COURTSHIP ACTIVITIES IK THE RED-THROATED DIVER. 263 
where the other was, and then it, too, rose and followed the others. They all 
three made off in wide sweeps, and were finally lost to view some miles away. 
I take it tliafc these three birds were not yet paired up for the season. 
Possibly here, as in the Crested Grebe (Pike, '13), some birds do not nest, but 
continue "courtship " actions throughout the season. The long flight to the 
tarn and away again so soon after is of interest ; it may have been a pursuit ; 
but, if so, it is interesting that the bird which took the chief initiative in 
courtship on the tarn was probably a female. 
Other Observations on the Red-throated Diver s Courtship. 
Before proceeding further, it will be as well to mention the actions 
•observed by others in the same species. E. Selous ('12) made observations on 
a family in Scotland, during Julj% at a time when the young were hatched, 
and were being looked after by both parents. Although he was watching 
steadily for over three weeks, he only saw " cdurtsliip " behaviour on three 
occasions. This in itself is of interest, as showing that so long as the breeding- 
season lasts — i. e. at any rate so long as the instinct for caring for the young- 
persists, and possibly until the autumn moult — the possibility of sexual 
ceremonies appearing in special circumstances will also persist. The obser- 
vations of Pike ('13) are of interest in this connection. He states that a large 
percentage of tlie Crested Grebes on a certain breeding area, although mated 
up, failed, for some unknown reason, to build or lay in the season when he 
was there : these birds, and apparently none of the other pairs, continued 
their well-known mutual courtship late into the season (i.e. after the normal 
time for incubation was over). Facts bearing on this problem are well 
known in other species ; for instance, in many birds, the final liberation of 
the parents from feeding the young, when these are old enough to look after 
themselves, is often marked by a recrudescence of various sexual activities. 
These are similar to the truly epigamic activities of the early part of the 
season, though they now, of course, have no function. Similarly, in birds 
which rear two or more broods, there is usually a recrudescence of epigamic 
ceremonies in the interval between broods. Looking at the matter from an 
opposite angle, we find that the song of many birds, e.g. the Nightingale, 
ceases immediately the young are hatched — i. e. as soon as the male embarks 
upon the new duty of helping feed the young. Mr. Eliot Howard informs 
nie that in birds such as the Buntings, in which the mules occupy territory 
long before the females arrive, the volume of song in the first period is 
greater than in the period immediately after the arrival of the females. This 
has been corroborated for other species, e.g. the Blackbird (Uewar, '20). 
la a very similar way, the female, on reaching a certain level of endocrine 
stimulation, will permit and indeed solicit coition ; her emotional activity 
will also find reliefer expression in the building of the nest. Coition brings 
-about egg-laying, and nest-building brings about the finishing of the nest j 
