Feeling would be the one that makes the most sense.
sorry for that question is wrong
Based on my interpretation of this website, I believe it's the astronomers. :)
The paragraph contained one sentence that wandered from the main topic about getting exercise walking to work for example which is not volunteering but otherwise the paragraph is very coherent and all tied together and the grammar and punctuation and spelling are all very good.
They need the ice in order to pursue their main food source - Polar Bears
They migrate more than a country away from their original home - Butterfly
The area that they inhabit is growing smaller due to their need for a specific climate - Polar Bears
Hope this helps.