Which wild animal gets spotted more in your city than others? Here’s the list

In San Francisco, it’s the coyote. In Oakland, the brown rat. And in San Jose, the wild boar.

These are just a few of the most “unusually common” mammals spotted across different Bay Area cities, according to the Chronicle’s analysis of data from iNaturalist, a social network that allows naturalists and amateur “citizen scientists” to identify and map species across the world .

To come up with the most unusually common animals observed in each city, The Chronicle downloaded more than 500,000 individual iNaturalist sightings made in the Bay Area over the past three years.

We defined whether a species was unusually common by looking at its sightings as a share of all sightings of its taxon (ie mammals or birds) in each city, and how that compared to the share of sightings of that species in the Bay Area as a whole. For example, coyotes represent just under 1% of all mammal observations across the bay, but 3% of all San Francisco observations. We only included species that were sighted at least 40 times in the last three years.

A few of the Bay’s cities and towns boasted large, majestic creatures as their most “unusually common” mammal. Mountain lions were spotted remarkably often in Santa Rosa, and in Inverness, northern elephant seals took the top spot. Petaluma’s was the Tule elk, an elk subspecies native to California that nearly went extinct in the 19th century. (In a rare conservation success story, about 5,700 Tule elk live in herds across the state now, according to the California Department of Fish and Wildlife.)

But smaller, more mundane species are the most unusually common mammals sighted in most places. Squirrels, for instance, placed first in six Bay Area towns: Berkeley, Richmond, San Mateo, Santa Clara, Sunnyvale and Walnut Creek. Rabbits were also quite common, with the black-tailed jackrabbit taking the top spot in three South Bay cities.

The Chronicle also examined each city’s most unusually common bird sighting. The most notably sighted bird for cities included burrowing owls (Berkeley), osprey (Richmond) and two species of duck: mandarin (Glen Ellen) and Muscovy (Walnut Creek).

While San Francisco’s official bird is the elegant and plumed California quail, the results of the analysis suggest its dark-horse counterpart could be the rock sandpiper, a small, hardy shorebird that local birders yearn to spot due to its relative rarity.

Damon Tighe, an Oakland-based biologist and prolific iNaturalist contributor, cautioned that the data cannot always accurately show how common a species is in an area, because the observations are so heavily biased by individual users’ preferences — where they like to go and make observations, or what type of organisms they like to look out for.

“If you look where I live, you’d think that Lake Merritt is one of the best places to see mushrooms in the entire Bay Area, and it’s definitely not,” Tighe said. “It’s because I happen to go there for walks and take pictures of wild mushrooms and upload them to iNaturalist.”

Instead, Tighe said, the iNaturalist data is best interpreted as a map of enthusiasm or “effort,” with outsize representation given to species spotted on popular trails. (Although he said it is pretty reliable for confirming that a species exists in a given region).

What’s more, for many iNaturalist users, user excitement begets more user excitement — and observations.

“That’s why you see sea lions being huge in Half Moon Bay,” Tighe said. “Out-of-staters that are coming here that happen to be iNaturalist users, they’re looking at iNaturalist and they’re like, ‘Oh man, I have all these sea lion observations in Half Moon Bay, I’m gonna go to Half Moon Bay to see my sea lions and make an observation there.’ And so it ends up being this self-fulfilling prophecy.” (Sea lions were the second most unusually common species in Half Moon Bay, according to the data.)

Still, effort and excitement have their limits. While San Franciscan naturalists may have eagerly sought out its wild coyote population, the city’s second-most unusually common species sighting was a far more common predator: the homo sapiens.

Susie Neilson (she/her) is a San Francisco Chronicle staff writer. Email: susie.neilson@sfchronicle.com

Leave a Comment

Your email address will not be published. Required fields are marked *