There is a simple saying in Spanish that goes
"No es lo mismo ser que estar" not easily translated to english unless you add more information to the phrase. "It is not the same to be (a person/animal/thing) than to be (in a place)"
You should learn that since it may help you identify where to use each one.
In Spanish we differentiate between being a person (ser) and being in a place (estar). Since the chicken is on the table, el pollo "ESTÁ" en la mesa. Another thing would be "this chicken is bad", since here we are talking about the chicken (being not a person but an animal in this case) the sentence would be "el pollo es malo".
EDIT: Diego's comment made me think "the chicken is bad" is an example that can lead to a missunderstanding unles there is more information in the phrase. The chicken is a bad chicken, it is dirty, breaks everything and the like, in this case
el pollo es malo
The chicken is bad -rotten- and you can't eat it, in this case:
el pollo está malo
Edit2: The missunderstanding is obviously in english. In Sapnish there is no missunderstading, since "el pollo es malo" is self explanatory while in English it is not.