HARBWICKE'S SCIENCE-GOSSIP. 



27 



eggs are perfectly white. Those birds that lay con- 

 spicuous eggs in an open nest find it necessary to sit 

 upon the eggs or young to hide them by their dull- 

 coloured upper .plumage, and thus elude the eye of 

 the passing jay or hawk. 



Instances of the observation of nests in a state of 

 transition between the open and the covered condition 

 have been rare, but one such example is supplied by 

 an American species. That acute ornithologist, 

 Wilson, describes the nest of the towhe bunting as 

 being "formed outwardly of leaves and pieces of 

 grape vine bark, and the inside of fine stalks of dried 

 grass, the cavity completely sunk beneath the surface 

 of the ground, and sometimes half-covered above with 

 dry grass and hay. " And he states further that 

 " the bird is remarkable for the cunning with which 

 he conceals his nest." Mudie informs us that some- 

 times the robin covers its eggs, and occasionally 

 constructs an arch of leaves where concealing foliage 

 is wanting, under which it passes to its nest ; he also 

 states that the goldcrest builds an open nest in pine 

 forests, but a domed one in other districts, where 

 presumably enemies are more numerous. He further 

 remarks that the long-tailed titmouse does not 

 uniformly confine itself to one style of nest, but often 

 constructs two entrances or means of exit instead of 

 one, the nest having a backdoor for escape. 

 (" Feathered Tribes of the British Islands.") These 

 are deviations, but deviations may not always indicate 

 progression, as many circumstances, the withdrawal 

 or destruction of some peculiar enemy, for instance, 

 might occasion a reversion to some former and 

 simpler type of nest. Possibly the habits of one 

 portion of a species might undergo change in a 

 particular region, such change being induced by 

 peculiar circumstances. It has long since been 

 pointed out that birds inhabiting pine forests are 

 different in structure from birds of the same species 

 inhabiting oaken or beechen forests. 



Nearly all birds that have acquired a habit of 

 building in darkened places lay conspicuous eggs. 

 Many birds build deceptive nests ; many produce 

 eggs that assimilate in colour with the lining of the 

 nest ; many sit upon the eggs to guard them ; and 

 some cover their eggs, but none of these means of 

 concealment and security seem to be equal to the 

 domed nest. Mr. Wallace, as quoted by Darwin, 

 gives his opinion that domed nests were originally 

 built to hide birds of brilliant plumage while sitting. 

 In Britain this theory would scarcely hold good now, 

 as none of our dome-builders possess conspicuous 

 plumage* though we cannot tell what kind of 

 plumage they might have possessed when they first 

 began to build domed nests.f 



* The magpie excepted. This bird preys on eggs of other 

 birds but it has sufficient intelligence to erect a screen to 

 protect its own. 



t It is interesting to notice here that the American quail that 

 lays white eggs has a domed nest, but our quail that lays 

 spotted or clouded eggs has an open nest. 



Of fifty of our smallest insessorial birds (omitting 

 very rare species) that build ordinary exposed nests 

 twenty-five are uncommon ; of fifteen that build in 

 darkened places six are uncommon ; of ten that build 

 domed nests none can be called uncommon : so that 

 it would appear that birds that build in darkened 

 places have advantages over those which build an 

 ordinaiy hemispherical nest in exposed places, but 

 those which build domed nests have still greater 

 advantages, as, by the aid of their domed nest and 

 general mode of nidification, every species is able to 

 keep up its numbers. 



No classification can be grounded on architecture, 

 or on the colour of eggs. Of the ten birds above 

 mentioned the "three willow wrens " have a close 

 kinship, but the others differ much, being included in 

 widely separated genera ; some have long tails, some 

 have short tails, some lay white eggs, some lay spotted 

 eggs, some build on or near the ground, some at a con- 

 siderable height, the only thing that is common to 

 them all is the vaulted nest. Yet one cannot but 

 imagine that these birds, along with others which 

 may have withdrawn from the British Isles, have 

 been originally subject to common, but, perhaps, 

 peculiar influences, to determine them to take action 

 in one respect nearly all ahke. 



However near two species may be, or appear to be 

 in structure, the marked differences we find in archi- 

 tecture and in the colour of eggs indicate that a long 

 time has elaiased since the two diverged from a 

 common parent. On the other hand slighter differ- 

 ences in nests and eggs almost certainly indicate that 

 a shorter time has elapsed since the period of diver- 

 gence. For instance the three willow-wrens are near 

 together, they are similar in size and plumage, they 

 build domed nests and lay spotted eggs, and the two 

 sparrows are similar in plumage, build domed nests 

 and lay spotted eggs. From these circumstances we 

 may infer that a shorter period has elapsed since the 

 three willow-wrens or the two sparrows began to 

 diverge, than that which has elapsed since the diver- 

 gence of two species like the swallow and the house- 

 martin, or the thrush and the blackbird ; birds which 

 though much alike in structure build very different 

 nests and lay very different eggs. 



In regard to superiority there are, in my mind, 

 four grades of birds : the water birds, the wading 

 birds, the scratching birds, and the perching birds, all 

 succeeding each other in intelligence. So far as 

 British birds go, our ten dome-builders stand in the 

 front, as being more artful as designers, adapters, and 

 executors than the rest of their kin. If all the nests 

 of British birds could be arranged in a chain the 

 simple cavity in the sand would stand at one end, and 

 the chef-d'ceuvre of the long-tailed titmouse at the 

 other. 



Lofthouse, 



George Roberts. 



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