In conjunction with a study evaluating the effects of fuels-reduction treatments on Mexican spotted owls in the Sacramento Mountains, the USDA Forest Service Rocky Mountain Research Station permitted by the U.S. Fish and Wildlife Service fitted 34 Mexican spotted owls with radio transmitters during the summer of 2004. From fall 2004 through spring of 2005 mortality rates were observed in owls with transmitters, mostly in adult males of the population. Approximately nine adult males and four adult females are dead or presumed dead. The number of male owl mortalities is higher than expected, causing concern over factors leading to their deaths.
The heavy winter snow pack on the Forest may have reduced the prey base or some other factor or factors may be at work. However, there is a chance that the weight of the radio transmitters caused additional stress to the owls and contributed to their mortality. Consequently the partners in the study determined that recapturing and removing radio transmitters from the surviving male owls was in the best interest of the population.
Data collection, important to managing the owls and their habit for the future will continue through females with radio transmitters. During this summer the researchers are collecting information on the birds? body weight and condition during recapture, prey base numbers, and summer 2005 female survival rates. Owl experts will complete an assessment by mid-September and decide whether removal of transmitters from female owls is advisable.
The Mexican spotted owl is listed as a threatened species under the Endangered Species Act. The loss of these owls is not expected to have a significant impact on the population especially since research has shown that new owls have filled many of the territories vacated by the mortalities.
The U.S. Fish and Wildlife Service has permitted the Rocky Mountain Research Station Scientists in Flagstaff, Arizona to conduct the study with the cooperation of the Lincoln National Forest and the New Mexico Department of Game and Fish.
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