Confused by a sentence from a article.
I read a article, and there is a sentence I'm so confused about.

Once the female lays her egg 40–150cm down, however, that’s it – her progeny is entirely on its own, effectively orphaned before its shell has cracked. She plays no part in tending the mound, with the burden of maintenance falling entirely to the male. Climate control is his obsession, and rotting compost his tool in sustaining an even incubation temperature.

What is the verb in the second clause of last sentence "and rotting compost his tool in sustaining an even incubation temperature. "?

Question

Confused by a sentence from a article.
I read a article, and there is a sentence I'm so confused about.

Once the female lays her egg 40–150cm down, however, that’s it – her progeny is entirely on its own, effectively orphaned before its shell has cracked. She plays no part in tending the mound, with the burden of maintenance falling entirely to the male. Climate control is his obsession, and rotting compost his tool in sustaining an even incubation temperature.

What is the verb in the second clause of last sentence "and rotting compost his tool in sustaining an even incubation temperature. "?

Answer

The verb is "is". Think of the sentence as "Climate control is his obsession, and rotting compost IS his tool in sustaining an even incubation temperature."

The reason they did not write "is" twice, is because they are referring to multiple things using the same verb. Honestly, this phrasing is not something you will hear very often in English.

Answer

I'd have to suggest that this construction is common enough, natural and seen more than people might consciously notice.
I hope that this comment is clear and a way to  better understanding.
.
Repeating "is" too many times without reason is ugly and likely to be noticed as repetition.
:)