COURTSHIP OF THE GREAT CRESTED GREBE. 519 
to rest on some firm support more than at other times, and that 
the hen incubates more than the cock, so that he has to build 
himself an extra resting-place). Possibly such platforms have 
something to do with receiving the young after hatching, and 
are built precociously. But this is mere guesswork—further 
watching must reveal their secret.. Mr. Selous, in a letter to me, 
says he thinks now that the platform is due to an aberration of 
the nest-building instinct inthe male. From Selous’ own records, 
however, it is clear that the male certainly uses it to rest on. 
Differences in building of the different kinds of nest. 
The bulk of the true nest is built by both birds together in a 
very short time. After that, it seems to be casually added to 
during the time of incubation. his is useful, for the nest would 
otherwise get gradually pressed down into the water. It also 
tends to lose its slightly cupped form, and to remedy this the 
sitting bird may often be seen to pick bits of weed from the inside 
or the outside of the nest and lay them on the rim. 
The cargoes of weed brought during incubation are often very 
small compared with those brought during the first building of 
the nest, and the whole action seems often to have rather the 
stamp of a habit about it—“ I am going to the nest, so perhaps 
I had better bring a weed or two along.” 
During the main building, one bird sometimes sits on the nest 
fer a short time ; during this period one bird might also lie along 
the nest in the passive pairing position, as an invitation to the 
other to pair. But apparently pairing and pairing-actions are 
gone through more often when the bulk of the nest is finished, 
or when a platform alone exists—nest-construction thus ap- 
pearing to use up most of the emotional energy of the birds. 
The cock’s platform.—It would be interesting to know if this is 
always made during the construction of the main nest, or if 
sometimes the cock set about it in cold blood, before or after the 
true nest was finished. It is quite possible that the cock and 
the hen stimulate each other to active nest-building as they do to 
courtship activities (p. 511), and that while they are in this 
excited state, and only then, some of the nest-building energy is, 
in the cock, diverted to his platform. 
The pairing platform.—This (only one recorded case) was 
already built when Selous first noticed it. Only small pieces of 
weed were added to it, and usually “in a very perfunctory 
manner” (Selous, 01, p. 342). After one bird had unsuccess- 
fully invited the other to pair, it often ‘‘manipulated the weeds 
a little with its bill” before coming off the platform. 
We thus badly want to know about the building of the pairing 
platform; and also whether, during its construction, the cock 
builds a platform for himself, as he does during the building of 
the true nest. 
