animals

artificial

birds

branches

breeding

building

clean

clear

construction

ducks

ecological

ecology

eggs

float

floating

fresh

grass

green

habitat

humanity

humans

ideal

imitation

improve

islands

lake

life

mating

natural

nature

nest

nesting

pipes

plants

population

pure

research

science

season

shelter

suitable

surface

tubes

twigs

vegetation

water

wilderness

wildlife

zoology