10 RUDOLF SÖDERBERG, STUDIES OF THE BIRDS IN NORTH WEST AUSTRALIA. 
the torrid zone. The varied character of the district is seen clearly enough from 
that the temperature is completely tropical. As to the rain, however, that is the 
case only in so far as S. Kimberley has but one rainy season, which comes in the 
summer months. Consequently, the seasons are two, summer (Dec.—April) and winter 
(April—Dec.), but the transition-time between them, during the months of Nov. and 
part of Dec., is characterized by great heat and whirlwinds (willy-willies), and is con- 
sidered the most torrid and hot season. If it is in general true that tropical Australia 
is under the influence of the changing of the monsoons it is only partly true of the 
visited. Dry land-winds prevail in the winter time; during the summer there are 
traces of the damp north-west monsoon from the sea visiting the district, bringing 
brief but violent stowers of rain, usually only towards the evening, some hour after 
sunset. This scanty rain is, besides, very uneven, so that certain vears are distinguished 
for their slight rainfall, while other years have more or less ample rain. Those re- 
gions, however, always suffer from lack of rain. The uneven conditions influence 
the flowering of the plants (the Hucalyptus) and through this also the bird-life. 
For the sake of comparison it ought to be noted here that the conditions in 
West Australia proper, to the south, are quite different. Thus we have here typical 
winter-rains and rainless or nearly rainless summers. The northern monsoon-rains 
are quite absent. The interior is occupied by the great sandy desert viz. the oldest 
Australian desert-nature. The difference of the mean temperature between the hottest 
and the coolest month of the year (Jan. and July resp.) is only 3” C. The summer- 
temperature is often (in the shade) above 40” C., not seldom up to 47”—48” C., ac- 
cording to reports by Mr. LouGE and 46” C. according to my own experience in the 
neighbourhoods of Mowla Downs in Dec. 1910. 
At the Fitzroy river the nature had the character of open savanna-wood with 
scattered Hucalyptus-trees, which prevailed in all places. After my and LAURELL'S 
separation from the Expedition at Lower Leverynga, where our journey with pack- 
horses began, it was, however, not many days before we saw signs, indicating that 
we were approaching the desert-like nature. The dry river-bed, the so-called Jurgarry- 
creek, which we now followed, begins up on the desert-mountains. 
The course of the river was now marked by a dry channel, which here and there 
was lost or hardly to be distinguished in the ground, but in other places it would cut 
its way down to about ten meters, where the ground formed an elevation. The 
occurrence of small water-filled hollows were now the necessary condition of life 
for the few species of birds which we met with during this journey and which gene- 
rally appeared in small flocks. 'The month of November is, as was said before, 
considered to be the driest season in Kimberley, when only those small pools of water 
are left. The proximity of the desert appeared more evident after six days of rapid 
travelling -southward, up the Jurgarry-creek. The ground here grew more deep in 
sand, hilly, and more sparsely overgrown by low trees, but more richly covered 
with Spinifex. At last ruin-like silhouettes of sandstone-mountains began to rise.on 
the horizon and two day's marches more southward the threshold of the desert 
was reached; it was a sandstone-plateau with undulating hills. (See plate 5, fig. 3, 4.) 
