For years, visitors to the Scottish island of Rum were puzzled to find the bodies of Manx shearwater chicks missing their heads, wingbones and leg bones. Then a few years ago, a hunter saw a red deer chewing on a chick. Scientists used that sighting to give them clues, and now it seems clear that the deer are eating parts of the chicks to give them the calcium they need to grow strong antlers.
This isn’t the only instance of supposed vegetarians eating meat. There are bird-eating sheep in the Shetland islands. In the U.S. the miniature video cameras biologists use to monitor nests are revealing that weasels, mice, ground squirrels, and white tail deer eat both eggs and birds. Canadian bird researchers capturing songbirds in mist nets were astonished to see deer eating the birds right out of the nets.
It all makes sense when we think about how animals choose what to eat. When they experience a deficiency, such as calcium or phosphorous, animals experiment with new foods. If they find something that solves the problem, they continue to eat it. Both eggs and nestlings are good sources of protein, fats, vitamins and minerals and they’re just right for a grazer who’s missing a little something in its diet.
So, how concerned should we be about the impact of omnivorous herbivores? It seems that they aren’t eating enough birds or eggs to harm the population. Wyoming Game and Fish chief biologist Reg Rothwell says, “It’s not a huge problem, and it’s probably been going on for eons.”