The Fascinating Fecal Sac

The Fascinating Fecal Sac

The fecal sac: such a simple object. It’s a bag of mucous membrane for the waste of young birds. It’s a helping hand in the challenging duty of keeping a nest clean of parasites.

by John Shamgochian
 

The fecal sac: such a simple object.
It's a bag of mucous membrane for the waste of young birds. It's a
helping hand in the challenging duty of keeping a nest clean of
parasites. Just like responsible dog owners bag up their pet's waste, so do
the birds. But for birds, their young's
droppings come self-wrapped, a futuristic diaper, if you will.


I
first discovered the droppings on May 4 as I sat on our back
porch, escaping the chaos of our evening household. As I bathed in the
evening tranquility, a House Sparrow fluttered down from the nesting
cavity in our roof. In her beak she carried a white object, which she
placed with care onto the branch of one of our two young apple trees.
She sat there for a moment before bending down and carefully wiping her
bill against the tree's smooth-barked branch. She flew back to her nest
and was back a few minutes later with another of the objects which, like
the time before, she similarly deposited onto the branch. It was only then  that I realized what these things were: fecal sacs. As I had this
revelation, I noticed how many of them there were. These bags of waste lined our tree's branches and our fence; although I have a slight
tendency to over exaggerate, I must admit that the number of white blobs
was quite impressive. 

Fecal sac 001Female House Sparrow with fecal sac. Photo by the author.

After
the bird left, I moved in for a closer look. I was surprised to see
that the sacs were more complex than I had expected. Each silky, white
blob had a small, dark handle from which (I presume) the parent bird
held the dropping. The
next day, while I was taking a good long squint at the sacs, I was
surprised to see a male sparrow land on our fence with what appeared to
be a sac clutched in his beak. Up to that point I had only seen a
female with the fecal sacs, with no sign of her mate. The bird sat there
for a moment before carelessly letting the bag fall to the
ground. It chose not to clean its bill as the female had but instead
flew straight back to its nest hole in our roof, demonstrating the
surprisingly opposite cleaning attitudes played out by human males and females. 


Fecal sac 003
Fecal sac, with finger for scale. Photo by the author.

Later I googled fecal sacs and found an article on Wikipedia (http://en.wikipedia.org/wiki/Fecal_sac).
I was amazed by how many curious behaviors revolve around that white
bag of ordure. Apparently the females of most species do remove the sacs
more frequently than their mates, which would explain the obvious
inexperience of the sloppy male sparrow I had seen. Apparently young
birds release their droppings seconds after eating; if they do not, the
parents may commence to peck their cloacas to
stimulate release.
Some
species will indicate if they're about to go. The Cactus Wren shakes
its body. The Curve-billled Thrasher points its back end skywards to
prepare the parents for the release of a white, slightly damp bag of
feces, neatly packaged and ready for immediate transportation, via beak,
to be politely dumped.


Oh, yes, and I forgot to mention that some hungrier parents will devour their young's feces with unusually disgusting gusto!

After
a few hours the outer surface of the sacs seemed to dissolve and the
young bird's waste sat there, unidentifiable from the droppings of their
parents.

The life of the fecal sac: short but fascinating.




JohnAbout the author:
John
Shamgochian, 13, is from East Providence, Rhode Island. His  favorite
birding spots include: "The Meadows" in Cape May, Plum Island in Ipswich
Massachusetts, Monomoy in Chatham, Massachusetts , and Swan Point
Cemetery in Providence, Rhode Island. John is one of The Eyrie's Student
Blog Editors. Check out more of his writing on his blog: http://johnsbirdingblog.blogspot.com/.

 

2012-10-18T13:00:00+00:00