Why do the hawks bring evergreen sprigs to the nest?

The nest has been growing steadily as the hawks bring sticks, leaves and twigs on a daily, even hourly basis. The Ustream live camera feed allows us to watch every detail of the hawks' attentive nest-building. We've been struck by the number of evergreen sprigs and fronds that they are weaving around the edge of the nest.

This afternoon, we also saw some free advertizing for City Paper!

John Blakeman offers some perspective on the significance of the evergreens in the nest:

"Nest watchers have noted that the haggards bring sprigs of evergreens into the nest. Almost all red-tails do this, for really unknown reasons.

The conventional explanation is that these pine or spruce twigs have fragrant volatile chemicals that drive off feather parasites. Indeed, such vapors do emanate from evergreens, and there must be a few bugs at a nest with evergreen sprigs. And yes, red-tails can have small populations of tiny feather lice. But these are seldom seen, and cause no health or feather problems in healthy birds. I have never been able to discover any of these on my falconry red-tails.

So repelling arthropod (bug) parasites is not really a factor.

And in fact, just look at where the haggards place the evergreen sprigs. If they are brought to the nest to drive out feather bugs, they aren’t in the right place. Most of them get placed out on the rim surface, where the birds stand, not where they squat. The aromatic vapors from these can’t effectively penetrate through the feathers to the birds’ skin surfaces, where the feather lice (what few there are) reside.

Frankly, the birds themselves keep the feather bugs in control by their frequent and prolonged preening. Nest watchers will see a lot of this, with a bird just standing there with its head turned around and probing through feathers all over its body.

This does two things. Mostly it distributes oil that the bird strokes off by touching its beak to the oil gland on the rump, beneath the feathers there. Then she strokes her beak through her feathers, getting a microscopic layer of this rain-repelling oil all over her body. Like a duck, water generally runs right off the hawk’s back, because of this oil.

Think of that when our formel will be sitting out there in cold March rains, keeping her two or three (we hope) eggs warm and dry. Periodic preening is crucial for this.

But the evergreen sprigs? They can’t be there to repel bugs. Wrong placement.

I really think they’re just really decoration, making things a bit more pretty (well, chromatically luminous for my academic colleagues) than just the bare sticks. I also think it behaviorally conveys commitment by the birds both to the nest and to each other. I don’t think unpaired red-tails ever carry around or do anything with evergreen sprigs.

For fun, I’ve tossed a few of these into my falconry red-tail’s chamber in March, and she does absolutely nothing with them. She pays no attention. It’s obviously a nesting and perhaps a pair-bond thing.

"Here, I brought you this. It shows I love you, and I like our nesting pad here. Don’t we got it good?"

And yes, my academic colleagues will cringe, as I internally do when I present such anthropomorphisms. No, red-tails don’t converse or even think lubby-dubby thoughts. It would be an error to explain what we are seeing in such thoroughly human or mammalian terms. Biologically, it’s not so clearly parallel.

But on the other hand, there are distinct behavioral parallels, although they are not neurologically exact. Hawk brain structure is very different from ours, and they can’t think too deeply on much of anything. Their behaviors are rather ritualistic, just going through the motions, as it were. Their brains aren’t big enough for much more than this.

But that should not discount all the wonderful behaviors we are privileged to watch. It can’t be denied that this is a committed, reproducing couple, tending diligently to bring a new generation of their offspring successfully into the Philadelphia skies.

Everyone can decide for themselves how these behaviors originate. If some wish to assign entirely human traits to these, so be it. It can be fun, and perhaps some children’s literature could derive from what will be seen. On the other end of the spectrum we are cold-hearted scientists, attempting to explain everything in quantitative metrics, and genetic and bio-chemical mechanisms.

But wait! I’m a scientist. But really, those are NOT the reasons I’m watching all of this. I’m as addicted to watching all of this as everyone else. I’m doing this because it’s just so profoundly exciting and fun, to be able go right in the living room and neighborhood of this bird family. We get to see it live and in person. How exciting, for each and all.

Once again, nothing like it in all the world."

–John Blakeman


As I read John's comments about the evergreens, I remembered Barbra Streisand's hit song of a few years ago entitled "Evergreen," and the final stanza of those lyrics does resonate with the commitment of the Franklin hawks to each other:


Two lives that shine as one
Morning glory and midnight sun
Time we've learned to sail above
Time won't change the meaning of one love
Ageless and ever evergreen