The starling is a remarkable bird in a number of ways. It is much more social than most British birds. The continental starlings fly back to their breeding places where their sexual organs mature in spring. The British starlings are more tolerant of foreign birds than of their compatriots, probably because the latter are more apt to be sexually active, and thus arouse their jealousy. The starling seems to be splitting up into two species, as Charles Darwin believed that species sometimes do. During winter the continental birds have very small ovaries and testicles, and show no sexual behaviour. But although these organs get smaller in the British race after the breeding season in April, they increase in size in autumn, and there is a good deal of love-making, and sometimes even mating. Among the well-known London roosts are the Marble Arch, and St. Martin's Trafalgar Square.