The main difference between the U and the F would seem to he 
one of intensity. The F is most common when two birds approach 
each other closely. F is more often the preliminary to an actual 
attack (?). It is possible that the F represents a relatively 
greater intensity of the attack drive alone, but I doubt it. 
It sometimes precedes retreat (?). The orientation of the F is 
often peculiar; paralell with, or pointed away from, the 
opponent. The head may be bent or flagged away from the mate (or 
opponent?). This latter would seem to be caused by a relatively 
great activation of the escape drive. The actual posture itself 
would suggest the presence of strong escape elements. 
Pattern C. CHOKING. A complicated derived movement (see 
discussion several weeks ago). Associated with pecking at nest 
material? 
This pattern is also presumably due to the simultaneous 
activation of both the attack and escape drives. It is most 
frequeztt during lengthy boundary disputed. Often a prelude to 
actual attack. Is it ever a prelarude to actual escape? It is 
noticeable that, during disputes in which Choking is employed, 
the birds in the Choke posture more often than not face away from 
their opponents. Due to activation of the escape drive? 
DISCUSSION. The main problem involved in any attempt to 
elucidate the threat behavior of the Black-headed Gull is: why 
does it have so many different forms of threat? 
These different types might, of course, be due to different 
relative strengths of the two drives involved. The above account, 
however, would seem to suggest that this is improbable. Each main 
threat pattern seems to vary considerably, within itself, as far 
as the relative strengths of the two drives are concerned. Could 
it be that the Erect threat patterm, the Long Call threat pattern, 
and the Choking pattern, represent increasing actual intensity of 
both drives? 
What positive evidence do we have for this conclusion? 
All rather indirect# Reasons for thinking the E less intense than 
the U-F. When a complete mutual display is performed, the E 
practically always follows the U-F. This would suggest that part 
of the motivation has been consumed by the performance of the U-F; 
the remaining motivation causing the E. Moreover, as the breeding 
cvcle progresses, mutual display between partners becomes cursory. 
But. if any part at all of the mutual display is carried out, it 
is the E. Reasons for thinking the U-F is less intense than 
Choking. Choking is never (or practically never) seen during 
mutual display between partners. It is particularly characteristic 
of long drawn-out boundary disputes, when one would normally expect 
that stimuli provoking both attack and escape would be strongest. 
