(CNN) Someone is shooting the Mojave Desert's wild burros dead, officials say. Now, they're offering $18,000 to whoever helps nab the suspects.

Over the last three months, Bureau of Land Management officials have found the bodies of 42 donkeys covered in gunshot wounds near the California-Nevada border. They were killed illegally in the Clark Mountain Herd Area.

"We will pursue every lead until we've arrested and prosecuted those responsible for these cruel, savage deaths, and we welcome the public's help to bring the perpetrator or perpetrators to justice," BLM deputy director for policy and programs William Perry Pendley said.

Under the Wild Free-Roaming Horses and Burros Act , burros are protected as "living symbols of the historic and pioneer spirit of the West." As such, they can't be killed, harassed, captured or branded in 10 Western states controlled by the Department of the Interior or the US Forest Service.

Details about the crimes are slim, but BLM officials told the Los Angeles Times a few of the burros were killed while drinking water from nearby springs. Many of them were juveniles.

BLM spokeswoman Sarah Webster didn't have updates on the case Monday, but she said investigators haven't identified any suspects yet.

Officials urge tipsters to call 800-78CRIME or visit wetip.com to anonymously submit information.

Violating the Wild Free-Roaming Horses and Burros Act can result in a fine up to $2,000 or up to one year in prison, or both, for each count charged.

Burros are a beloved symbol of the Old West

The dependable donkey was a popular pack animal during the Gold Rush, but they have a testy history with local ranchers.

In the 1950s, both burros and wild horses were hunted by ranchers whose vegetation they munched on, and their populations dipped, according to the American Wild Horse Campaign