She's Back! F257 - an Island Fox with a Story

F257 was true to form in 2023. She was captured during island-wide counting on Santa Rosa Island for the fifth year in a row!

This charismatic female island fox was first captured and radio-collared in the fall of 2019 as a pup of that year. She was collared in the territory where she was born and there were thoughts she might provide additional data on how far female offspring disperse from their parents' territory.

 

She didn't go anywhere. F257 remained in the coastal plain of her childhood. She has been captured each year, not only in the same area, but in exactly the same location. A highly unusual occurrence.

 

Health checks in 2020, 2021, and 2022 found F257 healthy even during years of drought. She even was videoed after receiving her new radio collar. But physical evidence revealed that this healthy female island fox had not become a mother. Island foxes typically have pups in their second year, but they can breed before they are a year old if resources are available. During the 2021–22 drought years, most female island foxes did not breed.

This year F257 approached breeding season as a middle-aged fox–4 years old.

The rainy winter suggested a boom of resources for island foxes. We all waited to see what would happen with F257.

When she was captured in September, F257 showed evidence of nursing pups. 

Island fox females who have NOT been nursing have white bellies.

Females that have been nursing have pink bellies.

F257 has added her genes to the population of island foxes on Santa Rosa Island. We hope she continues to thrive and tell her story.

More on island fox reproduction.

Sex and the Single Island Fox

When it comes to reproduction, island foxes are not your typical canine. 

A female dog will go into heat and become reproductively receptive even if there is no male dog nearby. Dogs have spontaneous ovulation, they have a determined reproductive cycle which includes a spike of hormone to release the ovum or egg into the female's reproductive tract. Not so with island foxes. 

Captive breeding occurred from 2000 - 2008

During the period of captive breeding to increase island fox populations, it was discovered that female island foxes, without access to a male partner, did not show the elevated hormone patterns signaling they had ovulated. These single females did not go into heat.

A similar reproductive behavior occurs in members of suborder Feliformia, or the cat branch of carnivores (cats, otters, wolverines, ferrets, etc.), and in bears. These species have induced ovulation–some physical or hormonal stimulus from the male is required to stimulate or initiate ovulation.

To date island foxes are the only canine observed to have this reproductive trait. However, research on this facet of reproduction is minimal. It is unknown if gray foxes, the ancestor of island foxes, are induced ovulators. 

Gray foxes (Urocyon cinereoargenteus) are an ancient species. Some sources consider them the most basal or closest to the root of the canine family tree. In Decline and Recovery of the Island Fox the authors suggest induced ovulation may be a primitive trait shared between these ancient canines and other carnivores, like cats and bears. Spontaneous ovulation may have evolved later in the branches of the canine family tree that gave rise to red foxes and wolves. Compare gray fox and island fox.

The single female island fox? 

Well, she just doesn't waste her reproductive energy if there is no eligible mate at hand. 

What other animals are known to have induced ovulation? rabbits and camels