282 THE ANIMALS OF NEW ZEALAND 



Tipper current its vis inertiae makes the wind blow past it, and so 

 its stock of energy is increased. When it descends it will be 

 moving faster than the lower stratum of wind, and will again 

 develop new energy if its inertia is sufficient to prevent its 

 attaining the new velocity of the wind at once. So that the bird 

 m.ust fly against the wind when ascending, and with it when 

 descending. Thus the energy constantly lost by the friction of 

 the air is partially renewed by these manoeuvres. This explains 

 why the birds can sail longer in a high wind than in a calm. It is 

 because in a high wind, and with a high sea, there is much greater 

 difference between the velocities of the wind near the surface and 

 a short distance above it; and this, again, is an explanation of 

 why an albatross keeps so close to the surface of the sea, only 

 just topping the waves and occasionally rising high in the air. 



The sooty all)atross makes no sound when at sea ; but, when 

 breeding, the sitting bird on the nest gives a wailing cry, like 

 "pee-u, pee-u," which is similarly answered by its mate, flying 

 around. 



Order Impennes. 



Wings short, covered with scale-like feathers. Tail composed of 

 narrow rigid feathers. Tarsi very short, the anterior toes united 

 by a web ; the hind toe very small and united to the tarsus. 

 Southern Hemisphere. 



It is stated in the Introduction that New Zealand, together with 

 the neighl)ouring islands, may be looked upon as the headquarters 

 of the penguins, as all the genera except one, SpJieniscus, are 

 found here. Besides this, there is evidence that points to New 

 Zealand l)eing the centre of dispersion. The oldest penguin 

 known, Palaeeudyptes antarcticus, is from the Eocene or 

 Oligocene rocks of New Zealand. It is a true penguin, and except 

 tliat tlie wing is proportionately longer than in living penguins, it 

 shows no intermediarv character. The onlv other known fossil 



