The traditional English rhyme about counting magpies, beginning "One for sorrow, two for joy..." only goes up to ten, suggesting that larger magpie groups were uncommon in times past.
This certainly ties in with my memories of growing up in the English countryside in the 1970s when magpies (Pica pica) were common birds but usually encountered singly or in pairs.
It is now very common to see large flocks of magpies - I counted 24 in a single field last week. I never saw large flocks like that when I was young.
Has there been any research into this increased flocking in the species? And if so, what explanation is there?