Monday, February 21, 2005

JOHN BLAKEMAN ON PREENING AND ECTOPARASITES

Marie,

Lisa’s remarks on the role of the “essential oils” emanating from the pine needles are significant. I thought about her comments, and this came to me.

Red-tails that aren't incubating spend up to an hour or more most mornings preening. In doing so, they transfer oil from a gland on their rump to the feathers of the body. Hawk watchers can often see this. The bird pokes her bill down into the feathers of her upper rump, where she gets a microscopic layer of the feather oil on the beak. She then strops the oil-laden beak on feathers all over her body.

This daily feather maintenance is absolutely essential. Remember, on the wettest, windiest days, our red-tails aren't passing the time inside any dry shelter. They are stuck out there in all of the worst weather, and if their feathers aren't properly oiled, rain will soak through and quickly kill the hawk by hypothermia. Daily preening is not for beauty.

Like most birds, our hawks are similar to turtles, in that they carry their houses with them where ever they go. Their houses, of course, are the feathers, which keep heat in and water out.

How might pine needles be involved in all of this? Lisa’s thoughts are particularly cogent. A sitting, incubating red-tail does, indeed, preen, but she can't spend an hour on her feet doing this. She’s pretty much bed- or nest-ridden. She still has to get the oil from her oil gland out over her feathers. But because she has to spend most of her time with her naked belly skin (the brood patch) tucked right up to the developing eggs, preening time and effort becomes a bit problematic.

Here is where the pine needles might enter. When red-tails preen, they not only spread protective feather oils, but they also comb out with their beaks very tiny feather lice. These very tiny bugs actually eat hawk body or contour feathers. The feather lice prefer to eat the white, un-pigmented portions of the brown body feathers. Preening greatly limits the damage feather lice can cause. The aromatic emanations of pine needles might restrict the feather lice while sitting on the nest.. Therefore, the sitting red-tail can apportion her meager preening time to only spreading feather oil. With the pine needles, she perhaps needn't spend much time combing out the feather lice. The pine needles may drive the lice away.

Red-tails have another arthropod ectoparasite, the hippoboscid fly. I have never found one of these large, slow, flattened flies on a healthy adult.. But virtually every immature bird has them. These things are the size of large house fly, but are very flattened. They don't fly very fast, but they move between the layers of feathers with great alacrity. These things live on blood they suck from their hawk hosts, and can be a real problem when the young red-tail begins to decline due to poor health or starvation. A healthy, experienced adult learns how to grab and kill the bugs with their beaks. But the newly-fledged youngsters don't recognize the pest, and they can run rather profligately between the feather layers. A single dose of parrot ectoparasite spray kills the hippoboscids in my captive birds. They never come back. The aromatic gases or odors coming off the pine needles may drive the hippoboscids off the incubating parents. They surely don't have much time to be poking around with their bills chasing these feather flies while still trying to maintain proper temperatures in the eggs beneath.

This would be a wonderful experimental study by an undergraduate ornithology student. Devise some trials where pine needles are placed next to cultures of feather lice and hippoboscids and record their reactions. This may solve the “Why evergreen sprigs?” question. Good thinking Lisa, something I hadn't considered.

One last note. For those watching the birds up close, check to see if the bird you are watching has evidence of feather lice. On first year birds, every single one of them does. Look on the brown contour feathers of the back. You will see that the margins of these are quite irregular, as though they've been eaten away. They have been. The feather lice eat away the white parts, leaving a very irregular brown edge.

Then look at the same feathers on any adult. You are likely to see some irregularity, but much of the whitish margins of these feathers will be unconsumed. The adults stay ahead of the feather lice. The youngsters aren't good at it. This is often an indicator of a hawk’s general health. Those in poor health or nutrition are badly feather eaten. Survivors have the lice, but with markedly reduced damage.

And for anyone concerned that these little arthropods might have jumped off my captive birds and infested my person, don't be alarmed. These very tiny bugs are absolutely confined to buteonine hawks. They couldn't even survive on the feathers of a pigeon or robin, let alone on human hair. The feather lice of my beloved red-tails pose no danger to me or anyone else. They stay on the hawk, or die.

Sincerely,

John A. Blakeman