Calculate the Standard Deviation of Fundamental Frequency (MFCC)
You calculate fundamental frequency of the signal with some pitch extraction algorithm, for example YIN, https://github.com/ronggong/pypYIN. It is a vector of numbers, then you calculate standard deviation of it, that would be a number.

Overall, this feature is not very important for detection. Also, the paper you are trying to reproduce is not quite modern, these days you can get much better results with VGGish and Audioset, something like

https://github.com/luuil/Tensorflow-Audio-Classification

or 

https://github.com/IBM/MAX-Audio-Embedding-Generator