- 15 * 
hi:’ eXOfSple* 
correct as 
o - d 1 * ~ U- e e t'J© 'I t a c fctv lti«a a nd tVii r ■, 
a* I ©an Judge . 
certainly 
A 
Tbs noefc quivering occurs in prolonged nest Ixiildlm 
? < i»*t VA ^ f® *■* #Jf to decide on purely oba©rv& tionsl 
evidence w:ifct external stimuli ^ if any, release ft. However 
there are two other situations where I can show that it l# 
t { i# 7old(:ji8g stimuli are of two quit© different 
!tir»d«, I have already described the first* How neut eutverdng 
ears be released by an intruder* And I have stationed the second 
sore briefly, how a brooding shag ns at quivers shortly infers 
r.sing to turn, its eggs* I have given reasons to tilin’? that 
tno intruder arouse© son© degree of aggressiveness in the 
incubating bird* Tea lever etiauli signal the Use to turn the 
*?£•# ^ere 10 esrtainly no res ©on to mpp oz& that they oak# the 
bird aggressive. At any rot© the *heg neve r shows any otli r sign 
Oi aggressiveness when about to turns its ©ago ^nd ont suet 
suppose that whatever iaa*es the bird turn its eggs also mk** 
it best quiver. On* nau dispose of the possibility that it 
In the neat quivering Itself which causes the turning, 'these 
two situations do not cover *11 the occasions when neat quivering 
o m • 
aeelde anything about the stimuli provoking the behaviour. 
To suwttfiM.th asst quivering is released in on# 
instance by stimuli from an Intruder which probably activate 
the eggreselv^iose of the ©hag la the other ins tv. ace it is released 
probaniy by seme rfcimilt from the eggs aetlv ting the tendeney 
to turn the eggs* There are therefore at least tv© oausai ly differ©] 
types of noct quivering, # 
h 
'V*t K 
^&L3aJ f/ ; - **•?**> V, J : to. 
bong hours of watching inactive shags waiting for 
eon* thing to ha;>*n booano acre interesting when I aborted 
to wntob the "ooafort aove:sents”, their ways of preening tueaseives 
no# »ujy f>x «.rd their a . ea the rn * how they sora tolled uni how they 
Siietohed £ yawned nd • ’ e mi f *.ny aspects 
of their daily life which I hadn't exp# died) that they rarely 
preen their tails 9 that they always us© the third cir. v to 
scratch theaeelTos and that this claw ta provided with a special 
C 0 '?;b, that they ■hold out their wings to dry after bathing but 
not as lorn? as eoraorftnta. But it also usds ne &w&rt of something 
which eeeeed acre Important in the flmd&Benfc.l ^roblesa of why 
animals behave an they da, 
% 
t shags have r ■ -lay .vm- & an a peaeesent 
funetlon towards potential aggressors. X hrve ct 1 led this 
seven* nt the tirward Gape, X noticed that thie display waa quit© 
often followed within e second or two by another aovenent. a 
very charsets ris tie etretohlng of the u > -»rr ms-ndible* If the two 
