- A water bird census was taken at three points on Upper Klamath Lake at weekly intervals extending over a period from September 9, 1936 to May 29, 1937. A total of 24,319 birds was recorded in field records and included thirty-two species. Totals of birds by weekly field trips show the following maxima: October 3 produced by pintail, December 24 produced by olden eye, January 16 by ruddy and olden eye, March 6 by ruddy, and May 1 by greater scaup together with western and eared grebe. During the winter months while the lake is frozen over, the birds are concentrated in open water near hot springs or where a strong water current is present. They consist of bottom feeding or diving birds during this time; principally meranser, bufflehead, pied-billed grebe, ruddy, golden eye, coot and greater scaup. The fall migrants consisted largely of widgeons while the spring influx was composed mostly of greater scaup, western an eared grebe. The most abundant species were the ruddy, golden eye, widgeon, coot and greater scaup, constituting 23%, 21%, 16%, 11% and 10% respectively of the total number of all birds observed. In frequency of appearance in field records, the greater scaup and coot were recorded on more than 80% of the field trips while the ruddy and golden eye were present in from 70% to 80% of the trips. Availability of feeding areas appears to be the principal factor causing fluctuation in number during the winter season. The temperature and precipitation conditions during the period of the census were not average. The dry tall characteristic of this region prevailed extremely late. The first precipitation of any consequence and in the form of snow occurred in late December. An extremely cold period during January and February followed this dry fall season. The spring season was later than usual, the temperature falling to moderate until late March. These variations from the average weather conditions produced three effects: first, a delayed fall migration; second, limited feeding area for the wintering birds due to restricted areas of open water while the lake surface was frozen; third, a delayed spring migration which was concentrated an of short duration.