All it shows is a 50% survival rate every year for bucks and 85% for does. I'd say he was just trying to show that it's not feasible to have "half" of all bucks be 4.5yrs or older. Would be a much more useful exercise if he used actual or predicted survival rates under different hunting scenarios.
In Montana with hunted populations, total annual buck mortality in mountain foothill areas is 46%, timbered breaks 41%, prairie badlands 61%. So survival rates are 54%, 59%, and 39%, respectively, in OTC areas of MT.
A ‘summary’ of sorts across western states would put OTC buck survival (after their yearling year) at 40-60%. So this jives too I guess. Yearling buck survival is around 50%, fawn survival varies as was mentioned in that post.
For LE areas there’s 60-70% survival (which I struggle with this as “LE” can mean 50 permits or 500 and thus affect survival rate).
Important to note that up to some level, hunting mortality substitutes for natural mortality in bucks. Similar to how predation is largely compensatory for fawns, hunting mortality is somewhat compensatory for bucks (to a certain point that varies year-to-year based on nutrition and weather).
Completely unhunted areas buck survival is around 70-80% and this could vary year to year. Given how much bucks expend energy during the rut their winter survival should vary not to the extent that fawn survival does but moreso than adult doe survival.
So using FWP’s example, take an
unhunted population of 100 fawns. Roughly 50 are buck fawns. 50% fawn survival = 25 buck fawns. (I think that’s high for fawn survival and more realistically it’s closer to 30% but again, lots of variability.) Yearling buck survival is 50%, so now we have 12 two-year olds. At 80% survival for the remainder, that leaves 10 3-year olds, 8 4-year olds, and 6 5-year olds. So from a starting population of 100 fawns (not including the does and bucks already out there), 6% would survive to be 5 if their adult survival rate was 80%.
This is useful for illustrative purposes but environmental variation, luck, an individual animal’s decisions, etc. all interact to determine its survival too.