BIRD MIGRATION xv 



One of the best examples of rapid migration is that of the Gray-cheeked Thrush. This 

 bird remains in its South American winter home so long that it does not appear in southern 

 United States until late April — April 25 near the mouth of the Mississippi and April 30 

 in northern Florida. The last week in May finds the bird in extreme northwestern Alaska, 

 the 4,000 mile trip from Louisiana to Alaska having been performed in about 30 days, or 

 about 130 miles a day. 



Generally the later in the season a bird migrates the greater is its average speed, but 

 not necessarily the distance covered in a single night. The early migrants encounter much 

 bad weather, and after one night's migration usually delay several days before making the 

 next flight. The later migrant finds few nights too unfavorable for advancing, so that short 

 flights taken on successive nights greatly raise the average migration speed. 



How do migrating birds find their wa}-? They do not journey haphazard, for the 

 familiar inhabitants of our door>-ard Marten boxes will return next year to these same boxes, 

 though meanwhile thay have visited Brazil. If the entire distance were made overland, it 

 might be supposed that sight and memon,- were the only faculties exercised. But for those 

 birds that cross the Gulf of Mexico, something more than sight is necessary. Among day 

 migrants sight probably is the principal guide, but it is noticeable that these seldom make 

 the long single flights so common with night migrants. 



Sight undoubtedly does play a part in guiding the night journeys also. On clear nights, 

 especially when the moon shines brightly, migrating birds fly high and the ear can scarcely 

 distinguish their faint twitterings; if clouds overspread the heavens, the flocks pass nearer 

 the earth and their notes are much more audible, and on very dark nights the flutter of 

 vibrant wings may be heard but a few feet overhead. Nevertheless, something besides sight 

 guides these travelers in the upper air. In Alaska a few years ago members of the Biological 

 Survey on the Harriman expedition went b}' steamer from the island of Unalaska to Bogoslof 

 Island, a distance of about 60 miles. A dense fog shut out every object beyond a hundred 

 yards. When the steamer was halfway across, flocks of Murres, returning to Bogoslof after 

 long quests for food, began to break through the fog-wall astern, fly parallel with the vessel, 

 and disappear in the mists ahead. By chart and compass the ship was heading straight 

 for the island, but its course was no more exact than that taken by the birds. The power 

 which carried them unerringly home over the ocean wastes, whatever its nature, may be called 

 a sense of direction. We recognize in ourselves the possession of some such sense, though 

 imperfect and frequently at fault. Doubtless a similar but vastly more acute sense enables 

 the Murres, flying from home and circling wide over the water, to keep in mind the direction 

 of their nests and return to them without the aid of sight. 



But even the birds' sense of direction is not infallible. Reports from lighthouses in 

 southern Florida show that birds leave Cuba on cloudy nights, when they can not possibly 

 see the Florida shores, and safely reach their destination, provided no change occurs in the 

 weather. But at fickle equinoctial time many flocks starting out under auspicious skies find 

 themselves suddenly caught by a tempest. Buffeted by the wind and their sense of direction 

 lost, these birds fall easy victims to the lure of the lighthouse. Many are killed by the impact, 

 but many more settle on the framework or foundation until the storm ceases or the coming 

 of daylight allows them to recover their bearings. 



A favorite theor>' of many American ornithologists is that coast lines, mountain chains, 

 and especially the courses of the larger rivers and their tributaries form well-marked highways 

 along which birds return to previous nesting sites. According to this theory, a bird breeding 

 in northern Indiana would in its fall migration pass down the nearest little rivulet or creek 

 to the Wabash River, thence to the Ohio, and reaching the IVlississippi would follow its 

 course to the Gulf of Mexico, and would use the same route reversed for the return trip 

 in the spring. The fact is that each county in the Central States contains nesting birds 

 which at the beginning of the fall migration scatter toward half the points of the 

 compass; indeed, it would be safe to say all the points of the compass, as some young 



