Recently I made an observation which left me rather curious and which also made me recall other observations I had made previously (but which I had not considered from the perspective I am about to attempt to describe below).
Near my town, there are abundant riparian woodlands and crop-fields as well as forest patches.
Accordingly, we have plenty of roe and red deer, as well.
I have frequently observed them feeding in the woods or on the field.
I was aware that European roe deer (Capreolus capreolus) were mainly browsers and that crops (graminoids) were not their primary forage if other resources were available because their digestive system is less adapted to processing grasses (such as wild graminoids or cereals) (Minder, I., 2015).
In fact, where woody plants are forbs are sufficiently available (e.g., in riparian woodlands), European roe deer tend to forage on these resources even if cereals are within their home range and easily accessible (Barančeková, M., 2004).
It would appear that the European roe deer feed on agricultural fields mostly when more appropriate resources (woody plants, brambles, forbs) are scarce or difficult to access (e.g., under snow) seasonally or spatially.
I have also learned that red deer (Cervus elaphus) are intermediate feeders (they are better adapted to grazing than the European roe deer but they also browse).
However, forbs are probably preferred over graminoids when accessible.
For both species, however, as stated before, cultivated crops and fodder might be important – especially during seasons when other forage is unavailable (winter, early spring).
Also, they might find it harder to differentiate between fodder crops and semiwild / wild meadow vegetation communities.
My observations concern the feeding behaviour of these two species on agricultural fields during late spring / summertime / autumn.
Early on, when I noticed them feeding on cropfields, I did not distinguish between the area fed on (e.g., edge, middle of the field, along tractor tracks etc.) and I also assumed that they were grazing on the crops grown there although cereals were not the only plant species growing on the field (while they predominate, the monoculture rows are interspersed with wild or naturalized species – Chamomilla recutita, Chenopodium spp., Cirsium spp., Convolvulus arvensis, Galium spp., Raphanus raphanistrum, Papaver spp., Stellaria spp., Taraxacum spp., Urtica spp. etc.).
Later I began paying closer attention and I noticed that:
- Roe deer frequently foraged not in the centre of the field but on the edges (along the forest or the road or verges) or in spots where the cultivated crop had been outcompeted, for example, due to damage by wind or water.
- In places where I could access the feeding patches without damaging crops, the crop stalks sometimes were not foraged at all on but rather both species of deer had been feeding on the ‘weeds’ (wild or naturalized forbs and grasses self-sown between the rows of the crops) between the crop lines or along tracks.
Many times I have observed roe deer who have turned their very backs at the crop-field foraging eagerly on field margins (wild forbs).
Generally, the roe deer are constantly sticking to wood edges, roadsides, fence-sides and field margins where these are available and where they offer cover or easy escape routes (because often field margins are adjacent to open roads and therefore the roe deer are not as comfortable feeding there, at least not during heavier traffic hours).
I have observed red deer foraging on woodland edge rather than on rather tall-grown cereals, as well.
This has made me wonder whether sometimes farmers and other people who observe these (and other) deer species feeding ‘on crop fields’ do not mistakenly believe that the deer are always consuming crops exclusively while, in truth, they might be foraging on edges or along tracks and their herbivory might be directed at the agricultural weeds rather than the cultivars.
It might be interesting and informative to analyze proportions of crops to wild weeds foraged by different deer species while feeding ‘on a field’ (including edges) as well as the spots that the deer frequent (e.g., weather-damaged, stunded crop areas vs. full-grown cereal monostands etc.).
Perhaps during late spring, summer and early autumn these deer rather act as ‘gardeners’ weeding out some of the unwanted wild forbs.
But because the deer seem to be feeding on the location where cereals have been sown and the forbs sometimes tend to be shorter than cereals, it appears visually that they are consuming cultivated plants.
Deer are sometimes disliked by farmers but the reputation may not be justified.
I believe that forbs are frequently preferred by deer (especially, roe deer) to graminoids and therefore, on cereal fields, they might hold a higher nutritional value than the cultivated crops.
The deer might even contribute to reducing the weed cover or reducing the growth rates in weed species (if herbivory, for example, reduces seed production or plant height (which affects seed dispersal) in these wild plants).
***
On 12th July I had a chance to observe two roe deer (a buck and a doe) feeding in an area where a wheat field is adjacent to a small grassland.
Currently, both wheat and grasses/forbs are of about the same height.
I observed the deer for ca. 15 minutes and they foraged exclusively on the grassland.
There were no obstacles to accessing the wheat field, nor any substantial differences in the shelter/vigilance factors on the two plots.
I find that this testifies to the roe deer’s preference for non-graminoids (wild forbs over cultivated cereals) although I did not have the opportunity to inspect which plants they had taken on the grassland.
References
Barančeková, Miroslava. (2004). The roe deer diet: Is floodplain forest optimal habitat?. Folia Zoologica. 53.
Minder, Isabelle. (2015). Adaptive parameters of the diet of roe deer in a coastal Mediterranean area. 10.13140/RG.2.1.2477.2320.
Notes by Ieva 