Coyotes have been expanding their range through San Francisco for years now, pushing into the Mission and Castro edges from Glen Canyon and Twin Peaks, following the green corridors and the easy pickings that come with dense residential living — compost bins not quite latched, the occasional unattended small animal, the general abundance of a city that produces a lot of edible waste. 18th Street sits at the kind of in-between zone where that makes sense: close enough to Dolores Park's open space, a few blocks from the residential blocks climbing toward the hill.

What makes a sighting on 18th worth noting isn't the coyote itself — urban wildlife officers will tell you the animals are more common than most residents realize, usually passing through unannounced — but the howling, which signals either a lone animal trying to locate others or a small group already coordinating. Either way, it's audible in a way that daytime sightings aren't, and it registers differently at 1am than a glimpse of a gray shape crossing a park path at dusk.

SF Animal Care and Control recommends hazing — making yourself large, loud, and present — if you encounter one. Do not feed them. Do not leave small pets unattended outside at night.

Anyone walking that stretch of 18th tomorrow morning won't see a trace. The coyotes will have moved on, and the block will look exactly as it did: corner stores, parked cars, the usual foot traffic. The only evidence is in the thread.