General terms are not necessarily abstract; a bird is no more abstract than a pigeon.
Halliday & Matthiessen (1999: 144-5):
In other words, the elaboration sets up a relationship either of
- generality (delicacy), of
- abstraction (realisation), or of
- token to type (instantiation);
- Generality/delicacy is equivalent to hyponymy and can be construed as either an identifying or attributive relation;
- Abstraction/realisation can only be construed as an identifying relation;
- Instantiation can only be construed as an attributive relation.