We have had an atypical beginning of spring.
March was characterized by unusually warm temperatures that persisted day by day rather than fluctuating between cold and warm spells.
The temperatures were favourable to initiate new vegetation growth and, as a result, many associated species (herbivores) also changed into their spring behavioural pattern.
Then April was warm until about the middle of the month when temperatures dropped quite suddenly and sharply (from > + 5° at night to < 0° at night).
Such temperatures have remained since (the night between Apr 21/22 was the first warmer night when it was, once more, above zero but with rain/snow).
March/early April temperatures were historically high while the current temperatures (Apr 16 – Apr 22) are nearing historical low.
During this strange period, I observed that the roe deer responded to the cold temperatures not by decreasing their activity but by increasing it in the hours (around midnight and around dawn) when it was significantly warmer.
Beavers, for example, did not change their activity pattern over the first cold nights but as the water temperature probably also gradually dropped (because the cold persisted), they became less active on the nights of Apr 20 and April 21.
Meanwhile, there were roe deer most everywhere, and I observed both males and females.
I believe that roe deer – a species that does not seem to accumulate body reserves – were impacted greatly by the sudden drop in temperatures.
Meanwhile, I also think that the warm March had caused the roe deer (especially, females who are investing in fetal development) to abandon the winter’s slow metabolism and to enter a spring mode (where metabolism is altered to include not only body maintenance but more rapid growth as well as perhaps recovery).
I suppose that the roe deer could no longer ‘fall back’ to their slow metabolism which is interesting to notice because some species can alternate between ‘torpor/diapause’ and ‘full metabolism’ very flexibly while others cannot.
The term ‘flexibility’ is rather paradoxical in this context because I believe that roe deer represent a highly flexible species which is capable of responding to dynamic weather conditions quite closely (e.g., they assumed their spring behaviour according to current year weather pattern and not current to some ‘annual tradition’ the way it is observed in other species).
When resources became sufficient to sustain the spring metabolism, the roe deer immediately switched while other species might be following more constant cues (e.g., photoperiod) and they might still be operating in half-winter/half-spring regime.
At the same time, the roe deer appear to have adjusted to food availability (seasonal diet composition) rather than to temperature variations and the drop in temperature failed to revoke a quick and flexible response.
The roe deer could not regress to a slow-paced metabolism and they had to increase their activity in order to gather enough resources to both support their spring metabolism and to help them through the environmental stress (cold weather).
However, they were flexible enough in choosing the hours in which to forage.
The roe deer were active precisely in the warmer hours and disappeared, for example, during the period at night when temperature drop sharply (around 4 am – 5 am) before sunrise.
Other species do not seem that flexible.
For example, beavers appear to have activity peaks and lows that are quite regular which might be due to their efficient thermoregulation by insulation.
They are not in as much need to be able to respond to hourly weather.
It could also be related to the fact that roe deer do not have such long digestion period and therefore they might not be as constrained by the cyclic nature of forage uptake and rumination, i.e., they can adjust the timing of their intake bouts more flexibly.
They also seem capable of switching between diets quite quickly because their winter diet in this area is rather agricultural and they had no trouble to replacing it with woodland edge/forest diet as soon as the new growth appeared in these habitats.
However, I noticed some anxiety among the roe deer during these colder nights.
Females were foraging in the forest interior where it was warmer but they were moving around in a rather restless manner.
Partly, this could have been due to the excess of last year’s dead vegetation that the frost had made stiff and rustling.
It was impossible to be stealthy, and the roe deer females might have been slightly stressed because they were no longer with their winter group relying on shared vigilance.
Some of these females might be first-time mothers and this might be the first year they are foraging on their own range without ‘adult supervision’.
The change of habitat (from more open where other types of senses are used to find food and to avoid threats) might have been unsettling for the younger generation.
I suppose it is quite lonesome and frightening for a female to leave the group foraging system and to begin moving through the riparian forests in a rather solitary fashion more rarely meeting up with others, not being able to see far (e.g., see other roe deer in distance if not to join them).
I do not think that roe deer females dislike riparian forests.
I only mean to say that the change is quite dramatic and the psychological impact (including the strain that is involved in switching from group-reliant to self-reliant behaviour as well as engaging other types of sensory cues) might be challenging to bear.
During the warmer weather, I did not observe as many females in the riparian forest during these hours and perhaps they were still foraging somewhere partly out in the open joined by their last year’s offspring or mothers etc.
When it became cold, females entrusted themselves to the forest interior microclimate where they moved about alone for a few nights.
Interestingly, during these cold nights, the females were foraging but the males were making intensely active territorial patrols and barking quite a lot (especially, during the first cold night and then also over the last two nights).
There were no signs of actual territorial conflicts (except in one case where a male might have trespassed into another male’s territory although I am not certain of it because if he did, he did not respond with defensive vocalizations and quietly retreated).
The males were just trotting around and barking while the females were foraging stealthily.
The males must have been subject to the impacts of cold, as well.
Males are not gravid, of course, but their territorial behaviour is quite energy-demanding and the energy needs by males and females during this time might not be strikingly different.
Thus, the males would have benefited from also foraging somewhere quietly.
Instead, they were all over the place, loud and stout.
I wonder if they were performing this territorial behaviour to keep company to the females without betraying their locations and without encroaching on their foraging patches.
To me, it seems that the roe deer males are incredibly attentive to the females and I even think that much of what we consider their springtime territorial behaviour is directed at supporting the females rather than at male-male competition.
For example, the males often accompany the females during this time when the female travels by herself or with her last year’s fawn.
It is as if they are helping the female to acclimatize to her new habitat use.
The males do not have to spend as much time in forest interior and, during summer, they often forage out in the open alongside young females who have not given birth but also probably alongside roe deer moms who have briefly left their fawns to feed.
During spring, they accompany the females rather closely as if ensuring that the female chooses to stay on his range not because she has no other choice (due to the philopatric nature of roe deer) but because she is pampered, protected and overall taken good care of.
When it became cold, the males probably could not accompany the females because the females needed as much forage as could be mustered in the warmer forest (which is not yet the most abundant foraging habitat during this month).
But they seemed to keep them company through their own loud trotting and barking (diverting predators’ attention from the females, as well?) despite such behaviour not being in their best interests.
Of course, there is another explanation, i.e., due to the cold weather other males, as well, might be seeking top quality forage which perhaps grows on neighbouring ranges.
But most ranges are quite equal in their share of resources and I do not suppose that the allure to trespass for foraging purposes was strong.
In fact, I began to suspect that males slightly intruded or approached other males’ range to perhaps entice the territorial behaviour in their neighbours so that these males could keep up with the barking and trotting despite the challenged involved.
Personally, I think that the springtime territorial behaviour might have evolved as competitive at some point during roe deer evolution but it sort of no longer serves this purpose and it has become focused toward nurturing the female’s needs.
However, as the old behaviour is strongly ingrained, males have to assist one another in revoking the necessary hormonal reaction although these ‘provocations’ might not be truly antagonistic but aimed at helping the neighbouring male to ‘keep his morale’ (to induce the physiological responses that are evolved for one purpose to serve their new psychological purpose).
Of course, biologists would probably laugh me off the face of the earth over these claims 🙂
Altogether, it appears that males spend quite a lot of time with their respective females (on their range) during spring and then their ways part close to parturition when they meet in some shared foraging patches but when the female-mother keeps to her own.
Notes by Ieva 