Explore: Predator

Cloud-free line-of-sight probabilities were calculated using two separate methods. The first was a variation of a method developed by the Rand Corporation in 1972. In it, CFLOS probabilities were calculated using empirical data based on five years of photograms taken over Columbia, Missouri and forecasted cloud amounts rather than climatological values. The second was a new approach using the Cloud Scene Simulation Model developed by Phillips Laboratory. Cloud scenes were generated using forecasted cloud fields, meteorological inputs, and thirty random numbers. Water content files were produced and processed through a follow-on program to determine the extinction coefficients at each grid point in the working domain. A reiterative routine was written to integrate the extinction coefficients along a view angle from the top of the domain down to the surface at separate points within the horizontal domain. The values of each point were summed and averaged over the working domain to determine the CFLOS probability for the target area. The nadir look angle was then examined for both methods. Stratus, stratocumulus, cumulus, and altocumulus cloud types were independently examined with the CSSM generated cloud scenes. Each method and cloud type were compared against the known CFLOS probability for nadir. Results indicate the method developed in 1972 underestimates CFLOS probabilities by as much as twelve per cent with horizontal cloud coverage ranging from 30 to 80 per cent. CSSM generated cloud scenes varied depending on the cloud type analyzed, with stratocumulus clouds measuring up the best against the known probabilities.

Sheep and lamb losses to predators have been determined since 1958. Predators kill many more lambs than sheep and therefore the upward trend of lamb losses in relation to sheep losses indicates that relative predator losses are increasing. Losses were estimated separately for each of the 33 states that showed definite losses and were then added together for areas and for the United States. The fact that independent estimates of predator losses in National Forest regions showed a high correlation with losses estimated from U.S. Department of Agriculture mortality data helps verify the accuracy of each set of estimates. During the 21-year period from 1958 through 1978, the area of predator damage was enlarged as losses tended to increase both eastward and southward. In general, adult sheep losses were about one third as great as lamb losses in the range states and two thirds as great in the farm states. Total numerical losses of sheep and lambs to predators were 1.5 million head in 1958 and 1.3 million in 1979. The percentage of loss steadily increased from 4.0 in 1958 to 6.8 in 1977, the year of the greatest percentage of loss. Sheep numbers declined during this period, in part because of predator losses. In fact, predator losses appear to have been a major cause of the decline of the sheep industry since 1960. The value of the loss increased fairly steadily from a low of USD25 million in 1961 to a high of USD103 million in 1979, the most recent year statistics were available. All of the eastern states showed relatively minor losses when compared with losses in the western states. Predator losses have had a significant effect on income from sheep. On the average, net income per ewe in 1974 would have increased from USD3.88 to USD8.12 if predator losses could have been eliminated.