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November 16, 2020

Saint Louis Zoo Endocrinology staff aid conservation efforts for Island foxes from over 1500 miles away
By Corrine
 Kozlowski, Endocrinologist

Island foxes are a small species of fox that live on the Channel Islands off the coast of California. In the 1990s, populations on several islands declined drastically due to disease and predation. By 2004, island foxes were placed on the endangered species list, and in 2008, they were designated as “critically endangered.” Recovery efforts were started to save these populations, including a captive breeding program, which involved research staff from the Saint Louis Zoo (see previous blog post). These efforts were successful, and in just eight years, foxes on three of the four islands were removed from the endangered species list. This was the fastest successful recovery of a mammal listed under the Endangered Species Act in 57 years! 

Island fox populations are currently stable. However, like many island-dwelling species, they are vulnerable to disease and unforeseen events, such as fire or drought. As part of an ongoing conservation program, the National Park Service conducts annual surveys of island foxes to gather population data and health information. These surveys involve trapping foxes across the islands and collecting information on sex, body condition, age and reproduction. For six years prior to delisting, staff from the Saint Louis Zoo Endocrinology Lab assisted these efforts by measuring levels of the thyroid hormone and cortisol in samples collected from foxes during these surveys. These hormones function the same way in foxes as they do in humans. Thyroid hormone regulates growth and metabolism when food is consumed. Cortisol makes energy available, allowing the body to use extra energy during times of stress. Together, these hormones provide important information about the health of island fox populations.

From these efforts, we have learned much about the physiology of island foxes. For example, we have found that cortisol production varies seasonally, with the highest concentrations in the winter months. This time of year represents the period when courtship and mating occur, and the increase likely reflects the extra energy needed for reproduction. Females that had given birth recently also had higher cortisol levels, probably due to the demands of caring for offspring. We also learned that young female foxes have higher cortisol levels than other foxes. Unlike males that disperse at 1 year of age, females often remain on their parent’s territory and care for their younger siblings. These females are subordinate to their parents, and this lower social status might lead to higher cortisol levels. Most foxes surveyed were in optimal body condition, and thyroid hormone levels were higher in these foxes compared to thinner animals. Thyroid hormone controls metabolic rate, and higher levels indicate that an animal has good nutrition. The fact that most animals were in optimal condition and had high levels of thyroid hormone suggests that that there is an appropriate amount and quality of food available for the foxes.

This collaborative conservation effort, which was recently published in the Journal of Wildlife Management, has provided new information about the biology of island foxes. By serving as a reference for continued monitoring, our data will help the National Park Service to identify future threats that may affect nutrition or increase stress in island foxes, including changing environmental conditions, predation and disease.  

Photo of island fox by Matt Duarte

Photo of park employee and island fox by Angela Guglielmino