During the lower-temperature, snow-cover weeks in November (ca. -5°C; snow depth ca. 10 cm), I observed roe deer tracks along our river.
They appeared to travel along the shore rather than foraging in the more open areas (hayfields) away from the river that had been harvested rather late in autumn and where there was no availability of shrub browse, either.
The riparian area consists of tall reeds, tall forbs (e.g., stinging nettles) but also some willows and a narrow band of riparian trees.
I noticed two things that drew my attention because they were more difficult to explain.
It seemed that the roe deer were drawn to beaver foraging trails (both the end of the trail where the beavers had browsed on young willows or larger trees and the upper end of the part of the trail where the beaver has ascended up the rather steep river bank before continuing toward the riparian grove) and general spots that are somewhat ‘precipitous’, i.e., that are located on the edge of a high river bank overlooking the river.
With respect of the high river bank (as well as some of the spots where beavers had struggled up the steep bank), I presume the roe deer might have been looking for potential snowslides.
Perhaps snow is less deep in these places where it is more difficult for the snow to accumulate and where it might slide down into the river more easily.
Therefore, these spots might offer some readily available forage that does not have to be scraped out of the snow.
It was impossible for the deer to drink or to cross the river in those spots and as the river was wide and the current was strong during this period, I do not suppose that deer were using these locations as lookouts for vigilance because it made more sense to keep vigilant of what lay on the other side (in the riparian grove).
The other observation was that of the roe deer seemingly approaching sites where beaver had been foraging on the dry land.
There was a rather consistent tendency for the roe deer to deviate from a linear path and to inspect beaver trails on land (and, as mentioned before, the spots where beavers had climbed up the slope to continue with their overland foraging expedition and which were also spots where beavers had sometimes left behind the materials they had been dragging or where beavers had even stopped to forage close to the water).
I believe that roe deer might make use of beaver after-foraging effects.
For example, beavers do not tend to strip bark from beneath the gnawing point.
Perhaps roe deer are pulling strips of bark from these tiny stumps because beavers have made them more readily accessible to the deer (the deer can seize the small pieces of bark and sapwood sticking up from the stump and bite them off or tear them off while they would not be able to bite off the entire stem, nor to tear off bark so close to the ground).
Also, beavers sometimes abandon branches they have collected near the river shore (in the central foraging spots), and roe deer might additionally gnaw on these materials which they might not be able to access otherwise.
Perhaps the chemical composition is also altered in plants already affected and killed by beavers vs. plants that roe deer affect and/or kill themselves (if the plant has died, it might have stopped producing chemical defenses).
I wonder if beavers somehow facilitate winter foraging for roe deer (possibly, also foraging during other seasons in this browsing species but during other seasons it is not as easy to observe deer tracks and to consider their movement patterns with relation to, e.g., beaver trails) which might be the reason why roe deer tended to ‘check out’ beaver foraging sites and other sectors on beaver trails.
I suspect there might be some type of relationship between beavers and roe deer because I believe that I have heard beavers slapping tails as roe deer are passing (crossing river or walking along the riverbank).
Perhaps the beavers were simply spooked (without having determined the species of the individual that spooked them) but I have witnessed this on three separate occasions and there might be some interference between roe deer and beavers.
Of course, it is also possible that the roe deer were not selectively walking to inspect the beaver foraging patches at all but that the layout of the tracks by the deer simply coincide with the tracks of the beavers because these two species forage on the same resources in winter.
Thus, both their tracks led to willow suckers and larger saplings/trees not because the roe deer followed beavers but because roe deer seek out the same forage as beavers do and, accordingly. they ended up in the same foraging spots.
Unfortunately, I did not have time to make comparisons on whether roe deer also deviate from linear path to approach some resources that were similar to beaver foraging patches at the same rate as they approached beaver foraging patches.
My subjective impression is that there were not that many foraging patches of these browse types available.
Thus, it is possible that beavers and roe deer visited them all.
On the other hand, in many such spots, beavers had taken all of the saplings resulting in small ‘stumps’ of stems less than 5 cm above ground (often cropped much closer to the ground) and still, roe deer had visited these patches.
It is possible that beavers also remove snow from around these foraging spots making the surrounding forbs more accessible, and that the deer do not approach to see if they can, too, get some last bites out of the beaver-foraged suckers but rather to utilize the spot that has lower snow depth and where the vegetation is revealed to them (does not have to be scraped out from beneath the snow).
This would constitute facilitation, as well.
Notes by Ieva 