COURTSHIP ACTIVITIES IN THE EED-THBOATED DIVER. 253 
Courtship Activities in the Red-throated Diver (Cohjmbus stellatus TontoT^Tp.) : 
together with a discussion of the Evolution of Courtship in 'Birds*. 
By Julian S. Huxley, M.A. (Communicated by Prof. E. S. Good- 
rich, M.A., F.R.S., Sec.L.S.) 
(Plates 14, 15, and 4 Text-figures.) 
• [Read 2nd November, 1922.] 
The following paper is a continuation of previous work on the sexual 
relationships in species of birds in which both sexes possess bright colours 
and also exhibit similar sexual ceremonies. The reader is referred to papers 
on the Great Crested Grebe and on the Dabchick (Huxley, '14 and '19). 
It is unnecessary to recapitulate at any length, but certain general con- 
clusions may be stated. 
1. In most, possibly all monogamous birds, a pre-mating and post-mating 
period may be distinguished. " Courtship " activities usually occur during 
both of these periods; but the majority of the "courtship" actions which 
are to be found described in the literature occur in the post-mating period, 
and therefore cannot be operative in any true form of sexual selection as 
imagined by Darwin. So far as pre-mating ceremonies occur and are 
effective in the choice of mates, they can of course find place in a scheme of 
true sexual selection. 
2. In birds in which the sexes are quite or almost similar, and both 
adorned with bright colours or special plumes, or other structures, which are 
displayed or otherwise used in sexual ceremonies, both sexes play a quite or 
nearly similar role during " courtship " ; very often ceremonies occur in 
which both sexes simultaneously play a similar role ; for such ceremonies the 
term " mutual " is employed. 
3. These mutual ceremonies may be " self-exhausting " — that is, may end 
in the birds resuming the ordinary routine of life ; or they may be a means 
of raising the emotional tone as a direct or indirect excitant to coition. In 
the Grebe, where self-exhausting display ceremonies were the rule, special 
pre-coition ceremonies were foand, in which attitudes resembling those 
employed at coition were adopted. 
4. An association of various of the birds' other activities with the sexual 
ceremonies was often observed. The "handling'" of nest-material is fre- 
quently so associated, as has been noted by many previous observers ; but 
actions like those of preening or of shaking the head, although originally 
quite without sexual significance, may also be used as part of the raw 
material of sexual ceremonies. 
* No. 21 of the Results of the O.'cford University Expedition to Spitsbergen in 1921. 
