Types of Wildlife Mortality

As a follow up from the last post, today we’ll go over the different types of wildlife mortality. There are many different ways your animals can die, when we discuss these ways, you can see how to prevent these types of mortality as much as possible.

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  1. Starvation and Malnutrition:
    • Starvation is death or debilitation caused by a lack of food quantity – more common among carnivores
    • Malnutrition is death or debilitation caused by a lack of food quality – more common among herbivores
    • Starvation and malnutrition usually affect certain age groups – especially the very old or very young – more severely than other age groups
  2. Accidents: In their natural environments, most wildlife populations exhibit low frequencies of accidental deaths. Major sources of accidents: highways, railroads, fences, power lines, towers, etc (obviously all man-made).
  3. Exposure: Death due to severe weather – usually most important near the outer limits of the animal’s geographical range.
  4. Harvest: Hunting, trapping, fishing
    • Harvestable Surplus: the number of animals that can be harvested (removed) from a population without affecting the size of the population at some later time (like the next breeding season)
    • Overharvest: taking more animals than consistent with management goals. How could this occur:
      • Poor law enforcement
      • Weather makes animals more vulnerable
      • Overestimate harvestable surplus – poor data!
    • Underharvest: taking too few animals. How could this occur:
      • Legal restrictions discourage hunters
      • Original population size underestimated
      • Management policy too conservative
    • Its important to remember: the over-all efficiency of hunters is low!!!

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5. Predation: quality control of wildlife populations – predation has a “sanitation effect” often removing the old, sick, or injured animals.

6. Disease: Wildlife disease is defined as a disturbance to the normal function or structure of an animal.

  • The causes of most wildlife diseases can be classified as:
    1. Infection or Non-Infectious: e.g., lead poisoning
      • Infectious Diseases of Wildlife – caused by a variety of pathogens including viruses, bacteria, endoparasites, or ectoparasites
      • Normal-Persistent Infections: Wildlife has evolved with, and are able to handle, most of the infectious diseases common in their environment. Infections or the normal abundance of parasites in an animal (the “parasite load”) can become a problem when an animal’s resistance is lowered. This can happen due to severe weather or by stress associated with crowding and poor nutrition. Wildlife diseases caused by normal parasites, those with which the animals evolved, are often a symptom of poor habitat conditions!
    2. Epizootic – term used to refer to widespread outbreaks of infectious diseases in wildlife populations (epidemic = human)
    3. Host-Parasite Relationship in Infectious Diseases – parasites involved in infectious diseases often complete their life cycle in more than one species of animal host.

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Now that we’ve discussed the top reasons for wildlife mortality, you can understand the parameters you will have to face as a wildlife manager in order to keep these types of mortality to a minimum within your animals. Next post we will go deeper in wildlife disease, which is one of the biggest types of mortality that can be hard to defeat by mere mortals.

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