18 THE ORNITHOLOGIST. 



What puzzles me much is that practically all the false "Cuckoo's" eggs I 

 have received have been of English origin. I have had many sets from the 

 Continent — roughly 1 should say two to every one received from British 

 correspondents — and only one of the foreign ones has been fraudulent ; 

 whereas quite half of those received from this country have been forgeries. 

 Whether the German and other Continental collectors are more honest than 

 the English " pointer out " I cannot pretend to say ; but one solution of the 

 question may be that my foreign supplies all come through second and 

 scientific hands, and they may reject the frauds before sending me the 

 genuine eggs. During 1894 and 18951 received from various British sources 

 many clutches with a " Cuckoo," or alleged " Cuckoo," included. Many 

 were palpably quite right on sight alone, some were equally visible frauds 

 and rejected forthwith, but there remained a residuum about which I could 

 not make my mind up with certainty, nor could my English friends help me. 

 " They may be right, but I think they are only so-and-so." In this dilemma 

 I decided to consult a correspondent in Sweden who has made the eggs of 

 the Cuculidss his study for many years ; I understand he has had some 600 

 genuine eggs of C. canorus through his hands, and his present collection 

 is of more than half that number. He most kindly examined my suspicious 

 eggs. Amongst the lot of about twenty sent him were purposely included three 

 or four of the genuineness of which I had no doubt, and which he verified 

 as correct, but nearly all the suspected ones proved, as I feared, frauds. 

 Here, however, comes the reason of my writing this article ! How to test a 

 doubtful ec/f) alleged to be a Cuckoo's. I believe the information will be new 

 to most oblogists in this country, as some of our first authorities whom I 

 have consulted know nothing of it. Eggs of the C. canorus are abnormally 

 small for the size of the parent bird ; this is so well known that it would not 

 be worth while repeating, but that from this comes what follows. A German 

 collector, whose name has not been given to me, considering this, mentally 

 asked : Is there any compensation for this small size ? He also noticed, 

 what hundreds of other collectors must have noticed without observing criti- 

 cally, that when a clutch of eggs containing a Cuckoo's egg is blown, the 

 Cuckoo's is harder to drill than the eggs of the foster-bird. Then the egg 

 must be denser in texture ; and so what the shell of a Cuckoo's egg loses in 

 size is compensated by greater density and weight. With this theory he 

 started a series of experiments, with the result that it is known that the 

 empty eggs of C. canorus weigh from 25 per cent, to 30 per cent, more than 

 those of a similar size laid by any other Passerine bird. If this theory is 

 correct, here we have a certain test of a genuine Cuckoo's egg. It must also 

 be borne in mind that Cuckoo's eggs are on an average more globular than 

 those of the various species they make their hosts ; but this is a very partial 

 test. Also, and a more valuable one — a Cuckoo's egg has no gloss, or only 



