Bigfoot in the Mir

Mir Yeshivah, Jerusalem, ten years ago. My chavrusa (study-partner) and myself were puzzling over the first Mishnah in chapter four of tractate Shabbos. It states that one may not on Shabbos insulate a cooked food with straw, dung, and suchlike, “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 explanation.

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 day!

Female malleefowl laying egg, pair cover up egg in moundBBC Natural History Unit

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. 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 cooking.

Still, we might wonder how much heat decaying leaves can actually produce. Is it really enough to warrant prohibiting it as a safeguard against using embers?

Well, a commonly used example in the Gemara 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 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. 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 again.

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 can fly.

I told my chavrusa about the mallee-fowl, and he was quite taken aback (actually, I’m not sure if he really believed me). 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.”

Malleefowl chick leaving nest moundBBC Natural History Unit

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