Our marvelous botanical gardens, El Charco del Ingenio, about which I have posted in the past, contains a silted-up reservoir that provides habitat for wildlife. Some time ago, artificial islands were built up out of the water to provide safe places for nesting birds.

A couple of months ago I found that the lake bed was dry, and that substantial mounds were being built on the margins of the original islands. The old reservoir had been drained for maintenance.

That this kind of work is being done is unsurprising: the preserve is managed sensitively and imaginatively. Every year, El Charco becomes richer, an relic of the original environment before population growth pressured wildlife and native plant populations.

What is unusual, though, is the scale of the work. Recently, I've noticed more and more heavy machinery being used on construction and road building projects in our part of Mexico. Here in the El Charco lakebed, I was surprised to find some heavy equipment doing the work, instead of the usual gang of shovel-wielding laborers.

The big Komatsu shovel looks almost new. Somehow, funding for El Charco must be sufficient to enable rental of gear like this; a miracle in itself.

A bulldozer shapes the margins of one of the islands, spewing clouds of black smoke as it scrapes the earth.

In other circumstances, such pollution would horrify me. But population density in our part of Mexico is low, and few smokestack industries feed components of smog into the air. At least locally, the atmosphere seems to be able to absorb what we humans put into it.

Someone will probably point out that the carbon footprint of these machines is huge, and of course she would be right. It's hard to know which might be better for the planet: huge diesel engines or gangs of manual laborers.

I'm ashamed to admit that I have a childhood affection for big machines belching black smoke. When I was ten, my father would take me on the steam train to New York City. We'd cross the Hudson River on a coal-burning ferryboat, past huge brick smokestacks throwing dark clouds into the sky. I understand the horrific impact that kind of industry had on us all. But my old-fashioned engineer's heart unaccountably still loves the look and smell of black smoke, the signature of what we thought of as progress at the middle of the last century.

In the case of El Charco, an investment of a couple hundred pounds of carbon results in a sanctuary for native wildlife of the Bahio. How can we tell if the environmental cost is balanced by the benefit? We're driving the egrets out of the city center (post). If we want to avoid their disappearance altogether, shouldn't we provide some sort of home for them?