It has been known for years that in a range of animals from insects to birds the males increase the quality and quantity of the sperm they ejaculate when those sperm are likely to find themselves in competition with sperm from another male.

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The problem will be worsened by global warming affecting the population balance of animal predators such as owls, snakes, birds and bats, animals that keep insects and rodents in check.

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They concluded that such upwellings might indeed account for the catastrophic fish deaths, but that they would not explain the deaths of insects, reptiles, birds and mammals, since these animals breathe air rather than relying on dissolved oxygen.

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