Why do starlings probably migrate to this country alone?

Because few other birds could travel so long, and continue such a rapid motion.

From some rude observations, it appears probable, that a pair of starlings in conjunction do not travel less than fifty miles in the day, visiting and feeding their young about one hundred and forty times, which, consisting of five in number, and admitting only one to be fed each time, every bird must receive in this period eight and twenty portions of food or water.