Potato Famine in Ireland
Between 1845 and 1852 much of the Irish potato harvest was destroyed by blight. A catastrophic famine was the result, as potatos were the staple diet of the country people. Half-hearted efforts to help by the government in England led to nothing. It is estimated that about 1 million Irish died either of hunger or of the typhus, dysentry and cholera that followed. Hundreds of thousands left the country.
From 1845 to 1847 the population of Ireland reduced from 8 to 6.5 million.
For more see Wikipedia.
That John Capper and family suffered in the famine is shown by two things:
a) his enlistment in the army in Dec. 1847 in the middle of the famine and
b) the family anecdote about the crow and cheese.