The discovery of a set of small footprints in the Colombian jungle has sparked renewed optimism in the ongoing search for four children who went missing last month after surviving a small plane crash.

The footprints were found on Tuesday about two miles northwest of the area where a plane carrying three adults and four indigenous children went down on May 1, CBS News reported.

The searchers believe the tracks belonged to the eldest of the group, a 13-year-old girl, Gen. Pedro Sánchez, commander of the Joint Command of Special Operations, told The Associated Press.

The other children are 9, 4, and 11 months old. All three adults, including the pilot, perished in the crash.

“We have a 100% expectation of finding [the children] alive,” Sánchez said.

“It’s not like finding a needle in a haystack, it’s like finding a tiny flea in a huge rug that moves in unpredictable directions.

“We found elements that are very complex to find in the jungle. For example, the lid of a baby bottle. If we’ve found that, why don’t we find the rest? Because the children are on the move.”

Some soldiers have walked over 1,000 miles through the Colombian Amazon in search of the four, he added.

The rescue effort includes more than 100 members of the special forces, in addition to upwards of 70 indigenous people from the region.

Last month, Colombian President Gustavo Petro falsely claimed that the children had been found alive.

“I am sorry for what happened. The military forces and Indigenous communities will continue in their tireless search to give the country the news it is waiting for,” he tweeted at the time.

Even more than one month after the crash, searchers believe the children have managed to survive because animals would have been drawn to their remains, Sánchez explained.

Other clues churned up over the weeks include towels, used diapers, and some scissors. It is unclear if the children intentionally left the items behind in order to aid possible searches.

Soldiers working in rotations are faced with up to 16 hours of heavy rain in addition to wild animals like jaguars, ocelots, poisonous snakes, and mosquitos. 

They are also at risk of getting lost in the dense jungle, where the visibility is often less than 70 feet.

The areas that have already been searched are marked with tape and whistles in case the children return and are able to call for help.

The search teams are also blasting the area with recordings of the children’s grandmother’s voice – though the sound is often muffled by the rain, Sánchez said.

Petro continues to make finding the foursome a priority. Sánchez confirmed that there is no deadline for wrapping up the search.