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NORTH OF NORTH (2025) costume appreciation: "Inuk Bridgerton" (Series Costume Design by Debra Hanson)

Older San Joaquin kit fox siblings sometimes stay home and help raise their parents' next litter instead of leaving to find their own territory. In an endangered population living in Bakersfield, California, researchers found that families with these helpers left their pups unattended significantly less often than families without them. The helpers were not doing the hard work of hunting and provisioning. They were guarding the den and playing with the pups, filling the gaps when both parents were away foraging in a city that was never supposed to hold foxes at all.

The San Joaquin kit fox is the smallest canid in North America, roughly four pounds, with oversized ears and a face built for hearing rodents move underground. It is endemic to the San Joaquin Valley in central California and is federally listed as endangered. The agricultural conversion that eliminated most of its grassland habitat pushed remnant populations into an unlikely refuge: the city of Bakersfield. Kit foxes now den under houses, in storm drains, beneath concrete slabs, and inside industrial lots across the city. They hunt ground squirrels on golf courses, forage in parks, and raise their pups in suburban backyards.

Tory Westall, Brian Cypher, Katherine Ralls, and David Germano studied parental care in the Bakersfield population and published their findings in the Western North American Naturalist in 2019. They monitored family groups containing mothers, fathers, and helpers across three periods of the reproductive season: before the pups were born, during early pup-rearing, and during late pup-rearing. They classified every observed behavior: den attendance, provisioning, guarding, grooming, and play.

Mothers did the most. That was expected. Fathers provisioned heavily, bringing food to the den at higher rates than either mothers or helpers. That was also expected. The helpers did something different. They did not provision at the same rate as either parent. Their primary contributions were guarding the den entrance when no parent was present and engaging pups in play, which kept the pups near the den and active without requiring a parent to be on-site. The result was measurable: litters in groups with helpers spent less time completely unattended than litters without helpers. A pup alone at a den entrance in Bakersfield is a pup exposed to coyotes, domestic dogs, cars, and every other threat that an urban landscape produces.

The genetics made the family structure stranger than it appeared. A separate study by Cypher's team using microsatellite DNA found that 39 percent of kit fox litters had multiple fathers, meaning the helpers were sometimes raising half-siblings rather than full siblings. Most helper-mother pairs were related, typically mother-daughter, but the researchers also documented sisters helping each other and in two cases, completely unrelated females living in the same family group and sharing pup-rearing duties. The kit fox family was not a fixed unit. It was a flexible arrangement that expanded and contracted depending on who was available, who was related, and how much food the city provided.

The researchers suggested that the urban environment itself enabled the helper system. Bakersfield's food supply, year-round access to ground squirrels, garbage, pet food, and irrigated landscaping that supports prey populations through the dry season, may be abundant enough that tolerating an extra mouth at the den costs less than it would in the depleted grasslands where the species evolved. A helper that eats some of the family's food but keeps the pups alive while both parents are hunting is a net gain in a city where food is everywhere and danger is constant.

Source: Westall, Cypher, Ralls, and Germano (2019), Western North American Naturalist / Cypher et al. (2024), Canadian Journal of Zoology / Smithsonian Profiles / USFWS.

Fritz Schwimbeck (1889–1972), “Ghosts”

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