These studies were prompted by the declining populations of the ring-necked pheasants (Phasianus colchicus) in the Tule Lake National Wildlife Refuge (NWR).  Concerns about the effects of current agricultural practices including the loss of habitat and the use of pesticides were evaluated.  From the summer of 1990 through the spring of 1993, the population of hens at Tule Lake NWR were compared with those of Lower Klamath NWR.  Changes in farming practices in the last two decades have nearly eliminated available habitat bordering agricultural lease lands at Tule Lake NWR.  The lack of alternative habitat has forced the pheasant and other wildlife to utilize less compatible monocultural croplands at Tule Lake NWR.  Adult hens were found to be both significantly lighter and had shorter tarsals than hens at Lower Klamath NWR which was not intensively farmed. This indicates incomplete skeletal growth and potential nutritional problems.  Poor habitat resulted in increased adult mortality, reduced nesting success, and reduced brood survival.  Most adult mortality resulted from golden eagle (Aquila chrysaetos) predation during the spring and early summer months at Tule Lake NWR before crops provided adequate cover.  Later in the season, spring planted crops provided cover to conceal nesting and renesting hens; however, only 0.21 young in 1991 and 0.02 young in 1992 were produced.  The extremely low reproductive rates were well below those required to maintain a stable population. Pheasant at Tule Lake NWR were also exposed to a variety of pesticides used on agricultural croplands at the refuge, including some of the more toxic organophosphorus insecticides such as disulfoton, methamidophos, and parathion.  Over half of the pheasants collected in and around potato fields sprayed with methamidophos had brain cholinesterase inhibition.  Two pheasant young, approximately 45 days old, were found dead along potato field sprayed 2 days earlier with methamidophos in 1990 at Tule lake NWR.  Brain cholinesterase inhibition was 90 and 92%.  Due to the lack of radio-equipped hens dying, while none of the young were radio-equipped, the extent of the effects of insecticide exposure on the survivorship of young was determined unknown.  Therefore the study concluded that the overriding factor impacting pheasant population at Tule Lake NWR was poor habitat especially in winter and spring when most predation occurred.  Poor habitat also resulted in extremely low brood survival.  Insecticides were not found to be the major factor impacting the pheasant population, although their role was most likely exerted on lower survival of young.

Learn more by reading the following full report:

Groves, R.A., Buhler, D.R., and Henny, C.J. Agricultural Practices and Insecticide Use Related to Pheasant Declines at Tule Lake National Wildlife refuge.  Oregon State University, and National Biological Survey, Corvallis, OR. 1994

Return to the Klamath Falls Field Office Reports

Visit the: Pacific Region - Environmental Contaminants-Investigating and Monitoring

Visit the: USFWS- Pacific Region Ecological Services Home Page