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
Not Only... But Also Australian television. These two episodes also survive intact, as do specially filmed performances of the "Behind the Fridge" live show from Australia and London, the latter in colour. The Australian performance has been available on DVD. Although they have since been viewed as "best-of"s (featuring new versions of "One Leg Too Few", "Shirt Shop" and "Pseudolene/Job Offer"), at least half of the material was new. A number of surviving sequences were compiled into "The Best of Not Only...But Also", screened by BBC2 on 24 December 1974. Cook and Moore persuaded the BBC (in part thanks to a pleading letter from