There is another, theoretical, consideration which might 
suggest that the Erect-Long Call-Choking progression is one of 
increasing intensity. As one goes up the scale these postures 
seem less and less explicable in terms of ambivalent intention 
movements; and they seem to incorporate more ritualized displacement 
activities. (What is the reference to calls originating as 
displacements? ) • 
It should be noted that the threat patterns due to greater 
actual intensity of both drives (if the above hypothesis is correct) 
seem to be more "intimidating" than those due to lower intensity 
of these drives. Thus we have seen birds in E retreat from birds 
in the F and Choking postures. (This whole aspect of the problem 
has to be gome over thoroughly). 
It should also be noted that, during a dispute if one of 
the gulls involved adopts a certain threat posture (F or Choking) 
its opponent usually does. Seems to be contagious. 
The other great problem involved in any attempt to describe 
and explain the threat behavior of the Black-headed Gull is the 
precise part played by the sex drive (in the restricted sense). 
It is presumably present whenever partners display to one another; 
(this display very often takes the form of threat). It does not, 
however, reveal itself in any overt act until comparatively late 
in the breeding cycle when FB, feeding, and copulations, occur. 
