Bird migration evidence. Seabirds fly low over water but gain altitude when crossing land, and the reverse pattern is seen in landbirds. However most bird migration is in the range of . Bird strike aviation records from the United States show most collisions occur below and almost none above . Bird migration is not limited to birds that can fly. Most species of penguin (Spheniscidae) migrate by swimming. These routes can cover over . Dusky grouse "Dendragapus obscurus" perform altitudinal migration mostly by walking. Emus "Dromaius novaehollandiae" in Australia have been observed to undertake long-distance movements on foot during droughts. While participating
The Bird That Drinks Tears gave their respective races a gift. Currently, Lee Yeongdo has written only one sequel to "The Bird That Drinks Tears" which is "The Bird That Drinks Blood". It is expected that Lee Yeongdo will write two more sequels, because of the quote in the series that mentions four birds. In the book there is a riddle about four bird brothers. One bird drank water, one drank poison, one drank blood and one drank tears. The riddle asks who of the four birds will die first. This riddle appears repeatedly throughout both "The Bird That Drinks Tears" and "The Bird That