short time energy function explanation Will someone be able to explain short time energy function for me in a simple way explaining all the variables in the formula?  

The issue that I have is in the formula the summation varies m like,

m=n-(N-1) to n

from my research what I understood is that n is the center sample of the window, so if the center of the window is, lets say 80 and if the window size is 160. Then there is a situation where “m” get a negative value discontinuing a loop in a programming environment. Is my understanding incorrect or is there a reason? Thanks in advance.
If you're trying to identify birds, you should look into the Mel-frequency Cepstral Coefficients (MFCCs). They are commonly used in speech recognition, and there's actually a fair amount of academic papers on bird song recognition using the MFCCs and various other features.

Short-term energy is definitely useful to extract areas of bird sound, but it probably won't be sufficient to just take an FFT and look for coefficients. For example, imagine the same two  bird sounds, but one is slightly higher pitch, or there is more/different noise present. The FFT coefficients will be significantly different. The MFCCs basically capture the shape of the spectrum, on a scale that emphasizes regions of the spectrum where more detail is needed, and discard some of the unimportant details.