robins remain in their nest for about 13 days. Just about every time
the nestlings gulp down some food, they poop. Let's see—that's
13 days x 4
babies x 356 insects and worms on average each day. That's a LOT
of poop! How on earth do robins keep their nest clean?
robins can't wear diapers of any kind, but they do put their poop in a
strong "bag" so the parents can carry it away. This bag is made
of thick, strong mucus that a parent robin can pick up in its sharp beak
and carry without puncturing, and is called a fecal sac. Fecal
sacs are just like disposable diapers for birds!
seconds of feeding, baby robins back up and poop. This ensures that whichever
parent brought the food will still be there to carry away the fecal sac.
Things About Fecal Sacs
the first couple of days after hatching, parent robins actually eat many
of their babies' fecal sacs. This sounds gross! But before the babies
are a few days old, their intestines don't have much bacteria to help
them digest their food. It's the bacteria that make droppings germy and
smelly. Before the bacteria kick in, the droppings are rich in only partially-digested
food items. Fortunately, at first the babies are still absorbing their
yolk sac so they don't suffer from malnutrition even though so much of
their food literally goes to waste. Their parents can take advantage
of the food still in the droppings. Eating from the droppings allows
the parents to give more of the worms and insects they find to their
babies rather than eating this food themselves. And once the droppings
start having more bacteria, the parents will stop eating them!
Out of Diapers
get rid of the fecal sacs of older babies, the parents carry them away.
Robins and bluebirds fly 20-50 yards away, and drop the sacs in flight.
Grackles almost always drop fecal sacs over water. Long ago, grackles
usually nested near rivers, and the flowing water would carry the droppings
far away. Now many grackles nest in conifers in people's back yards,
often far from rivers. But the instinct to drop those fecal sacs over
water is still strong, so grackles often drop them in swimming pools
and bird baths.
a fecal sac takes protein. It's worth the cost when nest sanitation
at risk, but as soon as baby robins leave the nest,
they stop producing fecal sacs. Now their droppings spatter instead
Besides the outer casing on nestling droppings, bird droppings have two parts:
brown fecal matter (the food waste from their intestines) and white urine.
Urine is produced by the kidneys as they filter the blood,
much of the waste is poisonous nitrogen-based molecules. The nitrogen in our
urine is in the form of urea, which is clear and yellowish, so toxic that it
must be diluted with a lot of water. The nitrogen in bird (and most reptile)
urine is in the form of uric acid, which is white. Uric acid is toxic, too.
But if it is very concentrated, it turns into a solid, or precipitates,
becoming chalky. Producing uric acid is one way that bird bodies conserve water.
This! Be a Poop Counter
If you know the whereabouts of a nest with nestlings—wrens,
bluebirds, robins, jays, or any other species—find
a place to sit close enough to see everything going on with binoculars
without bothering the parents, and watch them for 15 minutes.
How many times do the parents come to the nest with food? How
many times do they carry away a fecal sac? Based on your 15-minute
count, calculate the number of poops per hour (pph). If the parents
didn't carry it all away, how long do you think it would take
for the nest to get filled to the top with poop?
Journal or Discussion
baby birds never produce fecal sacs. Ducklings, grouse and pheasants,
raptors, and some seabirds that nest on cliffs are species that don't.
How do these
birds ensure that their nests will stay clean? What makes birds
that don't produce fecal sacs different from robins and other songbirds?
thoughts in a journal, or discuss as a class. Then see what our
Journey North science writer says here.
Fecal sacs aren't the only things parent birds carry away from nests
to keep the nests clean. Can you think of some other things parent
birds have to carry off? List as many as you can. Then see if you thought
of some that our Journey North science
writer didn't think of: Click here.
| Fecal Sac from Wren
|See the fecal sac?