Vol 'i 924 IV ’] LEWIS, Mutton-Birds of Phillip Island. 
89 
fact that the mate, No. 110, was never found subsequently in 
the hole, although this was examined at frequent intervals, and 
also owing to the fact that the bird (No. 82) deserted the egg 
only eight days after it was found with it. In another burrow 
two birds (Nos. 75 and 119) were robbed of their egg on 
November 20th, 1921, but were found on December 15th with 
a new egg, which they continued to incubate alternatively and 
continuously until January 16th, when observations were relin¬ 
quished. In this case it is quite possible that the egg was laid 
by a strange bird and adopted by this pair. It has been proved 
by experiment that the birds will adopt a strange egg if such 
is placed in the hole soon after they have been robbed. This 
is the only instance during four years of observation in which 
the two original birds were found with a second egg. 
In 1922 the rookeries were not visited until late in the laying 
season. In burrow No. 1, which was robbed on December 1st, 
1922, sixteen days later a strange bird and an egg were found. 
A further inspection of the burrows on December 26th showed 
that there were no fresh eggs. During December of 1922, fifteen 
other burrows were marked and the eggs taken from under the 
birds, but the birds were not branded with rings, as in the other 
cases. The eggs were all removed prior to December 4th, and 
the nests were not again inspected until December 26th, when 
no fresh eggs were found. 
Summarised the results of the four years’ observations are:— 
In 1920, in one burrow out of twelve a second egg was found; 
in 1921, three out of twelve; in 1922, two out of sixteen; and 
in 1923, none out of thirty-one; or a total of six out of seventy- 
one during the four seasons. In none of the six cases, however, 
was it conclusively proved that the original pair of birds owned 
the second egg. 
PERIODS OF SITTING BY PARENT BIRDS. 
In order to ascertain whether both parent birds sat on the 
egg, a burrow was selected and marked on December 6th, 1923. 
It was found that one parent sat until December 11th; the other 
until the 25th; then the first again until January 7th; the second 
again until January 19th, when the egg hatched, and the birds 
left the young one during the day. Of course during the night 
both birds came back to the burrow and fed the young one. It 
would thus appear that each bird sits for about a fortnight, when 
it is relieved by its mate, which takes its turn for a fortnight. 
In cases where the egg is taken, the birds continued to inhabit 
the burrow for a few days, both night and day, after which 
they came back only at night for a short period, and then finally 
deserted the rookery. 
CONCLUSIONS. 
As the result of observations and experiments carried out 
during the past four years, there seems to be fairly conclusive 
