306 Transactions. — Zoohn/y. 



their increase ; and it seems to me that it is in the working 

 of this same law that an explanation of the periodical appear- 

 ance of both the rats and parroquets Avill be found. 



During the summer and autumn preceding the great swarm 

 of 1884, while moving about various portions of the bush 

 country, I noticed that the nests of parroquets were unusually 

 numerous. Everywhere I went people had the unfortunate 

 young birds confined in cages, for what they grimly termed 

 "pets." A similar abundance of nests was again observed 

 last year, preceding the swarms of parroquets and rats which 

 have just taken place. 



A supply of food being the most important of the conditions 

 necessary to the increase of the higher or viviparous animals, 

 and the rats being herbivorous, wu naturally turn to the pro- 

 ductions of our forests when seeking an explanation of their 

 periodical appearance on the above-mentioned basis. Here 

 we are at once confronted with the facts that the swarms of 

 1884 and of the present year followed after heavy crops of 

 fruit tlu-oughout our beech-forests, and that such exceptional 

 crops are produced at intervals, both by the more homogeneous 

 beech-forest and the mixed bush of the low lands, though 

 they are not always coincident. That the upper portions of 

 our hills, which are mostly clothed with the various species of 

 beech, are the proper habitat of the bush-rat, I think there can 

 be little doubt. One hill in this district bears the name of 

 Kaikiore, the tradition connected therewith being that some 

 natives, while hiding from their enemies, subsisted on rats, 

 which they found in great numbers; and this, again, I think, 

 accounts for the statements made by the Maoris that the ap- 

 pearance of these rats on the low lands is due to their being 

 compelled to leave the hills through the failure of the kiekie 

 fruit ; for, though I consider the cause insufiicient, it must 

 often be coincident with the period of swarm . 



While venturing the above suggestions, I clearly perceive 

 that no explanation can be deemed satisfactory that leaves 

 the enormous preponderance of males in these rat-swarms un- 

 accounted for. Amongst English country-people, who have 

 the best opportunity of observing them, it is commonly 

 asserted that in litters of young rats the males produced out- 

 number the females by about seven to one. Whether this 

 is correct, or, if correct, whether it holds good of all the 

 species of the genus Mns, I do not know ; but, even if it is the 

 fact, it would be insufiicient to account for the disproportion 

 of the sexes found in our rat-swarms. 



Two questions here present themselves : (1.) Would a 

 sudden increase of numbers, consequent on an excessive food- 

 supply, afiect the usual proportion of the sexes '? In the case 

 of the hive-bee, whether a nymph shall develope into a barren 



