What Causes Does to Go into Estrus?


What signs signal a doe is in estrus? What is influenced by biology, and what’s influenced by the season and the doe’s environment? And what about the bucks — how do they know when the doe is ready to breed? What signs are they looking for?

Q. How does a buck determine the readiness and willingness of the doe?

The simple answer is this: scent. That’s the primary signaler. However, if we’re being less specific, a buck recognizes a doe is in estrus partly due to seasonal prompting and partly due to doe behavior. We’ll unpack more details about these two factors (seasonal prompting and doe behavior) below.

Also keep in mind that the doe’s behavior is an important part of the signaling process. If a buck was simply going on his own readiness and eagerness for the rut, then he would breed for about five months of the year. And this is in a literal sense. A buck is literally a willing breeder for four to five months, waiting only until he finds a female in estrus.

Q. How does the amount of daylight affect a deer’s behavior?


A deer’s body responds to seasons. Specifically, the body experiences physiological changes based on the amount of daylight and darkness. The amount of daylight dictates the breeding period, but also influences other physical traits like a deer’s coat. It changes from its summer coat to winter coat based on changes in the amount of daylight, not based on changes in temperature. In fact, you’ll find that a deer’s physiological events aren’t affected much by weather conditions or rising and falling temperatures.

Q. How can a deer’s body recognize a change in daylight and respond accordingly?

For animals, including deer, change in daylight prompts a chemical response in the body. And that alone drives behavior. More hours of darkness boost a deer’s melatonin levels and this change in melatonin activates a series of events depending on the season and the amount of daylight versus darkness. Among the outcomes of these changes is estrus.

But, also, a buck has its own series of events that define its breeding season, which differs from that of a doe. This points back to an answer cited above: A buck is a willing breeder for up to five months. A doe is not.

Q. How long is a doe in estrus?

Comparatively, it’s a short amount of time given a buck’s 5-month state of readiness. A doe must reach the perfect concentration of 1) luteinizing hormone, 2) estrogen and 3) progesterone. This perfect mix only lasts for two to three days, which means estrus is a two- to three-day affair.

Q. How long does a doe secrete the scent bucks rely on to signal a does is willing to breed?

The perfect mix and amount of the three “activating” hormones (luteinizing hormone, estrogen, progesterone) stimulate a doe’s distinct scent while in estrus, which is two to three days. And this distinct scent — brought on by estrus — limits a buck’s focus and distracts from his typical degree of vigilance. He’s single-minded.

Q. When a buck crosses the scent of a doe, what’s his next move?

Well, he tracks her down of course. Then, when he finds her, he hounds her and never leaves. He’s relentless. But the doe is unwilling until the hormone concentration is just right. And this concentration typically prompts the doe’s scent secretion a day before her cycle peaks, and she’s willing to breed. So in spite of a buck’s persistence, all variables must be aligned. Once the doe’s scent declines, the buck will leave to find another doe.

Q. How do we apply this knowledge of estrus and the breeding season to gain a better understanding of the “second rut” and “pre-rut”?

Given what we know of a deer’s estrus cycle — particularly its narrow window — there will be does not bred during the rut. These does will cycle back into estrus about 28 days later. That’s what’s considered the second rut. And it’s not guaranteed.

Typically the number of does that go unbreed during the rut are few in number. But keep in mind that a second rut is more common in areas with abundant food sources and healthy doe fawns that are entering estrus for the first time.

Pre-rut, meanwhile, is intuitive enough. It’s the period of time before peak rut when a few does reach estrus ahead of the majority of does in a given area. At this stage, bucks are searching for these few does, increasing deer traffic along funnels and corridors. But most of the bucks aren’t finding does in estrus during pre-rut, so this phase often creates optimal hunting situations. Once the majority of does are in peak rut, bucks are often paired with does in estrus and aren’t out looking and moving as actively as they tend to be earlier in the breeding season.

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