16 
10-3-63 ( cont. ) 
simply that Masked boobys, because they cannot easily escape 
are attentive, and defend the nest, eggs and chick with great 
vigor, while Browns Jbeing able to get airborne do so. I have 
the impression that both male Browns and Masked are more 
skittish tnan the females, and that the females are noticeably 
larger in both species. Brown Booby males also possess 
the hoarse voicey while female browns have the deep-full 
full throated cali^ R<x 
While working in the coloniespf these'"'two species, I 
had occasion to note interspecific behavior on a number of 
occasions. If an adult of either species enters the territory 
of a family group of the other species, any member of the 
family group, c?,?, or Chick recognizes and repels the intruder. 
It seems classically funny to watch a 2,200 gram ? Masked !l run 
out of Brown Booby town 11 by an 800 gram, partially feathered 
and still downy Brown Chick. The members of family groups also 
recognize intruders of their own species and attack vigourously. 
This seems to be particularly true when there is a small chick 
in the Family group. However, in the Masked Booby I suspect that 
several pairs of adults may ( on occasion ) share the dutys 
of raising a single chick. It is too bad that there are not 
more new nests to test out this suspicion. 
\) Airial behavior over the nesting colony is varied and 
colorful, A bird taking off ( Masked Booby ) gains altitude 
slowly and has to pass over nesting territories of other birds. 
If a defending bird is in the territory it squSks if the indi¬ 
vidual taking off is at an altitude below about 12 feet. If the 
!l intruder !i is low enough, he may receive a stout peck as 
sp rains for altitude, and once today I saw an immature ( Juv. ) 
Masked knocked off balance so as to crash in an undignified ! 
manner when he crossed the territory held by a female with 
a downy chick. Adults passing over often call, and I watched 
one marked male pass over a female several times, each time 
she would dll as if recognizing him, and he usually responddd 
witn his call ano, soon he landed next to the females Apoarently j 
they were a mated pair for there was no hostile behavior after f 
he landed. Neither was there a recognizable greeting ceremony". [ 
I.watched several fights on the ground today. One,where 
■I identified from voice two males as the contestants?lasted 
several minutes. A preliminary to the actual fighting 
was a series of head shaking movements. The head is moved up 
and down rapidly ( about 5 -9 times per second ) which the 
neck is twisted from side to side in a slower cadence ( one 
complete movement left to right to left to begin again takes 
bbuuv 1 to 1.5 seconds ). Then suddenly the battle is joined 
