COURTSHIP ACTIVITIES IN THE RED-THROATED DIVER. 265 
the different period at the time of observation. On the other hand, they are 
built up out of the same elements. 
Bent ('19) says of all the species of Diver, as well as of numerous other 
Pygopodes, that they migrate in pairs, or at least arrive at the breeding 
localities in pairs, and select the nest-site as soon as possible. He believes 
they pair for life. In all species it appears probable that both sexes incubate 
(although from my personal observations it appears that one bird, pre- 
sumably the female, takes much longer spells than the other ; and see Turner, 
'13). 
('ourtney, quoted by Chapman ('22), gives a beautiful drawing of a common 
courtship ceremony of the North American Loon {Colymhis immer), in which 
one bird rises into the erect position, and runs along the surface of the water 
in this attitude for some w-ay near another. 
Bent (loc. cit.) refers to the "maniacal" screeching laughter o'f this species 
in the breeding-season. 
Seidlitz ('13), writing of the Black-throated Diver^ says that each pair has 
a well-marked and large territory {Revier). He states that there are as 
many unpaired as paired birds ; these are birds of one, and possibly of two 
years of age. He does not mention whether these ever indulge in " court- 
ship " ceremonies. This would be a point of considerable interest. 
Bahr ('07) mentions the dipping of the beak into the water when the bird 
is nervous and afraid to return to the nest. He also, on one occasion only, 
saw a very remarkable performance by a single Red-throated Diver. The 
bird ascended to a great height, and then descended headlong, twisting and 
turning as it did so, the air rushing through the feathers making a noise 
" like a train." Such descents are, of course, well known in many birds, 
e.g. Rook. They are common in Louisiana Heron, Little Blue Heron, and 
Snowy Egret on returning to their rookery, and I have on one occasion seen 
a somewhat similar performance by our common British Heron. It is 
probable that these actions should be classed as play, and not as courtship. 
Hatch, quoted by Bent {loc. cit.), states that C. immer has a remarkable 
family habit. When the young are (apparently) well-grown, they sleep with 
their parents on the pool. In the early morning, before sunrise, the male 
parent gives a special call ; all draw near, and, after a little manceuvring, start 
to run over the water side by side in a line " at incredible speed," with the 
wings about a quarter-extended, the whole motive power being derived from 
the feet. They run thus for about 400 yards, then wheel, and return to the 
starting point. This is repeated several times and suddenly stops. It would 
be interesting to have further observations on this extraordinary ceremony. 
Interpretation. 
It will be seen from the above that (as in many, and indeed in most, of 
even our commoner birds) much remains to be known about the life-history 
LINN. JOURN. — ZOOLOGY, VOL. SXXV. 19 
