Sumatran tigers can’t seem to catch a break. This week, a study containing good news about the population of this endangered cat also carried a disclaimer that there was probably no cause for optimism.

The new study, published Tuesday in Nature Communications, relied on images from more than 300 trap cameras as well as data from decades of similar studies. The authors reported that tiger density in Sumatra’s three largest protected forests increased 5 percent per year from 1996 to 2014, suggesting that Indonesia’s preservation efforts are slowly working.

However, the increase was probably caused by an influx of tigers fleeing unprotected forests on the large western island in the Indonesian archipelago, where their numbers are dropping rapidly, the researchers said.