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A Dogs Dilemma 狗的两难境地 Finding a babysitter while you go out to work is, for example, an inconvenience. For the African wild dog, one of the continents most endangered carnivores, its a matter of life and death. New research shows that once packs fall below a certain size, there are not enough animals to both hunt food and stay at home protecting the young. The African wild dog has declined drastically over the past century. Habitual loss, persecution and unexplained outbreaks of disease have all been blamed. Only 3,000 to 5,000 animals remain, and the species is expected to go extinct within decades if the trend continues. Other large carnivores such as the spotted hyena face similar pressures, yet are not declining. Now Franck Courchamp of Cambridge University has found a reason why. The dogs weakness lies in its social organisation. Within each pack of up to 20 adults and pups, only the dominant male and female breed. The remaining animals help raise the pups, cooperating to hunt prey and defend the kill from other carnivores. Because pups cant keep up on a hunt, large packs leave an adult behind to protect them from predators, which include lions and hyenas. But leaving a babysitter also carries costs. A smaller hunting party is less able to tackle large prey and to defend the kill. There is also one less stomach in which to carry food back to the den, and one more mouth to feed when they get there. | 
