Tolerance of Incubating Pheasant Eggs to Exposure

Abstract

Michigan's ring-necked pheasant (Phasianus colchicus) population, in common with pheasant populations across the rest of the continent, underwent a decline in the mid-1940's. The decline was characterized by a lessened production of young, as evidenced by lower fall age ratios, and by a decreased proportion of hens observed with broods in summer. The average number of chicks in each brood, however, did not change significantly in Michigan during the years of decline and subsequent recovery. This suggests that the factors operating to limit reproduction prevented entire clutches from being laid or from hatching, or destroyed entire broods, rather than operating by destruction of eggs or chicks one by one. During the early years of the decline there appeared to be some correlation of lowered production of young with lowered mean temperatures and excessive precipitation in spring months. Allen (1946) reported this in Michigan, and Ginn (1948) found an apparent inverse correlation between amount of spring precipitation and fall kill. Kimball (1948) stated that 11 of 12 pheasant workers listed weather as a likely cause of the pheasant depression. In later years of the pheasant and during subsequent recovery, this apparent correlation has not always followed; it is now obvious that there is no simple relationship between spring weather and fall populations. Nevertheless, since climatological factors are influential in determining range of a species, and since there still was the suspicion that annual climatological conditions affect yearly population fluctuations of the shorter-lived species, experimentation to determine climatic toleration of pheasant eggs seemed worthwhile. A series of experiments was devised in which eggs in various stages of incubation were exposed to lowered temperatures or simulated rainfall for varying periods of time. Work was done at the Michigan Department of Conservations's game farm at Mason, Michigan, as part of Pittman-Robertson Project W-38-R, Survey of the Ringnecked Pheasant in Michigan. Examination of the literature reveals references to limited experiments with (1) exposure of unincubated pheasant eggs to lowered temperatures, (2) exposure of incubating pheasant eggs to higher than normal temperatures, (3) exposure of incubating and unincubated chicken eggs to lowered temperatures. But no references to the effects of lowered temperature on incubating pheasant eggs could be found. English (1941) found that unincubated pheasant eggs could be exposed to temperatures as low as 100 F. for a total of 5? hours in three 1ior 2-hour periods on alternate days without appreciable loss of viability. Romanoff et al (1938) reported on the effects of incubation temperatures varying between 950