Mar 29, 2023
“Bye, baby bunting,
Daddy’s gone a-hunting,
Gone to get a rabbit skin,
To wrap the baby Bunting in”
Back in 2020 I wrote a column entitled “Bluer than the Sky” which was a look into the world of bluebirds. Those remarkable flying pieces of sky that faithfully return every year in the early spring to their nest boxes in the Crowsnest Pass and Rocky Mountain foothills. The article revealed that one of the best places to observe these lovely cerulean passerines is North Burmis Road. It is a magical road that wends its way from Highway 3, almost all the way to Maycroft; along the foothills of that massive wall of unbroken limestone we call the Livingstone Range. The rolling open landscape adjacent to the road is perfect for these omnivorous bluebirds who can scoop all kinds of insects and seeds for their young out of the native grasses and sloughs.
Last year as I was cruising this beautiful roadway, one that parallels Highway 22, bird spotting, I had a very unusual encounter. I decided to break off of the main road, to the west, onto a small remote side trail that eventually dead-ended at an old dilapidated log house. It was a very secluded and serene spot and the old dovetailed log homestead I found was tucked well back into the middle of a small grove of aspen poplar. It was there, near the abandoned house, that I caught sight of what I thought was a single Sialia currocoides (mountain bluebird male).
On closer examination with my Bushnells I realized the coloring wasn’t quite right and its flight behaviour was not typically how a mountain bluebird moves. After carefully observing this spectacularly azure specimen I realized I was actually seeing a different, extremely rare bird. There is no mistaking an Indigo Bunting (Passerina cyanea) when you finally see one as its blue feathering is a deeper and stronger blue than the mountain bluebird. It was a shock to find it where I did.
It has always amazed me to realize that bluebirds are in fact not blue at all. Their feathers have no blue pigment whatsoever. Instead they pull off a neat optical trick on us called light scattering, somewhat like a prism works. Their feathers contain tiny pockets of keratin that are so small they fall into the category of nanostructures. They are smaller than the wavelength of visible light. Nanostructures are extremely small and are measured in nanometers (nm). As an example, a red blood cell nanostructure measures 7,000 nm but feather nanostructures are only several hundred nm. The size of the keratin nanostructure in a bluebird matches the wavelength of blue light, so while all other colours pass through the bluebird’s feather, the blue light is reflected and ta dah, you see a blue bird.
But I digress. It was almost dusk when I spotted the Indigo and that should be no surprise if you understand this bird’s eating habits. The Indigo, unlike the omnivorous mountain bluebird, is confined to hunt one single species of bug known as the weaver fly for its source of food and feeds on it exclusively. The weaver fly itself is yet another exotic creature. It cannot stand the heat of the sun but yet needs sunlight to propagate so it only comes out at sunrise and sunset. Remarkably, like the Indigo, the elusive Weavers have also evolved specialized nanostructures that lie within their crystal clear wings. Those delicate wings allow all wavelengths of light to pass through, making them somewhat invisible to the naked eye. Somehow the Indigo Bunting can discern the flying weaver as the rods and cones of the bird’s cornea have adapted to the Weavers nano masking trick.
On closer inspection of this elusive bird with my binoculars I was gob-smacked to notice that this male had a small protruding pouch on its chest. Even though the light was weak , I was also able to quietly observe him busy flying back and forth, diligently building an exotic nest with some kind of soft undercoat hair that he was gathering from somewhere in the bushes nearby. A little cautious searching revealed the carcass of a badger, yet another rare animal in these parts.
It took several visits to his spring nest site to finally get a closer look at his remarkably odd and so non typical pouch.
The Indigo is an elusive and unpredictable passerine and with every visit I had to crawl through tall grass slowly to get anywhere close to him. The plain brownish marked female always seemed to stay off in the distance, like a cranky wife with her arms folded, supervising the male’s methodical construction. Because I was relegated to working in weak light it was difficult to see the protrusion on the male’s lower chest closely. It appeared to be a sort of downwards facing flap but it was clear that it was something that looked, for all the world, like a pouch flap. I wondered to myself if it was a genetic miscalculation or aberration or perhaps some kind of a tumour. Later in the spring, on a perfectly lit evening in June, on the day of summer solstice in fact, I witnessed an event that left me speechless. The male was sitting quietly on his perfectly oval-shaped badger fur nest creation, with the area from the bottom of his chest to his undertail coverts distended. He fluffed up his feathers and then gently pushed forward his chest. The pouch flap lifted up and there underneath it were three small pale bluish-white eggs. What came to mind then was remembering that the Emperor Penguin male, who is forced to spend 65 days in brutal Antarctic weather covering and incubating a single large egg, also has a special sort of egg flap. The Emperor does not ever move from the nest site nor leave the egg uncovered nor have anything to eat during his ordeal.
As I watched quietly that day the Indigo gave another shuddering shake of his feathers and the flap promptly disappeared, neatly folding back into his abdomen as if it never existed. And off he went, leaving the female to take over in the old traditional covering manner on the eggs. I wondered then what evolutionary process had taken place that brought about such a specialized egg warming cover for this cobalt-colored cyanea. Why, unlike others of this Cardinalidae family, did the Indigo male evolve to have such a bunting? In our world it is a cuddly cocoon-like hooded outerwear for infants. In his it is a most unusual egg cover.
Because of my recent macular degeneration issues I found it hard to actually see the hatched weaver flies that the Indigo so depends on. If not for the Weaver’s brown helmet I would miss them entirely. But they were there and I observed that the female, like a night-time marauding bat, was very adept at picking them off midair. I wondered to myself about the specificity of the Indigo Bunting, only eating Weavers and how vulnerable that made them in the event that these oddly transparent flying insects did not hatch out. And I also wondered why the unusual phenomenon of the male Indigo’s flap has never before been documented? I never was able to photographically capture a view of it and I haven’t seen another Indigo since. Such a delicate balance is the case for the Indigo Bunting, a very different keeper of eggs.