Is it obligatory for someone who sees cows or chickens eating his brother's crops to remove them or inform him?

Whoever finds a Muslim's property being lost is obligated to safeguard it if he is able to do so without harm befalling his person, wealth, or status. If there is hardship or harm in doing so, then it is not obligatory upon him. The evidence for this is the Prophet's (peace and blessings be upon him) prohibition of squandering wealth, and Allah's command to cooperate in righteousness and piety. For indeed, leaving a Muslim's property unguarded is a squandering of wealth and a greater harm than failing to return a salutation. If safeguarding it is not obligatory upon him, then he must alert the owner of the property if it does not cause him hardship.