Canada geese in the wrong place, at the wrong time
On June 14, 52 adult Canada geese (Branta canadensis) were found dead in Contrecœur, Quebec. All carcasses were in the water of the St. Lawrence River in a relatively small area. Several seemingly healthy geese (no mortality) were present on the mainland nearby. The dead birds did not show obvious signs of trauma. Forty-nine of these geese were submitted for examination to the CWHC – Quebec Regional Center (Figure 1).
All geese were in a very good state of conservation; post-mortem changes were mild and similar between birds, indicating a relatively recent and synchronized mortality (all birds died at the same time or over a very short period of time). All birds were also in excellent body condition and their digestive tracts contained a large amount of food material (whole corn in the esophagus and stomach), indicating that the birds had been feeding very shortly before death. This indicates that the geese died from an acute condition.
On gross examination of the carcasses, the lungs were diffuse oedematous and the kidneys were diffusely congested. Multifocal cardiac hemorrhages and subcutaneous emphysema were observed in some of the birds. Tissues were collected from ten geese for microscopic examination. All geese examined showed a marked vascular congestion in one or more organs. Cardiac hemorrhages were also observed in 40% of the birds examined (Figure 2).
Table 1: Histological lesions detected in Canada geese during complete necropsy.
|Histological lesions detected||Number of birds affected|
|Vascular congestion – spleen||8/10|
|Vascular congestion – kidney||8/10|
|Vascular congestion – lung||6/10|
|Vascular congestion – intestinal tract||3/4|
|Vascular congestion – liver||2/10|
The features of this episode of mortalities (good body condition, recent feeding, synchronized mortalities and restricted spatial distribution), field observations, as well as the findings of the necropsies, point towards electrocution by lightning. This circumstantial diagnosis is supported by observations of violent thunderstorms in this area during the evening prior to the finding. Witnesses reported seeing lightning bolts falling on the water during these storms. The absence of trauma, which would probably have been present if the birds had been struck down in flight, suggests that they were struck by lightning while swimming.
Lightning-related mortalities have been reported in a few mammal species (roe deer, Australian sea lions, for example) and migratory birds, including bean geese, snow geese, Canada geese, and other species of waterfowls, as well as in whooping cranes.
When an individual is struck by lightning, a very short but very powerful transfer of electricity occurs. This charge transfer causes significant electrical disturbances in the heart, nervous system, and muscles, thus causing multisystemic failures. In humans, there are between 100 and 600 lightning-associated deaths in the United States each year; with a mortality rate of about 30% of cases, most of which are caused by cardiac arrest. No data is available for wild animals, but the number of reported cases undoubtedly underestimates this phenomenon. Burns, which are often superficial, are the most frequently reported lesions in humans struck by lightning, and although lesions of burns were not detected on the carcasses of the geese examined, their thick plumage may have covered subtle lesions.
Although the circumstances of this episode of mortality and the observations made during the examination of the carcasses pointed toward a diagnosis of electrocution by lightning, additional diagnostic tests were carried out to rule out other causes of group mortality, such as an outbreak of avian influenza or poisoning. Testing for Avian Influenza virus was negative. Toxicological analyzes are ongoing. Since all geese have died synchronously on the water and since no other species has been found dead in the same area, it is unlikely that these mortalities were associated with poisoning. It just seem that these geese found themselves in the wrong place at the wrong time.
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By Karine Béland and Stéphane Lair, CWHC – Quebec