COURTSHir ACTIVITIES IN THE IIBD-THROATED DIVER. 289 
valuable of the pair, and that in such species the display and song o£ the cock 
Las as its primary function that of drawing the attention of enemies away 
from the hen ; so that, if one of the two is sacrificed, it shall generally be the 
less '' valuable " male. 
(2) Where the species is capable of defence, or is unpalatable — i. e. does 
not require protective coloration — he postulates that courtship should be not 
elaborate, or may even be absent. 
(3) Where both sexes are of equal biological value (i. e. where both 
incubate), he postulates that both should indulge equally in display. 
The reasoning is undoubtedly ingenious, but can be shown not to be 
adequate to account for all the facts. 
As regards (1) , it should be remembered that the song of male " territory 
birds " is most powerful before any females have arrived. It could be 
no possible advantage to the species to have attention attracted to the 
males when there were no females present from whom attention could 
be drawn off. 
It is undoubtedly true that where only the female incubates, and where 
protection is desirable, dimorphism of sexual characters and behaviour will be 
encouraged. This I have pointed out in the body of the paper. Dr. Mottram 
simply restates the pi-obleui from a different angle, and with the epigamic 
side of the matter left out. 
(2) is sim[)ly not true in a number of cases. Herons and Egrets are well 
protected from enemies, but have an elaborate courtship. So do Swans 
(Selous, '13, and my own observations). So do Hav.ks, though here the 
displays are concerned with flight, not with bright coloration (Owen,'16-''22, 
Sparrow-Hawk ; Kestrel, my own obervations) ; and other examples could 
be quoted. 
(3) Where both sexes are of equal value, it would appear on the face 
■of it biologically desirable that both should be rendered inconspicuous when 
concealment is in any way desirable, if, as Dr. Mottram would have us 
believe, the chief function of display is to attract the attention of enemies. 
However, in the Grebes, all of which take great pains to conceal their nest, 
and are protectivel}'^ coloured so long as they are in the normal swimming, 
feeding, or resting attitudes, elaborate mutual courtship does occur, and at 
once makes tlie jtair conspicuous. The same, to a less extent, is seen in Divers. 
The vocal duets of Owls which go on in the breeding-season (Huxley '19) 
are difficult to account for on any theory vvhich relates them only with 
attracting the attention of enemies. 
Finally, Dr. Mottram makes the point that since many birds " get on " 
without bright colouring in one or both sexes, and yet reproduce, therefore 
when bright colouring is present it cannot be supposed to have any relation 
to reproduction. This, however, is an old fallacy, repeatedly exposed since the 
•early days of the evolution controversy. It would be equally justifiable to say 
LINN. JOURN. ZOOLOGY. VOL. XXXV. 21 
