Field Guide 78 · Big game biologyMountain goat · Black Hills · Survival
Beetle-killed pine tracked adult goat survival in the Black Hills
FDR Research Desk · Field-craft, method, and evidencePublished
In the Black Hills dense ponderosa pine between granite outcrops died in a mountain pine beetle epidemic that peaked in 2012. If you follow this small introduced goat herd, the decision is whether a district puma count should set your read of adult survival or whether the timber change belongs in that read too. The authors' reason is that dead pine in the travel corridors may let goats detect predators more easily. That mechanism was not measured. Lehman and colleagues reported in PeerJ that from 2006 through 2018 the top annual survival model for marked adults included cumulative mountain pine beetle disturbance and that the relationship was positive. Puma abundance was not among the survival-model terms the paper describes. In competing models the intervals for age class and sex both overlapped zero.
STEP 1 · Cause of death
Puma was the largest single cause in a 17-death tally
The marked sample was 47 adults at least 3 years old in Custer, Pennington and Lawrence counties. Thirty-three were females and 14 were males. Yearlings and 2-year-olds were not marked, so kid and subadult survival is outside this result.
Puma predation was the largest share of cause-specific mortality at 8 of 17 deaths. Cause categories included predation, fall, drowning and unknown. The results give that 8 of 17 figure and do not list the other causes. Predation required evidence the goat was alive when attacked, including hemorrhaging. Predator identity used cache sign, drag marks, scat, hair, necropsy and bite marks.
STEP 2 · Survival swing
One low year sits inside a higher mean
Biological years ran from 1 June through 31 May. Pooled annual survival of marked adults ranged from 0.538 to 1.000 and the mean was 0.902. The 95 percent interval on the mean runs from 0.825 to 0.979.
In 2007 abundance was about 50 to 70 animals and survival was 0.538 with a 95 percent interval from 0.285 to 0.773. The puma-caused mortality rate among marked goats that year was 0.289 and it was the leading cause.
From 2000 to 2018 the cited average annual growth rate was 1.02 with an interval from 0.88 to 1.16. That interval spans decline and growth. South Dakota Department of Game, Fish and Parks surveys are the source of that growth figure. The collar mean is a separate number.
The authors say a study limited to 2006 through 2010 or to 2011 through 2018 would have reported a much different result. Our read is that 2007 should not set your view of this herd.
The puma population increased substantially from 2006 to 2012 and then remained relatively stable through 2018. Those estimates include kittens and cover the Black Hills Fire Protection District. Goat abundance estimates cover the core of the mountain goat range. Survival was 0.79 from 2006 through 2010 and 0.97 from 2011 through 2018. That district-wide puma estimate is not a goat-core measure of cat pressure.
STEP 3 · Beetle cover
Cumulative beetle hectares had a positive survival coefficient
The models tested age, sex and cumulative mountain pine beetle disturbance. The paper's model term for sex is gender. Competing models also included year. Puma abundance was not among the survival-model terms the paper describes.
Cumulative beetle hectares came from 99 percent annual home ranges laid on Black Hills National Forest maps of killed trees for 2006 through 2018. The maps used aerial surveys, aerial imagery and aerial photos.
The top model coefficient on cumulative beetle hectares was 0.580 with a 95 percent interval from 0.302 to 0.859. The relationship with survival was positive. That covariate carried a model weight of 0.972.
The authors hypothesize that the beetle kill increased the ability of goats to detect predators because tree cover fell in the corridors between granite outcroppings. They also say open canopy may have raised understory forage and they did not measure forage. They say puma predation and the vegetation change are hard to separate. Our read is that the beetle term also follows the later years, so it does not isolate timber from the separate puma series.
A 2016 personal communication cited in the paper says that from 2006 to 2012 86 percent of the mountain goat range had been affected by beetle disturbance. The paper places the epidemic peak in 2012.
A reasonable approach when glassing this herd is to treat green pine and beetle-killed openings as different travel cover and to read them beside any puma estimate. The authors suggest lower tree density beside escape terrain and fewer white-tailed deer near the goat core as possible long-term measures. This study did not test either. This study does not show that clearing forest improves survival.
Our proposed observation is two crossings between the same outcrops. Glass one through standing green pine and one through beetle-killed timber. On each visit record whether goats use the crossing and how close hiding cover sits to the trail. Those notes can show travel and cover at the crossings you watch. They cannot show where goats die and they cannot estimate marked adult survival or the model's coefficient. A carcass with cat sign is not a confirmed puma kill. In the study, predation required site evidence that the goat was alive when attacked, such as hemorrhaging, and carcasses were necropsied. A later published survival estimate that falls while beetle-killed crossings stay open and the district puma estimate holds steady would lower the weight we give opened pine. A published survival drop as young pine closes those crossings would raise that weight. Either published change is a reason to look again.
STEP 4 · Unsettled splits
Age and sex effects were not resolved
Captured goats were aged by horn annuli and classed as adults from 3 to 9 years and old adults at 10 years and older. The crew expected lower survival for old goats and for males. In competing models the age-class coefficient was 0.333 with an interval from negative 0.772 to 1.439. The gender coefficient was 0.471 with an interval from negative 0.585 to 1.526. All 12 year coefficients had intervals overlapping zero. The opened results do not define the reference level for age or sex, so we do not treat the sign as a finding. Intervals that overlap zero leave age and sex unresolved. A missed difference does not show that the effects are zero. The authors say small samples could explain why these age and male results contradict earlier research. The analysis omitted random effects for years and for individual goats.
STEP 5 · Local herd
Survival here comes from one introduced Black Hills herd
Mountain goats were introduced into the Black Hills in 1924. The paper describes a heavily forested system unlike the open alpine habitats typical of the native range. Marked goats came from a population of about 50 to 130 animals. The authors hypothesize that one or several pumas specializing on goats could strongly affect a herd this small. They also hypothesize that white-tailed deer have sustained the puma population. A diet study they cite found deer were 83 percent of puma diets and white-tailed deer were 63 percent of the total diet. Those diet shares sit outside the 47 collars.
The paper reports adult survival for this marked sample. It does not report hunter success and it does not set current rules. Check the state wildlife agency for seasons and methods. Watch travel cover and avoid judging the herd from a short run of years.
The authors presume ponderosa regeneration will thicken woody cover again in the primary goat range. They say the death of one or two specialist pumas may also explain the later survival rise. This paper cannot settle the regeneration idea or the specialist puma idea.
NOTES AND SOURCES
Fully Drawn Research is an independent data analysis desk, not affiliated with any state wildlife agency, transportation agency, mapping provider or outfitter. This guide reports published research and FDR's reading of it. The field observations proposed here were not tests of hunting or fishing success.
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