1 8 BIRD BEHAVIOUR 



related to the former ; both hop upwards or side- 

 ways on boughs and trunks, resting on their stiff- 

 pointed tails, and letting themselves slip back if, 

 which is seldom the case, they want to descend. 

 The Nuthatch, which is not stiff-tailed, has the 

 advantage of these extreme specialists in being able 

 to climb in any direction, down as well as up. 



Swimming is generally performed by alternate 

 strokes of the feet when the bird is on the sur- 

 face, and simultaneous strokes when it dives ; 

 but Auks, though they swim like other birds on 

 the surface, propel themselves when below with 

 their half-closed wings, and the Penguins never 

 use their feet in the water at all, apparently, but 

 rely entirely, both on and under the surface, on 

 their flipper- like wings. Land- birds can gener- 

 ally swim if they are put to it, those which run 

 swimming with their legs I have seen a young 

 Peacock thus save himself ; those which rely on 

 their wings will flap themselves ashore, which I 

 have seen a Swallow do after it had fallen in ; but 

 they soon become draggled and exhausted, and 

 except for the large flightless runners, cannot go 

 any distance, in spite of being unable to sink. The 

 giant runners, however, are as strong swimmers as 

 beasts. I have known of a Cassowary making land 

 after a four miles' swim in a by no means calm 

 sea. Land-birds when swimming sink low in the 

 water, but, curiously enough, so do some of the most 

 specialized divers ; the Cormorants swim with the 

 tail awash, and the allied Darters only show the 



