As I have been observing roe deer during winter, several questions have been raised in my mind concerning the group formation (including group stability and structure) and winter territoriality between groups.
It is thought that winter territoriality perhaps does not really exist in roe deer but I there must be some degree of exclusion due to the specifics of herding behaviour, philopatry and the necessity by roe deer adult males not to lose their range prior to spring when they would re-establish strict boundaries.
Accordingly, I would like to understand whether roe deer form flexible winter groups or fixed groups.
By flexible groups I would imply a system where the individuals remain in their home range (which they do not defend) and they can group up with other individuals who spend their summers in nearby ranges.
Within such system, on some days (in some locations), the individual would be found with some other individuals (forming a temporary group) but, on other days (in other locations), the individual would group up with other individuals.
For example, if the individual decided to forage in the northern part of its former summer range, they might form a herd with the individuals who usually live there.
Then this individual might separate from the aforementioned individuals and group up with other roe deer when it forages, for example, in the southern parts of its range.
Such strategy would imply that the functions of grouping (anti-predator defense, information exchange regarding resource availability etc.) are highly important and can override social attachments.
On the other hand, fixed grouping would be observed if individuals herded on basis of their social relationships and if they still sort of maintained a territory (or at least its core) against neighbouring groups.
I would assume if it were the case, such groups would be formed on basis of female-fawn associations combined with female inter-relatedness as well as the male’s location.
I suppose fawns might remain near their mothers and females might associate more closely with their mothers, sisters, aunts etc.
Meanwhile, as males would not wish to give up the range they would be thereafter defending as territory, they might remain more stationary and attached to their core area, less willing to allow other males on their range or to roam out of their range onto that of other males.
This type of winter grouping might be based on kin and social dominance rather than solely on the functions of grouping behaviour.
The system might also imply the greater readiness among individuals to defend and to protect other individuals as well as to share resources with them because they are offspring, relatives or past/future breeding partners.
I would imagine that females might apply both strategies (fixed and flexible) while males might be overall limited to the fixed strategy.
I would also imagine that the application would differ based on location and that the fixed strategy would be observed in core areas as well as the most profitable foraging patches while the flexible strategy would be observed in the marginal areas of the range as well as suboptimal foraging patches.
However, this would suggest an element of territoriality which is not founded upon defense of an entire range but which is founded upon social/kin structure and unwillingness to share core areas (exclusion from core foraging patches).
There might also be differences between landscapes.
For example, I have observed larger groups of roe deer in open, homogeneous landscapes vs. mosaic-type, patchy landscapes and these larger groups might be comprised of a greater number of individuals who do not perhaps associate on daily basis and whose associations are not based on kin and mating relationships.
I will write down some of my actual observations that might contribute to understanding how these winter herds are formed and how cohesive they actually are.
Firstly, sometimes I have observed herds of, e.g., 5 – 8 animals that, upon disturbance, scatter and run into different directions.
At other times (but perhaps, more importantly, in other places) I have seen larger groups (e.g., 10 individuals) who, upon disturbance, all run in the same direction (the way red deer mostly would).
I have also observed situations where there is a larger group of animals but, upon disturbance, it splits in two groups and each takes its own course.
I think that these are three different circumstances.
The first type of observation concerns a patchier landscape where there are several foraging patches but some of them are larger than others (and this is where the grouping occurs) while the shelter/resting sites are also scattered in all directions.
It seems to me that in such landscapes, the individuals are familiar with one another and they might meet one another during the summer season, as well.
When they group together on a larger foraging patch (e.g., an arable field), they are moderately cohesive because they are no strangers to one another.
However, when the time comes to seek cover, they split into groups that might be based on their summer social formations (e.g., mothers with offspring, related females and their offspring) and each such group takes the direction toward a shelter that they might have been using separately during summer and that might still be used more or less exclusively by each subunit.
This makes me wonder whether shelter is perceived differently than foraging patches when it comes to winter herding behaviour and resource protection.
For example, in one specific occasion, a herd of about 8 animals split in three groups.
One group ran toward one patch of riparian forest on the other side of a decorative conifer plantation.
Another group ran across the field toward a small forest (partly riparian but many metres upstream from the patch selected by the first group).
The third group took flight up and across the railway where there are yet other shelter-type habitats.
I decided that this was where these groups had originally come from and they have gathered on the larger field to forage and while doing so, they acted rather cohesively (they were not further than a few metres from one another) but, upon perceived threat, they departed toward their core area and its shelter.
On the other hand, in a mosaic-type, patchy landscape I have also observed larger groups of roe deer travelling together along features that would be defined as shelter rather than foraging areas.
This group seemed consolidated and they might have used foraging sites as well as shelter commonly.
They also appeared to be led by a male (he was the first in the line and he barked at me when we stumbled upon them).
This group lived in a landscape that was perhaps patchy but the patches were also small and, in fact, there were no large foraging areas.
This group could be defined as ‘forest roe deer’ compared to the first type of situation where the roe deer were ‘agricultural’.
Perhaps in areas where forest predominates and foraging patches are small and scattered, roe deer form more or less permanent herds that do not split into subunits and that often travel together without reverting to a more divided use of ranges.
However, interestingly, in this area I rarely observe grouping behaviour in the first place and most of the times roe deer there wander around alone, in pairs or in very small groups.
The ‘permanent grouping’ behaviour that I observed befell in a comparatively long and cold winter which was more similar to the winters I experienced in the early 1990-ies as a child.
Accordingly, I would venture to guess that the roe deer grouped up in response to cold conditions (perhaps in order to form trails and to use them commonly or in order to use the scarce resources over the entire range of the group).
It might be important to note that the winter when the roe deer appeared to travel in group was cold in a ‘thorough manner’, i.e., the temperatures did not fluctuate and there was little freeze-thaw cycling.
Rather, it was cold all the time – all through the winter season.
Returning to the observation regarding a group of ca. 10 roe deer running off as a group in one direction, this observation was made in an open, homogeneous landscape.
Groups seem to be larger there and more frequently formed in the first place.
Secondly, shelter is usually found only on one side of the large field where the roe deer gather.
Accordingly, there is not much choice where to run.
The best option is to take shelter in the nearby forest and the nearby forest is located only on one side of the field.
Consequently, all the roe deer run toward that shelter.
The third observation concerns a circumstance where I believe that two roe deer groups had met and that these groups were foraging on the same field but they did not forage cohesively.
One of these groups was foraging on the right side of the field (which was also less optimal because it was closer to the highway and the riparian forest was scarcer there – it was a more exposed area with higher risk of disturbance) while the other was foraging on the left side of the field (plenty of shelter all around, further from the highway).
When disturbed, these groups each took another direction and one of them crossed the highway while the other retreated deeper into the riparian forest/private country estate habitat.
I would not call these groups subunits because I do not believe they had ever united in their efforts to keep vigilance etc.
I believe those were two separate groups one of which was ‘local’ (they lived on the respective side of the highway and used the riparian habitat on daily basis) while the other had crossed from the other side of the highway where there are large fields and sparse riparian forest.
The latter group might have been struggling to obtain resources and they might have arrived to forage on the margin of the range used by the former (‘local’) group where they were tolerated but not integrated into the group and where they fed in the less optimal area taking shelter toward their original range despite the implicit danger of crossing the highway.
Thus, I would say that the roe deer winter organization is very complex and it might involve an element of range exclusion.
There are two aspects to this that I have yet to figure out:
- Do roe deer act inhospitably toward individuals who roam into their core areas? For example, if a roe deer individual has to take flight, do they feel equally secure to take flight into the most profitable direction or do they have to take account of who lives there? I have sometimes seen roe deer taking flight into directions which are not highly logical (they are not running toward the closest shelter or they are crossing dangerous features such as roads, or they are taking the long course which exposes them to danger rather than taking the short course and vanishing off into some woodland). Perhaps roe deer are aware that they are not welcome everywhere despite there being no exclusive territoriality during winter. Maybe they prefer to take shelter in known areas rather than intruding into ranges of other roe deer.
- Would several adult roe deer males group up in winter? I believe I have observed groups where more than one adult roe deer male is a part of the winter group but I am not certain what type of situation it has been. For example, would two males join a relatively cohesive group that perhaps also travels together or exchanges other favours or would they at times tolerate one another as part of different subunits while feeding in large foraging patches or suboptimal, marginal patches?
I believe that these observations lead to two additional conclusions:
- Roe deer might be more defensive regarding (more reluctant to accept strangers into) their shelter habitats (including fawn birthing and early fawn hiding habitats) compared to foraging habitats;
- Roe deer might be more tolerant of other roe deer under conditions of food scarcity which is interesting because it indicates at certain ethics among the deer, i.e., if neighbours are suffering poorer conditions (which is the case of the roe deer crossing the highway because on their side of the highway there is hardly any forage during winter), they are tolerated on the focal group’s foraging patches and also during harsher winters, roe deer might travel together in order to utilize all foraging patches including those that befall within the typical sheltering areas and which are not vast, open agricultural fields.
Notes by Ieva 