preen gland

[John Chardine]

This Gentoo Penguin is exposing his/her preen gland, AKA the uropygial gland. The gland secretes a complex of waxes and oils which the bird spreads over its plumage as it preens. What is not so well known is that this is not done specifically to waterproof the feathers. Feathers are naturally waterproof due to their fine-structure which prevents water from penetrating due to its surface-tension. This is the same idea behind the fine-weave in a tent keeping out water. If you doubt this, find a feather and thoroughly wash it with dish detergent in hot water. Dry off and sprinkle water and you'll see that it beads-up.

The waxes and oils in the preen gland act as a feather conditioner. They make the feathers more slippery so that the microstructural parts slide over each other and thus any microscopic holes in the feather that might let water in are quickly repaired.

When oiled birds are cleaned they are not fully waterproof until they have had a chance to preen and spread the conditioner all over.

[Jim Buescher]

Amazing and informative. Do all penguins have this gland? TFS

[John Chardine]

Pretty well all birds have the gland Jim, so yes all penguins do.

Interestingly there are at least a couple of seabirds that have a very "loose" feather structure and are not very waterproof (again nothing to do with preen oil). Cormorants are divers and their plumage is designed to soak up some water so that the dives are easier. When then are on dry land they spread their wings to dry out. Remarkably, one of the most pelagic seabirds in the world- the Sooty Tern- has loose plumage as well, and will become water-logged and drown if it sits on the water. Hence it does not, and from this we know that this species stays aloft at sea for months at a time, never touching the water, and never touching down on land either.

[Ilija Dukovski]

Great information John, TFS.

Remarkably, one of the most pelagic seabirds in the world- the Sooty Tern- has loose plumage as well, and will become water-logged and drown if it sits on the water.

This might be true for the related Bridled Tern too.
The only time I've seen a Bridled Tern off of the coast of
Massachusetts, it was standing on a floating driftwood.
As a general rule, I think, this far north one looks for southern terns
by looking for floating object in the water. They are most likely to stand
on one. Now, with the info about the Sooty Tern, it makes perfect sense to me.
Thanks.

[Chris Sloan]

Remarkably, one of the most pelagic seabirds in the world- the Sooty Tern- has loose plumage as well, and will become water-logged and drown if it sits on the water.

This is not true, from personal experience. We occasionally see Sooty Terns sitting in the water like ducks on pelagic trips off of the Outer Banks, and I even have a picture of one doing so.

I haven't ever seen a Bridled do this. Bridleds are commonly found floating on driftwood, so much so that the default assumption is that a tern floating on driftwood is a Bridled. I have occasionally seen Sooty Terns on driftwood, but very rarely - only once that I can specifically remember. No idea why that is the case.

I would be very surprised to learn that Bridleds do not have water resistant feather oils, since for a pelagic bird that would be fairly disastrous in many circumstances.

[Linda Dulak]

I have no experience with the terns, but the amazon parrots don't have a preen gland as well. Their feathers are very resistant to water and if you see them in the rain, it rolls off their feathers just like that of any other bird. But, then you will see that the feathers do get wet and they change color so those vibrant greens turn an olive green until the feathers dry again. I'm assuming that the change in color is due to the interaction of the water with the feather structure.

Linda

[John Chardine]

This is not true, from personal experience. We occasionally see Sooty Terns sitting in the water like ducks on pelagic trips off of the Outer Banks, and I even have a picture of one doing so.

I haven't ever seen a Bridled do this. Bridleds are commonly found floating on driftwood, so much so that the default assumption is that a tern floating on driftwood is a Bridled. I have occasionally seen Sooty Terns on driftwood, but very rarely - only once that I can specifically remember. No idea why that is the case.

I would be very surprised to learn that Bridleds do not have water resistant feather oils, since for a pelagic bird that would be fairly disastrous in many circumstances.

Thanks for this Chris. In the OP I should have said "if it (the Sooty Tern) sits on the water for any length of time"

The Birds of North America account for the Sooty Tern was written by several friends and colleagues of mine who were the Sooty tern world authorities at the time of writing. Here's the link to the first page of the account:

http://bna.birds.cornell.edu/bna.htm...s/introduction

Note this sentence which is elaborated later in the account:

"At sea, the Sooty Tern may perch on flotsam or the backs of surfaced sea turtles, and it is able to alight on a calm sea surface briefly and take wing again. But Sooty Tern plumage apparently has little waterproofing; individuals quickly become waterlogged when held on the water."

Re. your comment about "water resistant feather oils in Bridled Terns", the original theme of this post is that it is not feather oils that make birds water resistant to begin with. It's simply the micro-structure of the feathers. The waxes and oils are feather conditioners. BTW to my knowledge, Bridled Terns have "normal", waterproof plumage.

[John Chardine]

I have no experience with the terns, but the amazon parrots don't have a preen gland as well. Their feathers are very resistant to water and if you see them in the rain, it rolls off their feathers just like that of any other bird. But, then you will see that the feathers do get wet and they change color so those vibrant greens turn an olive green until the feathers dry again. I'm assuming that the change in color is due to the interaction of the water with the feather structure.

Linda

Thanks Linda. I did not know that parrots lacked a preen gland.

[William Malacarne]

John
Cockatoos, Cockatiels and African Greys have glands, but they produce a powdery substance for preening their feathers, no oil or wax.

Bill

[Norm Dulak]

John: It's just the amazons that lack a preen gland. As Bill has stated, a lot of the other species have powder to condition the feathers. And the other S. American parrots have preen glands. It's only the amazons that don't.

Linda (from Norm's computer)

[John Chardine]

Thanks Linda. I had no idea parrots were so variable in this regard.