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Virus has been found to cause mortality in a number of avian species both in
Michigan and across the United States but during the spring and summer months it
is not unusual for mortality unrelated to a West Nile Virus infection to occur
in a variety of avian (bird) species. In the spring, as adult birds
migrate north, they are exposed to many changes in weather, availability of
food, and competition with other birds of their own species as well as other
species. This is an extremely stressful time of the year for all adult birds
and any change in the weather or habitat may result in malnutrition, exposure,
and dehydration. The main activities of adult birds in the spring revolve
around establishing territories, courtship, and breeding, As a result of these
activities the animals are often-times more susceptible to injury or death due
to trauma (flying into a house, being hit by a car, etc), predation (either
mammalian or avian), intraspecies competition (injuries inflicted by a member of
the same species), or interspecies competition (injuries inflicted by a member
of another avian species).
months bring about vast quantities of young birds which, because of their age,
are susceptible to many of the same problems faced by the adults during the
spring as well as some additional problems. Young, naive birds are very
susceptible to traumatic injuries (falling out of their nest, injuring
themselves as they fledge from the nest, and competition between siblings),
predation (either while still in the nest or during fledging), diseases due to
an undeveloped or underdeveloped immune system (lack of resistance to bacterial
and viral diseases), malnutrition and/or exposure, and developmental problems.
Adult birds may also be more susceptible to mortality as they attempt to
incubate, brood, care for, and protect their eggs and young.
conclusion, it is possible that birds found dead in the spring and summer may
have died from a West Nile Virus infection, but it is more likely that for the
majority of species of birds in the state that death is due to some other
factor. Please continue to use the On-Line WNV
Sick and Dead Bird Observation Report to report instances of bird and mammal
mortality. This data will be used to detect trends, over time, to
determine a normal baseline wildlife mortality figure.