reproductive physiology in relation to deer management

Mammal Review Volume 4 Number 3 September 1974

Reproductive physiology in relation to deer management D. I. CHAPMAN Lurkmead, Barton Mills, Bury St. Edmunds, Suffolk.

CONTENTS Introduction Regulation of the numixr of d&

Age structure of the herd puberty

. Ovulation i d conct$tion r a k Variation of conception rate with Gestation period . Fecundity Foetal s u r v i h Sex ratio of foetuses'and fa& Application of the information

Time of year to cull Selection for breeding summary . References .

.

.

. 61 . 62 . 62

. 6 4

. 6 4 . 66 . 66 . 68 . 68 . 69 . 71 . 71 . 72 . 73 . 73

aee

ABSTRACT One of the more important aspects of deer msnagement is the regulation of the number of animals in the herd. It is the fertility and fecundity of the female, rather than the male, that affects the rate of increase and the number of female deer that affects the size of the population. The various parameters of reproductive physiology of female deer are discussed and the information available with regard to the species of deer occurring wild in Britain is reviewed and summarized.

The time of year to cull deer and the importance of the female as well as the male for selection for breeding are briefly discussed.

INTRODUCTION There are many aspects to deer management and several of these require a knowledge of the reproductive physiology of the animal, if they are to be performed in a logical manner and to achieve the desired results. For example, is it best to cull either male or female deer or both if we wish to maintain a certain level of population ? How many deer, if any, should be culled each year? How soon will an animal with desirable characteristics pass these on to the herd ? The aim of this paper is not to answer these specific questions, but to discuss the various parameters of deer reproduction that need to be considered when managing deer and to review what is known with regard to the species of deer which occur wild in Britain: exotic species of deer in zoos will not be considered. A knowledge of all parameters will not necessarily be required for each aspect of management; it depends upon what the deer are being managed for, venison ?, hunting?, amenity?, population control? and how it is desired to achieve these aims.

61

bL U. I . Chapman

REGULATION OF THE NUMBER OF DEER Perhaps ope of the most important aspects of deer management is the regulation of the number of animals. In Britain, this almost always means culling because natality usually outweighs mortality. Last year the Forestry Commission alone culled about 8600 deer in Britain in order to check the increase in the deer population. In a given deer population, whether it be in a deer park or in the wild, what we want to know is how the population is changing. Is it increasing or is it decreasing and by how much? Even if a deer herd is increasing in size and animals are having to be culled in order to keep the numbers constant, the potential increase of the herd may not have been realized. A change in management might cause a greater .increase, and consequently a greater cull with the production of greater revenue from the sale of meat or animals. Therefore, the potential increase of a herd as well as its actual change and the factors affecting them are also important.

In farming, it is sometimes said that 'the bull is half the herd' but with most, if not all, species of deer this statement is untrue. If the bull among a herd of cows is infertile then it does not matter how many cows there are, no calves will be born. In the species of deer that form herds such as Fallow (Duma damu), Red (Cervus eluphus) and Sika deer (Cervus nippon), there are always plenty of males to mate with the females and so it does not platter about the numbers of males present or if the occasional male is infertile. The only time male fertility may become important is in a small, enclosed herd in which there are only one or two male deer; a situation analagous to the bull and the cows. Male fertility can also be ignored in species such as the Roe deer (Cupreolus capreolus) where, although they tend to form small groups rather than herds, there are usually several males in the vicinity. A female deer not mated successfully with one male will stand a good chance of being mated by another male. Bramley (1970) has recorded about twenty-three male Roe deer in 360 acres and, despite popular belief, Roe deer are not monogamous. The sexual behaviour of wild Chinese muntjac deer (Muntiucus reevesi) and wild Chinese water deer (Hydropotes inermis) in Britain do not appear to have been recorded. Although Chinese muntjac deer apparently form family groups of adult male, adult female and two immature animals (Dansie, 1970; Dubost, 1970) it seems likely that there must be interaction amongst groups and the males are polygamous (Dubost, 1971). Therefore, for all practical purposes male fertility in deer can be ignored. It is the fertility and fecundity of the female that affects the rate of increase of the population and it is the number of female deer that affects the size of the population.

If a herd is to maintain itself, it is the proportion of female fawns that survive from birth until they themselves produce fawns that is relevant, not the proportion of female fawns born. The number of female fawns, which survive to the age at which they themselves produce fawns, produced by a female in her life time is termed the net reproduction rate. Therefore, the ability of a herd to maintain itself is based not only on its reproductive potential but also on mortality and, in wild herds, on movement in and out of the area: subjects which are the prerogatives of later contributors. However, mortality cannot be divorced entirely from reproductive potential although perhaps it should be regarded as survival rate.

The various parameters of reproduction in female deer will now be considered. Young deer will be referred to as fawns, regardless of the species.

Age structure of the herd The age of the deer in the herd, the proportions of the various ages and the construction of a life table for females is necessary before full use can be made of some of the other parameters. It is no use knowing that puberty occurs at a certain age if the proportions of deer above and below that age are unknown. If fecundity tends to decrease after a certain age, then the number of deer in the herd above that age needs to be known.

Methods of determining the age of mammals have been reviewed by Morris (1972). The degree with which the various age classes need to be identified will depend upon the species being studied. If, as occurs in Fallow deer in southern England, pregnancy occurs first when

Reproductive physiology in deer management 63

the deer are yearlings and there is no evidence of changes in fecundity with age, it is only necessary to distinguish two age groups-fawns and adults. With a seasonally breeding species such as Fallow deer, the young of the year often form a readily distinguishable group. If the fawns and adults are counted as soon after parturition as possible, the numbers of young can be compared with what was expected from the number of adults entering the previous breeding season, and an idea of the survival rate (or mortality) during pregnancy and parturition can be obtained. Mortality is often high during the first year (0-12 months) of life and hence if the fawns are counted as late in the year as possible, the approximate proportion of animals entering the breeding population can also be calculated.

With deer which breed throughout the year, e.g., Chinese muntjac, it is not possible to recognize distinct year classes in the field and it is necessary to rely on rather arbitrary groups based on size or some morphological feature. Chinese muntjac deer fawns, for example, loose their spotted baby coat at about 6 weeks of age (Chapman & Dansie, 1970). The various age categories which can be used and the methods of determining them have been reviewed by Bigalke (1968).

Life tables can be obtained by shooting either the entire population, a rather drastic measurs., or a representative sample or, indirectly, from the total mortality and determining the ages of the animals. The total mortality each year can be used to give an approximate reconstruction of the herd at a particular time or a population can be reconstructed when all the deer present at a given time have died. This last method entails a study period as long as the maximum life of the deer. Samples of deer taken by shooting have to be viewed with great caution if they are to be used to calculate the age structure of the herd. Bias can be introduced by the intentional or unintentional selection of identiliable age groups or the susceptibility of a particular class to be preferentially shot. Andersen (1953) found that male Roe deer were much more suscept- ible to being shot than the females and this was even more marked with the fawns. Male deer with different degrees of development of hard antler can be readily identified. Chinese water deer are exceptional in that the male does not carry antlers, but on the whole they have larger maxillary canines than the females. However, it is much more difficult to distinguish age groups of living female deer, apart from fawns, and the age structure of a large sample of this sex probably represents a reasonable picture of the age structure of the female deer in the herd.

Table 1 Age structure of ninety-one adult, female Fallow dcer and 144 adult, female Red deer culled in a park

in southern England

Fallow deer Red deer

w-) No. % No. % Age

1.5 2.5 3.5 4.5 5.5 6.5 7.5 +

Total

30 33 54 38 18 20 23 16 9 10 17 12 7 8 7 5

10 11 7 5 3 3 8 6

14 15 28 20 91 100 144 100

Life tables for male and female Red deer from various areas of Scotland have shown a high proportion of young deer with very few animals over 8 years of age (Mitchell, 1967). The age structure of a sample of 144 adult female Red deer and ninety-one adult, female Fallow deer culled from an enclosed population in southern England is given in Table 1 0. I. Chapman, unpublished observations). Fifty-nine percent of the female Roe deer, excluding fawns, shot at Kal0, Denmark in 1950 were less than 3 years old (Andersen, 1953). These figures emphasize a fact which is often not appreciated by people managing herds of deer, that the

64 D. I. Chapman

mean age of the deer in the herd is often very low. The mean age of the entire herd of Roe deer, which was shot at Kale in 1950, was 2.0 years, if the age of the fawns was assumed to be 6 months, and 78 % of the deer were 3 years old or younger.

The age at which puberty is attained affects markedly the rate of recruitment to the deer herd as Mitchell (1969) has calculated for Red deer (Table 2).

Puberty may be found by examining the uterus and ovaries from deer culled at various ages. Because puberty is attained relatively early in life in most species of deer, tooth development and wear generally provide a ready means of age determination. Alternatively, field observations of animals of known age will indicate the age at which parturition first occurs and a knowledge of the gestation period will enable the age of sexual maturity to be calculated. In Britain, all species of wild deer, with the exception of the Chinese muntjac, are seasonal breeders. Therefore, an examination of deer killed after the rut, which is the customary time to kill female deer, will indicate the proportions of the various age groups which have ovulated and conceived.

Table 2 Calculated maximum number of fawnsper 100 females in relation to ageat puberty

Puberty

Max. no. Age at puberty lint fawning fawns,l00 Age at

( Y e a d

4 months 1 100 1 year 4 months 2 73 2 years 4 months 3 60 3 years 4 months 4 51 4 years 4 months 5 45

Puberty is a characteristic of the species but it is affected greatly by environmental conditions. In Scotland, the majority of wild, female Red deer become sexually mature at just over 2 or 3 years of age (Table 4) and fawn for the first time at 3 or 4 years. On the Isle of Rhum, about 40 % of 2 year-olds and 85 % of 3 year-olds are sexually mature (Mitchell & Lowe, 1967). However, tame, captive, female Red deer on this island came into oestrus and conceived first as yearlings, probably because of the improved plane of nutrition (Guinness, Lincoln & Short, 1971). Similar results have been reported in Yugoslavia where about 30% of the yearlings may become pregnant (Valentincic, 1958) and in New ZeaIand where about 80 % of the yearlings breed and fawns have been found with mature Graffian follicles (Daniel, 1963). An examination of 241 female Red deer in a park in southern England indicated that none of the thirty-four fawns was pregnant, but that 88% of the sixty-seven yearlings and 97 % of the 140 adults were pregnant (D. 1. Chapman, unpublished observations). Correspond- ing values for wild Sika deer from southern England were fawns (22 % pregnant, n = 9), yearlings (85% pregnant, n = 20), and adults (95% pregnant, n = 95) (D. I. Chapman, M. T. Horwood & E. H. Masters, unpublished observations). Puberty in S i b deer therefore usually occurs at 16 months of age but a small proportion of fawns may attain puberty and become pregnant at 4-6 months of age (Chapman & Horwood, 1968).

Ovulations have been recorded from Roe deer fawns but further studies are required to confirm these observations (Chapman & Chapman, 1971). The age of puberty of female deer is summarized in Table 3.

Ovulation and conception rates There are many hazards which the egg or embryo has to survive during gestation and before it becomes a fawn capable of breeding and giving birth. If the number of fawns entering the breeding population is lower than expected from the number of breeding females present, an


analysis of why the deer are not breeding or where mortality is occurring may be useful. Are the animals failing to conceive or is there a high pre- or post-natal mortality? Ovulation and conception rates also give an indication of the reproductive potential of the deer and whether these are being realized.

After ovulation has occurred, the ruptured Graffian follicle in the ovary develops into a corpus luteum which either remains if the animal conceives or regresses and disappears quite quickly if the animal does not become pregnant. Therefore, ovulation rates can be determined from the presence of corpora lutea in the ovaries of animals killed at the appropriate time of year. Conception rates can be determined from an examination of the uterus for an embryo or foetus. Examination of uteri from deer killed at various stages of pregnancy will give an idea of prenatal mortality or, in other words, the survival rate of foetuses.

Table 3 Puberty. and ovulation and conception rates'

Chinese muntjac S. England Chinese water S. England Fallow, wild S. England Fallow, park S. England

Red S. England

Red Scotland ROe England

Roe Denmark ROe Sweden Sika S. England

c. 6 c. 6

16 16

16

16, 28 or 40 I5

15 - 4 or 16

100

100 98

97

-

- 100

100 100 99

25 100 25 Chapman & Dansie (1970) - 75 16 Middleton(1937) 53 94 53 h s t r o n g e t a l . (1969)

176 91 176 D. I. Chapman (unpublish-

147 92 147 D. I. Chapman (unpublish-

- 85 533 Mitchell (1969) 77 96 28 Prior (1968); Chapman &

24 96 24 Strandgaard(1972a) 179 91 179 Borg (1970) 116 87 116 Chapman & Horwood

ed observations)

ed observations)

Chapman (1971)

(1968); D. I. Chapman, M. T. Horwood & E. H. Masters (unpublished observations)

* W i t h the exception of Chinese muntjac deer, fawns of the year have not been included.

Fallow, Red and Sika deer are seasonally polyoestrous and if they do not conceive the first time they are mated, they will come into season again about every 3 weeks and this may last throughout the winter unless they become pregnant. It does not appear to have been recorded whether Chinese muntjac, Chinese water and Roe deer are mono- or poly-oestrous. Captive Red deer on the Isle of Rhum in Scotland exhibited up to six oestrous cycles per season, the last occurring in mid-March. The mean length of seventy-eight cycles was 18.3 daysf1.7 although a few animals, not included in the above calculation, exhibited either short cycles of 7-9 days or long cycles of 34-59 days (Guinness er ul., 1971).

Most Fallow deer in southern England are born in June, although fawns have been born as late as October which suggests that late matings have occurred (Chapman & Chapman, 1970). Further support for this view has been obtained from the presence of unusually small but apparently normal foetuses (Armstrong er al., 1969). Similar occurrences have been found in Red deer (Mitchell & Lincoln, 1973) and Sika deer (Horwood, 1966). Roe deer exhibit the phenomenon of delayed implantation, the ova being fertilized in July-August but the blastocyst only becoming implanted in the uterus at the end of the year (Short & Hay, 1966). Where Roe deer are culled before implantation has taken place, the number of corpora lutea give a reasonably accurate estimate of the number of foetuses which may be carried (Chapman & Chapman, 1971; Strandgaard, 1972a). In this species, implantation of the

66 D. I. Chapman

blastocyst appears to be an efficient process. Corpora lutea also give a reasonable estimate of the number of foetuses carried by Fallow deer (Armstrong e? al., 1969) but in Chinese muntjac deer (Chapman & Dansie, 1970), Red deer (Miller, 1932; Douglas, 1966) and Sika deer (D. I. Chapman, M. T. Horwood & E. H. Masters, unpublished observations) accessory corpora lutea are frequently produced. The accessory corpora lutea are usually smaller than the corpora lutea of pregnancy and the use of corpora lutea to estimate conception rates in these species may lead to errors if the two types are not distinguished correctly. Ovulation and the consequent production of corpora lutea can occur during pregnancy and so differences in the numbers of embryos and corpora lutea should not necessarily be taken as evidence of embryonic loss.

Conception rates are important as an indication of the potential recruitment to the population. Adult Scottish Red deer may not become pregnant every year and those that have not been pregnant the preceeding season are termed 'yeld'. Yeld females are more likely to become pregnant in the present year than those females (milk hinds) that gave birth in the preceeding season. The mean conception rate of Scottish Red deer of 3 years of age and above was 92% for yeld animals and 78% for milk animals (Mitchell, 1969).

The ovulation and conception rates for the different species of deer are given in Table 3. The conception rates are minimum values because in many cases no attempt was made to recover blastocysts, and deer without a readily visible embryonic sac or embryo were considered not to have conceived. Some of these animals might have conceived at a later oestrus.

Variation of conception rate with age In order to be able to calculate the net reproductive rate, it is necessary to know whether there is a change in conception rate with increasing age. It has already been shown how the age of puberty in female deer may markedly affect recruitment to the population: this is really a special case of variation of conception rate with age.

The conception rates of Red deer from various localities in Scotland were obtained from the presence of embryos in female deer shot after late November. These values together with values for Fallow, Red and Roe deer from southern England and Roe deer from Denmark are given in Table 4. Similar information for other species of deer do not appear to have been published.

With monotocous species, pregnancy is an all or none affair, whereas with polytocous species such as the Chinese water deer and the Roe deer, the conception rate will decrease if the incidence of multiple conceptions decline but the animals may still be pregnant. Therefore the data for Roe deer is based upon the presence of corpora lutea, not foetuses, as many of the deer were shot before implantation occurred. The percentage conception is based upon the assumption that each Roe deer should have had two corpora lutea as twins are commonly carried by this species. Values above 100% indicate that a proportion of the deer had three corpora lutea.

When the conception rate in yearling Roe deer is compared with that for all the older animals, it is clear that in England and in Denmark, there is a lower incidence of twins in animals pregnant for the Ibst time. There is, however, no indication of a decline in conception rate with increase in age. Swedish Roe deer appear to be more fecund and the difference in conception rates between yearling and adult deer was not signilkant (Borg, 1970).

Female, Scottish Red deer appear to lose conditionwitheach pregnancyand lactationwith the result that successive pregnancies occur later and later until conception fails to occur (Mitchell & Lincoln, 1973). This appears to occur to a lesser extent with park deer in southern England.

Gestation period In seasonally breeding species of deer, the approximate length of gestation can be calculated from the time of the rut to the time of parturition. Precise values can only be determined by observation of mating, separation of the sexes and observation of parturition. This method is the only reliable one for deer which do not have a regular breeding season.

Tabl

e 4

Var

iatio

n of

conc

eptio

n ra

te w

ith a

ge

Ref

eren

ce

Age

0

Spec

ies

0

1 2

3 4

5 6

7 8

9101112131415 A

rmst

rong

er u

l. (1969);

D. I.

Cha

pman

(unp

ublis

hed

obse

rva-

k 2

tion)

0 f? I? g '"5.

And

erse

n (1953)

2 B B I.

D. I

. Cha

pman

(unp

ublis

hed

obse

rva-

1 Fa

llow

n

14

4 10

14

3 6

4 12*

(S. E

ngla

nd, W

ild)

%

0 100

100

93 100

83

100

92

Fallo

w

n 13

28

17

9

7 10

3 14*

(S. E

ngla

nd,P

ark)

%

0 86

100

100

86

80 100

86

Red

n

26

44

71

62

81

52

53

38

28 27 15 18

11 4

2 1

Mitc

hell(

1969

) (S

cotla

nd)

%

0 20

69

90

93

83

87

84

93 74 60 78 82 75 50 100

Red

n

34

67

23

17

7 7

8 28*

(S.

Engl

and)

%

0

88

91

84

86

86 100

93

tions

) RO

e n

11

710 7

3 4

2 1

1

Prio

r (1968)

ROe

n4

6 913 8

6 3

2 3

1 (D

enm

ark)

%

0 78 104

113

100

100

100

133

100

* 7

year

s pl

us o

lder

ani

mal

s.

(Eng

land

) %

0

79 120

107

100

100

75

100

100

5. 3

rl

68 D. I. Chapman

The length of the gestation period affects the rate of recruitment to the population: deer with a gestation period longer than 6 months must have, on average, less than two pregnancies a year. In fact, with the exception of the Chinese muntjac, all the wild deer occurring in Britain are seasonal breeders and have only one pregnancy per year. The female Chinese muntjac is not a seasonal breeder, the gestation period is approximately 7 months, and it can undergo a post-partum oestrus (Chapman & Dansie, 1970). Therefore, in theory, this species may have four pregnancies in a little over 2 years but what actually happens in wild deer is unknown.

The gestation periods of deer are given in Table 5.

Table 5 Rurring period, time of parturition and RLsration period

Rutting Species period

Parturition period

Chinese muntjac - Chinese water about Dec. Fallow Oct.-NOV.

Red Sept.-Da.

ROC Aug.

Sika Sept .-Nov.

- May- July June-July

May-June

April-June (England) May-July (Denmark)

May-June

Gestation DaysfS.D.

c. 210 180-210 229i2.7

233f3.5 231i4.5

c. 290

21 .8 f3.7

Reference

ChaDman & Dansie (1970) . , Middleton (1937) Prell(1938); Chapman & Chapman (1 970) Prcll(1938k Guimks eid. (1971); Mitchell & Lincoln (1973) Re11 (1938); Prior (1968); Strandgaard (1972a) Prell(1938); Horwood (1971)

Fecundity The number of fawns born per pregnancy can only be determined accurately by observation of parturition. The presence of more than one fawn following a female deer is no evidence of twins having been born. This fact is stressed because the fallacy is still believed by many people. A reasonable approximation of the number of young born per female can be obtained from the number of foetuses carried, provided it can be shown that there is negligible pre-natal mortality between the time of year the specimens are obtained and the time of parturition. The incidence of multiple conceptions, in those deer that normally have more than one fawn, depends upon environmental conditions. The incidence of twins in White-tailed deer (Odocoileur virginimur) in America was lower in animals on a low plane of nutrition than those on a high plane (Verne, 1967, 1969). Overcrowding and consequent social stress were thought to reduce the incidence of twins in Roe deer in Denmark (Andersen, 1961).

Chinese water deer usually carry two or three foetuses but up to six have been recorded, although few precise figures have been published. Middleton (1937) recorded an average of 2.3 foetuses in twelve deer (range 2 4 ) in England. Roe deer commonly carry twins in Eng- land; the incidence varying with the locality and from year to year (Chapman & Chapman, 1971) and similar values have been recorded in Denmark (Andersen, 1953; Strandgaard, 1972a). However, in Sweden, triplet embryos are far more frequent (Borg, 1970) and, in Norway, quintuplet embryos have been recorded but this is probably exceptional (Myrberget & Raiby, 1972). The number of fawns per pregnancy have been summarized in Table 6.

Foetal sanival An indication of foetal survival, or pre-natal mortality, can be obtained by comparing the proportion of females pregnant at various stages of gestation. However, most female deer are culled, by tradition, in the first half of pregnancy and so there appears to be virtually no information on the survival rate of foetuses in the various species of deer which occur wild in Britain.


There was little evidence of pre-natal mortality in twenty-five Chinese muntjac deer which were examined at various stages of gestation by Chapman & Dansie (1970). Only two deer were not obviously pregnant but from the appearance of the uterus and ovaries, and because the deer were lactating, it was thought that parturition had occurred recently. However, abortion of a near-term foetus could not be ruled out.

Table 6 Number of fawns per pregnancy

~~

%

Single Twins and over Species Locality No. Triplets Reference

Chinese muntjac Chinese water Fallow

Red

Red ROC ROe ROe Sika

S. England S. England S. England

S. England

Scotland England Denmark Sweden S. England

31 100 0 0 12 0 75 25

270 99.3 0 7 0

218 995 0 5 0

1500 99.9 0 1 0 77 21 74 5 24 17 75 8

179 5 44 52 116 100 0 0

Chapman & Dansie (1970) Middleton (1937) Armstrong t t a/. (1969); Chapman & Chapman (1969,

unpublished observations) D. I. Chapman (unpublished

observations) Mitchell (1969) Chapman & Chapman (19771) Strandgaard (1972a) Borg (1970) Horwood (1966); D. 1. Chapman, M. T. Horwood &E. H. Masters (unpublished observations)

The following percentages of 266 adult Fallow deer were found to be pregnant at various stages of gestation (D. I. Chapman, unpublished observations).

No. % Pregnant December 116 87.9

April-June 20 90-0 January-March 130 96-9

These figures are based upon the presence of apparently viable foetuses. Many of the deer killed in December had ovulated and may have been pregnant but no attempts were made to collect blastocysts. The true percentage of deer pregnant in December is therefore likely to be higher than the figure given.

Sex ratio of foetuses and fawns The sex ratio of the deer born and surviving to breeding age is obviously important because it is the number of female deer that affects the future size of the population. The sex ratio of animals reaching puberty may be different to the sex ratio of fawns born, which again may be different to that of the embryos. These changes may occur because of differences in survival rates (mortality) of the sexes at different stages of development.

The sex ratio of foetuses from a sample of female deer killed is readily determined and it is difficult to believe that the sex of the foetus S e c t s the chances of the mother being killed. However, whether the sex ratio of newly born fawns and older fawns observed is representative of the population depends upon whether the chances of the animals being seen or killed is the same for both sexes. When the entire population of ninety-one Roe deer fawns were shot at Kal0 in 1950, it was found that the chances of the male fawns being shot was far greater than that of the female fawns as the figures in Table 7 show (Andersen, 1953). In other words, if the first twenty-five fawns killed (27.5 % of total) had been regarded as a

representative sample of the entire fawn population, the sex ratio would have been calculated

70 D. I. Chapman

as 257 males per 100 females, whereas in fact it was found to be 98 males per 100 females when all the fawns had been killed. An apparent large increase in the sex ratio in favour of males has been found in Fallow deer in southern England if the sex ratio of foetuses, newly born fawns found and older (c. 6 month) fawns culled are considered (see Table 8, D. I. Chapman, unpublished observations). These figures strongly suggest that sex ratios based upon a sample of fawns culled are probably valueless as an indication of the true sex ratio of the fawns in the herd. Similarly, figures for newly born fawns seen or caught must also be viewed with suspicion when used for estimating the sex ratio of the total fawn population. However, these figures do indicate that the chances of survival of female fawns are better than that for male fawns and that after the fawns in a population have been culled, the sex ratio of the fawns left is probably in favour of the females.

Table 7 Change in sex ratio of Roe &cr fawns during culling (Andemen, 1953)

No. of fawns present % of total present Date

d 9 Total d 9

1 Oct. (Start of cull) 45 46 91 49 51 1 Nov. 27 39 66 41 59 1 Dec. 6 13 19 32 68 15 Dec. 1 9 10 10 90

The above facts must be born in mind when considering the sex ratios of foetuses, newly born fawns and fawns killed some months after birth, for the various species of deer that are given in Table 8.

The sex of the fawns may be influenced by the age of their dams. Female Red deer in their prime tended to produce a higher proportion of females (Jensen, 1967) and the same appears to be true for Scottish Red deer (Lowe, 1969). The age structure of the population Will, therefore, influence the sex of the progeny.

Table 8 Sex ratios of foetuses, ntwIy born fawns and older fawns

Sex ratio d per 100 8 Reference Newly born Older

Foetus* fawn* fawn* Species Locality

Chinese muntjac S. England 100 (25) - - Chapman & Dansie (1970) Chinese water Fallow S. England 110 (145) I23 (138) 160 (52) D.I.Chapmanfunpublished

Ked Scotland 108 (231)** - 113 (98) Mitchell, McCowan &

- - - - observations)

Parish (1971)

observations) ROC England 117 (65) - - Chapman & Chapman

(1971); Rior (1968) Denmark 100 (36) 114 (265) 96 (91) Andmen (1953)

111 (186) Strandgaard (1972a & b)

D. I. Chapman, M. T. Horwood & E. H. Masters (unpublished observations)

S. England 110 (86) 115 (206) 132 (79) D.I.Chapman (unpublished

Si S. England 121 (73) - 82 (51) Horwood (1971);

Figurm in brackets are actual no. of deer. ** Foetus from yeld hinds only.


Application of the information The following example will illustrate the way some of the factors may be used in order to find out whether a herd is increasing or declining.

All the Roe deer on an estate at Kal0 in Denmark were shot in 1950 and the following facts published by Andersen (1953). Of the 213 deer killed, there were ninety-one fawns (45 8, 46Q, thirty-three yearlings (9 & 2 4 9) and seventy-one adults (19 8, 52 9). None of the fawns was pregnant and so puberty occurred at about 15 months of age. The yearlings carried an average of 1.56 fawns per pregnancy whereas the adults carried an average of 2.01 fawns per pregnancy. There was no evidence that fecundity of adult deer decreased with increasing age. Taking all the female deer together gave a mean of 1.25 fawns per pregnancy. The mean age of all the female deer was found to be 2.68 years.

It can be calculated, therefore, that the number of fawns likely to be produced by 100 female Roe deer in their lifetime will be:

No. of female deer x fawns bornlyearlg x average age of or lOOx 1.25 x2.68 = 335

The sex ratio of foetuses was unity and so 100 female deer will, in theory, produce an average of 168 female fawns in their life time. Therefore, the deer are more than replacing themselves in their own life and the population should be expanding rapidly. The deer would not have been replacing themselves if the number of fawns born had been less than 100.

Using the above pregnancy rates we can calculate the number of fawns the fifty-two adult female deer killed at Kal0 in 1950 are likely to have produced earlier in that year. The yearlings would not have contributed to the fawns born in 1950 because these deer would have been fawns themselves at the time the present fawns were conceived. Of the fifty-two adult deer, twenty-one were yearlings when they conceived and so, in theory, should have produced :

The remaining thirty-one deer were adult when they conceived and, in theory, they should have produced :

31 x2.01 = 62 fawns which gives a total of ninety-five fawns born in 1950. In fact, a total of ninety-one fawns were shot when the deer were killed. Therefore, if it can be assumed that no females left the area without their fawns between the time of parturition and the end of the cull, the survival rate appears to be high. This has been confirmed by Strandgaard (1972b). These facts apply, of course, only to the Roe deer at Kals in 1950 but the example illustrates the need for a knowledge of the age of puberty, age structure of the population, fecundity, number of pregnancies per year and variation of fecundity with age.

Andersen's (1953) data have also been used by Quick (1962) who has calculated that seventy- six adult females should have produced 133 fawns, but that as only ninety-one were shot, the mortality must have been about 32 %. He appears to have made the error of assuming that the seventy-six adult and yearling deer would have contributed to the fawns born in 1950, forgetting that twenty-four of them were yearlings and would not have conceived in 1949. If the fawns are included, the average number of fawns per female per year is 1.25 not 1.75 as calculated by Quick (1962).

TIME OF YEAR TO CULL Deer management, particularly in Britain, involves culling and deciding the best time of year to cull deer also requires a knowledge of the reproductive physiology of the species. The culling of certain species of deer is traditionally carried out at certain times of the year but, in fact, this is based upon the reproductive cycle even if this was not consciously recognized by our prede- cessors. Female Fallow deer are traditionally culled in the winter. At this time of year, the fawns are reasonably capable of looking after themselves and the adult females, although pregnant, are not heavy with young. Furthermore, the animals will be in better condition

21 x 1.56 = 33 fawns

72 D. I. Chapman

than at the end of the winter and fawns will be of sufficient size to make it worth marketing the carcase. If female Fallow deer were culled in the summer, many fawns would probably starve and those fawns that were killed would not be of sufficient size to market. Male Fallow deer are culled in the late summer and they should be in good condition at this time of year, which is, traditionally referred to as the ‘fat buck season’. If the deer are killed later in the year in the rut, the meat will be tainted and after the rut, they will be in poorer condition because of the stress of rutting.

In seasonally breeding species of deer, most animals give birth in a fairly restricted period, although there are the ones that give birth early as well as the stragglers. The time of parturition may vary between localities. In Scotland, newly born Red deer have been found on the Isle of Rhum from 20 May to 3 July with a peak at 7 June, whereas on the mainland, in Glen Feshie, fawns were found from 28 May to 5 July with a peak at 13 June (Mitchell & Lincoln, 1973). Therefore, for humane reasons alone, female deer should not be culled just before the time of parturition nor for some time afterwards.

With species of deer that breed throughout the year, such as the Chinese muntjac, the question of when to cull is difficult to answer. Parturition in this species has been recorded in most months of the year, although of seventeen born in the London Zoo, none was recorded in January, February or March (ZuCkermaM, 1953). Because these animals can probably survive independently of their dams at 2-3 months of age (Dansie, 1970), it would appear that March might be a good time to cull the females. However, this suggestion would need confirming for each area where culling was to take place because Chapman & Dansie (1970) considered that parturition had recently occurred in an animal killed in early February. The rutting periods, and times of parturition have already been summarized in Table 5.

SELECTION FOR BREEDING Deer are often managed with a view to changing the characteristics of the stock in some particular way. This assumption is implicit in that deer with poor (i.e., small) or misshapen antlers are usually culled preferentially. This theme appears time and time again in articles on hunting deer and implies firstly that the factors are genetically controlled and secondly a knowledge of the genetics of deer. Cadman (1967), for example, states that the quality of Fallow deer is controlled by shooting the males selectively and in his census of deer, he divides them into good and bad. Unfortunately, our knowledge of the genetics of deer is almost non-existent and any attempt to alter antler characteristics by breeding, which often means selective culling, although new blood is sometimes imported, rests purely on chance. In this aspect of deer management, the male will have more influence on the herd than the female. It should be remembered that although antlers are only camed by the male (reindeer excepted), the character is transmitted by both sexes. Furthermore, at each mating only half of the male’s genes will be passed to his offspring which will only pass on a quarter and so on. Consequently, the genetic influence of an imported animal soon becomes diluted out.

There appears to be no concrete evidence that selective shooting alters the shape or size of antlers. Selective shooting of Roe deer on an estate in Denmark in the 1930s did not increase the size of the antlers compared with the antlers of deer shot on the same estate in the 1920s before this form of management was practised. Improved antlers were only obtained when the entire herd was killed and replaced with deer from another area where the deer grew larger antlers (Andersen, 1961). The trophy value of Red deer antlers in many areas of Scotland has declined during this century despite efforts to halt or reverse it (Lockie, Mutch & Cooper, 1967).

The problem is aggravated further by the fact that the antlers carried by a deer one year may bear little resemblance to those camed in preceeding or subsequent years. Over 30 years ago, Voormann (1939) concluded that the shape and size of Roe deer antlers varied quite irregularly from year to year and this work has been amply confjrmed by Strandgaard (1 972b) with wild Roe deer which could be unequivocally identified from year to year. It is probable


that this irregularity of antler growth applies equally well to other species of deer. Although this has not been proven neither has the beneficial effect of selective shooting. Andersen (1961) has concluded that the only certain result of selective shooting is that the hunter will build up a collection of poor trophies!

Antler size varies with age and one wonders how many animals shot because they had apparently poor antlers for their age, were really younger animals with good antlers. This discussion on antlers may appear rather far removed from the topic of this review, but if more was known about the genetics or hereditability of certain characteristics of deer, deer management for these characteristics might be placed on a firmer foundation rather than on empiri scism.

If this review appears to be rather academic, a moment should, perhaps, be spent pondering upon the words of a member of the Forestry Commission whose job is the day to day management of deer: ‘The obvious does not always apply in questions of animal behaviour, and ill- conceived attempts at control which are not based on a general understanding of the behaviour and population dynamics of Roe often prove expensive and ineffective’, (Prior, 1968).

SUMMARY The regulation of the numbers of animals in a population is one of the more important aspects of the management of either wild or park deer. The size of the population and its rate of increase is affected by the fertility and fecundity of the female and, in general, not by that of the male. The following factors affect the recruitment to the population: age structure of the herd, age at which puberty occurs, ovulation and conception rates and their variation with age, gestation period, fecundity, foetal survival and sex ratio of offspring. Information is available on many of these factors for the species of deer which occur wild in Britain, but only for specific sets of conditions, namely those under which the observations were made. The interaction of these various factors and how they respond to changing conditions are largely unknown. An improved plane of nutrition for female, Scottish Red deer leads to earlier puberty (Guinness, Lincoln & Short, 1971) and an improvement in overall fertility of the population. However, does an increase in the population lead to increased social stress and a reduction in fecundity as it appears to do in female, Danish Roe d m (Anderson, 1961)? Until questions such as this can be answered satisfactorily, one cannot predict what will happen in a particular situation and each population must be investigated.

Little is known of the genetics of deer and, at present, breeding for a particular characteristic rests almost solely on chance. There is no evidence to support the view that selective culling achieves the desired changes. Breeding experiments need to be carried out and suggestions along these lines have been suggested already by Short (1968) although such work need not necessarily be limited to antler characteristics.

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reproductive physiology in relation to deer management

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