COURTSHIP ACTIVITIES IN THE BED-THROATED DIVER, 267 
The "Plesiosaur" or "race" ceremonies, then, appear to be competitions 
for a mate. It is of interest to find that when three birds are participating 
in these ceremonies^ their respective sizes indicate that they may be either 
two males and a female or two females and a male. This is in accordance 
with the rest of the facts observed about courtship in this species — the two 
sexes appear to play almost identical (or interchangeable) roles. 
The only occasions when I observed the dive followed bj' the " Penguin- 
like" emergence, also seemed to be in this pre-mating period. The erect 
"Penguin" attitude, however, as Selous' observations show, is not only con- 
fined to this period, although he does not record diving followed by this attitude. 
There is, however, another possible interpretation of the participation of 
three and four birds in these ceremonies, which may be best understood after 
a brief digression. In the Buntings, as Mr. E. Howard kindly informs me, 
during the period while male and female are both present on the territorv, 
but coition and nest-building have not yet begun, every day begins in the 
same identical way. The male wakes first : later, the female emerges too 
from her roosting-place : after a short time the male flies at her, eager for 
coition. She however flies off", and there follows what Howard calls the 
"sexual flight," when the female, dodging and twisting, is pursued closely in 
her rapid flight by the male. Eventually the birJs seem to get exhausted, 
and alight. Such pursuit flights are of course w'ell known among many 
species. "What is o£ special interest, however, is the fact that once the 
flight has started, it is a source of great excitement to other males in the 
vicinity, and, although these males may have been long in occupation of 
territory, and mated, yet one or more will usually join the rightful male in 
the pursuit. In passing, it should be observed that this instinct of other males 
to join in the excitement of these pursuits appears to be at the bottom of 
those undignified skirmishes of the House-Sparrow, in which a single 
unwilling female is mobbed by a number of males ; and see also Bent, op. cit., 
pp. 186-191, where the Californian Guillemot is described as becoming very 
much excited at the sight of an act of coition by another pair. 
It is conceivable that the Plesiosaur race of the Diver may be a mutual 
" post-mating " ceremony, essentially identical with the " snake-ceremony " 
described as occurring later in the birds' history, but, since it takes place 
before the nest is built and other activities share the birds' mind, differing in 
its greater intensity. If so, then the participation of three or four birds in 
the ceremony may be due to others joining in under the influence of 
excitement — others which are either wholly unmated, or else are mated but 
temporarily without their mates. Since there were almost always several 
birds on the lagoon, while the nesting-pools hardly ever had more than a 
single pair on them, and since further the greater level of emotional excite- 
ment in the Plesiosaur ceremony is unmistakable, it would be quite 
intelligible that the threes and fours were only seen on the lagoon, and only 
performing in the Plesiosaur, not in the " snake " ceremony. 
19* 
