The roe deer females have been more difficult to spot over the last two months as they have resumed a stealthier, more concealed lifestyle in the riparian forest habitats sticking close to the shelter of deciduous trees and shrubs.
However, I have been able to observe them at times and on, a few of such occasions, I have witnessed them engaging in activities which I could only describe as exercising.
For example, one of these females (and this case story closely resembles the two others, thereby, I will use it as a representative account) was observed running through the sparser woodland over the distance of about 500 metres without any cause to such behaviour.
Typically, it is assumed that deer would run in order to escape threat (real or perceived) or perhaps, in some situations, in order to play (I have seen a roe deer male and female running together and prancing playfully slightly before the mating season).
However, this female was alone and there was no threat to have spooked her.
The local roe deer population is altogether not easily perturbed.
Running away is seldom their first reaction to disturbance (such as people and even people with dogs passing by) because they have come to know our habits and, especially if they have taken good cover behind woody vegetation, they would rather wait until the disturbance ceases.
Female roe deer close to parturition would be even less likely to take flight in such a conspicous manner (my observations refer to the period of the second half of April which is about half a month or a month from fawn-birth that should occur in May/June) because they are overall unwilling to draw attention to themselves and they are probably impeded by their late-stage pregnancy which would render an active escape the last option.
I observed the female from a spot which about midway in her run.
The female never noticed me.
I kept watching the area that she had run out of, and there were not even people or people with dogs walking.
Females are also not obliged by territorial males (a male may have taken flight from another male under similar circumstances).
Accordingly, I could not help but conclude that this female was not running away from anything and that perhaps her running activity was induced precisely by lack of threat.
Namely, she might have deemed the area safe enough to indulge in some exercise.
It is known that exercise can improve the condition of pregnant human females.
I do not see why it would not be of assistance to gravid females of other species.
Animals probably cannot expend as much energy in exercise and there might be a trade-off between the benefits of exercising and energy losses.
This could be of particular significance to individuals who are subject to predation threat and/or a rugged terrain.
The adult roe deer in this area are not preyed upon by any natural predators and the terrain in the riparian habitats is moderately rugged (long grasses in unmanaged meadows, some fallen trees, shrubs, riparian slopes).
On the other hand, the trade-off might be more complicated than a simple ‘exercise = expenditure’ scenario because exercise can boost metabolism leading to a more efficient assimilation of nutrients.
I wonder if these females who have had to undergo a dietary change from the wintertime diet to the new spring woody growth (which might be more difficult to digest despite the roe deer being highly adapted to such browse), should engage in physical activities in order to assist their bodies through the transition.
Human females risk accumulating excess fat and suffering poorer cardiovascular health during pregnancy but I am not certain whether the same conditions apply to wild species where the potential of accumulating fat is rather low and where at least moderate mobility is a constant part of daily routine.
On the other hand, the ‘sprinting’ type of activity that I observed would quite directly affect heart health and improve blood circulation.
Blood vessels in the umbilical cord serve as feeding ‘tubes’ to deliver nutrition from the mother to the fetus.
Thus, enhancing blood circulation might be a method for the roe deer female to send the nutrients she has acquired to her baby in order to improve its development.
Also, this has been a ‘tricky’ year with respect to temperature fluctuations and brief periods of above average warmth are replaced by brief periods of below average cold.
In roe deer that do not accumulate much fat, the effects of these fluctuations might be mitigated by maintaining hearth health because a healthy heart is needed to pump blood through the cold-shrunk blood vessels while periods of above-average warmth might be equally straining on the cardiovascular system.
Additionally, it might be important for the females to keep a high muscle tone which would be of great help during the labour.
Some muscle tone is already achieved through the daily activities of walking along a slope and overcoming obstacles (such as coarse woody debris).
If the females appear to be engaging in sprint-type of exercise, they might be aiming at specific muscle groups and perhaps these particular muscles are also involved in parturition or they might be weakened by the growing fetus during the pregnancy.
Also, females are subject to both temperature stress and the stress imposed by the high concentrations of secondary metabolites in the new woody growth.
Such exposure might lead to oxidative stress that is damaging to muscles (but also to other organs and body functions).
Exercising could reduce the impacts of the oxidative stress.
Perhaps it is important for the female to reduce the amount of secondary compounds as well as reactive oxygen species that may circulate into placenta.
It is also known that moderate exercise already during pregnancy can improve the quality of milk that the baby later receives (Harris, J.E. et al., 2020).
Accordingly, there are truly many benefits to exercising that roe deer females might share with the females of other (mammalian) species.
However, I should like to pay closer attention to the specifity of roe deer diet during pregnancy as well as to the type of exercise (sprint) that the females appear to favour as these considerations might be informative on the specific purposes of adding aerobic exercise to the already moderately active lifestyle of the riparian forest habitat roe deer females.
References
Harris, J.E. et al. Exercise-induced 3′-sialyllactose in breast milk is a critical mediator to improve metabolic health and cardiac function in mouse offspring. Nat Metab 2, 678–687 (2020). https://doi.org/10.1038/s42255-020-0223-8
Notes by Ieva 