Laura Erickson's For the Birds

When most people ask me about birds, they first apologize, believing I’ll think their questions are stupid. But the stupidest question I ever came up with turned out to have a pretty interesting answer.

The day I got my first injured nighthawk to take care of, I discovered that it produced two completely different kinds of droppings, which didn’t jibe with anything I’d seen in other birds. After I’d cared for several nighthawks, I came to realize that the two different droppings types are typical of the species, but even though I was curious about it, the issue of droppings somehow didn’t seem like a fitting topic for investigation. But the more I handled these handsome and gentle-spirited birds, the more I wanted to learn about them, and it slowly dawned on me that nobody else knew anything about their unique digestion either. Nighthawks are difficult for people to keep alive in captivity because they need frequent hand-feeding, so it was hard to find anyone who had observed what I saw.

Then I decided I was approaching the question from the wrong direction, and I started reading general ornithology textbook chapters about bird digestion. That’s when I learned that some birds have a structure called a caecum. Just in case your memory of general biology is no better than mine, the caecum is a pair of intestinal offshoots branching out where the small intestine meets the large. In humans, the appendix occurs at the site of our caeca. Ostriches, chickens, Ruffed Grouse, and some other birds have very well-developed caeca. The descriptions of a chicken’s caecal droppings matched exactly what I saw for nighthawks.

So all I needed to find out was whether nighthawks also have well-developed caeca, which seemed like the kind of basic question I could surely find an answer to somewhere. But none of my textbooks or reference works on birds had any itemization of which birds have a caecum and which don’t. I didn’t find proof that nighthawks have a caecum until I went to the UMD library and found a book published in 1898 about the structure and classification of birds.

It turns out that early ornithologists used the caecum as one of the primary pieces of evidence in establishing the taxonomic order of birds, much of which is still accepted today. This 95-year-old book explained that the reason ornithologists originally concluded that owls aren’t related to hawks and falcons is that owls have large caeca while other birds of prey have none at all. Although I had an intuitive sense of the relationship of owls to nighthawks because of their excellent nocturnal vision and soft, pencilled plumage, it turns out that internally these two groups are even more similar, sharing virtually identical digestive systems. Some ornithologists believe that owls were originally insect eaters that eventually adapted to taking bigger prey. So wondering about nighthawk droppings ended up leading me to the explanation of why nighthawks are illustrated near owls in field guides, as well as giving me some insight into the work ornithologists were doing a hundred years ago. Not bad for a stupid question.