Mystery of the dying ferns

Something is happening to the ferns!

This is quite a mystery to me as the bird nest ferns in the faculty of arts and social science in NUS all appear to have been met with a very hungry caterpillar or died off. More than 5 trees with a few ferns on each of these trees appear stricken with this predicament.


How it looks like normally

Could somebody perhaps explain to me or hazard a guess as to what may have caused this? Is this normal? I apologize for the poor photo quality. I will attempt to take more on Monday.