Which experiment should be conducted as a field investigation? observing changes in the nesting behavior of wood ducks measuring the fermentation rate of yeast in salt water determining the germination rate of a new soybean hybrid investigating gene expression in fruit fly offspring

The answer is A. observing changes in the nesting behavior of wood ducks 
A field investigation includes observation of free-living animals in their natural habitat without affecting them, their behavior, or their habitat. So, observing changes in the nesting behavior of wood ducks is an example of the field investigation. An investigator will simply observe the changes, not affecting wood ducks in any way.In all other choices, to determine phenomenon, some changes would be necessary. For example, to measure the fermentation rate of yeast in salt water or the germination rate of a new soybean hybrid, investigators need to change the environment of the non-free-living species, respectively. The same is for investigating gene expression in fruit fly offspring.