Every ecosystem has its devotees. There is a boundless human appetite to observe, understand and catalogue the world around us.
No niche interest is too small to sustain our interest, it seems, and in the world of industrial infrastructure there are aficionados of the most curious things.
Hayes tells me, for example, that he has recently come into contact with a vibrant community of streetlight enthusiasts.
Another unsung element of the industrial landscape with a dedicated following is the humble manhole cover. Most of us sail through life breezily unaware of the 130kg slabs of metal that punctuate the streets. For the connoisseurs, however - the drainspotters, as they're known - photographing the world's manhole covers is a serious business.
And if you pay attention from city to city and country to country, you'll see it's not as thoroughly bizarre a pastime as it sounds. The regional diversity is surprising, as is the quality of some of the designs on show. There's an arrestingly ornate - almost floral - specimen from Budapest (left) highlighted in Brian Hayes's book.
"Manhole covers are a bit like postage stamps," he says. "They're mass-manufactured but available in great variety.
"What's the attraction? I'm not a collector, so I have to speculate. But I think it's the sense that there's a finite universe of them out there. So even if you can't get them all, you can get close, or you can focus on completing a specified sub-set."