The Legacy of Mexican Wolf F521

Female Mexican Gray Wolf at Wildlife West Nature Park
Photo Credit: Paula Nixon

The deadline to submit comments on the 2017 Wolf Release Proposal is tonight at 11:59 pm.  If you have read it, maybe you wondered about the wolf called F521 (her studbook number) and how it came to be that so many of the small population of Mexican wolves living in the wild are so closely related to her.

I first discovered F521 years ago in a monthly status report.

She was born on the side of a mountain in 1997 at the Cheyenne Mountain Zoo in Colorado Springs.  Zookeepers called her Estrella, star in Spanish.  She and her littermates were special because of their genetics, a mix of two of the three lineages of the small captive population.

At the age of five, F521 was released with her mate and family (2 juvenile pups and five new pups) in the White Mountains of Arizona. It was the summer of 2002, early on in the Mexican wolf reintroduction effort (at the time there were approximately 26 wolves living in the wild), and no one knew how this family, named the Bluestem Pack, would adapt to life in the wild.

In the first few weeks they had to be hazed away from a ranch and killed a blue heeler before settling in and chasing down their first elk.  They established a territory and the next spring F521 gave birth to her first litter of wild-born pups.  She remained the alpha (breeding) female of the Bluestem Pack for six years, outliving one mate, finding another, and continuing to raise new litters of pups each year.  Some of those pups went on to establish new packs and have litters of their own.

In 2008 one of F521’s female offspring, F1042, replaced her as the alpha female in the pack.

The old wolf, probably no longer welcome in her pack, sometimes ran alone and sometimes ran with another pack.  In December of 2010 she was found dead in the Gila National Forest, killed in an illegal shooting.  F521 was thirteen.

Once again it is breeding season for wolves and the Bluestem Pack still lives in the White Mountains with F1042 as the alpha female.  In late April or early May  pups will be born.

The numbers cited in the 2017 proposal are surprising and alarming. Of the eighteen potential breeding pairs living in the wild in 2017, three  have one adult that is a descendant of F521 and fifteen have both adults that are descendants of F521. Inbreeding has always posed a threat for Mexican gray wolves.  They came so close to extinction that there were only seven founders when breeding in captivity began.

Fifteen years ago when F521 was released in the wild she was a star not only in name, but also in the genetic potential she offered to the wild population.  She did her part—  she lived wild and free for more than eight years and raised lots of pups.

The most recent estimate of Mexican wolves living in the wild is 113. A combination of too few wolves being released and too many wolves being killed illegally has led to the current dire situation.

More wolves from the captive population need to be released immediately.

The 2017 proposal is a start—2 families and 10 cross-fostered pups—a move in the right direction.

Please take a moment to send an email to in support of the proposed releases.


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