no SPRING 



sweet, though the whole style of building is less compact 

 and precise. 



A ruder but more laborious type of nest is built of mud 

 by the swallow and house-martin. Neither the swallow's 

 open saucer nor the house-martin's enclosed hemisphere has 

 the delicate workmanship of the goldfinch's or long-tailed tit's 

 nest, but both need as careful labour. The collection of the 

 mud, little by little, from the ponds and puddles is not more 

 troublesome than the similar task of the magpie or blackbird ; 

 the critical part of the task is working the pellets into a tough 

 mud crust, which will cling to a wall or beam, and support 

 the brooding bird and the young. To add to the nest too 

 rapidly would destroy it by making it top-heavy before the 

 foundation was dry ; and the birds seem to know this well 

 since they are dilatory builders. A few fine straws are mixed 

 with the clay, like cow-hair in old-fashioned mortar, but the 

 strength of the fabric is chiefly due to the slow building and 

 the way in which each pellet is moulded with the beak, and 

 the line kept true by the pressure of the bird's breast. The 

 nests of these two species are the most highly developed 

 examples of mud-building among British birds, though 

 neither of them approaches in ingenuity the wasps' nests built 

 in a somewhat similar way out of wood gnawed and chewed 

 into a pulp. Zealous use is made of mud in a different way 

 by the nuthatch. Alone among our birds, the nuthatch has 

 the habit of blocking up the mouth of a hole to a convenient 

 size for its own exits and entrances. It is the same safeguard 

 for the eggs and sitting bird which is developed to an extra- 

 ordinary extent in the case of the African hornbills. The 

 cock hornbill walls up the hen on the eggs, only leaving a 

 small hole through which he feeds her. The hen nuthatch 

 is left free to come and go ; but the entrance is made too 

 small to admit larger enemies. Nuthatches choose a bright 



