good morning, little blue bird

Indigo Bunting

His tail looks a little worse for wear, but he has maintained the deep blue color of his body feathers throughout the summer.

I was barely out of my car at the Old Cedar Road parking lot when a beautiful Indigo Bunting hopped up on a tree nearby, posing briefly in the bright sunlight before flitting off into the forest.  What a nice treat for the first bird of the morning.

Indigo Bunting

In fact, he is a surprisingly uniform blue.

In the next few weeks, this colorful male will molt into its winter plumage and become drab brown, like the female, before migrating to its winter home in Central America. Indigo Buntings, like most other bird species, replace their feathers twice a year, but these brightly colored males take at least two years to become completely blue.

the distraction lure

Some bird mothers go to great lengths to distract predators away from their nest and/or fledgling chicks.  They feign injury, flapping like they are wounded but can’t fly, chirping loudly to attract attention to themselves and away from their chicks.  I’ve seen Kildeer do this many times, as they lead me on a merry chase away from their nest.  For example…

But I’ve never heard of small songbirds using this strategy, until I saw it in action today when a female Indigo Bunting led me all over the backyard as I tried to find her nest and her chirping chicks.

indigo bunting-female feigning injury

Here I am, look at me, I’m helpless with my broken wings.”

Wings fluttering, hopping sort of helplessly through the grass, chirping continuously, and flying weakly from spot to spot, this female Indigo Bunting put on quite a show.

Moving around in the underbrush of the wildflower garden, I discovered two of her chicks, also chirping loudly, but hidden from view until one of them tried to cross a patch of grass.

indigo bunting-fledgling

Bunting chicks may fledge (leave the nest) after only 8 days, and can hardly fly more than 10 feet, so they tend to stay hidden in low, dense vegetation.

indigo bunting fledgling-

Not a very adept flyer yet…

indigo bunting-fledgling

The chick is not even fully feathered yet, has short stubby wing feathers, and no tail. It would be easy prey for a wandering cat…

Meanwhile, its mother is still chirping away at me, from all over the garden.

indigo bunting-female

first here…

indigo bunting-female

then here… (see that faint tinge of blue on her shoulder?)

indigo bunting-female

and finally right out in front of me.  Older females may be much bluer than this, with streaky blue patches on their shoulders, back, and tail.  But their overall drab plumage helps camouflage them while they care for the chicks.

indigo-bunting-male

A brightly colored male Indigo Bunting would attract way too much attention if he were feeding chicks in the nest.

Fun facts:

  • although Indigo Buntings are about the size of a Goldfinch and the female sort of resembles a female Goldfinch (but lacks those distinctive wingbars), they are actually members of the Cardinal family.
  • the blue color (especially evident in males) does not come from a blue pigment, but is due to special reflective particles in the feathers that scatter light and reflect blue wavelengths.  Read more about blue coloration in animals by clicking here.

A crazy day in the backyard

Even though it was chilly and overcast yesterday, the backyard was humming with visitors.

Brrr... Minnesota springtime is chilly.  A female Baltimore Oriole huddled up to stay warm.

Brrr… Minnesota springtime is chilly. A female Baltimore Oriole fluffed up to stay warm.

While the Yellow-rumped Warblers swarmed the suet feeders (as many as 8 on the feeder at one time), the Baltimore Oriole and his girlfriend (?) monopolized the oranges, a Least Flycatcher, a Swainson’s Thrush, and an Ovenbird perched near the garden hunting the dead mealworms I had thrown there, and an Indigo Bunting and a pair of Rose-breasted Grosbeaks tapped into the seed feeders.  It was hard to get anything done while looking out the window every couple of minutes.

This Indigo buntingis as bright blue as his cousin the Cardinal is red.  At least they have the bright colors in common.    Buntings are probably the smallest member of the Cardinal family, and sing a much prettier song than Cardinals do.

This Indigo Bunting is as bright blue as his cousin the Cardinal is red. At least they have the bright colors in common. Buntings are probably the smallest member of the Cardinal family, and sing a much prettier song than Cardinals do.

Like other small songbirds, Indigo Buntings migrate north in the spring at night, using the stars to navigate their way.  You can read more about how their navigational abilities were discovered in an earlier blog post.

Least Flycatchers may be small but they are obviously successful because they are one of the most common flycatchers seen in the northern U.S.

Least Flycatchers may be small but they are obviously successful because they are one of the most common flycatchers seen in the northern U.S.  They dart out from a favorite perch over and over, chasing small insects.

I have never seen an Ovenbird in the backyard before.  Perhaps it saw how much the Flycatcher was enjoying the mealworms and decided to get a few for itself before moving on.

I have never seen an Ovenbird in the backyard before. Perhaps it saw how much the Flycatcher was enjoying the mealworms and decided to get a few for itself before moving on. Their striped breast and bright rusty crown stripe make them easy to recognize.

Ovenbirds are grouped with the Warblers, but they certainly don’t act like them.  Instead of flitting around in the tree tops, these little birds search through the litter of the forest floor picking up small insects and other invertebrates.  They might be hard to spot among the dense vegetation of the forest, but their loud, repetitive call, “tee-cher, tee-cher, tee-cher” alerts you to their presence.  The female weaves a globe of grass and twigs, kind of resembling a Dutch oven, for her nest — hence their common name.

Swainson's Thrush may be a plain brown bird with a few streaks down its breast and a buffy ring around its eye. but like other thrush species (except Robins) it has a melodious song.

Swainson’s Thrush may be a plain brown bird with a few streaks down its breast and a buffy ring around its eye. but like other thrush species (except Robins) it has a very melodious song.

More often heard than seen, Swainson’s Thrush can be really difficult to locate in a dense forest as they hide behind vegetation and face in several different directions to sing.  Territorial males can get so antagonistic toward each other, they engage in a sing-off, each producing louder and louder cascades of flute-like sound, spiralling up or down the scale.

Part of the reason so many birds are congregating in the backyard right now is because of the delay in warm spring weather in the upper Midwest.  Early, mid, and late arriving migrants are stacked up here, waiting for that warm front from the Gulf that will carry them north on the final leg of their migration.  Meanwhile, I feel like I’m back in the tropics, with a huge diversity of birds flitting around in the backyard.  Most likely, that will end soon.

Navigation by stars

One of the little birds that has been a frequent visitor to the bird feeder this spring is the Indigo Bunting.  Its striking blue color makes it a favorite discovery, and it has a rather cheerful song.

bunting and goldfinch

But what is really special about these birds is their phenomenal ability to navigate their way from wintering areas in Central America and the West Indies to breeding areas in North America at night, using cues from the patterns of stars overhead.

When I was a grad student at Cornell, I took a class from Steve Emlen, who earned his Ph.D. by finding out just how the Indigo Buntings navigated.  He designed something really sophisticated (called “Emlen cages”) to measure his captive buntings’ migratory activity and direction at different times of year.

The bird stands on an ink pad, surrounded by a funnel of blotter paper with a wire mesh top (not shown).  When exposed to the night sky, a migratory bird hops from the ink pad upward landing on the blotter paper, leaving footprints that indicate its preferred direction (N in the spring, S in the fall).

The bird stands on an ink pad, surrounded by a funnel of blotter paper with a wire mesh top (not shown). When exposed to the night sky in a planetarium, a migratory bird hops from the ink pad upward landing on the blotter paper, leaving footprints that indicate its preferred direction (N in the spring, S in the fall).

But the night sky constantly changes as constellations rotate into and out of view, so what were the birds really using as cues for direction?  Emlen even tried to confuse the buntings by showing spring migrants the fall night sky, but they still oriented northward.

The answer was that the birds used the North Star, not individual constellations, and their orientation (toward the north or toward the south) depended on what time of year their biological clock told them it was.  Yes, birds can tell time — most animals can.  Hormones that tell them it’s time to breed are also telling them go north.  A slightly different mix of hormones tell them it’s time to leave the breeding ground and  fly south.

The amazing wonders of the natural world…

Yes, it was a long trip, but I'm a guy and don't need to ask for directions.

Yes, it was a long trip, but I’m a guy and don’t need to ask for directions.

True Blue

Spring is in many respects a celebration of color, as plants and animals emerge from a very blah-colored winter dormancy.  We have been barraged by a profusion of pinks, reds, oranges, yellows, golds, browns, chestnuts in the past couple of weeks as the spring migrants have passed through here.  These bright colors are all products of pigments synthesized or ingested and metabolized by their exhibitors.  You’ll notice I left some colors out.

The blues:  Blue color in animals is produced by structural reflections of incoming light, not a pigment.  As a result, the true coloration on an animal often changes as their position changes relative to the observer.

The greens:  Green color is a mixture of blue and yellow, so green is a mixture of pigment and structural reflection.

Tree Swallow

Here’s how it works.  The underlying color of a blue bird is black (or brown) and is produced by melanin pigment.  Feathers that appear blue have air spaces in their pigment-containing cells that reflect short wavelengths (blue light) but transmit longer wavelengths.  Thus red and yellow (longer) light wavelengths are absorbed by the melanin pigment and blue light is amplified and reflected back to the observer’s eye.  The structural organization of the air spaces determines the intensity and hue of the “blue-ness”.

This Tree Swallow looks bluer than the previous one.  It might be older (first year birds are often more brown), or the incoming light might be oriented differently in the two birds.

This Tree Swallow looks bluer than the previous one. The bird might be older (first year birds are often more brown), or the incoming light might be oriented differently in the two birds.

Blue color ranges from purplish on the head to turquoise on the belly feathers in this Indigo Bunting.  The primary wing feathers lack those light reflecting air spaces, probably because it might weaken them for the flight function.

Blue color ranges from cobalt on the head to turquoise on the belly feathers in this Indigo Bunting. The primary wing feathers lack those light reflecting air spaces and show the underlying brown/black melanin pigment.  Modification of internal structure might weaken the feather, making it unsuitable for flight.

A similar process of light scattering and absorption explains blue colors in insects, like dragonflies.  In some species, the outer cuticle is transparent, and the scattering of blue light and absorption of longer wavelengths occurs in the layer just beneath the cuticle.  This is the basis for the blue color of the male Eastern Pondhawk.

eastern-pondhawk-blue male

In other species, the light scattering occurs in a waxy layer above the cuticle, and can be removed by dissolving the wax.  The animal then becomes the color of the underlying pigment.

There is no doubt that blue coloration is striking and noticeable in animals, and it seems to be used to call attention to some aspects of the animal’s anatomy.  What could be more striking than seeing an animal advertise this?

Male vervet monkey showing off his blue scrotum.  In Simonis and Berthier, Intechopen.com article:  "How Nature produces blue color"

Male vervet monkey showing off his blue scrotum. In Simonis and Berthier, Intechopen.com article: “How Nature produces blue color”