Sometimes I enjoy tracking the prints left by the paws and the hooves etc. of the varied riparian dwellers and visitors.
After in snowfall which occurred perhaps in November, 2023, I noticed roe deer (it appeared there were two adults and a fawn) frequenting the band of emergent and riparian tall forbs (reeds but also Himlayan balsams and stinging nettles etc.) as well as some beaver-browsed willows between the line of water and the narrow strip of riparian ‘forest’ (the forest itself has been cleared to make space for haymeadows that come as close as 20 m – 0 m from the riverbank).
The roe deer had been trailing there also in summer as I had found their hoofprints in the mud including the prints of a very young fawn.
During summer, they cross the river, as well, although during winter I have only observe crossing when the river was entirely frozen over.
It would seem that the roe deer attempt to avoid cold water (a behaviour which I will touch upon later in this post).
During autumn, they tread in a meandering line at times approaching vegetation patches further from the shore and at times walking down almost to the very water (although they did not appear to be drinking there).
Then the weather changed and there were periods of thaw when the riparian area was greatly flooded and chunks of ice were thrown onto the shore making the terrain rugged or very wet.
These periods were exchanged for freezing temperatures (ca. – 10°C) when the pools of water froze over (even I could walk over them) and the chunks of ice were, once more, incorporated into the contiguous ice cover making them less treacherous.
During this period, the riparian area was not visited by the roe deer and even the beavers seemed to choose the banks that were on the other side where they are high and extend into what might be comparatively described as a forest (a riparian tree and shrub strip wider than 20 m).
The roe deer altogether seemed to have ‘moved out’ from the part of their range on these riparian narrow forests limited by hay meadows and they were observed further up the slope where the forest band was wider (at least 50 metres) or in the uphill private garden patches.
Meanwhile, roe deer kept closer to the river on the far side of the river meander where the riparian forest has not been cleared and where it covers the entire slope stretching down to the very water (with 1 – 2 m wetland gap) in most places.
The thaw and freeze ‘cycles’ (they were not truly cyclical in the sense of a rhythmical sequence but they replaced one another) were rather short mainly.
Then there was a longer spell of about 1 – 1.5 weeks of low temperatures (ca. – 10°C) which I have mentioned above.
During this time, I observed the roe deer crossing the river on the ice but did not return to the riparian area itself only passed through it to access the river.
In the beginning of February, there was a longer period of warm weather (ca. +5°C) and most of the ice and snow was gone although in shadowy spots slush and some compressed ice cover from the former thaw-freeze cycles remained.
During thaw, it was not very possible to determine the presence of the roe deer by the river because the riverside is not covered in mud (and the very shoreline mud was still mostly under the most massive chunks of ice washed out on the shore) and the underlying vegetation is rather dense.
However, the thaw was followed by a drop in temperatures once more (-6°C at first and then down to ca. -8°C).
This cold spell did not cause for the icebridge to form across the river but it was accompanied by heavy snowfall making it, once more, possible to track animals in the river area.
In the period between the change in weathers (from mild to freezing) the roe deer were again observed in the riparian strip between the narrow riparian forest and the waterline.
Then as the snow accumulated and the temperatures remained freezing, they did not return.
In conclusion, it appeared that the roe deer used the riparian area (which was poorly sheltered by any trees and which was surrounded by an open hayfield) quite often in autumn while the snow cover was relatively thin and the temperatures were still mild – around or minimally below zero.
Then as the temperatures dropped, the roe deer migrated to the more densely forested area.
They might have returned during the thaws but I find it unlikely because right after some snow fell once more, the flooded riparian area bore no roe deer tracks.
During the longer period of freezing temperatures the roe deer arrived to cross the river that had frozen over.
Once the ice had broken, the roe deer disappeared.
After a longer period of mild weather (above zero), the roe deer might have returned already (it is difficult to say) but it is clear that they were (still) there when the temperatures dropped suddenly and ice covered the flooded pools.
Then as the temperature stayed low, the roe deer disappeared.
I have tried to explain this behavioural pattern and I have come up with the following assumptions:
1
Roe deer might be cold intolerant.
Unlike the reed deer which actually swam/waded across the river under freezing temperatures, the roe deer only crossed the river once it had entirely frozen over.
Roe deer are smaller than red deer and perhaps they are less energy efficient due to greater surface to volume ratio as noted in other species whereby many larger species seem to be better adapted to cold (Bergmann’s rule).
Roe deer might have limited their use of this particular riparian area after fall because:
- It was frequently flooded over and their hooves could break through the thin ice because the periods of freezing after the periods of thaw were too short to cause formation of thick ice. The roe deer might have wished to avoid getting their feet wet.
- The riparian area is not well insulated by the forest which has been cleared to a narrow strip and which is bordered by an open hayfield. In this area, the air is often very moist and it feels colder than it does in other, better sheltered areas. The roe deer kept using areas close to the river where these areas were covered in forest. The roe deer altogether were observed more frequently under tree cover.
2
The riparian area had a moderate snow depth which was perhaps slightly greater then under tree cover (where the roe deer had migrated to) but the hayfields were covered in extremely deep snow and it was difficult to plow through it.
The roe deer used the open habitats of the private gardens which were uphill but there they could travel along the roads and paths as well as some orchards and small tree groves.
Additionally, the garden area is sheltered from all sides by riparian trees that are the main travel routes for the roe deer and along these routes they can essentially circle almost the entire garden area.
Due to the presence of the tall trees on all sides as well as smaller trees in the orchards, the microclimate is probably more favourable and the roe deer can afford expending some energy in plowing through the snowier patches.
3
The frequent formation of ice and the subsequent breakage of it and redispersal of ice chunks caused much of the vegetation to be covered beneath the ice while other vegetation was submerged during the thaws and remained thus also after the short cold spells.
Vegetation might have not been accessible in this riparian strip.
However, I do not believe that the accessibility was the only issue.
The study by Jones, K. et al. (2009) in which the use of willows previously cut by the beavers was analyzed (as a ‘side topic’ in order to assess the impact of additional herbivores on the regeneration of riparian vegetation browsed by beavers), it was found that roe deer avoided browsing on flooded willow stands that were growing in the shallow parts of lakeshore while the roe deer browsed on willows in the drier riparian area (the roe deer density was supposed to be similar in both areas).
The willows were not growing in very deep water and they were probably accessible to the roe deer but the roe deer apparently did not prefer to browse while standing in water.
The presence of water (either the specific body of water or the flooded wetland area) might be a strong determinant for roe deer foraging choices with regard to habitat use.
4
While the roe deer behaviour can be explained as that of seeking more favourable microclimate, avoiding wet areas, avoiding deep snow and being unable to access vegetation under ice and water, I also felt that there was something about the qualities of the plants themselves that stimulated these changes in behaviour.
There are many willows growing along the river in the more open spaces.
There must have been periods when it was difficult for the roe deer to find forage because both during warmer and colder spells (apart from the prolonged warm spell), the snow cover remained rather deep.
Many fields and also garden patches have been harvested and ploughed and they did not provide much of forbs cover.
When the roe deer crossed the river (without browsing on the riparian willows on this side), they, in fact, accessed some fields that had oilseed rape winter cover but that were very close to roads and other disturbances and I hardly imagine the roe deer would have crossed unless they were struggling to find food on this side.
Also, the riparian willows were growing in some spots where due to terrain, the shore was not as flooded and it was ‘passable’.
The willows were never flooded greatly (0 – 5 cm).
Still, the deer did not seek them out during the cold season apart from earlier in the autumn (until November when it became cold permanently) and apart from this week in February which followed a longer warm spell which felt rather springlike.
Thereby, I was wondering whether there might be some qualities to the vegetation itself (in this case, the willows) that are not attractive to the roe deer during cold weather (despite the fact that ungulates do browse on willows in winter).
As the roe deer seemed to return to the willows (forbs were hardly accessible even after the warm spell below the flood pools and remnants of shoreline ice) after the long warm spell and as they had been using the willows during autumn while the temperatures had not dropped significantly yet, I wonder if roe deer avoided ‘frozen willows’.
There might be some changes in the plant chemistry that occur during cold weather and these riparian willows were subject to colder weather (due to microclimate) than other tree species deeper in the forest bands.
For example, during winter, ungulates often feed on conifers which are not the preferred forage (but which also grow in favoured microclimate sites where it is warmer and where snow cover is not as thick).
Perhaps another reason for this choice is that the conifers do not go entirely dormant during winter (unlike deciduous species).
The flow of sap and access to needles (leaf substitute) are probably important factors but roe deer are browsers that also consume twigs and younger shoots.
Perhaps as the weather grows cold, the sap freezes in the trees that cease any circulation while conifers with their evergreen photosynthesizing activity might also somehow keep the phloem and the xylem structurally different (warmer, not frozen).
If the plant (such as a very exposed riparian willow) ceases any sap activity, its phloem and xylem might be structurally different and more deeply frozen.
It might be more difficult for the roe deer to snap off any twig or to separate the bark from the underlying, far more nutritional layers.
Where the roe deer fray the trees, freeze-exposed deciduous trees might not ‘give up’ these underlying levels easily and only the outer bark might come off which is not what the roe deer is looking for.
Also, the trees might freeze from the outside.
With the air slightly damper by the river (which does not freeze over for most part), ice crust might form on the bark of the trees.
Additionally, the roe deer (who apparently is less cold tolerant than other ungulates) might detest the experience of eating ‘popsicles’ during the cold weather.
The roe deer is highly selective because its stomach is small and it has to picky about what it eats as it takes energy to digest the forage and at any given time the stomach can be filled with only so many items.
As the passage along the relatively shorter oesophagus is quicker, the frozen pieces end up soon in the stomach and the roe deer might experience cold from the inside as well as outside.
Therefore, the roe deer might turn to the riparian willows before they have grown fully dormant and before they have been subjected to freezing temperatures and they might return to this resource during or shortly after long and warm spells when the shoots might have thawed and when there might have been even some slight photosynthesizing activity in the bark.
As I mentioned before, I also observed that the beavers avoided these exposed riparian willows and foraged in the denser forest patches where they actually could not access highly preferred tree species and foraged on hazels.
I do not suppose that beavers mind the wetness and while they might prefer tree cover due to slower movements in snow and they might enjoy the forest microclimate during the cold weather, there might be also some aspect of chemical and structural changes in the riparian willows that are not favourable during the coldest months in highly exposed sites (if other options are available).
Altogether it is rather interesting that the roe deer in this area perhaps demonstrate a slightly migratory behaviour.
Also, I suspect that this emigration out of the riparian area (where during summer at least 4 adults are often observed and stay regularly; perhaps it is their core area) leads to a merging of two otherwise rather separated roe deer local subgroups that then commonly use the private garden patches but each travel on their side of the riparian forest slope.
References
Jones, K. et al. (2009). Willow (Salix spp.) and aspen (Populus tremula) regrowth after felling by the Eurasian beaver (Castor fiber): Implications for riparian woodland conservation in Scotland. Aquatic Conservation: Marine and Freshwater Ecosystems. 19. 75 – 87. 10.1002/aqc.981.
Notes by Ieva 