COURTSHIP ACTIVITIES IN THE KED-THKOATED DIVER. 291 
Thus there is a good prima facie case for applyint;' Dr. Mottram's ideas to 
cases of bright coloration in the males of palatable species in which the 
bright colour is not specially associated with display, and especially in forms 
in which the female alone looks after eggs and young. 
It is, however, becoming clear that many side issues of the problem can 
best be attacked by statistical methods : and this I propose to do as oppor- 
tunity offers. 
Postscript 2. — The last number of ' British Birds' (vol. xvi. p. 318) con- 
tains an article by Mr. N. Gilroy on the nesting habits of the Black-throated 
and Red-throated Divers to which reference should be made. 
The Black-throated Diver is mentioned as dipping its bill in the water 
when nervous because scared off its eggs. This extends my observal^ions of 
the beak-dipping of the Red-throated Diver to another species. 
Of courtship, the following remark is made — " The pairs may be observed 
on the tarns for a considerable time before nesting begins, and one is fre- 
quently treated to the extraordinary display which takes place, not only 
during courtship and pairing, but even when actual breeding has commenced 
— when both birds propel themselves through the water almost vertically." 
This, so far as it goes, confirms my observations. J. S. H. 
8th May, 1923. 
List of Literature. 
Bahr. '07. The Home Life of some Marsh-birds. London, 1907. (Divers.) 
Bent. '19. Bull. U.S. Nat. Mus. Washington, no. 107. (Divers.) 
Chance. '22. The Cuckoo's Secret. London, 1922. 
Chapman. '08. Camps and Cruises of an Ornitliologist. New York, 1908. (Pelicans, &c.) 
Chapman. '22. Bird Lore, xxiv. p. 1. (Loon.) 
Dabwin. '71. Descent of Man. London, 1871. (See esp. p. 277.) 
Dewar. '20. Brit. Birds, xiv. p. 89. (Blackbird.) 
Gboos. '98. The Play of Animals. (Eng. Trans.) Nevr York, 1898. 
G-OLDSCHMiDT. '20. Mechanismus und Phvsiologie der Gesohlechtsbestimmung. Berlin, 
1920. 
GuKNEY, J. H. '13. The Ganuet. London, 1913. 
Hays. '18. .L Exp. Zool. xxv. p. .571. (Rabbits.) 
Howard, E. '07-'14. The British Warblers. London, 1907-1914. 
IIowarb. '20. Territory in Bird Life. London, 1920. 
Huxley. '14. Proc. Zool. Soc. 1914, p. 491. (Crested Grebe.) 
Huxley. '16. Auk, xxxiii. p. 1.52 & p. 256. (General.) 
Huxley. '19. Brit. Birds, xiii. p. 155. (Dabchick ; Owls.) 
Huxley. '21. Nature, cviii. p. 565. (General.) 
Huxley. '22 a. J. Roy. Soc. Arts, Ixx. (Sex-deterniinatiou.) 
Huxley. '22 b. Brit. Birds, xvi. p. 99. (Assortative mating.) 
Levick. '14. Antarctic Penguins. London, Heinemann .& Co., 1914. 
IjLOyd-Jones & Hays. '18. J. Exp. Zool. xxv. p. 463. (Rabbits.) 
Lloyd-Mokgan. '21. Brit. J. Psychol, xi. p. 206. (Psychical selection.) 
Marshall. '22. The Physiology of Reproduction. London, Longmans, Green & Co., 1922. 
Morgan. 19. Carnegie Publ. no. 285. (Inheritance of sexual characters; sexual selection.) 
