HOW BIRDS FLY

A systematic exposition of how birds fly. Freedman proceeds from the simpler factual information—muscle strength, feather shape and construction, skeletal design—to more demanding aerodynamic principles as he introduces the many known factors and alludes to those not yet determined. Air sacs and hollow bones account for lightweight bodies; pliant feather shafts and curved shape allow for flexible movement; and other adaptations (such as the alula) respond to changing air currents and flight plans—gliding, soaring, landing. Appropriate airplane comparisons are made and the special features of hummingbirds receive their own small section. Bjorklund's soft-focus pencil drawings are adequate for pointing up particular aspects (arm-wing bone similarities, close-up feather structure), wholly unsuited to species identification.