1. What do the following words have in common?

FALL
HORN
BALL
TUNNEL

2. What do the following words have in common?

STRIKE
CURFEW
PETROL
OIL
STARK
THRASH
SWAT

HINT:
1. Each word can be preceded by a different, but related word.

Answers:

1. Each word can be preceded by a weather-related term:

RAINfall / FOGhorn / SNOWball / WIND tunnel 

2. Changing one letter in each word will give the name of a bird:

SHRIKE
CURLEW
PETREL
OWL
STORK
THRUSH
SWAN