The animals that feed on herbivores like insects, birds & mammals in terrestrial ecosystem, are called :

primary carnivores

The correct answer is Option (4)- primary carnivores

Herbivorous : 

All animals depend on plants (directly or indirectly) for their food needs. They are hence called consumers and also heterotrophs. If they feed on the producers, the plants, they are called primary consumers.

Obviously, the primary consumers will be herbivores. Some common herbivores are insects, birds, and mammals in the terrestrial ecosystems and molluscs in the aquatic ecosystem.

Carnivorous :

The consumers that feed on these herbivores are carnivores, or more correctly primary carnivores (though secondary consumers). Those animals that depend on the primary carnivores for food are labeled secondary carnivores. Carnivorous form the third tropical level.