VOL. xm] SEXUAL HABITS OF LITTLE GREBE. 157 



drink and at once raised again. Whether the birds are really 

 drinking, or whether it is a ritual act like the habit-preening 

 of P. cristatus, I am not yet sure. The journeys may occasion- 

 ally be broken by a duet. The Great Crested Grebe does not 

 seem to have this journeying habit. 



Influence of Weather. — The Dabchick appears to feel 

 change of weather even more than the Great Crested Grebe. 

 On a cold, overcast day, one would be lucky to hear a couple 

 of duets in a whole morning, although if the morning before 

 had been warm and light the pond would have been ringing 

 with them. 



Sex Differences. — I was not able to distinguish 

 differences in the quality of the sound emitted by male and 

 female, although the existence of a difference is possible. 

 Difference in size between the members of a pair is, however, 

 always clear and more marked than in P. cristatus. There 

 is also, I believe, a slight difference in brilliance of coloration. 



Duet Ceremonies in Other Birds. — Vocal sounds 

 uttered simultaneously by both birds of a pair are of course 

 found in many species of birds with mutual ceremonies, but 

 they are usually subservient to ceremonies based on visual 

 display. This is so in the Great Crested Grebe, where the 

 bouts of head-shaking are almost always accompanied by a 

 special note. The answering of call-note with call-note 

 cannot be properly called a duet, nor can the conversational 

 interchange recorded by Kearton to take place between male 

 and female Snipe when both are brooding together. In 

 certain Owls, however, true duets exist. I have myself 

 heard them in the Barred Owl {Strix varia) in Texas and in a 

 smaller species in the Rocky Mountains. In the latter species 

 the duet is rudimentary. The birds sit on neighbouring trees 

 in the twilight and answer each other with a special note, 

 similar in the two sexes, for half an hour or more. It is an 

 action, I would say, of purely sexual significance, although 

 not worked up into any elaborate ceremony of high emotional 

 tension. This quality of raised emotion and short specific 

 ceremonial is distinct in the Dabchick, and also in the 

 above mentioned Strix varia. This bird has a definite 

 phrase in hoot, beginning low, increasing in rapidity and 

 rising in pitch at the same time up to a climax, and then 

 sinking with a swooping sound and something of a break in 

 the voice to a last single note. Rhythm and pitch are both 

 very definite. According to the Negroes, the bird says: 

 " Who, who, who, who cooks for you -all ? " The phrase 



