Second European Roe Deer Meeting in Brixen, Italy, October 1994.

Individual variation in Food Intake among

Danish Roe Deer (Capreolus capreolus).

Introduction

Roe deer food selection was examined in 7 different Danish biotopes from analyses of the contents of 1745 rumens. In general roe deer fed on a wide variety of plant species. Food choice varied considerably throughout the year and some plant species vary seasonally in importance. (Petersen & Strandgaard 1992).

There was considerable variation in rumen content between deer examined at the same time in the same biotope, indicating individuality in roe deer food selection. The present paper presents preliminary results from two Danish locations: Kalø and Borris.

Kalø is situated in Eastern Jutland on a moraine formation and comprises chiefly fertile clay soil. The landscape is a mosaic of woodlands, hedges and farmland. The forest is chiefly beech (Fagus silvatica)(50%), other deciduous trees (20%) and conifers (30%). The farmland is cultivated with wheat, barley, rape, beets and seed grass. The area has a roe deer population of about 200 deer.

Borris is a western Jutland moorland and plantation area. The soil is chiefly sandy and the landscape is a mixture of conifer plantations, willow scrub, heather moor and grassy plains. The area has a roe deer population of about 1000 deer.

Material and methods

During the period 1972 to 1978, the contents of 1104 rumens from deer derived from Borris and 146 from Kalø were examined. Data were gathered on the plant species present and of the amount of each species present in each rumen. In the analysis, we have differentiated between plants present in the diet and those of greater abundance. As far as possible, the composition of plant species are determined by 5% volume intervals.

Results

Borris

99 different plant species were found in the rumen content of Borris deer, comprising 4 plant groups ie: heather, herbs, grasses and trees. On an annual basis heather comprised 45%, herbs 16%, grasses 19% and trees 11% of the total amount of food by volume. Other food items (9%) were mainly farm crops (barley). Heather (Calluna vulgaris) is taken all year round and is the most important dietary item throughout, except in summer. (Petersen & Strandgaard 1992). It occurred in 65% of the rumens investigated, although not all deer utilised heather to the same degree. Of 377 deer analyzed during winter months (Nov.-Feb.) 56 (15%) had taken heather only ( 95% of the rumen content), 305 (81%) had taken heather together with other food items and 16 (4%) had not taken heather at all. From the summer months (May-July) 1/3 of the rumens contained heather and one single deer had taken heather only. Table 1 shows the proportion of the deer which had taken heather and those which had 50% and 95% heather in the rumen content broken down by month.

Graminids (Table 2) were found in all months and 75% of the analyzed rumens contained grass. Grasses are taken during May to July in quantities that would be of importance for overall nutrition. However, relatively few deer had eaten large quantities of grass. Only 96 (9%) of the rumen contained 50% grasses and only 9 deer (1%) had taken nothing else but grass. In 275 ( 25%) of the deer, no grass was found.

Herbs (Table 3) represented by 55 different species were found in 568 (51%) of the rumens investigated. Herbs were present all year round but only in larger quantities during May-July. In May to September, 2/3 of the deer had taken herbs but mainly in smaller amounts. Only 54 (5%) of the 1104 rumens examined contained 50% herbs and only two deer had fed exclusively upon herbs. The 54 deer with 50% herbs by volume in the rumen had taken a great variety of species, but only a few in larger amounts. Yarrow (Achillea millefolium) and sorrel (Rumex acetosa/acetosella) were the species most often found and in largest quantities. Single individuals had eaten large amounts of some species otherwise only found as fragments in other deer, for example, one rumen contained 90% penny cress (Thlaspi arvense). Other herbs, which mostly occurred sporadically but which comprised more than half of the rumen content in some animals, included clover (Trifolium sp.), corn spurrey (Spergula arvensis) and buttercup (Ranunculus sp.).

Tree species (Table 4) occurred in 432 (39%) of the rumens and throughout the year. Few deer took tree material in great amounts and only 74 (7%) of rumens contained 50% by volume. Deciduous and conifer tree species were taken in winter months, particularly bog myrtle (Myrica gale) but also birch (Betula sp.), pine (Pinus sp.), fir (Abies sp.) and norway spruce (Picea abies). Out of 21 rumens examined from May, 6 contained Picea, 6 willow (Salix sp.), 2 rowan (Sorbus aucuparia), 2 broom (Sarothamnus scoparius), 1 elder (Sambucus nigra) and 1 a mixture of different deciduous trees. In the autumn, bog myrtle commonly occurred. Only 12 deer (1%) had taken nothing but trees. From the 8 samples from summer months, broom (3), Picea (2) and willow, poplar (Populus sp.) and rowan were each taken once, whereas 4 from the autumn all contained bog myrtle only.

Kalø

51 different plant species were found in the rumen content of Kalø deer, comprising 4 plant groups ie: herbs, grasses, trees and agricultural crops made up the bulk of the dietary intake. On an annual basis anemone (Anemone nemorosa) represented 21%, other herbs 25%, grasses 2% trees 34% and crops 18% of the total consume. Anemone (Table 5) occurred in nine months, but was only important in late winter and spring. On an annual basis 31% of the deer had taken this species but only 16% of the rumen contained 50% and only 13 deer (9%) had eaten only anemone.

Other herbs were found throughout most of the year, but only in midsummer did they play an important part in the diet and few deer had taken herbs only (Table 6). Herbs taken by Kalø deer were mainly wood sorrel (Oxalis acetosella) and sweet woodruff (Galium odoratum). Graminids (Table 7) were sparsely represented in the rumens from Kalø, but were taken almost all year round, mainly as fragments since most rumens contained less than 5% by volume. One deer taken in March had exclusively eaten grass. In early spring, grass is of particular importance for the roe deer at Kalø. Observations have shown that it is mainly amongst tussock grass that the first green sprouts are to be found.

Trees (Table 8) were found all year round, but only in the winter months did they form the basis of the diet of Kalø roe deer. 2/3 of the studied rumen contents tree species. 1/3 had 50% and 13% had eaten species of trees only. In winter the diet was dominated by conifers whereas one deer in May had only Beech leaves in the rumen and one deer shot in August had eaten only twigs from different deciduous trees.

In addition to the food items mentioned above, deer had taken farm crops in both study areas.

Discussion

Overall, the investigation of the rumen contents showed that roe deer had eaten most of the plant species present in the biotope, and that they responded to patterns of food availability during the year. But this does not mean that all available plants are equally attractive or that all deer seek the same food items at the same time. Furthermore, examples from both Borris and Kalø show that some of the most numerous and widely distributed plant species may never be utilised. Although bog heather (Erica tetralix) and crowberry (Empetrum nigrum) both grow all over the Borris area they are found only in restricted amounts in the diet. Crowberry was found in 83 samples out of 1104, mostly as fragments. Only 20 rumens contained 5% crowberry. Bog heather was found in 41 samples but only in 7 in amounts of 5%. Despite this, one deer had eaten nothing but this species.

Dogs mercury (Mercurialis perennis) is widely distributed at Kalø but was found in one sample only where it amounted to 55% of the rumen content. Lesser celandine (Ficaria verna) is found in two deer only as fragments although it grows all over the forested area. The situation with clover species is also interesting, since these are common in both areas and are generally supposed to be valued food item. However, clover occurred in only 43 out of 1250 samples and amounting to only 0.3% of the total food intake at Borris and only 2.4% at Kalø. Despite this, two deer from Kalø in July and August had only clover in the rumen.

Individual variation in choice of food is more pronounced amongst Kalø deer than Borris deer. For the four main food items (Tables 1-4) 10% of the deer from Borris had taken one food item only whereas 23% of the deer from Kalø had taken only one (Tables 5-8).

Why some deer predominantly select certain food items can not be explained from the information available. The fact that this characteristic is more pronounced amongst deer from Kalø could suggest that it reflects the deer biotope. For example, the utilization of trees in the two areas show interesting differences.

Although deer have greater access to conifers at Borris, few deer took substantial amounts of these dietary items, except during early summer, when young shoots of norway spruce were taken. This was not the case at Kalø where deer took conifers in large amounts during winter, perhaps reflecting the absence of heather at this site. Heather was widely distributed at Borris where the deer have access to this plant species all year round. At Kalø, anemone seems to replace heather to some degree as the most important single food item. However, anemone is not available as forage all year round as heather is at Borris. Even though it is common and widespread, grazing can be highly restricted. The influence of deer foraging can be directly observed, since in some areas, plants can be seen to have been eaten almost completely. Furthermore anemone seems to be nutritionally relatively poor (Strandgaard unpubl.).

That roe deer utilize trees to a higher degree during the winter at Kalø may reflect the poorer range of winter feeding opportunity at Kalø compared to Borris. However, this can only partly explain the phenomenon, since some Borris deer never take heather at all in winter. Correspondingly at the same time of the year there are deer from Kalø that have eaten anemone only and others which have not taken anemone at all.

One problem associated with the determination of diet based upon rumen contents from killed deer is that it only detects plant species taken shortly before the death of the animal. It is not possible to tell whether a deer containing only one food item in the rumen would, the next day, have eaten something else, or whether a deer having not taken an available plant species would have utilised this species after the sampling period.

What the material presented here does show clearly is that there is considerable variation in diet between individuals and this confirms the necessity for larger samples in order to give a representative picture of roe deer utilization of the food resources in a given biotope.

References

Petersen, M. R. & H. Strandgaard (1992): Roe deer's food selection in two different Danish roe deer biotopes. CIC-symposium "Capreolus" in Salzburg.

Table 1: Borris - Calluna vulgaris

Table 2: Borris - Graminids

Table 3: Borris - Herbs

Table 4: Borris - Trees

Table 5: Kalø - Anemone nemorosa

Table 6: Kalø - other herbs

Table 7: Kalø - Graminids

Table 8: Kalø - Trees