COMPETITION BETWEEN MARTINS 201 



JNIartins build in close proximity to one 

 another, owing probably to shortage of accom- 

 modation, and, in their case, the nests have to 

 be so situated as to be sheltered from the wet. 

 If water drips upon them for any length of 

 time, the mud, of which they are composed, 

 crumbles and large pieces fall away, with the 

 result that the eggs or the young are precipi- 

 tated to the ground. Consequently, not every 

 house or perpendicular cliff will answer the 

 purpose of a breeding station. A few pairs 

 build their nests beneath the eaves close against 

 the walls of my house, and year after year the 

 result is much the same ; after every downfall 

 of rain, the water collects into rivulets, trickles 

 down over the eaves, is absorbed by the mud 

 and destroys the nests. Thereupon, the birds 

 set to work and rebuild ; but again the nest is 

 destroyed, and again they rebuild, and so on 

 throughout the summer, and only on rare 

 occasions do they succeed in rearing offspring 

 at the proper season. Similar conditions must 

 prevail in many situations ; but, clearly, the 

 more binding and plastic the building material, 

 the longer the nest will withstand the action of 

 the dripping water and the greater chance will 

 there be of the young being reared in safety. 

 Observe, therefore, how far-reaching an effect so 

 small a detail as the nature of the mud can have 

 upon the status of the species in any given 

 locality. Where the conditions are favourable, 

 there the birds must congregate to breed, and, 

 like the Guillemot, if each individual exercised 



