The U.S. Fish and Wildlife Service denied a request by environmental and conservation groups to list the coyote as endangered in the territory that overlaps with the Mexican wolves.

The groups said that the similarity of appearance to a Mexican wolf warranted the listing as a way to prevent people from accidentally killing the wolf.

However, the Fish and Wildlife Service found that the resemblance between the Mexican wolf and the coyote is not similar enough that the two canines cannot be distinguished from each other.

Related: Conservation groups ask for federal protections for coyote to protect Mexican wolves

The agency looked at whether law enforcement struggled to tell coyotes from wolves.

“Mistaken identity accounts for only a small portion of Mexican wolf mortalities,” Brady McGee, the Service’s Mexican Wolf Recovery Coordinator, said in a press release. “Listing coyotes under the Endangered Species Act would have a minimal impact on Mexican wolf recovery, while imposing an extreme burden on law enforcement, affecting their ability to protect the Mexican wolf in Arizona and New Mexico.”

Chris Smith, a southwest wildlife advocate with WildEarth Guardians, described the decision as incredibly disappointing. However, he said it is not a surprise. Groups like WildEarth Guardians have criticized the Fish and Wildlife Service in the past for policies that they say could harm the wolves.

Smith said the Fish and Wildlife Service does not always advance the best policies for the wolves.

Coyotes are one of the species with essentially no protection, which means they can be killed year round and using a variety of methods.

Smith said he believes the reasons the WildEarth Guardians and other groups gave for protecting the coyote within the Mexican Wolf Experimental Population Area were sound.

The January petition listed incidents where wolves were killed because someone mistook them for coyotes.

While it is a federal crime to kill a Mexican wolf, a person who has mistaken a wolf for a coyote cannot be convicted. This is because the McKittrick Policy requires the government to prove that the person knew they were killing an endangered species.

“We pretend to revere [wolves] and we pretend to protect them,” Smith said. 

But, he said, having a lookalike species with no protections places the wolves in danger.