260 Transactions. — Zoology. 



winter insects hybernate, and the birds have to go to warmer 

 latitudes. But when the spring conies on the insects in high 

 latitudes come out, and the birds go back again to feed upon 

 them. As this is the breeding-season they naturally breed in 

 high latitudes. There are, however, several migratory birds 

 in the tropics which never go to cold climates, but regularly 

 change their quarters twice a year ; and most of these migra- 

 tions may be due to the fruits of different trees ripening at 

 different times. In North America there are some birds 

 which do not return by the same route which they follow 

 when flying south, and these deflections also seem to be due 

 to different fruits, on which they feed, becoming ripe at dif- 

 ferent seasons of the year in different places. 



But change in the food-supply is not an adequate explana- 

 tion of all cases of migration. For example, swifts migrate in 

 Central America, while swallows remain all through the year. 

 Ducks certainly do not leave their winter quarters for want of 

 food ; and our godwit would find just as much food on the 

 shores in winter as it does in summer. In New Guinea three 

 or four species of bronze cuckoo are residents, and, if they can 

 find food all the year round, so also could the migratory species 

 which go to Tasmania and New Zealand ; and certainly 

 insects in New Zealand, even in summer, are much less plen- 

 tiful than they are in New Guinea or Australia. Evidently 

 our two migratory cuckoos are not attracted here by the 

 abundance of insect life. It is probable that these migrations 

 may be due to the habit of resorting each year to the same 

 place to breed, a habit which is common to many birds, 

 whether migratory or not. Probably they like the site of 

 their old nest, and have grown accustomed to it ; it has pro- 

 tected their young in former years, and they have found suffi- 

 cient food in the neighbourhood. They do not like new 

 experiments, and year after year they return to build them 

 nests in the same places that they did before. Instances are 

 known of this taking place although the surroundings of the 

 nest had been greatly altered by cultivation ; thus showing 

 that the return to the ancient breeding-place had become an 

 instinct. No doubt this love of home must be taken into 

 account, as well as the food-supply. It is this that explains 

 the two cuckoos coming to New Zealand ; while in the case 

 of the Limnicolce we must suppose that they return annually 

 to the feeding-ground of their forefathers, and that this also 

 has become an instinct. How strong this migrating instinct 

 is we can judge from the fact that swallows not unfrequently 

 leave their late broods of young ones to perish in their nests 

 while they fly south. 



The shore-birds retain the same specific characters, no 

 matter where they wander, because all breed together in the-- 



