Our previous investigations of some of the lesser-known canids suggested that deviations from the patterns exhibited by the more extensively studied species such as wolves and coyotes might be found in other canids. We used fecal estrogen and progestin profiles from captive colonies to describe the basic reproductive pattern of island foxes (Urocyon littoralis). Based on sustained increases in levels of fecal progestin as indicative of ovulation, we determined that 11 of 13 females housed with males ovulated. In contrast, we detected no ovulations in 10 females housed alone and only 1 possible ovulation among 10 additional females housed in female–female pairs. Of the 2 females with males that failed to ovulate, 1 did ovulate the subsequent year while with the same male, and the other failed to ovulate when paired with a yearling male, perhaps due to his immaturity and inexperience. Significantly higher fecal estrogen levels in ovulating compared to non-ovulating females suggest that estrus was induced by the presence of a male. However, these results cannot distinguish whether male-induced estrus was followed by an induced or spontaneous ovulation, because estrogen levels indicative of estrus were always followed by ovulation. Fecal cortisol levels did not differ by ovulatory status, indicating that ovulation was not inhibited by stress mediated by glucocorticoids. Our results are the 1st to provide evidence of induced estrus, perhaps followed by induced ovulation, in a canid species, features that could have selective advantage for this less social, more secretive canid.
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