by Birds are unexpected stowaways for ocean ships. The phenomenon is so common that it has a term—ship-assisted migration. Italian zoologist Maurizio Sarà was the first scientist to systematically study the phenomenon of birds hitchhiking. In 2021 Sarà embarked on a month-long research voyage in the Mediterranean where he aimed to investigate marine species such as dolphins and sea turtles, but during the voyage he kept noticing birds landing on the boat. He started recording. An average of 3 birds stayed on board per day, with a median stay of 42 minutes, and birds stayed overnight on board. Thousands of ships sail the Mediterranean every day, and billions of birds cross the sea in their migrations. They stop on islands, but islands are far less common than boats, and Sarà estimates that as many as four million birds may hitch a ride on ships in the Mediterranean during their migrations. Approximately 90,000 commercial vessels sail the world’s waters on a regular basis each year. Sarà speculates that the birds thus developed a new migration strategy, using boats to get through the most tiring part of the migration and to recover from fatigue.
