A declining population of ring-necked pheasants (Phasianus colchicus) was
studied at Tule Lake National Wildlife Refuge (TLNWR) from the summer of 1990
through the spring of 1993. Pheasant densities/50 ha at TLNWR in 1989, 1991, and
1992 were considerably lower (16.86, 8.49, and 6.81) than the >62 density seen in
the mid-1950s. Mean body weight of hen pheasants at TLNWR was significantly
lower than hens at nearby Lower Klamath National Wildlife Refuge (LKNWR) which
was not intensively farmed. Mean tarsal lengths of hens at TLNWR were also
significantly shorter than hens at LKNWR, suggesting reduced skeletal growth and
potential nutritional problems. The lack of adequate cover was responsible for poor
early nest success at TLNWR. Later in the season, spring planted crops provided
adequate cover to conceal nesting hens; however, only 0.21 young in 1991 and
0.02 young in 1992 were produced per radio-equipped hen. These rates are
extremely low compared to rates required to maintain a stable population. Most
adult mortality occurred during the spring and early summer months at TLNWR
before crops provided adequate cover, and long before pesticide applications. The
main predator of the pheasants was the golden eagle (Aquila chrvsaetos). Of special
concern at TLNWR was pheasant and other wildlife exposure to anticholinesterase
(antiChE) insecticides used on agricultural croplands at the refuge. Direct toxicity of
antiChE compounds (in this case methamidophos) killed 2 young pheasants, but no
adult radio-equipped hens died as a direct result of insecticide intoxication. This
finding was of particular interest because 15% of the adult pheasants collected in
and around potato fields had 55% brain ChE inhibition. The extent of the effects of
insecticide exposure on the survivorship of pheasant young was uncertain as they
were not radio-equipped. The overriding factor impacting the pheasant population at
TLNWR and to a lesser extent LKNWR was poor habitat, especially in the spring
when most mortality occurred. The poor habitat also resulted in extremely low
recruitment (up to 1 September). Nearly all adult mortality and most of the low
recruitment occurred before the insecticide spray season. The population was nearly
extirpated during the severe winter of 1992-93. / Graduation date: 1995
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/35200 |
| Date | 28 February 1995 |
| Creators | Grove, Robert Allan |
| Contributors | Buhler, Donald R. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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