Scent of roe deer vs. red deer

Roe deer and red deer are the two more common cervids in my area.

As I have observed them quite frequently, I have come to a conclusion that they differ in the intensity of the trace scent that they leave.

Roe deer appear to leave no scent at all or very little scent concentrated around urination or defecation patches.

My dog and I tend to spot roe deer mainly based on visual or auditory cues.

Meanwhile, red deer leave a strong scent that even I can identify and which appears to persist even after the individual has been gone from the specific patch for a longer while because upon encountering the scent, we do not necessarily come across the individual who left it.

Of course, we do not track the animal but I am referring to sites where the encounter probability is high.

Upon encountering roe deer and red deer individuals up close, I would not say that the scent intensity is rather universal between sexes.

That is to day, neither roe deer males and females not leave strong scent traces.

The same could be claimed regarding age groups (roe deer adults vs. fawns).

Red deer females also appear to smell as intense as red deer males although the male scent is stronger during rut which is probably the result of his active effort to cover himself in his own urine in order to appear more attractive to mates (and the strong scent could be possibly also a byproduct of some hormonal surges during rut).

Red deer females perhaps smell a bit more intensely in spring (according to my personal observations) in the pre-parturition period.

I have fewer observations during winter and the time of calving in red deer (before the females aggregate in mother-offspring unit herds).

I cannot make any claims regarding the scent of red deer calves, either, because I have never met a calf without a mother group and the scent of mothers mask any scent the calf might emanate.

I was wondering why there is such a difference between the scent traces in roe deer vs. red deer and my conclusion was that it could be related to the different anti-predator strategies in the two species.

Roe deer rely on not becoming noticed (both with respect to fawns and adults).

The main strategy is to stand still (or to lie still in the case of fawns) until the danger passes and the predator moves on without having spotted the prey, and frequently the individuals lead solitary lifestyle (less so during winter) which, additionally, emphasizes the importance of not becoming noticed which is more easily achieved when the individuals are scattered across the landscape.

Meanwhile, red deer rely on herding behaviour and group vigilance as well as probably flight (fleeing in a relatively straight line).

They forage more often out in the open and in larger herds.

Larger herds are spotted more easily by predators than smaller herds, and herding in large groups is not a strategy of never becoming noticed (occlusion, standing still) but on noticing the predator first (through group vigilance) and fleeing timely across the plain landscape (which offers relatively little few hiding opportunities but which enables to run fast).

With such differing strategies, roe deer would benefit from not emitting, nor leaving a strong scent.

Leaving a scent is dangerous for solitary species because once the individual is discovered, he or she becomes chased without risk dilution effect (in a group the predator(s) can focus on this or another individual and the risk concerning any particular individual is lower than in solitary or pair situations).

Meanwhile, red deer do not attempt to achieve such level of ‘invisibility’.

However, then one might wonder why the red deer need to have a strong scent in the first place because emitting a vaguer scent would be an additional benefit (there is no such thing as being too secured).

Scent is important in communication, and I suppose that at least partially the scent differences could be explained by differential social mechanisms in the two species.

Roe deer do not form groups in summer, and in winter their groups are small (it is probably easy to keep track of all the individuals).

Their home ranges are also small and meeting up with the ‘buddies’ (including fawns who have begun to leave their nursing stations) is probably easy.

Roe deer female and male ranges (territories in the case of males) mutually overlap and the mate-finding process involves less of travel and searching.

In fact, roe deer can be even monogamous (or polygamous with one buck mating with two or more females that reside on his territory) and it is not necessary (at least for females) to track down potential mates.

I suppose that the territorial ‘barking’ in roe deer might have evolved in order to compensate for relatively vague scent-marking signals which cannot fully advertise territorial intent.

These conditions might not apply to red deer that aggregate in large herds, range over vaster areas (not too vast but possibly vaster than those of roe deer), separate between male and female herds etc.

For example, having a specific cue scent might be important to reunite female with her offspring within the setting of a larger herd that includes multiple mothers and multiple young.

Red deer stags might also have to track female scent during the rutting season.

There could be other aspects to the scent difference between the two cervid species.

I wonder if such differences occur among other cervids and if they can be explained by these same mechanisms (predation, sociality).

That is to say, I wonder if other cervids that rely on hiding and not becoming noticed also have vaguer scent than cervids who apply less elusive anti-predator strategies.

Similarly, herding behaviour, mating behaviour etc. could be compared with respect to scent produced.

(I am not educated enough to discuss hormonal and other body chemistry processes involved as well as secretions relative to body size or perhaps forage type etc.).