development, 205 Industrial Rd. G,
Cranbrook, British Columbia, V1C 7G5, Canada.
2
Department of Population Medicine, Ontario Veterinary College, University of Guelph, 50 Stone Rd. E, Guelph, Ontario,
N1G 2W1, Canada.
3
Canadian Wildlife Health Cooperative, CWHC National Office, University of Saskatchewan, 52 Campus Drive, Saskatoon,
Saskatchewan, S7N5B4, Canada.
4
Canadian Wildlife Health Cooperative, Department of Pathology and Microbiology, Atlantic Veterinary College, University
of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island, C1A 4P3, Canada.
5
Department of Geography and Environmental Studies, Wilfrid Laurier University, 75 University Avenue West, Waterloo,
Ontario, N2L 3C5, Canada.
6
Cobequid Wildlife Rehabilitation Centre, 2220 Irwin Lake Rd, Brookfield, Nova Scotia, B0N1C0, Canada ̶ Posthumously.
Abstract
This article summarizes the results of necropsy findings on 420 bald eagles (Haliaeetus leucocephalus) from the 3
Canadian Maritime provinces over a 26-yr period. It shows that, as in other regions of North America, anthropogenic
factors dominate the diagnosed causes of mortality in this species, representing close to 50% of the cases. These factors
included vehicular collision (n=57; 14%), electrocution (n=47; 11%), poisoning (n=38; 9%), snares and other trapping
devices (n=35; 8%), gunshot (n=20; 5%), and other (n=5; 1%). At least some cases of trauma of unknown cause (n=79;
19%) and some unknown causes of death (n=53; 13%) may have also involved anthropogenic factors. As in several
Correspondence: Pierre-Yves Daoust, Canadian Wildlife Health Cooperative, Department of Pathology and
Microbiology, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue,
Charlottetown, Prince Edward Island, C1A 4P3, Canada. Email: daoust@upei.ca.
MATHIEU et al. 160
other regions of North America, lead continued to be the most common source of poisoning in this species. Other
causes of mortality identified, such as conspecific fights (n=11; 3%) and drowning / hypothermia (n=4; 1%), are
natural challenges faced by these birds. Although bald eagles are not considered a species at risk in Canada, results of
this study indicate that human-related causes of death are an ongoing issue in the Maritime region as elsewhere.
Therefore, mitigating measures aimed at their reduction, for example those in relation to lead-based ammunition and
fishing tackle, pesticide use and trapping, should continue to be implemented and expanded.
Key Words: Anthropogenic factors, Bald Eagle, Canada, Haliaeetus leucocephalus, Maritimes, Mortality.
INTRODUCTION retrospective study identifies the causes of death that bald
eagles have encountered in the Canadian Maritime provinces
Identifying, monitoring and mitigating potential causes of
(New Brunswick [NB], Prince Edward Island [PEI], Nova
morbidity and mortality in wildlife are important activities
Scotia [NS]) over a 26-yr period (1991-2016), based on data
that contribute to conservation. Bald eagles (Haliaeetus
from a long-term wildlife health surveillance program
leucocephalus), like many other raptors, can be negatively
carried out by the Canadian Wildlife Health Cooperative
affected by human activities. Once hunted as pests or
(CWHC; www.cwhc-rcsf.ca).
trophies, bald eagles are now protected under provincial
jurisdiction in Canada, and by the Bald and Golden Eagle
Protection Act and the Migratory Bird Treaty Act in the MATERIAL & METHODS
United States (US) (U.S. Fish & Wildlife Service 2018a, Carcasses of bald eagles found dead or in poor health and
2018b). However, these regulations do not preclude harm subsequently euthanized were submitted by conservation
from environmental contaminants, day-to-day human- officers, park wardens, biologists, wildlife rehabilitation
related activities, poaching, or habitat fragmentation and centre staff, or the public to the Atlantic regional centre of
destruction from urban and agricultural encroachment. This the CWHC, Atlantic Veterinary College, University of
became evident in the mid-20th century when the population Prince Edward Island, where they were necropsied. All
of bald eagles plummeted in the US as a consequence of necropsies were performed by 3 experienced wildlife
breeding failure due to the extensive use of pathologists who provided a consistent level of examination
dichlorodiphenyltrichloroethane (DDT), poaching, and over the 26-yr duration of the study. Individual necropsy
habitat loss (Fraser 1985; Richardson and Miller 1997). The reports were reviewed carefully by 2 of the 3 pathologists
species was listed as “endangered” under the US Endangered and, for each carcass evaluated, the following information
Species Preservation Act in 1967, but it subsequently was collected: province of origin; month and year when the
recovered and was delisted in 2007 (U.S. Fish & Wildlife bird died or when the carcass was found; history of the
Service 2019). Its recovery across North America is largely circumstances under which the bird was found; age class
attributed to the ban on general use of DDT in Canada and (nestling, immature [
MATHIEU et al. 161 original cause of the problem that had led to the bird’s performance liquid chromatography, with a detection limit capture could be clearly identified. of 1.0 μg/g. Primary causes of death were divided into 10 categories: Statistical analyses were conducted using SAS 9.4 trauma, electrocution from power lines, emaciation, (Copyright © 2002-2012; SAS Institute Inc., Cary, North poisoning, conspecific fight, infection, idiopathic disease Carolina, USA). Univariable exact logistic regression (disease process identified, but cause undetermined), models were fitted to examine associations between the odds nestling mortality, drowning / hypothermia, and unknown of being diagnosed with select causes of death (i.e., trauma, (no cause of death identified). Criteria for each of these electrocution from powerlines, emaciation, poisoning, all categories are defined in Table 1. Lead concentration in liver human-associated causes of death) and the following or kidney (on a wet weight basis) was determined by atomic variables: age, sex, body condition, season, and province. absorption spectroscopy, with a detection limit of 0.25 μg/g Significance level was set at α=0.05 for these models, and in early years, improving over time to
MATHIEU et al. 162 more subjective and also implies the need to look further for proportion of human-related causes of death relative to the a cause of death. Causes of death thought to have been total number of submissions (Figure 2) human-related were also grouped. These included all known Sixty-six of the 79 birds diagnosed with trauma of causes of trauma (trauma of unknown cause excluded), unknown cause had bone fractures and/or internal electrocution and poisoning. hemorrhage. Most of the remaining birds had focal acute or The same univariable regression modelling approach was chronic superficial soft tissue lacerations. The hemorrhage in used to examine associations of select causes of mortality 2 birds was of a diffuse nature without good evidence for the with characteristics of the locations in which the birds were source of blood, suggesting the possibility of anticoagulant found. Human population density (persons per km 2) of poisoning (Murray 2011). Liver analysis for the presence of dissemination areas (small areas with populations of 400-700 anticoagulant rodenticide was done on 1 of these 2 birds and persons) was extracted from the 2016 Canadian census was negative. In 4 birds, the severity, distribution and nature (Statistics Canada 2019) as a proxy for anthropogenic risks of soft tissue trauma (epidermal, dermal and soft tissue to bald eagles. A road network dataset was used to examine necrosis) was considered compatible with electrocution and potential effects of major roads on bald eagles (ESRI Data & survival of the birds for some time post-injury. The history Maps 2019). Finally, locations of contaminated lands were available for 1 of the 79 birds with trauma of unknown cause obtained from the Federal Contaminated Sites Inventory suggested a lightning strike. This bird was observed to which tracks known sources of environmental contamination “simply fall” from the sky during a severe thunder storm and that could pose a risk to human health or the environment hit the ground with its wings folded and feet bent back (Treasury Board of Canada Secretariat 2019). Human toward its tail. Necropsy revealed a large internal blood clot, population density was categorized as low (≤50 persons/km2) compatible with trauma from the bird’s impact on the ground. or higher (>50 persons/km2); distance to roads was Trauma was confidently attributed to a human cause in 117 categorized as near road (0 ̶100m from a road) or off-road of 196 (60%) total cases of trauma (Table 1), vehicular (>100m from a road); distance to contaminated lands was collision being most common (57/196, 29%). Non-target categorized as near (
MATHIEU et al.
Table 1. Primary causes of mortality in 420 bald eagles (Haliaeetus leucocephalus) submitted for necropsy from the 3 Canadian Maritime provinces between 1991
and 2016.
163
Table 1. Primary causes of mortality in 420 bald eagles (Haliaeetus leucocephalus) submitted for necropsy from the 3 Canadian Maritime provinces between 1991
and 2016 (Cont’d).
MATHIEU et al.
164
MATHIEU et al. 165 Figure 2. Number of bald eagles submitted, percent of eagle submissions due to human-related mortality causes and three- year moving average of percent of eagle submissions due to human-related mortality causes in the Maritime provinces, 1991-2016. vascular fibrinoid necrosis, as described in waterfowl by involving the head and neck with puncture wounds or Wobeser (1997). Lead levels in kidney or liver were also fracture of the skull in 3 of them. The 6th bird may have been determined for 100 of the 392 bald eagles with a diagnosis drowned by the conspecific; its plumage was very wet, and other than lead poisoning. Of these, 2 birds had lead levels it had puncture wounds in the skin and muscle mass of its above 2 µg/g indicative of elevated lead exposure, but less right leg. Four of the remaining 5 birds suspected of having than levels considered clinically toxic (Wobeser 1997; died following a fight with a conspecific had severe soft Wayland and Bollinger 1999); 1 died of carbofuran tissue trauma involving the head and neck, including a skull poisoning and the other of electrocution. Five other birds had puncture in 2 of them. The 5th bird had only subcutaneous lead levels between 1 and 2 µg/g; 2 died of emaciation, 1 congestion of the head, but another eagle had been seen from trauma of unknown cause, 1 from vehicular collision, “picking up its head” shortly before it died. and 1 was euthanized because of suppurative polyarthritis. Nine of 10 cases of infection consisted of locally extensive Exposure to organophosphates and carbamates (OP/CM) infectious processes, such as pododermatitis, arthritis, and accounted for 7/38 (18%) cases of poisoning, and cellulitis, at least some of which may have resulted from barbiturates accounted for 3/38 (8%). local trauma with secondary bacterial infection. All 11 deaths attributed to conspecific fighting involved Staphylococcus aureus was isolated from 4 of 7 cases in adult birds (6 females, 5 males). Nine of these deaths which bacterial cultures were attempted. Pasteurella occurred during the nesting season (April and May). This multocida was isolated from 1 case, and bacteriology results cause of death was confirmed in 6 birds based on a case were inconclusive in 2 cases. The only generalized infection history of direct observation of an aggressive interaction considered to have resulted from a systemic process was a between 2 birds, in one case involving 2 males that both died case of suppurative polyarthritis involving the left elbow during the encounter. Lesions in 5 of these 6 birds consisted joint and both tarsometatarsal joints from which S. aureus of extensive skin lacerations and subcutaneous hemorrhage, was isolated; the source of this infection was not determined.
MATHIEU et al. 166 Table 2. Demographic, temporal and geographical data for all cause of mortality categories diagnosed among 420 bald eagles (Haliaeetus leucocephalus) submitted for necropsy from the 3 Canadian Maritime provinces between 1991 and 2016. Table 3. Univariable exact logistic regression models estimating the associations between bald eagles being diagnosed with select causes of death (i.e., trauma [all causes], electrocution from power lines, emaciation, or poisoning) and age, sex, body condition, season, and province in which the birds were found (1991-2016). Significant associations are in bold characters.
MATHIEU et al. 167
A presumptive diagnosis of drowning / hypothermia was human cause, but less likely to die of poisoning, than adults
made in 3 of 4 birds (excluding the bird presumably drowned (Tables 3 and 4).
by a conspecific) based on the facts that their carcass had No association could be found in our study between causes
been found ashore, that their plumage was very wet, and that of mortality and spatial variables examined (human
no significant gross lesion was found. The 4th bird was population density, proximity to roads, and presence of
actually found alive in water. According to the conservation contaminated lands), except that emaciated birds were less
officers who picked it up, it could not get out and was having likely (OR=0.395, 95% CI: 0.182-0.827) to be found near
trouble staying afloat. It died shortly thereafter. roads than farther away from roads.
All 53 birds with an unknown cause of death were in
moderate to good body condition (Table 2). Eleven had DISCUSSION
recently ingested food, raising the possibility of poisoning.
Bald eagles, as upper-trophic level piscivores and
The possible involvement of organophosphate, carbamate or
scavengers found in habitats often affected by human activity,
barbiturate poisoning was examined in 8 of these birds, and
are important bio-sentinels of environmental health and of
all results were negative. Nine birds were found under a
the impacts of human activity on wildlife. Monitoring their
power line or electrical transformer but showed no gross
health can help identify emerging threats to wildlife and
evidence of electrocution.
human health and may be used in the development of
Based on univariable exact logistic regression models,
effective conservation programs. Identification of threats
birds in moderate to good body condition were more likely
associated with population declines of some avian species
to die of trauma due to human causes, of electrocution, and
(i.e., DDT and lead) have resulted in regulatory changes and
of all human-related causes combined, but less likely to die
population rebound (Avery and Watson 2009; Government
of poisoning, than birds in poor body condition (Tables 3 and
of Canada 2013; U.S. Fish & Wildlife Service
4). Females were less likely to die of electrocution than
2019). Documentation of on-going causes of death provides
males. Immature birds were more likely to die of trauma of
Table 4. Univariable exact logistic regression models estimating the associations between bald eagles being diagnosed with
select causes of death (i.e., trauma of human cause, trauma of unknown cause, or all human-associated causes of death) and
age, sex, body condition, season, and province in which the birds were found (1991-2016). Significant associations are in
bold characters.
Trauma-human Trauma-unknown Human COD
[OR (95% CI)] [OR (95% CI)] [OR (95% CI)]
Age Adult 0.57 1.75 0.75
(0.37, 0.95) (0.97, 3.26) (0.49, 1.16)
Immature - - -
(ref)1
Sex Male 0.64 1.43 0.85
(0.39, 1.04) (0.84, 2.42) (0.557, 1.304)
Female (ref) - - -
Body Good 6.86 1.63 3.26
condition (2.89, 19.88) (0.82, 3.49) (1.88, 5.79)
Poor (ref) - - -
Season Summer 1.83 0.64 1.40
(0.92, 3.62) (0.30, 1.29) (0.79, 2.49)
Fall 2.43 0.41 2.05
(1.29, 4.61) (0.18, 0.87) (1.19, 3.57)
Winter 3.25 0.69 2.49
(1.69, 6.33) (0.32, 1.40) (1.38, 4.54)
Spring (ref) - - -
Province New 2.04 1.14 1.46
Brunswick (1.21, 3.44) (0.60, 2.12) (0.90, 2.37)
Prince 1.08 1.53 1.46
Edward (0.57, 1.98) (0.79, 2.92) (0.86, 2.50)
Island
Nova Scotia - - -
(ref)
1 ref, referent (the reference category to which the other categories are compared).MATHIEU et al. 168 supportive science-based evidence for the creation of new other factors besides size are at play in this cause of death. policies and practices that are needed to further protect bald Immature raptors, being less experienced flyers and thus at a eagles and other wildlife from preventable mortality higher risk of mishaps when landing or taking off from an associated with human activity (e.g., lead poisoning). electric power structure, are commonly reported to be more Trauma prone to electrocution than adult birds (Boeker and Trauma was the most commonly diagnosed cause of death, Nickerson 1975; Fitzner 1978; Ferrer and Hiraldo 1992; accounting for close to half of the carcasses examined (Table Dawson and Mannan 1994). We did not identify an age 1). This high proportion is consistent with the findings of predilection associated with electrocution, but we did similar mortality studies in bald eagles and other raptors in observe that bald eagles dying of trauma of human cause North America (Coon et al. 1970; Deem et al. 1998; Driscoll were more likely to be immature than adult. It is interesting et al. 2004; Smith et al. 2018; Simon et al. 2020). However, in this context that 1 adult female that died of electrocution it contrasts with the low proportion of trauma reported for had hepatic lead levels indicative of elevated exposure, bald eagles in Saskatchewan (22%) where toxicosis was suggesting that, as a neurotoxin, this amount of lead may found to be the most prevalent cause of death (Scott and have resulted in some degree of incoordination predisposing Bollinger 2015). to this accident. A large proportion of the trauma cases were of unknown Emaciation cause; some of them could have been of human origin, such The proportion of birds dying of emaciation in our study as collisions with vehicles or power lines or from (10%) is consistent with findings of other studies on causes electrocution, while others may have had a natural cause, of mortality in bald eagles in which the proportion of cases such as collisions with trees. Vehicular collision, the most of emaciation ranged from 3 ̶ 8% (Russell and Franson 2014; commonly identified cause of traumatic injuries in this study, Scott and Bollinger 2015; Smith et al. 2018; Simon et al. may be more likely to occur when bald eagles scavenge road 2020). No effect of age or season on emaciation was detected, kills. Non-target capture in snares or traps targeting as was also found by Smith et al. (2018) in Ontario. It was furbearers is generally only considered a minor cause of nonetheless surprising that emaciation was rarely identified trauma contributing to bald eagle mortality (Coon et al. 1970; as a cause of death in winter, when food sources would be Driscoll et al. 2004; Harris and Sleeman 2007; Scott and expected to be least abundant (Table 2). However, bald Bollinger 2015; Smith et al. 2018). However, the number of eagles are semi-obligate scavengers and might benefit from deaths from this cause in this study corroborates the findings a time of year when animals of other species are more likely by Fitzgerald et al. (2015) and Proulx et al. (2015) that such to die from starvation. non-target captures are an ongoing cause of bald eagle Poisoning mortality in Canada. It is also likely an underestimate since Compared to some other Canadian reports, poisoning was it was based in large part on voluntary reporting by trappers. not a commonly identified cause of bald eagle mortality in A number of measures aimed at mitigating this cause of the Maritime provinces. Poisoning was only diagnosed in 9% death in bald eagles have been proposed and implemented in of the bald eagles in this study whereas it was diagnosed in some, but not all, Canadian provinces (Fédération des 26% of bald eagles examined in Ontario (Smith et al. 2018) trappeurs gestionnaires du Québec 2014; Fitzgerald et al. and in 53% of those examined in Saskatchewan (Wayland 2015). and Bollinger 1999; Scott and Bollinger 2015). However, the Electrocution possible presence of poisons was not systematically Electrocution, the second most commonly identified cause determined in all birds for which this information would of bald eagle mortality in our study, is a well-known cause have been pertinent, such as some of the emaciated birds or of death of large birds which, given their large body size and those with an unknown cause of death. wide wingspan, are at higher risk than small birds of In this study, we determined that birds in poor body spanning electrical components and thus contacting at least condition were more likely to have died of poisoning than 2 points of energized or grounded hardware (Lehman et al. those in moderate or good body condition. This can likely be (2007). Ferrer and Hiraldo (1992) found that female Spanish attributed to the fact that lead accounted for most cases of imperial eagles (Aquila adalberti) were more prone to poisoning (74%) and that half of the birds with lead getting electrocuted on power lines than males and attributed poisoning were emaciated, a typical manifestation of this this difference to sexual dimorphism in this species, with type of poisoning. Lead poisoning was also identified as the females having a larger body size. In contrast, we observed most common cause of poisoning in bald eagles in Ontario that male bald eagles, which are typically smaller than (14/23, 61%), in Michigan (176/185, 95.1%), and in several females, were more prone to electrocution. This suggests that American states combined (484/762, 63.5%) (Russell and
MATHIEU et al. 169 Franson 2014; Smith et al. 2018; Simon et al. 2020), but not sodium pentobarbital for euthanasia of domestic animals can in Saskatchewan (20/121, 16.5%) where OP/CM were the result in secondary intoxication of these birds if carcasses of more common cause of poisoning (Scott and Bollinger 2015). euthanized animals have been improperly disposed of In this study, potential subclinical effects of lead did not (Langelier 1993; Russell and Franson 2014; Simon et al. appear to be common among 100 bald eagles with a cause of 2020). death determined to be something other than lead poisoning Other causes of mortality in which hepatic or renal lead levels were determined. Conspecific fights, infectious or idiopathic diseases, Our findings, along with those in other provinces, indicate nestling mortality, and drowning/hypothermia were that lead poisoning continues to pose a threat to bald eagles infrequent individual contributors to mortality in our study, in Canada. Although the use of lead ammunition to hunt which is similar to findings in other studies of causes of migratory game birds, including waterfowl, was banned in mortality in raptors (Coon et al. 1970; Deem et al. 1998; Canada in 1999, it is still used for hunting upland game birds Morishita et al. 1998; Driscoll et al. 2004; Harris and and small and large game mammals (Martin et al. 2008). Sleeman 2007; Russell and Franson 2014; Scott and Therefore, as semi-obligate scavengers, bald eagles continue Bollinger 2015; Smith et al. 2018; Simon et al. 2020). No to be exposed to lead through consumption of unretrieved birds were diagnosed with either avian cholera or infection carcasses or discarded offal from animals killed with lead by West Nile virus, which were the 2 most frequently ammunition (Stauber et al. 2010; Bedrosian et al. 2012; diagnosed infectious diseases of bald eagles in Saskatchewan Cruz-Martinez et al. 2012). Lead fishing tackle also and Ontario, respectively (Scott and Bollinger 2015; Smith represents an ongoing threat (Scheuhammer et al. 2003). It et al. 2018). Most cases of infection were of a focal nature is predicted that, in the absence of a legislative change, the and could have been secondary to local trauma, and some of use of lead ammunition will increase over the next decade, them could potentially have been linked to human activities. and the level of lead released annually into the environment Human-related mortality will increase from 5,000 tons (in 2016) to 5,800 tons by 2025 Human-related causes of mortality, including trauma, in Canada (Government of Canada 2018a). Alternatives to electrocution and poisoning, accounted for approximately lead ammunition and fishing gear, made from materials such half (48%) of the bald eagle mortalities in this study. This as copper or copper-zinc alloy, steel, tungsten or bismuth, are proportion may be overestimated since carcasses are more safer for the environment and are available commercially likely to be found and reported in populated areas and these (Government of Canada 2018b). areas are where mortality events are more likely to be due to Exposure to OP/CM accounted for 18% of the cases of human-related activity (Scott and Bollinger 2015). poisoning and nearly 2% of all eagle mortalities in our region. Conversely, it may be underestimated since some cases of Organophosphates and carbamates, introduced as an trauma of undetermined cause and some cases with an alternative for pest management following the ban on unknown cause of death may have been related to human organochlorine insecticides in the early 1970s, are widely activities. Regardless, our findings are consistent with other used pesticides that often result in the non-target exposure of human-related mortality patterns reported for bald eagles in bald eagles and other wildlife (Henny et al. 1987; Allen et al. North America that range between 30 ̶ 74% (Coon et al. 1970; 1996; Elliott et al. 1996; Fleischli et al. 2004; Wobeser et al. Harris and Sleeman 2007; Russell and Franson 2014; Scott 2004; Cowan and Blakley 2015). Poisoning of bald eagles by and Bollinger 2015) and indicate that anthropogenic factors OP/CM commonly results from scavenging on livestock continue to play a dominant role in mortality of this species carcasses illegally laced with OP/CM used as coyote (Canis in North America. The fact that birds in moderate to good latrans) baits to prevent livestock predation (Allen et al. body condition were more likely to die of human-related 1996; Cowan and Blakley 2015). Continuous monitoring of causes (specifically, trauma and electrocution) than birds in the use of OP/CM and increased public awareness of the poor body condition indicates that most traumatic injuries consequences of illegally baiting wildlife with OP/CM-laced were acute and that birds were otherwise healthy at the time carcasses are needed to mitigate future poisonings. In their of death. recent study, Hertz-Picciotto et al. (2018) highlighted the Study limitations human health hazards associated with organophosphate By the nature of the data involved, particularly the pesticides and advocated for a global ban on their identification and collection of carcasses, this and other agricultural and non-agricultural use. similar wildlife mortality studies are often limited by strong Three bald eagles in our study were identified as having biases such as observer density and awareness and the size, died from barbiturate poisoning. Because of bald eagles’ visibility and degree of preservation of carcasses (Coon et al. reliance on scavenging, the use of barbiturates such as 1970). Carcass counts alone most often underestimate actual
MATHIEU et al. 170
mortality by a large margin (Ponce et al. 2010), and estimates the current Maritime ecosystem, which is likely facilitated
of overall total mortality, even moderately accurate, are by its scavenging feeding habits, the diversity of its diet, and
difficult to achieve (Loss et al. 2014). The cost of some the abundance of shoreline. Nonetheless, human-related
diagnostic tools to identify more subtle causes of mortality causes of death, either direct or indirect, are an ongoing issue
may also limit their use to only a subsample of cases. For all in the Maritime provinces (MacDougall 2005), as they are in
these reasons, the proportion of various causes of mortality other Canadian provinces, and should not be ignored,
identified in this study may not be fully representative of the especially if mitigating measures are available. Reduction of
Maritime population of bald eagles at large, but more of the negative human impacts (e.g., through updated policies
segment of that population in relative proximity to human pertaining to lead-based ammunitions and fishing tackle,
habitation. pesticide use and trapping methods) is needed to better
Our failure to identify associations between causes of protect bald eagles and their habitats across Canada.
mortality and various spatial variables, for example between
trauma of human cause and proximity to roads, does not rule ACKNOWLEDGEMENTS
them out. Further studies would require a more detailed
We wish to thank all the people from the 3 Maritime
understanding of habitat characteristics and their change
provinces, particularly the provincial conservation officers
over time, possibly through satellite-based detection
and park wardens, who submitted carcasses of bald eagles
methods. Moreover, the location at which an eagle carcass
over the many years of this project, and Darlene Weeks and
is found may not represent the area where the factor that
Fiep de Bie, who helped in the necropsy of these carcasses
caused its death was encountered, even in the recent past.
throughout the duration of this project. Dr. María Forzán
Therefore, foraging and yearly movements of the birds must
also contributed substantially to the work involved.
also be considered. For example, bald eagle nesting habitat
(i.e., the home range in which they tend to display aggression
toward other eagles) is small and varies between 1 and 2 km LITERATURE CITED
in diameter. However, their yearly movements can easily Allen, G. T., J. K. Veatch, R. K. Stroud, C. G. Vendel, R.
encompass the 3 Maritimes provinces as well as H. Poppenga, L. Thompson, J. A. Shafer, and W. E.
Newfoundland and Labrador and the state of Maine and even Braselton. 1996. Winter poisoning of coyotes and raptors
further in rare instances, these movements being largely with Furadan-laced carcass baits. Journal of Wildlife
dictated by food availability (Austin-Smith and Gibson Diseases 32: 385 ̶ 389.
1994). Similarly, a detailed study of differences in habitat Austin-Smith, P., and M. Gibson. 1994. Bald eagles in the
characteristics and human demography between the Maritimes. Nature Watch East. Canning, Nova Scotia,
Maritime provinces and other regions of Canada, such as Canada.
road density, intensity of hunting and trapping activities, and Avery, D., and R. T. Watson. 2009. Regulation of lead-
pesticide use, would be required to explain some of the based ammunition around the world. Pages 161 ̶168 in R.T.
differences noted in prevalence of causes of mortality Watson, M. Fuller, M. Pokras, and W.G. Hunt, editors.
between these regions. Ingestion of lead from spent ammunition: implications for
wildlife and humans. The Peregrine Fund, Boise, Idaho,
USA. DOI 10.4080/ilsa.2009.0115
CONCLUSIONS Bedrosian, B., D. Craighead, and R. Crandall. 2012. Lead
The results of this retrospective study are in agreement
exposure in bald eagles from big game hunting, the
with similar work by others on causes of death of bald eagles
continental implications and successful mitigation efforts.
in Canada (Wobeser et al. 2004; Desmarchelier et al. 2010;
PloS One 7(12):e51978. doi:10.1371/journal.pone.
Cowan and Blakley 2015; Scott and Bollinger 2015; Smith
0051978.
et al. 2018). Despite the important caveats mentioned earlier,
Boeker, E. L., and P. R. Nickerson. 1975. Raptor
studies like this and others can provide valuable insight into
electrocutions. Wildlife Society Bulletin 3: 79 ̶ 81.
the short- and long-term population health trends of wildlife
Coon, N.C., L.N. Locke, E. Cromartie, and W.L. Reichel.
species as well as identify some of the natural and
1970. Causes of bald eagle mortality, 1960-1965. Journal
anthropogenic factors that affect their survival. The
of Wildlife Diseases 6: 72 ̶ 76.
population of bald eagles in Canada is currently “not at risk”
Cowan, V.E., and B. R. Blakley. 2015. A retrospective
(Government of Canada 2011) and has actually increased
study of cases of acetylcholinesterase inhibitor poisoning
markedly in PEI in the last few decades (MacDougall 2005).
in the coyote (Canis latrans) and the bald eagle (Haliaeetus
This species therefore appears to be supported adequately byMATHIEU et al. 171 leucocephalus) in the Canadian Prairies. Journal of Clinical Fitzner, R. E. 1978. Behavioral ecology of the Swainson’s Toxicology 5(2). DOI: 10.4172/2161-0495.1000235 hawk (Buteo swaInsoni) in southeastern Washington. PhD Cruz-Martinez, L., P.T. Redig, and J. Deen. 2012. Lead dissertation. Washington State University, Pullman, from spent ammunition: a source of exposure and Washington, USA. poisoning in bald eagles. Human-Wildlife Interactions 6: Fleischli, M. A., J. C. Franson, N. J. Thomas, D. L. Finley, 94 ̶ 104. and W. Riley, Jr. 2004. Avian mortality events in the Dawson, J. W., and R. W. Mannan. 1994. The ecology of United States caused by anticholinesterase pesticides: a Harris’ hawks in urban environments. Arizona Game and retrospective summary of National Wildlife Health Center Fish Department, Final Report. Urban Heritage Grant LOA records from 1980 to 2000. Archives of Environmental G20058-A, Tucson, Arizona, USA. Contamination and Toxicology 46: 542 ̶ 550. Deem, S. L., S. P. Terrell, and D. J. Forrester. 1998. A Fraser, J. D. 1985. The impact of human activities on bald retrospective study of morbidity and mortality of raptors in eagle populations - a review. Pages 68 ̶ 84 in J. M. Gerrard Florida: 1988-1994. Journal of Zoo and Wildlife Medicine and T. N. Ingram, editors. The bald eagle in Canada. White 29: 160 ̶ 164. Horse Plains Publishers, Headingly, Manitoba, Canada. Desmarchelier, M., A. Santamaria-Bouvier, G. Government of Canada. 2011. Species profile - Bald eagle. Fitzgérald, and S. Lair. 2010. Mortality and morbidity https://wildlife-species.canada.ca/species-risk- associated with gunshot in raptorial birds from the province registry/species/speciesDetails_e.cfm?sid=323 Accessed of Québec: 1986 to 2007. Canadian Veterinary Journal 51: March 2020. 70 ̶ 74. Government of Canada. 2013. Driscoll, C., E. Miller, G. D. Therres, V. Milne, B. Findley, Dichlorodiphenyltrichloroethane. https://www.ec.gc.ca/ and K. Endress. 2004. An interagency investigation into toxiques-toxics/Default.asp?lang=En&n=98E80CC6-1& causes of bald eagle (Haliaeetus leucucephalus) and xml=13272755-983C-4DF5-8EA2-E734EFC39869 golden eagle (Aquila chrysaetos) mortality in Maryland Accessed March 2020. 1988-2004 (Abstract). In C. K. Baer, editor. Proceedings of Government of Canada. 2018a. Study to gather the Joint Conference of the American Association of Zoo information on uses of lead ammunition and non-lead Veterinarians, American Association of Wildlife alternatives in non-military activities in Canada. Veterinarians, and Wildlife Disease Association. San https://www.canada.ca/en/environment-climate-change/ Diego, California, USA. services/management-toxic-substances/list-canadian- Elliott, J.E., K.M. Langelier, P. Mineau, and L.K.Wilson. environmental-protection-act/lead/using-more-lead-free- 1996. Poisoning of bald eagles and red-tailed hawks by ammunition/lead-ammunition-executive-summary.html carbofuran and fensulfothion in the Fraser Delta of British Accessed March 2020. Columbia, Canada. Journal of Wildlife Diseases 32: Government of Canada. 2018b. Moving towards 486 ̶ 491. using more lead-free ammunition. ESRI Data & Maps. 2019. North America major roads. https://www.canada.ca/en/environment-climate-change http://arcgis.com Accessed March 2020. /services/management-toxic-substances/list-canadian- Fairbrother, A. 1996. Cholinesterase-inhibiting pesticides. environmental-protection-act/lead/using-more-lead-free- Pages 52 ̶ 60 in A. Fairbrother, L. Locke, and G. Hoff, ammunition.html Accessed March 2020. editors. Noninfectious diseases of wildlife. 2 nd Edition. Harris, M. C., and J. M. Sleeman. 2007. Morbidity and Iowa State University Press, Ames, Iowa, USA. mortality of Bald eagles (Haliaeetus leucocephalus) and Fédération des trappeurs gestionnaires du Québec. 2014. Peregrine falcons (Falco peregrinus) admitted to the Eagles and trapping: how to avoid accidental catches. Wildlife Center of Virginia, 1993-2003. Journal of Zoo and https://www.uqrop.qc.ca/upload/files/fascicule_oiseaux_p Wildlife Medicine 38: 62 ̶ 66. roie_ang_r.pdf Accessed March 2020. Henny, C. J., E. J. Kolbe, E. F. Hill, and L. J. Blus. 1987. Ferrer, M., and F. Hiraldo. 1992. Man-induced sex-biased Case histories of bald eagles and other raptors killed by mortality in the Spanish imperial eagle. Biological organophosphorus insecticides topically applied to Conservation 60: 57 ̶ 60. livestock. Journal of Wildlife Diseases 23: 292 ̶ 295. Fitzgerald, G., J. A. Tremblay, J. Lemaître, and A. St- Hertz-Picciotto, I., J. B. Sass, S. Engel, D. H. Bennett, A. Louis. 2015. Captures accidentelles d'aigles royaux et de Bradman, B. Eskenazi, B. Lanphear, and R. Whyatt. pygargues à tête blanche par les trappeurs d'animaux à 2018. Organophosphate exposures during pregnancy and fourrure au Québec. Le Naturaliste Canadien 139: 82 ̶ 89. child neurodevelopment: Recommendations for
MATHIEU et al. 172 essential policy reforms. PLoS Medicine Russell, R. E., and J. C. Franson. 2014. Causes of mortality https://doi.org/10.1371/journal.pmed.1002671 in eagles submitted to the National Wildlife Health Center Holroyd, G. L., and D. M. Bird. 2012. Lessons learned 1975-2013. Wildlife Society Bulletin 38: 697 ̶ 704. during the revovery of the peregrine falcon in Canada. Scheuhammer, A. M, S. L. Money, D. A. Kirk, and G. Canadian Wildlife Biology & Management 1: 3 ̶ 20. Donaldson. 2003. Lead fishing sinkers and jigs in Canada: Langelier, K. M. 1993. Barbiturate poisoning in twenty- review of their use patterns and toxic impacts on wildlife. nine bald eagles. Pages 231 ̶ 232 in P. T. Redig, J. E. Occasional Paper no. 108. Canadian Wildlife Service, Cooper, J. D. Remple, and D. B. Hunter, editors. Raptor Ottawa, Ontario, Canada. biomedicine. University of Minnesota Press, Minneapolis, Scott, S. J., and T. K. Bollinger. 2015. The causes of eagle Minnesota, USA. mortality in Saskatchewan, 1992-2012. Canadian Wildlife Lehman, R. N., P. L. Kennedy, and J. A. Savidge. 2007. Biology & Management 4: 31 ̶ 39. The state of the art in raptor electrocution research: A Sibley, D. A. 2014. The Sibley guide to birds. 2nd Edition. global review. Biological Conservation 136: 159 ̶ 174. Alfred A. Knopf, New York, New York, USA. Loss, S. R., T. Will, and P. P. Marra. 2014. Refining Simon, K. L., D. A. Best, J. G. Sikarskie, H.T. Pittman, estimates of bird collision and electrocution mortality at W. W. Bowerman, T. M. Cooley, and S. Stolz. 2020. power lines in the United States. PLoS ONE 9(7):e101565. Sources of mortality in bald eagles in Michigan, 1986– doi:10.1371/journal.pone.0101565 2017. Journal of Wildlife Management 1-9. DOI: MacDougall, D. G. 2005. The essential natural features and 10.1002/jwmg.21822 critical human disturbance parameters of sustainable bald Smith, K. A., G. D. Campbell, D. L. Pearl, C. M. Jardine, eagle Haliaeetus leucocephalus nesting habitat on Prince F. Salgado-Bierman, and N. M. Nemeth. 2018. A Edward Island. MS thesis, Royal Roads University, British retrospective summary of raptor mortality in Ontario, Columbia, Canada. Canada (1991-2014), including the effects of West Nile Martin, P. A., D. Campbell, K. Hughes, and T. McDaniel. virus. Journal of Wildlife Diseases 54: 261 ̶ 271. 2008. Lead in the tissues of terrestrial raptors in southern Statistics Canada. 2019. Dictionary, Census of Population, Ontario, Canada, 1995-2001. Science of the Total 2016. https://www12.statcan.gc.ca/census- Environment 391: 96 1̶ 03. recensement/2016/ref/dict/index-eng.cfm. Accessed July McCollough, M. A. 1989. Molting sequence and aging of 2020. bald eagles. The Wilson Bulletin 101: 1 ̶ 10. Stauber, E., N. Finch, P. A. Talcott, and J. M. Gay. 2010. Morishita, T. Y., A. T. Fullerton, L. J. Lowenstine, I. A. Lead poisoning of bald (Haliaeetus leucocephalus) and Gardner, and D. L. Brooks. 1998. Morbidity and golden (Aquila chrysaetos) eagles in the U.S. Inland mortality in free-living raptorial birds of northern Pacific Northwest region—an 18-year retrospective study: California: a retrospective study, 1983-1994. Journal of 1991– 2008. Journal of Avian Medicine and Surgery 24: Avian Medicine and Surgery 12: 78 ̶ 81. 279 ̶ 287. Murray, M. 2011. Anticoagulant rodenticide exposure and Treasury Board of Canada Secretariat. 2019. Federal toxicosis in four species of birds of prey presented to a Contaminated Sites Inventory. https://www.tbs- wildlife clinic in Massachusetts, 2006-2010. Journal of sct.gc.ca/fcsi-rscf/opendata-eng.aspx Accessed March Zoo and Wildlife Medicine 42: 88 ̶ 97. 2020. Ponce, C., J. C. Alonso, G. Argandoña, A. García U.S. Fish & Wildlife Service. 2018a. Bald and Golden Fernández, and M. Carrasco. 2010. Carcass removal by Eagle Protection Act. https://www.fws.gov/birds/policies- scavengers and search accuracy affect bird mortality and-regulations/laws-legislations/bald-and-golden-eagle- estimates at power lines. Animal Conservation 13: protection-act.php Accessed March 2020. 603 ̶ 612. U.S. Fish & Wildlife Service. 2018b. Migratory Bird Treaty Proulx, G., D. Rodtka, M. W. Barrett, M. Cattet, D. Act. https://www.fws.gov/birds/policies-and- Dekker, E. Moffatt, and R. A. Powell. 2015. Humaneness regulations/laws-legislations/migratory-bird-treaty- and selectivity of killing neck snares used to capture canids act.php Accessed March 2020. in Canada: a review. Canadian Wildlife Biology & U.S. Fish & Wildlife Service. 2019. History of bald eagle Management 4: 55 ̶ 65. decline, protection and recovery. Richardson, C. T., and C. K. Miller. 1997. https://www.fws.gov/pacific/ecoservices/BaldEagleDelisti Recommendations for protecting raptors from human ng.htm Accessed March 2020. disturbance. Wildlife Society Bulletin 25: 634 ̶ 638.
MATHIEU et al. 173
Wayland, M., and T. Bollinger. 1999. Lead exposure and AVC to complete a joint residency in morphologic and
poisoning in bald eagles and golden eagles in the Canadian wildlife pathology in 1994. Scott then became a wildlife
prairie provinces. Environmental Pollution 104: 341 ̶ 350. pathologist and the first staff member for the Canadian
Wobeser, G. A. 1997. Diseases of wild waterfowl. 2nd Wildlife Health Cooperative, Atlantic Region. His primary
edition, Plenum Press, New York, New York, USA. focus is using scanning and targeted wildlife health
Wobeser, G., T. Bollinger, F.A. Leighton, B. Blakley, and surveillance to develop evidence-based management
P. Mineau. 2004. Secondary poisoning of eagles following strategies for the protection of wildlife health throughout
intentional poisoning of coyotes with anticholinesterase Canada.
pesticides in western Canada. Journal of Wildlife Diseases Colin Robertson is an
40: 163 ̶ 172. associate professor in the
ABOUT THE AUTHORS Department of Geography and
Environmental Studies at
Amélie Mathieu is a wildlife
Wilfrid Laurier University and
veterinarian with the British
an associate with the Canadian
Columbia Ministry of Forests,
Wildlife Health Cooperative
Lands, Natural Resource
(National Office). Colin is
Operations and Rural
interested in understanding the
Development. She received her
role that environmental change has on the health of human
Doctor of Veterinary Medicine
and animal populations and how GIS and spatial modelling
degree from the Université de
tools can help to understand the wildlife health.
Montréal in 2012, after which
Helene Van Doninck was a wildlife veterinarian and the
she completed veterinary
founder of the Cobequid Wildlife Rehabilitation Centre.
internships in small animal medicine, zoo medicine and
Dr. Van Doninck saw far too many cases of lead poisoning
wildlife health and a combined residency (ecosystem health
in avian wildlife. She became a leader in promoting the
and conservation medicine) and master’s program (Master of
elimination of lead
Science in Veterinary Preventive Medicine) at the Ohio State
in ammunition and
University, the Columbus Zoo and Aquarium and The Wilds.
fishing tackle, not
Jane Parmley is an associate professor in the Department
only in this region,
of Population Medicine at the
but also in the rest
University of Guelph and an
of Canada and in
epidemiologist with the Canadian
the United States.
Wildlife Health Cooperative
She is sorely
(National Office). Jane is
missed.
interested in messy but fascinating
Pierre-Yves Daoust is a wildlife pathologist with a
health challenges and works to
particular interest in the marine environment. He is Professor
better understand the many drivers
Emeritus of Anatomic
that influence health and the
Pathology and Wildlife
interconnections between humans, animals and our shared
Pathology in the Department
environments.
of Pathology &
Scott McBurney used his BSc
Microbiology, Atlantic
(Honors) in wildlife biology,
Veterinary College,
University of Guelph during a 6-
University of Prince Edward
yr resource conservation career
Island, and former Director of
as a National Park Warden.
the Atlantic regional centre of
Despite a love for National
the Canadian Wildlife Health Cooperative.
Parks, he continued to have a
passion to apply veterinary Received 22 April 2020 – Accepted 20 July 2020
medicine to the field of wildlife
health. Therefore, Scott returned to university, graduating
with a DVM in the first veterinary class of the Atlantic
Veterinary College (AVC). Subsequently, he returned to theYou can also read
