Description

The nesting population of greater sandhill cranes on Malheur National Wildlife Refuge, Oregon had declined from 236 pairs in 1971 to 181 pairs in 1986 when predator control began. The population has continued to decline to 168 pairs in 1989. Some of the decline is attributed to lost habitat on Mud, Malheur and Harney Lakes due to record high lake levels 14 pairs. Losses on Mud, Malheur, and Harney lakes had already taken place by 1986, but could not be verified until a comprehensive pair count was completed in 1988. The remainder of the decline is attributed to the low recruitment of young into the population during the years 1971 through 1985. In 1991, a total of 214 crane pairs were counted on the refuge. This represents a significant increase compared to the 177 pairs counted in 1990. This is an increase of 37 pairs over 1990 numbers. These new recruits are a result of our efforts towards reducing predator impacts on crane production. In 1991, 219 coyotes were removed by the following methods: aerial gunning 36 percent, calling and shooting 20 percent, trapping and snares 37 percent, and denninq 7 percent. An estimated 33 ravens were removed using 33 dozen eggs injected with DRC1339 and an additional 15 ravens were shot. Three raccoons were taken by trapping plus five by shooting, for a total of eight. Sandhill cranes experienced a poor production year in 1991. Overall sandhill crane hatching success was only 50 percent. This is considerably below our control program goal of 75, and is the lowest nesting success recorded for the Malheur crane flock during the predator control program. Predators took 25 percent of the monitored nests this year raven one percent, raccoon zero, coyote five percent, and unidentified predators 18 percent. Flooding and infertile or rotten eggs accounted for losses of 12 and 13 percent of nests, respectively. Although predation accounted for loss of 25 of the nests, it is likely that many of the nests which were recorded as predated were flooded andor abandoned and then predated because of the cool wet weather in May. This poor weather caused flooding of several nests in the Blitzen Valley, and apparently killed embryos in some eggs, as several pairs were sitting on eggs containing dead embryos. Crane colts were counted from the air on 4 September in the DoubleO and Blitzen Valley using ADCs Husky aircraft. This aerial data was supplemented with ground counts in the Blitzen Valley. Using a combination of ground and aerial count data, a total of 15 colts produced was tallied on the refuge in 1991. Only one colt was recorded in the DoubleO, one from Malheur Lake, and the remainder from the Blitzen Valley. The sandhill crane objectives of the 1991 effort were to have a nesting success of 75, fledging success of 25, and recruitment of 15. The actual outcome was 50 percent nesting success and seven percent fledging success, yielding a recruitment rate of 3.4 percent. Poor weather appeared to be the main cause of low productivity this year, although a study of crane colt survival showed predators to be a problem still.

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