Behavior Driven Development is an extension/revision of Test Driven Development. Its purpose is to help the folks devising the system (i.e., the developers) identify appropriate tests to write -- that is, tests that reflect the behavior desired by the stakeholders. The effect ends up being the same -- develop the test and then develop the code/system that passes the test. The hope in BDD is that the tests are actually useful in showing that the system meets the requirements.

**UPDATE**

Units of code (individual methods) may be too granular to represent the behavior represented by the behavioral tests, but you should still test them with unit tests to guarantee they function appropriately. If this is what you mean by "TDD" tests, then yes, you still need them.