Oct.^, 1872] 



NATURE 



457 



ox THE RETENTION AX D COLOURING OF 

 Ecus, .LVD THE PROTECTIVE MIMICRY 

 OF SOUNDS 



I. T S it known for how long a time a bird possesses tlie 

 ■•■ power of retaining its ec^Lj? 



Last summer, from the number of nests in tliis neigh- 

 bourhood, the writer was able to study the habits of king- 

 fishers {HaliYoit vagans) \\\\\\ more facility than usual. 

 The movements of one pair excited much interest. On 

 the igth October this pair were observed to be busily 

 engaged in excavating a home in the back of the turf 

 chimney of an empty cottage. After many days spent in 

 hard labour, this was abandoned ; subsequently several 

 tunnels were commenced, in some of them considerable 

 progress was made ; then they were in like manner de- 

 serted. The seventh resting-place, begun November 

 26 (there must still be a witchery about number 

 seven even at your Antipodes), was finished, occu- 

 pied, and therein, on December 24, a brood was 

 hatched. Can there be reason to doubt that the eggs 

 in the ovary of the female must have been in a for- 

 ward state in the third week in October ? At the close 

 of that month the first egg to be laid must have been 

 ready for extrusion. From personal observation we know 

 that our kingfisher lays nearly every morning till the clutch 

 of eggs is completed ; the number of eggs to a clutch 

 varying from five to seven. Here we have a bird engaged 

 in laborious, almost incessant exertion, for quite six weeks, 

 physically in a condition analogous to that of a pregnant 

 animal. Three of the homes excavated and ab.andoned 

 were so far finished that the chamber was hollowed out, 

 so that a deposit of eggs must have been imminent on 

 three occasions during that period of six weeks. It is 

 well known that the domestic fowl, on a change of quarters, 

 will, in its strange home, sometimes retain the egg for 

 hours beyond the usual time of laying, often depositing 

 what is called a double-yoked egg, but we have to do 

 with the freedom of wild nature. It is easy to suggest 

 that our kingfisher relieved itself by dropping its egg ; 

 obviously that would be opposed to the marked instinct 

 of so persevering and painstaking a nest- builder ; besides, 

 would that mode of acquiring ease be twice repeated by 

 a bird that endured such toil to make a hiding-place for 

 its progeny — toil only to be appreciated by those who 

 have watched its daily work ? 



2. Can a bird influence the colour of its eggs proteo 

 tively ? 



A proposition that few physiologists would answer in 

 the affirmative, yet naturalists have held, perhaps still do 

 maintain, diverse opinions as to the cause of abnormally 

 coloured eggs. The following facts are laid before your 

 readers for information : — Rather late in last summer a 

 female bittern (B. poiciloph-rus) was slightly wounded and 

 secured. It was kept within a grassy enclosure. While 

 thus confined it laid an egg of a pale bluish green colour, 

 precisely like that of a heron. The egg of our bittern 

 is about the same size; its normal colour of a similar 

 olivaceous buft' as that of your B. sfellaris. This buffy 

 olivaceous tint harmonises well with the half-faded leaves 

 of aquatic plants of which the nest is often built, such as 

 those of Typha angtistifolia, Carcx virgata, &c. ; in fact, a 

 bittern's nest is by no means an offensively obtrusive 

 object. 



Having had eggs from several nests under observation, 

 I have noticed that bittern's eggs do now and then vary 

 .w lint from buffy brown to pale olivaceous ; but in no 

 case approximately to that blue green of the heron's egg. 



In the instance cited, was the peculiar colouring used 

 as a means of securing for the egg the protection of the 

 rcidurc of the grass in which it was deposited ? or was it 

 merely the effects of a brief confinement and a slight 

 Iccal wound t The conditions under which this egg was 



laid may be considered as somewhat analogous to those 

 under which the cuckoo laid No. 26 specimen in the 

 aimous series of eggs formed by Herr Baklamus (see vol. 

 f p. 508) ; nor is the occurrence of this peculiar-looking 

 bittern's egg without its use in estimating the value to be 

 ace orded to certain abnormally coloured eggs as illustrat- 

 ing and supporting a theoi-y not adverse to the proposi- 

 tion — Can a bird influence the colour of its eggs pro- 

 tectively ? 



3. Are the eggs of the cuckoo ever approximately 

 coloured like those of its dupe for protective purposes .? 



In vol. V. p. 501, may be found a brief note, stating that 

 the eggs of our whistler, or small cuckoo, were not coloured 

 approximately to those of its dupe, nor, indeed, would 

 such precaution appear necessary, when the form of the 

 nest of its victim was considered. Last season one of the 

 writer's children brought in a nest of the blight bird 

 (Zosterops latc>■alis')co\^^.■Avc\V!\^g four eggs, one of which was 

 a puzzle indeed ; it was found on comparison, that although 

 a shade darker in colour, it resembled the rest of the eggs 

 in the nest, pale green-blue, spotless and unstained as 

 those of the homely russet-clad hedge-sparrow. In size 

 and shape it was like that of the small cuckoo. Hundreds 

 of eggs of the Zosterops (a new colonist, yet already one 

 of our commonest birds) have passed under the notice of 

 the writer, but none have resembled the specimen alluded 

 to. That it might possibly have been laid by a whistler 

 seemed at length the only solution of the problem, how an 

 egg of that size and shape came into that nest. The 

 Zosterops does not belong to the purely indigenous genera 

 of NewZealand ; like the Chrysococcyx 7m.di its usual dupe, 

 the Cerygone,\X. is to be found in other colonies far beyond 

 the bounds of ferny Maori-land. It builds a suspended 

 nest, another indication of its foreign origin. It is ciuite 

 likely that in warmer climes the small cuckoo may readily 

 avail itself of the advantages presented by this mode of 

 construction, as ensuring a greater degree of safety from 

 reptilian egg-robbers. The open cup-shape of the Zoste- 

 rops' nest would disclose to its owner the marked contrast 

 between its own clear blue-green eggs and the large, 

 greenish-dun egg of the parasite ; hence the effort at pro- 

 tective mimicry. This would be unnecessary, as before 

 pointed out, in the dimness of the domed structure of the 

 Geryaone. If the egg described is that of the small cuc- 

 koo, it is the first instance known to the writer of the 

 Zosterops being used as a dupe. It should be noticed that 

 last season the small cuckoo appeared in greater numbers 

 than usual in this neighbourhood, where the nests of the 

 blight bird, in the aggregate, now outnumber those of every 

 other species of bird. 



These facts are communicated under the impression 

 that they may be of interest to ornithologists, and in fair- 

 ness should not be withheld, the rather as the writer does 

 not yet give in his adhesion to the theories of Herr 

 Baldamus. 



4. On the Mimicry of Sounds. 



When camping for some days on a river-bed, where 

 many species of birds abounded, the writer and one of his 

 sons (well acquainted with bird voices) frecjuently heard 

 what they took to be one of the notes of the Heematopus, 

 but that wader was nowhere to be seen ; at length we 

 traced the call to the Piopio {Keropia ernssirostiis) a bird 

 with feeble powers of flight, yet one that delights in the 

 open glades of river-beds. The mimic cry was always 

 given when near to a stream, just where the red-bill 

 {Ha-Diatopus) would be likely to be found. A pair of red- 

 bills can drive away a hawk ; now a hawk, " from his 

 place on high," perceiving something near the water, 

 might forego its swoop on hearing the mimicked note of 

 the wary, yet bold red-bill. We have observed our grey 

 warbler give an exact imitation of the cry of our common 

 tern {S. antarctica) one of the boldest birds in defence of 

 its young. Thomas H. Potts 



Ohinitahi, June 29 



