ALBUQUERQUE, N.M. (AP) — A record number of captive-born wolf pups has been placed into the wild as part of an effort by federal and state wildlife managers to boost the genetic diversity among Mexican gray wolves in the Southwestern United States.

The interagency team announced the results of this season’s cross-fostering program Thursday. They say the work of integrating the 20 pups into the wild wolf packs took place over a six-week period in April and May.

A dozen pups were fostered into four packs in eastern Arizona, and a total of eight were spread among three packs in western New Mexico.

Cross-fostering involves placing pups less than 14 days old from captive breeding populations into wild dens with similarly aged pups to be raised as wild wolves. The wolf recovery team says cross-fostered pups have the same survival rate as wild-born pups in their first year of life and survival rates using the technique are generally higher than other wolf release methods.

“Managing genetics is one of the biggest challenges facing Mexican wolf conservation, even as constant progress is being made on numeric recovery,” said Jim deVos with the Arizona Game and Fish Department. “Science has proven that cross-fostering young pups works in increasing genetic diversity.”

The captive-born pups came from litters at facilities in Missouri, Kansas, California, Arizona and New Mexico.

This marked the first time the New Mexico Department of Game and Fish has participated in the cross-fostering effort since rejoining the recovery program last year. State officials say the added cooperation helped given the challenges presented by the coronavirus pandemic.

Since 2014, the wolf recovery team has documented at least 10 cross-fostered wolves surviving to the end of the year and being recruited into the wild population. Not all wolves are collared and counted, so officials say that number is likely higher.

The latest survey shows there are at least 163 wolves in the wild in the two states. That represents a nearly 25% increase from the wolves counted at the end of 2018.