How do birds’ feathers grow? They seem too complex to be just dead cells extruded from the skin. Do they grow at the tip or the base? If they grow at the tip, there must be blood vessels through the spine - do birds bleed if you pluck a feather?
IIRC, they DO bleed a drop or so if you pluck a feather.
–Tim
Owning a bird, I can speak from direct observation.
A feather grows from a follicle, much as a hair does (both are, evolutionarily and developmentally, modified scales). The principal difference, as scr4 notes, is that feathers are more complex than hairs. The feather, therefore, continues to develop after growing from the follicle. At this stage, it’s commonly called a “blood feather”, and will bleed if broken; indeed, birds have bled to death through broken feathers. The feather is wrapped in a proteinaceous sheath, for protection.
After a time, the feather dies, with the structure remaining intact, of course. At about the same time, the sheath loosens, and the bird preens it away, the pieces thereof forming a major component of the bird dander that falls on my trousers (in the wild, birds preen each other around the head and neck; my budgie, which has no other bird, looks like it has some sort of punk hairdo at molting time, since it difficulty getting rid of the sheath).
Feathers are truly cool. I wish I could grow them.
As Akatsukami said, feathers grow from follicles and papillae. These feather pimples are laid down on birds in patterns called “feather tracts” (so birds have areas where they have no feathers). A feather is grown out and up from the papilla and surrounding follicle, growing from the base. The tip is the oldest part while the base is the youngest. (We were able to use this fact to determine that the isotope signatures of carbon and nitrogen varied between the tip and other portions of the 2nd primary feather, indicating changes in diet of Laughing Gull (Larus atricilla) kids - Mom and Dad started feeding them more fish than beetles or blueberries. We went out about every 3-4 days to measure these feathers from marked kids and on the last day we yanked the feather out. Not to worry, they wouldn’t miss it, and will often grow a replacement. I noticed the change in diet anyway - their barf had more fish the older they got.) These feathers can grow as quickly as 3 weeks.
Once the feather is fully grown, the “feather pulp” (papilla) recedes. We’ve pulled growing flight feathers from Magpies, Canada Geese, Crows and have never had trouble with bleeding (they sort of pop out, like from a socket) and usually there is a bit of feather pulp left in the rachis (the quill). I haven’t pulled full pinfeathers (bloodfeathers) but I could imagine it to be quite messy, especially if they were cut rather than pulled. Sometimes some of the birds I band will seem to deliberately blow their feathers (particularly tail feathers) - sort of an avian version of the lizard losing it’s tail. So there is all sorts of muscle control around the feather despite its inanimate state. But, like I said, we’ve had little trouble with bleeding when pulling a feather.
Thanks for the informative answers! I, for one, am glad I don’t have feathers - hate to have so many appendages that can bleed (and hurt, I’d imagine) if damaged! Though I guess there aren’t that many bloodfeathers at one time…
I have seen an adult catbird with all of its tailfeathers gone. Presumably, a cat or maybe a hawk grabbed it by the tail and all the feathers were pulled out. It was the clumsiest catbird I ever saw fly!
I guess it’s like a comparison of if you want your hair yanked out or your head pulled off.
It’s funny you should mention Gray Catbirds (Dumetella carolinensis), Wood Thrush - they are one species I’ve seen do this a lot. They’ll also lose some body feathers. A couple of times individuals that I’ve caught have blown so many feathers I half expect them to end up looking like a plucked chicken. Sometimes I catch them again later on so they seem to survive just as well as those who keep all their feathers.