Do birds have a sense of smell and how sensitive is it?

Yes, and though it is highly variable from species to species, research is leading to a higher estimation of birds’ smelling abilities.

Sensitivity to odors varies among orders of birds with the size of the olfactory bulb in the brain relative to that of the cerebrum. The bulb tends to be small, but it is well developed in some birds, especially those that fly and hunt by night, and research has found that some birds with relatively small olfactory bulbs can smell well enough to detect certain odors.

Scientists now suspect that most birds can use the sense of smell in daily activities, and individual species have been found to have high sensitivities adapted to needs like mating (finding a female in season by detecting gland secretions), feeding (smelling carrion or worms), or even finding their nesting burrows.

Some birds can smell just a trace of a substance that might lead them to food. For example, bacon fat poured on the surface of the ocean has been known to attract black-footed albatrosses from more than 18 miles away.

Turkey vultures have been used to find leaks in a 42mile-long oil pipeline; when ethyl mercaptan, which smells like rotting meat, was pumped through, the birds gathered at the leaks.