Mir Yeshiva, Jerusalem. My chavrusa and I were puzzling over
the first mishnah in chapter four of maseches
Shabbos. It states that one may not on Shabbos insulate a
cooked food with straw, dung, and the like, "because they
increase the heat of the food." My chavrusa and I were
trying to understand how that is possible.
"I've got it!" I exclaimed. "These things ferment and
decompose, producing heat in the process."
"How did you figure that out?" asked my chavrusa.
"A little bird told me," I replied.
And the funny thing was that I wasn't just using a figure of
speech. A little bird really had taught me the
Mallee-fowl are a group of birds found from Malaya to
Australia. About the size of a chicken, mallee-fowl are
unusual in appearance in that they possess extremely large
feet; hence their scientific name "megapodes," which is Greek
for "big foot." The extraordinary thing about mallee-fowl,
however, is not their feet, but the way in which they
incubate their young.
Birds lay eggs, and eggs have to be kept warm. Most birds
accomplish this with the most obvious local heat source: that
of their own bodies. But mallee-fowl use a different system
entirely. During the winter, the male mallee-fowl excavates a
hole in the ground. Astonishingly, this hole can measure four
feet deep and twelve feet across. It then proceeds to fill
this hole with every scrap of vegetation in the area and
covers it with a layer of sand.
The moist, warm vegetation begins to decompose. Bacteria eat
away at the organic material. As a result of this process,
heat is given off, and the incubator begins to warm up.
Now it is ready to receive eggs. The female mallee-fowl
arrives, digs a hole in the litter, and lays her eggs. The
male mallee-fowl then covers the area with a mound of earth
that can measure up to fifteen feet high and thirty feet
across. This little bird with big feet can move half a ton of
earth in a day!
Organic matter produces heat as a by-product of its
decomposition. This is why such material may not be used on
Shabbos to insulate food, as explained in the mishna
in maseches Shabbos that we were learning. The concern
is that if one uses such material for insulation, one may
come to use even better heat-emitting material: embers. And
if one uses embers, one might come to stir them up, thus
transgressing the prohibition against kindling fire and
This safeguard was not extended to all materials -- only to
those that emit heat. Still, we might wonder how much heat
can actually be produced by decaying leaves. Is it really
enough to warrant prohibiting it as a safeguard against using
A commonly used example in the gemora of a food that
cooks easily is an egg. And the mallee-fowl's incubation
chamber can, if not correctly administrated, produce so much
heat that it will actually cook its own eggs rather than
hatch them. Astonishingly, the mallee-fowl manages to detect
and prevent this from happening.
Mallee-fowl eggs need to be incubated at a steady temperature
of 95 degrees Fahrenheit (35 C). The mallee-fowl's beak is
extremely accurate at sensing temperatures, and it constantly
plunges its beak into the mound to measure the heat. When the
mallee-fowl detects that the rotting vegetation is giving off
too much heat, it uses its big feet to rapidly kick away the
mound, sometimes until the eggs are virtually uncovered. When
the temperature has adequately dropped, it covers them up
Eventually, the mallee-fowl's remarkable work pays off and
the eggs hatch. A slight disadvantage of the incubation
technique is that the emerging chick finds itself buried
under several feet of hot sand. It digs its way to the
surface, a procedure that can take up to fifteen hours. Soon
it is strong enough to run away, and within a few hours it
I told my chavrusa about the mallee-fowl, and he was
quite taken aback (actually, I'm not sure if he really
Personally, I was struck by the novelty of the situation. In
the heart of the ultra-Orthodox section of Jerusalem, my
chavrusa and I were poring over a two-thousand year
old text and were aided by a bird living eight thousand miles
away. It gave me fresh insight into one of my favorite verses
from the Torah: "He teaches us from the beasts of the earth,
and from the birds of the Heavens He makes us wise."