Ep. 506: Deer Biologist Explains Why Scrapes Peak Two Weeks Before the Rut w/ Dr. Karl Miller (Part 1)

Beau Martonik sits down with Dr. Karl Miller of the University of Georgia, where he spent 40 years leading deer research and mentoring close to 100 graduate students. Karl grew up hunting the Pennsylvania big woods before he went south for his PhD, and much of what hunters take for granted about rubs and scrapes came out of his lab.

The core of this conversation is signpost communication. Karl walks through why bucks make rubs in the first place, and what one of his students found when he ran a chemical analysis on forehead gland secretions: 67 different compounds, and not one of them in higher concentration in dominant bucks than in subordinate ones. No dominance signal at all. What varies is the mix, deer to deer, which means every buck is leaving something closer to a name than a rank. He also explains why the loser of a sparring match will walk up and lick the winner’s forehead.

Then he gets into scrapes, and the finding he clearly loves most. Scraping activity peaks about two weeks before peak breeding in almost every study ever run on it. Karl’s hypothesis is that this isn’t coincidence or anticipation. It’s that buck urine deposited in scrapes may be acting as a priming hormone on the does, pulling their cycles into synchrony, and the two-week lag matches the length of a doe’s follicular wave. He and a graduate student demonstrated the same mechanism in Eld’s deer using a control group and a group exposed to male urine, and the treated group entered estrus together with enhanced hormone profiles. Then he flips it and explains flehmen, the vomeronasal organ, and how a buck taking doe urine into his mouth routes it past the smelling part of his brain entirely and straight to the part that runs his reproductive physiology. Both sides priming each other.

Also covered: 3,600 rubs per square mile on an unhunted Georgia herd, roughly six per acre; the interdigital gland and the 11 compounds that actually do track with maturity; why a tarsal gland’s smell comes from bacteria and not from the gland; the staph and listeria living on it; the castrated buck that ran an entire rut in two weeks on a testosterone dose they overshot; young bucks making 15 percent as many scrapes as mature bucks; and a stretch where he and Beau land in different places on whether there’s any point in doctoring a scrape.

This is part one of two. Part two is deer vision and camo, and it’s out Tuesday, September 1st.

Topics:

00:00:00 — Intro

00:19:25 — What everybody had wrong about rubs in the seventies

00:25:04 — 67 compounds, and why a rub isn't a dominance display

00:26:09 — Why the loser of a sparring match licks the winner's forehead

00:38:32 — 3,600 rubs per square mile, and how many one buck makes in a year

00:49:08 — The three things a buck does at a scrape

00:52:56 — Why a tarsal gland actually stinks

01:01:45 — 39 bucks on one scrape, and 85 percent of visits after dark

01:04:30 — Scrapes peak two weeks before the rut

01:06:24 — Priming hormones, and synchronized estrus

01:10:09 — Flehmen, and the does priming the bucks right back

01:21:59 — Adding scent to a scrape, and whether it does anything

01:35:00 — What a broken age structure does to the rut you're hunting

Dr. Karl Miller’s published research: Google Scholar, search “Karl Miller deer UGA”

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