Delta-oriented programming allows software developers to define software product lines as variations of a common code base, where variations are expressed as so-called program deltas. Monitor-oriented programming (MOP) provides a mechanism to execute functionality based on the program's execution history; this is useful, e.g., for the purpose of runtime verification and for enforcing security policies. In this work we discuss how delta-oriented programming and MOP can benefit from each other in the Abstract Behavior Specification Language (ABS) through a new approach we call Delta-oriented Monitor Specification (DMS). We use deltas over monitor definitions to concisely capture protocol changes induced by feature combinations, and propose a notation to denote these deltas. In addition, we explore the design space for expressing runtime monitors as program deltas in ABS. A small case study shows that our approach successfully avoids code duplication in monitor specifications and that those specifications can evolve hand in hand with feature definitions.