I was considering how motivation competes with self control. Clearly there is potential for conflicts between the agencies of the mind, since the goals of different agencies vary and often lead to competing needs. The brain is operating with the notion that there are some goals which need to be met.
Motivation is the mechanism by which one's goals are met.
Reflex and instinct can be classified as types of motivation. In this instance, the sender may have direct communication with the agents which can cause the hand to move. Here instinct invokes a high level motive to build a nest, which may involve spawning off several sub-motives, such as finding materials, then putting them together, etc. Because it would be difficult for a bird to learn how to build a nest, the instructions for building a nest are hard-coded into the birds knowledge base. Similarly, because it would be difficult to explain to the bird why she should build the nest, an agency could be hard-coded into her mind which knows to send appropriate motives around in certain occasions, which cause her to want to built a nest.