steered in part by recognizable landmarks. Arguments against the 

 theory of landmark memory are chiefly that unescorted young birds, 

 without previous experience, can find their way to the winter 

 quarters of their species, even if the wintering area has a radically 

 different landscape and vegetation than the breeding grounds. 

 Experimental findings and field observations indicate landmarks 

 are used in navigation by certain birds, but the degree of use varies 

 considerably among the species (Bellrose 1972a). 



To a land-dweller traveling the ocean, the vast expanse may seem 

 featureless but the reverse may be true for a seabird blown over land 

 by a storm. In the latter situation the differences in vegetation and 

 topography "obvious" to land-dwellers are completely foreign to a 

 seabird as it has had little previous experience to help interpret these 

 "strange objects." Griffin and Hock (1949) observed the flight 

 behavior of gannets displaced far inland away from their nests. The 

 bird appeared to search randomly until the coastline was met, then 

 the fliers pursued a much more direct course home. Herring gulls, 

 displaced about 250 miles from their nest in 2 consecutive years, 

 returned the second year in one-sixth the time required the first year 

 (Griffin 1943). To birds such as gannets, albatrosses, and 

 shearwaters, which spend almost their entire lives traveling 

 thousands of miles at sea and return to very specific nesting areas, the 

 "featureless ocean expanses" are probably very rich in visual cues. It 

 is difficult to believe a bird dependent on the sea for its livelihood 

 cannot help but be aware of wave direction, islands, reefs, atolls, 

 concentrations of floating flotsam, organisms, currents, clouds over 

 islands, fog belts, etc. 



Much migration takes place at night and great stretches of the 

 open sea are crossed to reach destinations. Nights are rarely so dark 

 that all terrestrial objects are totally obscured, and features such as 

 coastlines and rivers are just those that are most likely to be seen in 

 the faintest light, particularly by the acute vision of birds from their 

 aerial points of observation. Even if terrestrial objects are completely 

 obscured on a very dark night, the migrants are still able to assess 

 their surroundings during the day before starting out again. 



Some birds, especially colonial seabirds, seem to be able to fly 

 unerringly through the densest fog, particularly in the vicinity of 

 their nest site. Members of the Biological Survey, proceeding by 

 steamer through a dense fog from the island of Unalaska to Bogoslof 

 Island in the Bering Sea, recorded flocks of murres, returning to 

 Bogoslof after quests for food. The birds broke through the wall of fog 

 astern, flew by the vessel, and disappeared into the mists ahead on the 

 same course as the ship. On the other hand, radar observations of 

 migrating birds have indicated strong directional movements on 

 clear nights but often completely random movements in heavily 

 overcast or stormy weather. Possibly some birds can perceive the 

 position of the sun through an overcast as honey bees are known to do. 

 It is less likely the stars could be detected through overcast at night. 



Careful studies have been made on the homing instinct in various 



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