Why there is no such thing as a migratory carnivore

Robin and the Honey Badger respond: It’s true that carnivores give birth to immobile young. Nevertheless, there must be a more basic reason why, worldwide, no carnivore has adapted its reproduction to keep up with the full circuit of any migratory herbivore. In the Serengeti, where wildebeest, zebra, Thomson’s gazelle and eland migrate hundreds of kilometres each year, neither lion nor spotted hyena nor cheetah nor painted dog migrate in tandem. Instead, these predators tend to reside year-round in a fixed area and to endure a season of hunger when the migratory herbivores are away. Similarly, in Alaska, the barren-ground caribou migrates from taiga to tundra and back each year, yet the wolf accompanies it only part of the way and thus misses the birth season of its prey when killing would theoretically be easiest. The reason is that herbivores use microbial fermentation in gut chambers to convert green fibre to saturated fatty ions. These components of saturated fats are an optimal source of energy for muscles. By contrast, the carnivores rely on costly denitrification of the excessive protein in their diets, which leaves them with glucose, a suboptimal fuel for muscles relative to saturated fatty ions. Because the grades of fuel differ between the two trophic levels, the inability of carnivores to migrate is thermodynamically inevitable rather than being a mere accident of phylogeny.