When summer’s bounty of bugs, seeds, and nectar starts to wane, most birds in Colorado seek warmer climes with good food to offer. But one group of birds sticks it out year-round, subsisting on nothing but leaves and twigs: the galliforms. Ivett—who once spent a week in a remote Oaxacan town eating literally only beans—can attest that the human digestive tract is not well suited to an unvaried diet of tough plant matter, but it turns out that such a diet can be quite pleasant if you’re a pheasant. The secret to the birds’ success lies in their specialized digestive anatomy, which lets them comfortably enjoy Colorado’s snowy winters.
“Galliform” comes from the Latin word gallina, meaning “chicken”. So it includes all those chicken-like birds such as pheasants, turkeys, grouse, and quail. The hundreds of species in the Order Galliformes live on every continent except Antarctica. They are mainly terrestrial birds, with strong beaks and legs. They are specialized for powerful bursts of flight and short glides at low elevations. Because they are not long-distance migrants, they stay lean and mobile to avoid predators.
White-tailed ptarmigan will often roost in the snow.
The well-adapted digestive anatomy of these birds starts before the stomach with an organ called the “crop”, a pouch where a great deal of food can be stored. This organ allows some birds to gather a whole day’s worth of calories in less than an hour. While other permanent residents like chickadees flit around, shivering to keep warm and constantly eating to replenish their energy, a grouse’s crop allows it to take a relatively calm approach to winter. For a white-tailed ptarmigan, that might mean cozying up in a roost beneath the snow with a crop full of willow twigs. A Gunnison’s sage grouse might do the same with a tasty supply of sagebrush leaves.
All that cellulose and lignin in plant matter are extremely difficult to break down, so the next stop is a two-part stomach. First, the birds bathe their food in digestive enzymes. Then the chemically weakened food goes into a strong, muscular gizzard, where it is pulverized with the help of foraged grit. The birds eat pebbles and sand for this purpose. Find the right gravel roadside at sunset, and you can watch grouse gather to gussy up their gizzards and socialize. Wild turkeys have even been known to use cast-off .22 shells to grind their food (but please pick up your empties).
The small intestine does what it can, then sends the toughest plant material right to the large intestine. Nutrient-rich liquid travels to the bird’s pièce de résistance, the true secret to its year-round success as an avian herbivore: the cecum.
The cecum is probably best described as “really gross.” Lydia once worked on a project dissecting small mammals, and the yuck factor of tapeworms, liver flukes, and testicular nematodes was nothing compared to a whiff of a cecum. This organ, which sits between the small and large intestines, is full of bacteria that ferment incredibly difficult-to-digest materials. With remarkable speed, the bacteria anaerobically extract a number of volatile fatty acids, which are a significant source of energy for the birds. If you’re not impressed yet, think about this—thanks to two very long ceca (cecum, plural), a dusky grouse lives all winter on a monotonous diet of spruce needles while maintaining a body temperature of around 40°C (104°F).
Winter may be tough for wild animals, but there’s no need to bail if you're quail. You don’t need a vacation house if you’re a grouse. And if you’re a chukar, you’re one tough…we’ll stop there.
Lydia Delehanty and Ivett López Garcia work at Walking Mountains. Lydia spent most childhood dinners eating and learning about galliforms, thanks to her hunter-ornithologist father. Ivett is a Naturalist with a passion for conservation biology, ecology, and environmental education.
