Dominik Mosur was mimicking the sound of a bird call while on a walk through the park by San Francisco’s Pine Lake on Monday afternoon when something stunning happened: A tiny little bird, with vermillion red underparts and a dark chestnut crown, popped up into his view.
For the first known time in California, Mosur had spotted a slate-throated redstart, a species of bird seen in Mexico and South America. Mosur dropped down to his knees on the trail and began taking pictures before putting the word out.
Within the hour, two to three dozen birders gathered. It was the rarest sighting of his more than two decades of bird watching — and big news for the birding community.
“It was pretty amazing,” said Mosur, who bird-watches both as a hobby and for a living as an animal exhibit curator for the Randall Museum in Corona Heights Park. “I said a little prayer, thanked the creator for putting me in this place at the right time.”
Commonplace in the American tropics, the slate-throated redstart has rarely wandered north from Mexico into the American Southwest, according to the National Audubon Society.
The bird is about “three nickels worth of feathers and bone,” Mosur said. It’s bigger than a hummingbird, smaller than a sparrow and about the size of a goldfinch.
The one he spotted has been seen as recently as Saturday morning hopping around in the willows on the south side of Pine Lake, near Stern Grove. Based on its red underparts, Mosur said it probably came from the Sierra Madre in Northern Mexico.
In the days since his discovery, bird watchers from as far as San Diego and even Florida have flocked to San Francisco to get a look at the little bird, Mosur said. The sighting was featured on a podcast by the nonprofit American Birding Association.
“California really does have it all from a natural history perspective,” host Nate Swick said on the “American Birding Podcast.” “So when California added a new species to its already quite expansive state list, it is a big deal. This week, they got one.”
While the bird is regularly seen in southeast Arizona and has also been spotted in New Mexico and Texas, Swick said the sighting in San Francisco was an “outlier.”
Langtian Lang felt “extremely lucky” that the bird landed so close to his home on the west side of San Francisco. The local birder, who birds with wife Kaylyn and 19-month old son Lukas on the weekends, went to see slate-throated redstart on Wednesday.
“I wasn’t sure it was real at the beginning until some of the photos came out, and then definitely was excited,” Lang said. “This was a bird I’d never heard of before.”
He called the sighting a “mega rarity.”
Amanda Seyfer drove from Oakland with a friend to see the bird Saturday morning. They weren’t the only ones there. Seyfer and her friend joined a group of people with binoculars who followed the bird as it jumped from branch to branch, deep in the brush.
“It was really cool,” Seyfer said. “It’s a very cute bird.”
Mosur has gone back to see the bird several times since he first spotted it.
A birder since 2001, Mosur has made rare sightings in the city before. He leads bird walks and is always on the lookout for birds, which he said is like playing “real-life Pokémon.”
But spotting a bird before anyone else in the state of California is a first for him.
“Ten years ago, I would have said this is the crowning achievement of my career,” he said. “Nowadays, I just think this is really cool.”
“I hope this gets attention to birding.”
Reach Michael Barba: michae...@sfchronicle.com