If the equal-mass lead and feathers are resting on 2 separate scales, gravity pulls down on each with the same force. However, in principle the scale reading may be infinitesimally smaller for the feathers. If buoyancy is considered, feathers displace more air volume than an equal mass of lead, so the buoyant force on them is larger than it is on the lead. So, the feathers push ever-so-slightly less hard on the scale than the lead does.
Work Step by Step
This is discussed on page 271.