| A | B |
|---|
| incubate | to keep eggs warm until they hatch |
| contour feather | strong and lightweight, this helps birds steer in flight |
| down feather | soft and fluffy,this provides insulation for birds |
| preening | process of rubbing oil into feathers with a beak |
| carnivore | meat-eating animal |
| omnivore | animal that eats both plants and animals |
| placental mammal | mammal whose embryos develop in the uterus |
| gestation period | time during which an embryo develops in the uterus |
| umbilical cord | attaches the embryo to the placenta |
| monotreme | mammal that lays eggs with a tough leathery shell |
