For the Birds Radio Program: Indigo Buntings: The Inside Story
Today Laura Erickson gives the inside scoop on Indigo Buntings. 3:52
Last week I taught a bird class at a camp for sixth and seventh grade girls offered every year at the College of St. Scholastica in Duluth. It’s great fun for me–I have a class of only seven girls, and we get to study birds in depth for a full week. We watch behavior of wild birds on the college campus, study captive birds in the classroom, and dissect one poor unfortunate bird–this year an Indigo Bunting that had been hit by a car and donated to the school. This particular bird was a male, and since it was June, he was in full breeding condition–on the inside as well as outside.
Indigo Buntings are beautiful birds, and it seems somewhat sinful to even think about cutting one open to check its innards. The girls weren’t squeamish–girls seldom are–but we all felt a little sad about this poor, dead bird, so we studied it from the outside first, checking out how most of the blue feathers were only blue at the tips, and rather brown and drab near the body. It’s the way the feathers overlap that gives the bird its apparent solid blue coloration. The blue color in feathers isn’t caused by a pigment–if we were to ground up bright blue feathers, we’d get a dull brown powder. Blue in birds is strictly a structural color. If you hold even the boldest blue feather up so light shines through it, you can see its dull true color. Cardinals always look vivid red even in poor light, but Blue Jays look a bit grayer in dim light.
We also studied the bird’s beak and tongue. Like most seed eaters, Indigo Buntings have a short, thick beak. In the hand, the girls could see how the inner edge of the beak is strongly angled rather than straight. A seed is cracked and held securely in the bend while the fleshy tongue extracts the meat and pushes it down the throat. Indigo Buntings and their sparrow relatives find this spare tool quite sufficient to fulfill all their eating needs.
We also looked at the cleft palate-like most birds, Indigo Buntings can’t suck up water in their beak because the cleft palate lets air in to prevent a vacuum. To drink, they fill the beak with water and then pull their heads back to let it dribble down their throat.
We plucked feathers from the body and then made our first cut. Birds don’t have ribs in front, and to get to the keel bone we had to first remove the pectoral muscles. These gigantic muscles, used to power the bird’s wings, weighed over 17% of the bird’s total weight. Indigo Buntings have a pretty small stomach, but it’s muscular–what we call a gizzard–to crush and mash the seed hearts swallowed whole. Since seeds are so digestible, the intestines were very small–only about 2 ½%of the bird’s weight–almost the same mass as the heart. Almost twice as weighty were the testes–this being a breeding adult. These huge organs were at their maximum size–by fall they would have shrunk so small that they would have been difficult to find. Avian sex organs are no more than excess baggage come time to migrate to the tropics for the winter, but this time of year the hormones they produce trigger song, territoriality, and romance. We ended up very sad that this little bunting was dead, but grateful to it for the lessons we took away from the dissecting table–especially that we never need to turn off our hearts when we turn our minds on.