134 ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



be regarded as natural "labels", which indicate the presence of 

 other specific differences that may be much more difficult to detect. 

 The theory of recognition marks is strongly supported by the 

 fact that animals which turn white in winter commonly do not 

 do so completely, but retain small dark patches. The Ptarmigan 

 (Lagopus mutus, fig. 1105), for example, retains black markings 

 on the side of the tail, while the male in winter plumage is further 

 distinguished by black streaks near the eye. 



SOCIAL MAMMALS (MAMMALIA). A large number of mammals 

 affect the gregarious habit, and some examples of the benefits 



Fig. 1105. Male Ptarmigan (Lagopus mutus} in Winter Plumage 



accruing have elsewhere been given. Wolves, for example, hunt 

 in packs, and sometimes secure their prey by very ingenious 

 devices (see vol. ii, p. 16). The herding together of various 

 Hoofed Mammals is distinctly of advantage in defence, and many 

 such forms post sentinels to warn them of approaching danger 

 (see vol. ii, p. 365). -Troops of Baboons and Monkeys make 

 well-organized raids, while their tactics during retreat from foes 

 are often decidedly skilful, and have reference to the well-being 

 of the community (see vol. ii, p. 363). The cubs of the Fur- 

 Seal benefit by the mode of life in their " rookery " (see vol. iii, 

 p. 492). To consider in detail all the groups of mammals in 

 regard to social habits would be an almost endless task, and the 

 present purpose will perhaps be sufficiently served by taking one 

 or two typical and interesting cases. 



