Sources of Mortality in Bald Eagles in Michigan, 1986–2017

Abstract

As bald eagle populations recover, defining major sources of mortality provides managers important information to develop management plans and mitigation efforts. We obtained data from necropsies on 1,490 dead bald eagles (Haliaeetus leucocephalus) collected in Michigan, USA, conducted from 1986 to 2017 to determine causes of death (COD). Trauma and poisoning were the most common primary COD categories, followed by disease. Within trauma and poisoning, vehicular trauma (n = 532) and lead poisoning (n = 176) were the leading COD subcategories, respectively. Females comprised a greater number of carcasses for most COD diagnoses. The proportion of trauma and poisoning CODs significantly increased in the last few years of the study in comparison to a select few years at the beginning. Trauma CODs were greater in autumn months during whitetail deer (Odocoileus virginianus) breeding and hunting seasons and in February, when aquatic foraging is unavailable and eagles are likely forced to scavenge along roadsides. Poisoning CODs were greatest in late winter and early spring months, when deer carcasses containing lead ammunition, which are preserved by the cold weather, also become a supplemental food source. The major infectious disease CODs, West Nile virus and botulism (Clostridium botulinum type E), were more prevalent during summer months. We recommend moving road‐killed carcasses, especially white‐tailed deer, from the main thoroughfare to the back of the right‐of‐way, and the transition from lead ammunition and fishing tackle to non‐toxic alternatives to decrease these main anthropogenic sources of mortality for bald eagles, and other scavenger species. © 2020 The Wildlife Society.

Illegal killing of nongame wildlife and recreational shooting in conservation areas

“…Similarly, illegal persecution, often shooting, also is an important cause of death of golden eagles ( Aquila chrysaetos ) in North America and Europe (U.S. Fish and Wildlife Service, 2016; Whitfield & Fielding, 2017), and bald eagles ( Haliaeetus leucocephalus ) in Michigan (Simon et al, 2020). Finally, the decline of rattlesnake populations in several states is well documented and associated with heavy persecution (Parker & Brown, 1973; Warwick, Steedman, & Holford, 1991).…”

Successful medical management of an acute case of pentobarbital toxicosis in a wild bald eagle (Haliaeetus leucocephalus)

“…Acute secondary sodium pentobarbital toxicosis in wild animals has been documented as a cause of acute death in wild, captive and domestic animals worldwide. [9][10][11] A recent review of causes of mortality in bald eagles in the Canadian Maritime provinces between 1991 and 2016 demonstrated that barbiturate toxicoses was the cause of death of 3% of bald eagles presented for postmortem examination during the study period. Though poisoning was a relatively infrequent cause of death compared to other causes, the prevalence may be underestimated, as the presence of poison was not evaluated in all cases of nonspecific clinical signs or unknown cause of death.…”

“…Acute secondary sodium pentobarbital toxicosis in wild animals has been documented as a cause of acute death in wild, captive and domestic animals worldwide 9–11 . A recent review of causes of mortality in bald eagles in the Canadian Maritime provinces between 1991 and 2016 demonstrated that barbiturate toxicoses was the cause of death of 3% of bald eagles presented for postmortem examination during the study period.…”

Assessment of a voluntary nonlead ammunition outreach program on midwestern national wildlife refuges

“…This issue was again demonstrated during 2012 when 58 bald eagles were collected across Iowa, Minnesota, and Wisconsin with 60% of the birds having detectable lead concentrations linked to consumption of white-tailed deer gut piles containing lead bullet fragments (Warner et al, 2014). During 1986During -2017 in Michigan, lead poisoning was the second leading cause of bald eagle death followed by vehicular trauma demonstrating the long-term and broad scale nature of the problem (Simon et al, 2020). Other research has demonstrated broad scale mortality of bald eagles linked to lead ammunition corresponding to fall firearms deer hunting seasons (Cruz-Martinez et al, 2012;Golden et al, 2016;Hunt et al, 2006) and other hunting activities (Haig et al, 2014;Herring, Eagles-Smith, & Wagner, 2016).…”

“…Of particular concern is lead poisoning in bald eagles (Cruz-Martinez et al, 2012;Warner et al, 2014). In Michigan, mortality by ingestion of lead bullet fragments was the second leading cause of death among bald eagles during 1986-2017 (Simon et al, 2020). Despite concern for bald eagles, the complexity and polarization surrounding firearms and ammunition (Smyth, 2020;Whitney, 2012) has fostered a climate of trepidation among natural resource decision-makers (Cromie et al, 2019;Schulz et al, 2019).…”