In the previous line, Ross mentions kilos of cocaine. Tennessee is quite far away from his hometown of Miami (where cocaine can be acquired at more inexpensive prices). Thus, he tends to send his product up to TN where he can easily fetch a large profit.
"Birds" and by extension, "chickens" are urban slang for kilograms of cocaine. Our rapper here is claiming that buy distributing a kilogram of cocaine, or "crossing the street" with it, he earned eighteen thousand dollars.