Differences of thermal properties of white-tailed deer pelage between seasons and body regions

J. tk4q'~ BioL VoL 3, pp. 131 to 158 © Prrpmon P rm Ltd 1980. Printed in Great Britain

0306-4~3/a0/0701-0151$02.00/0

DIFFERENCES OF THERMAL PROPERTIES OF WHITE-TAILED DEER PELAGE BETWEEN SEASONS A N D BODY REGIONS NADINE K. JACOBSEN* Department of Natural Resources, Cornell University, Ithaca, NY 14850. U.S.A.

(Received 24 April 1979: accepted in revi.¢edform 20 February 1980) Abstract--l. The thermal properties of the winter and summer pelages of white-tailed deer were studied for 11 body regions and related to the body surfaces effective in conductive heat transfer during lying activity. 2. Coegficients of apparent thermal conductivity differed significantly between body regions within each wa~onal pelage, and between seasons. Compression of the hair layer simulating changes in posture during lying activity significantly increased the thermal conductivity coefficients of the winter pelage only for the lower legs, whereas in the summer pelage the thermal conductivity coefficients of all body regions were significantly increased with compression. 3, The physical depth of the nonpiioerected hair layer was from 1.86 to 8.67 times as deep for the winter as for the summer pelage, with the greatest changes in the regions of the body trunk. Total thermal resistance of the pelage is greater in winter than summer, because the hair layer of the winter pelage is both thicker and of a higher specific resistance. 4. Changes in the physical depth of the hair layer with development of the winter pelage were monitored in two deer maintained in captivity. As the fall moult progressed from October to December, the estimated thermal resistance of the nonpiloerected pelage increased from 29 to 93% of that of the fully developed pelage of January. 5. The influences on total conductive heat transfer to the bedsite substrata of several physiological and behavioural responses of white.tailed deer are discussed.

INTRODUCTION WHITE-TAILED doer (Odocoileus viginianus) have two seasonally distinctive pelage& A moult in spring from the winter-to-summer pelage produces the relatively thin reddish-brown pelage of guard hairs that is characteristic of summer; it contrasts strongly with the grey-brown, thick winter pelage of both guard hairs and underfur th/tt develops during the fall moult from summer-to-winter pelage (Severinghaus & Cheaturn, 1956). Although physical characteristics of the two seasonal pelages are easily recognized, seasonal differences in thermal properties have not been reported for the body regions effective in conductive heat transfer between a recumbent white-tailed deer and its bedsite substrata. Stevens (1972) mainly sampied the dorsal regions of the body trunk and legs in determining thermal conductivity coefficients of the winter pelage and how the coefficients were affected by compression of the hair layer. She did not study differences in these characteristics between body regions within individual winter pelages. Other studies have also measured thermal properties for the dorsal region of the winter pelage (Hammel, 1955; Moote, 1955). The thermal properties of the summer pelage of white-tailed deer have not been reported. Knowledge of the conductive heat transfer during recumbency is important to the study of the annual cycle of energy economy of white-tailed deer because * Present address: Division of Wildlife and Fisheries Biology, University of California, Davis, CA 95616, U.S.A. 151

an average 60% of each 24-h day is expended in lying resting or ruminatihg activities 0acobsen, 1973) on subetrate that may be frozen, muddy or dry, depending on the season. This is a report of differences of thermal properties of the fully-developed winter and summer pelages of white-tailed deer with body region and compression of the hair layer as affected by postures during recumbency. Such information is useful for thermal modelling of conductive heat transfer of the hair layer in direct contact with the bedeite substrata, and for the interpretation of temporal variations in behaviour and activity of white-tailed deer in diffc~rent thermal environments. MATERIALS AND METHODS

Pelage samples Pelages without visible evidence of either deterioration or initiation of a new moult cycle were obtained from white-tailed deer ranging in body weight from 34 to 66 ks. and in age from 0.8 to 3.5 yr. The inner surf-__ees__of the intact winter (IM, 2F) and summer (IM, 21:) pelts were carefidly cleaned of adhering tissue, and a sample of 9-cm diameter was cut from each half of the body. except for the dorsal and ventral regions that were cut along the midline (Fis. t). O'he domd back region was inducted to allow comparisons with other report&) A ult-borax mixture was applied to the inner surface of the samples, which were then stored individually in plastic bags at 256 g. Measurements were made on thawed samples brushed free of the mixture and allowed to dry to evaporate moisture from the pelage. Skin thicknesa was n~asured with a caliper at four different sites across each pelage sample. At

NADINE K. JACOBSEN

152

Fig 1. Locations of pelage samples cut from each seasonal pelage: (1) neck: (2) upper foreleg; (3) middle foreleg; (4) lower foreleg; (5) sternum: (6) dorsal: (7) side: (8) belly; (9) upper hindleg; (10) middle hindieg and (1 I) lower hindleg.

these same four sites, the physical depth of the hair layer was measured as the height of extinction of a calibrated probe inserted perpendicularly into the hair layer until it touched the skin. Care was taken not to disturb the natural orientation of the hairs or the physical depth of the hair layer. Length of the guard hairs was measured as the point of extinction of the same calibrated probe inserted parallel to the hair fibres at about the same four sites.

Apparent thermal conductivity coeO~cients Analysis of heat transfer through non-homogeneous fibrous insulating materials, such as these pelnges of whitetailed deer, involves detailed studies because several modes of heat transi'er may he occurring simultaneously or as coupled processes (Birkebak, 1966; Cena & Monteith, 197Sa, b, c; Davis & Birkebak, 1975). For a given sample, however, it is practical to determine empirleaily the total amount of heat that flows from one surface to another when a given temperature difference is maintained. Under these ¢onditi0m the term "apparent thermal conductivity coefficient" (ASTM, 1974) is preferred. The apparent thermal conductivity coeff~ent of a pelage sample was calculated from a model of steady-state onedimensional heat conduction (Kreith, 1965); conductive heat transfer and temperature difference agron the pelage sample were measured by a standardized test method describod by Evans (1971) and Stevens (1972): AT where k is the appexent thermal conductivity coefficient (W m - I K-t), Qk the conductive heat transfer (W m-a). and AT the temperature difference (K) for heat tramfer across d. the distance (m) monitored. The apparatus was constructed from two 12-cm long copper cylinders, each encased separately in eapanded styrofoam lr~__.~n with o ~ y the 8-cm ~ exposed. The distance betwem the two end platm was coatrolled by u l j t m m m U of the m ~ frame. cylinde~ was perfuasd with an ethylene.~yool mlulion circuhttod from a temlmmture.¢amtrollod warm or mid bath 0qmlab, models TEg-MIO4 and TE45-Pl~-2). "l'ne pliable amq~le ~ pmitionod between the two endplates with the skin smfa~ in direct contact With a 2..~:m diameter heat flux disc, slightly recessed into the bottom (warm) plate and continuonsly monitored by a millivolt recorder {Thomwaite Associated, model 310). Expanded styrofoam end__a~__ the interior of the assembled apparatus. Conductive heat transfer acrnss each pelage sample was measured in duplimtte at temperatures representative

of seasonal differences between the body tissue surface (308K) and the substrata of the recumbent animal estimated at 273K for winter and 291K for summer samples (Jacobsen, unpublished data). For all body regions of the winter and summer pelages the differences in temperature averaged respectively 35.5 + 0.5 (n = 198) and 17.2 + 0.1°C (n = 218). Temperatures were monitored by thermocouples, two attached to each endplate, and an output was displayed on a recorder throughout the measurement period. All values were obtained after the apparatus had equilibrated. The apparatus was calibrated periodically against standards of styrofoam and glass wool similar in thickness to the pelage samples tested. A coefficient variation of 7.9~ (n = 51) was obtained for repeated measurements of the standards at similar differences in temperature. Changes in apparent thermal conductivity coefficients with compression of the hair layer of the pelage sample were measured by techniques described by Stevens (1972). The pressures tested were 0, 20, 980 and 1960 N m -2 for the winter pelage, and 0, 20, 98, 490 and 980 N m- ' for the summer pelage. The pressures tested for winter and summer differ because the hair layer of the summer pelage samples was markedly less resistant to compression. The above values were considered representative of the compression of the hair layer that might occur at different regions of the body surface during the recumbency of deer of 980 N body weight or lighter. For each pelage sample, the coefficient of thermal conductivity was computed from the relation identified in equation (1), with d representing the effective distance measured under compression.

Monitoring the fall moult Changes in the physical depth of the guard hairs with growth of the winter pelage were studied on a tamed adult female (Deer A) and juvenile male (Deer B) white-tailed deer maintained in captivity on a high-quality diet available ad libitum. The depth of the nonpiioerected hair layer was measured biweekly between 15 August and 30 January at 11 body regions (see Fig. l) on each side of the body. A thin calibrated probe was inserted perpendicular into the hair layer until it touched the skin, and the point of extinction was read as the phyl~ai depth. Care was taken to minimize disturbance of the natural orientation of the hair. Both deer accepted my presence during the measurements without apparent alarm behaviour or change in orientation of the hair layer. Progress of the spring moult could not be followed, because of the hair.pulling behaviour of the deer, as observed in other captive species (Cowan & Raddi, 1972).

Statistical analyses The effects of body location within each seasonal pelage were evaluated at 0 N m -~ by analysis of variance, and differences among means within each seasonal pelage were tested by Tukey's w-procedure (Steel & Torrle, 1960). The effect of compression of the hair layer within a body region was evaluated by the nonparametric Krmkai--Wallis oneway analysis of variance test (Siegel 1956). Regression analysis was by the method of least squares, and significanoe was determitagl by the F-test. Comparison of the means was by the Student's t-test. P r o b ~ y values less than 5 ~ were regardod as signit~ant. All values reported are mean + standard error.

RESULTS AND DISCUSSION

Physical characteristics Variations of skin thickness, depth of the hair layer and length of guard hairs with body r e , o n and between Season---a]-~ages are Summarized ifi Ta"~|e 1.

Differences of thermal properties of white-tailed deer pelage

153

Table 1. Variation of skin thickness, hair depth, and hair length of the samples representing winter (W) and summer (S) pelts of white.tailed deer. Values are mean + standard error of the mean. Analysis of variance with Tukey's test was performed at ON m - ' for each season: means within a season followed by the same superscript are not significantly different (P > 0.05) Body region Neck Foreleg Upper Middle Lower Trunk Back Side Belly Sternum

Season

Skin thickness (mm)

Hair depth (mm)

Hair length (mml

Ratio depth/length

W S W/S

1.5' 4- 0.1 1.5' 4- 0.1 1.00

22.2''¢ 4. 0.1 4.4 h 4. 0.4 5.04

37.5 h' 4- 1.1 17.5~ + 3.5 2.14

0.59 0.25

W S W/S W S W/S W S W/S

!.9 "h + 0.1 1.4" 4- 0.6 1.36 1.8-h 4- 0.4 1.5" ± 0.1 1.20 1.2" 4- 0.2 1.1~ + 0.2 1.09

17.5b'' 4- 4.5 3.7 b + 0.5 4.73 1!.6"b 4- 2.4 3.0' b 4. 0.2 3.87 4.3" 4- 1.2 2.3" + 0.3 1.87

29.0 b 4- 6.0 17.0'~' 4. 1.0 1.71 29.5 b 4- 6.5 15.(Pb` 4- 1.7 1.97 13.5~ 4- 7.6 il.O'b ± 0.1 1.23

0.60 0.22

W S W/$ W S W/S W S W/S W S W/S

1.8"h 4. 0.2 1.4" + 0.1 1.29 1.4~ 4- 0.1 1.6" + 0.4 0.88 1.9"b 4- 0.4 1.64 4. 0.1 1.19 2.4 b 4- 0.3 1.6" 4- 0.1 1.50

29.0" + 2.0 4.5 ~' 4. 0.7 6.44 17.5"~ 4- 5.5 3.4"h 4. 0.9 5.15 20.0b'' "6 3.1 3.9~ 4. 0.2 5.13 26.0~" + 4.1 3.0~b 4- 0.3 8.67

53.~ ::t:2.0 22.0~h" 4- 0.7 2.41 49.0a 4- 9.0 27.0¢ 4- 1.0 1.81 46.0~d ± 2.5 27.8 c 4- 3.8 1.65 48.1 ed 4- 3.7 28.Y 4- 7.0 1.70

0.55 0.20

W S W/S W S W/S W

1.9-b + 0.1 1.8" 4. 0.2 1.06 1.4" 4. 0.5 1.3" 4. 0.2 1.08 1.2" 4. 0.4 1.1" 4- 2.2 1.09

24.5d= 4- 0.5 4.0 b 4. 0.3 6.12 13.5k ± 75 3.5~b + 0.5 3.86 4.1" 4" 1.0 2.2~ 4- 0.2 1.86

44.5 ~a ± 1.5 21.5 "~ 4- 0.5 2.07 35.0b~ 4- 2.5 25.0 ~ -t- 8.0 ! .40 13.8" 4. 2.2 10.(Y' + 1.0 1.38

0.55 0.19

0.39 0.19 0.32 0.21

0.36 0.13 0.44 0.14 0.54 0.11

Hindleg Upper

Middle Lower

W/S

Skin thickness of winter pelts averaged 1.13 times thicker than of summer pelts of white-tailed deer (13 5:0.1 vs 1.5 + 0.1 ram), a difference that was not statistically significant (P > 0.10l Variation of skin thickness with body region was significant within the winter pelage (P < 0.05), with the body trunk and upper limbs tending to be of greater average thickness than other body regions. Body-region variations in thickness were not significant within the summer pelt samples. The depth of the hair layer increased significantly (P < 0.005) in winter, a difference averaging 5.25 times as thick in winter as in summer pelage samples (16.3 + 1.9 vs 3.1 + 0.2 ram). Variation in the physical depth of the hair layer with body region was also significant (P < 0.005) in both seasonal pelages. In general, the depth of the hair layer was greatest for the dorsal and ventral surfaces of the trunk, and least for the lower legs. This pattern was more pronounced in the winter pelage where depth of the hair layer o f the lower legs was only 0.14 of the physical depth of the dorsal region of the trunk.

0.39 0.14 0.30 0.22

Length of the guard hairs also differed significantly between seasonal pelages and between body regions within, a seasonal pelage (both P < 0.005). For all body regions, the guard hairs of the winter pelage averaged 1.66 longer as compared to the summer pelages (35.1 + 3.1 vs 21.1 + 1.7 ram, respectively). Increases in length of the guard hairs of the winter pelage were greatest for the body trunk, where increases in physical depth also were most pronounced.

Apparent thermal conductivity coe~cient Variation with season and body region. Apparent thermal conductivity coefficients (TCC) of the uncompressed pelage were significantly (P < 0.005) smaller for the winter (Table 2) than summer pelage (Table 3). Therefore, less heat will flow through a unit thickness of the winter compared to the summer pelage per unit area and per unit temperature difference. Coml~arison of each body region indicated only the body regions of the lower legs did not differ seasonally (P > 0.20). For the .9 body regions that varied seasonally, the difference in apparent T C C values of the summer

154

NADtNE K. JACOBSEN Table 2. Changes in the apparent thermal conductivity coefficient of the winter pelage of white-tailed deer with body relglon and pretture applied to the sample. Values represent mean 5: standard error. Analysis of variance with Tukey's test was performed at 0 N m- z; means followed by the same superscript are not significantly different {P > 0.05) Body region

Thermal conductivity coefficient(mW m- I K- i) 0 N m -2 2 0 N m -2 9 8 0 N m -2 1960Nm -2

Neck Foreleg Upper Middle Lower Trunk Back Side Belly Sternum Hindleg Upper Middle Lower

P*

41.7~b + 1.2

41.5 + 1.9

37.2 -t- 0.5

37.3 + 0.8

NS

40.2"h -1- 1.4 40.7.h 5:0.6 50.1' 5:2.4

40.5 + 1.6 43.5 5:0.8 60.2 5:!.9

37.8 5:0.7 39.6 + 2.2 72.7 5:3.4

45.4 ± 3.7 40.8 5:3.2 75.1 5:2.0

NS NS <0.05

40.5~h 5:0.7 40.8~b ± 1.4 37.9" 5:0.5 38.54 5:0.7

39.9 5:1.3 41.3 5:1.3 39.4 5:0.9 36.5 ± 0.7

39.5 5:2.1 40.25:2.7 36.4 5:1.7 39.9 5:1.1

40.0 5:2.0 41.l 5:3.8 42.2 5:2.7 36.0 ± 0.3

NS NS NS NS

42.8~h 5:1.2 43.4h 5:1.3 50.1~ 5:0.8

42.1 5:i.6 49.1 5:2.3 60.5 5:1.3

41.1 5:1.9 45.8 5:2.3 64.5 5:1.3

37.4 5:1.9 45.2 ± 2.6 68.7 ± 2.2

NS NS <0.05

* Probability (significance) values for comparisons of pressures within a body region by the non-parametric Kruskal-Wallis one-way analysis of variance test. compared to winter pelage samples averaged 32 + 4.3% (range from 7 to 54%). Within each seasonal pelage, the apparent TCC values also differed significantly between body regions of the winter pelage (P < 0.005) and the summer pelage (P < 0.025) (Tables 2 and 3). The ventral surfaces of white-tailed deer that are subjected to mechanical abrasion and are in contact with the bedsite substrata have, in winter compared to summer, both a greater depth of hair layer, underlying thickness of skin, and also do not conduct heat readily. Studies of the relations between the apparent TCC and the morphological types, thickness and bulk density of hair fibres are needed as they vary with body resion and

K - l reported mainly for regions the dorsal body trunk of white-tailed deer in winter pelage (Hammel, 1955; Moore, 1955; Stevens, 1972). The 15% larger coefficients for the regions of the lower legs of the winter pelage obtained in this study than reported by Stevens (1972) may be because of differences in the physical areas sampled. No apparent TCC values have been reported for the summer pelage of white-tailed deer. Although the summer pelage allows more heat to flow through a unit thickness, its coefftcients are smaller than values reported for hair coat of cattle, which varied from 71.4 to 95.2mWm - t K - t (Blaxter, 1962; Bennett,

seasonal pela~.

Effect of compression. Although the apparent TCC of the winter pelage tend to be smaller at 1960 than 0 N m - 2 the differences were not statistically signifi-

The apparent TCC values obtained in this study agree with the range of from 33.3 to 48.8 mW m - t

1964).

Table 3. Changes in the apparent thermal conductivity coefficients of the summer pelage of white-

tailed deer with body regions and pressure applied to the sample. Values represent mean + standard error. Analysis of variance with Tukey's test was performed at 0 N m- =; means followed by the same superscript are not significantly d i f f ~ t (P > 0.05) Body region

0Nm-2

Thermal conductivity coefficient(roW m-t K- t) 2 0 N m - ~ 9 8 N m - Z 490Nm-= 980Nm-=

Neck Foreleg Upper Middle

52.2~b + 1.5

61.1 + 1.6

80.1 + 4.2

116.2+ 2.6

51.3"~ -4- 1.3 43.7" + 0.6

57.8 + 2.2 48.7 + 1.3

64.4 + 3.7 64.6+ 8.1

86.3 + 2.1 71.9 -I- 2.0

Lower Trunk Back Side Belly Sternum Hindleg

53.4"b + $.5

62.7 + 4.8

"/0.9 + 2.9

104.2 5:0.2

10"/.95:7.6

<0.001

54.4"b + 4.0 62.7b 5:0.4 53.8"' + 0.7 48.5 "b 5:3.3

59.9 5:2.3 63.8 5:0.6 59.2 5:0.6 56.2 + 2.1

67.7 5:3.0 97.5 -t- 0.6 80.9 5:0.5 75.3 5:2.4

72.6 5:3.8 100.8± 0.9 95.5 + 0.8 109.65:7.5

74.1 :I: 1.7 105.65:0.2 1 t9.0 4- 0.5 114.8 5:6.8

<0.05 <0.01 <0.001 <0.05

60.1' -I- 3.0 57.8"~ -t- 3.7 54.5"b 5:6.3

65.5 ± 0.7 68.0 -i- 3.0 61.1 5:4.4

78.4 5:1.9 86.7 5:8.3 67.65:1.6

i01.0 -t- 1.2 112.9 -I- 4.3 117.25:7.4 120.2 5:9.1 80.9 ± 0.2 93.05:2.1

Upper

Middle Lower

136.0 -t- 7.3

P* <0.05

94.4 + 4.6 <0.001 87.8 + 10.5 <0.01

<0.01 <0.01 <0.001

* Probability (significance)values for comparisons of pressures within a body region by the nonparametric Kruskal-Wallis one-way analysis of variance test.

Differences of thermal properties of white.tailed deer pelage 0:0 -

SUMMER 7,000617*006~X]

155

Thermal resistance Variation with season and body region. Thermal re-

sistance is the reciprocal of thermal conductance, a value obtained by dividing the apparent thermal conOO6 ductivity coefficient (Tables 2 and 3) by the respective seasonal thickness of the sample hair layers (Table I Resistance to heat flow increas~ linearly (P < 0.005) T with physical depth of the hair layer of each seasonal 002 pelage (Fig. 2). The substantial increase in total therreal resistance of the winter pelage of white-tailed I , l , I i J t J t ,. 0 deer is accompfished mainly by increases in physical u 0 I 2 3 4 5 6 z<[ depth of a hair layer of greater specific thermal resistDEPTH OF PELAGE (mm) I--. ance. The total thermal resistance of the pelage may (n I 0 0 WINTER increase with piloerection of the hair layer (HammeL w " if • -0.021:)*0.0257(X) ne 0 80 1955) and decrease if moisture penetrates the pelage f • 0.99S N" II .J (Lentz & Hart, 1960). Different values may also be < Sb" O000e5 obtained if the pelts sampled are measured in a fresh, 0 60 ~ e W untreated condition. ~,This pattern of seasonal difference in the thermal 0 40 e~/~ resistance of the pelages of white-tailed deer agrees with changes of the dorsal and side regions of the body reported for other species (Scholander et al., 0 20 01l , / l 1950; Hart, 1956; Dawson & Brown, 1970). The low 0 C" , I , J i I i 0 5 I0 15 20 25 30 thermal resistance values found for the lower legs of DEPTH OF PELAGE (mm) white-tailed deer (about 10% of those of the body Fig. 2. Seasonal variation of the total thermal resistance as trunk) resemble the patterns of body-region differences of the winter pelage reported by Seholander et a function of physical depth of the summer and winter aL (1950) of only 20-33% for caribou, Dall sheep (Ovis pelages of white-tailed deer. Values ate for the uncompressed pelage (ON m-2). daili), and domesticated reindeer. Such regional differences in thermal resistance may function similarly to the insulative flexibility of the guanaco pelage (Lama ouanicoe) as described by Morrison (1966). As facultative "thermal windows," a white-tailed deer in winter cant (P > 0.05); only the regions of the lower foreleg pelage can allow a large increase in dissipation of and lower hindleg of the winter pelage significantly body heat following exercise or, for maintenance of increased with compression of the hair layer (Table 2). thermal balance, decrease heat loss across these These results generally agree with the findings of regions of the lower legs by appropriate physiological Stevens (1972) for the several body regions evaluated and behavioural responses. in winter pelage. A reduction in the coefficients at • Change with.progression of the fall moult. The esticertain higher static pressure may be because of ran- mated thermal resistance of the winter pelage of d o m instrumental error or differencesin heat transfer white-tailed deer increased with progression of the fall characteristicsas the physical depth of the hair layer moult from October through December (Fig. 3), was reduced, or ah interaction of both. The thermal mainly because increases in length of the guard hairs structure of the winter pelage is complex owing to and underfur influence the physical depth of the presence of both guard hairs and underfur that form a pelage. However, the influence that growth of underdense, thick hair layer.The role of each hair fibre type fur hairs has on the physical depth of nonpiloerected in thermal energy transfer and a possible shift in the hair layer is not partitioned from increases in length relative importance of each with compression of the of the guard hairs. Values of thermal resistance were hair layer have not been characterb.ed. not computed for September because the transitional The general lack of sensitivity to compression pelage contains hairs of both seasonal pelages. observed for the winter pelage may be important to Regions of the body trunk apparently continue to inthe thermal economy of white-tailed deer, since deer crease in physical depth through early January, remain recumbent during winter storms, allowing whereas body regions of the middle and lower legs snow to accumulate over their body surface to 15 cm did not. or more (Jacobs~ in preparation). That may greatly As the winter pelage increased in physical depth increase the total insulation between body tissues and with progression of the fall moult, the estimated averthe thermal environment. age total thermal resistance of the 11 body regions In contrast to the winter pelage, the apparent TCC increased from 36 + 2.2% in October, to 77 + 5.5% of the summer pelage Of white-tailed deer increase in November, and 93 + 1.9% in December (of the significantly with compression of the hair layer of all fully-developed pelage measured in January) for Deer body regions (Table 3). Values increased from !.36 to A: the pattern was similar for Deer B as thermal re2.60 with an increase in compression from 0 to sistance increased from 29 + 5.5~o to 66 + 7.4% to 980 N m -z. The patterns of response to increased 93 :t: 2.5~/~ respectively. This suggests that under compression may he related to the lack of underfur similar ambient thermal conditions, white-tailed deer and morphology of the less dense hair layer of guard may lose substantially more heat during early fall than late winter. Further studies are needed to evaluhairs. 008

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156

NADINEK. JACOBSEN

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UIX~ Mid. Lo~ Bock Side BeSt,S~n,mL.~,~_ Mkl.Lo,,ef I,NECI(II--- FORELEG---I I

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Fig 3. Changes in the estimated thermal resistance with growth of the n o n p i l ~ winter pelage measured in October (solid bar), November (stippled bar}, and December (open bar) ~tpramd u a pcrcentaF of the fully developed pelage of January. Numbers in parenthes~ are the phF~ad depth (ram) of the hair layer measured in January. Th© upper and lower figures illustrate the pattern o¢ change observed respectively in a tamed adult female (Deer A) and juvenile male (Deer B) white-tailed deer. ate any significant change in the apparent TCC of the different body regions (Table 2) with progre~on of the moult cycle.

Conductive heat tran~er durino lyino activity Physiological and behavioural responses to changing thernud environments may modify the rate and direction of thermal exchange between a recumbent white-tailed deer and the substrata of its bedsite. Vasocomtrietion of peripheral vasculature reduces the flow of warm blood into throe tissues and, as the tissues cool, reduces the temperature difference between the exchange surflzas, and thus the potential that drives the flow of heat. That can be equivalent to increasinii the thicknem of the hair layer intervening between the skin and the thermal environment of an animal Bchavioural respom~ can alter the total surface area effocfive in conductive heat transfer during lying

activity, the body r,wom of varying thermal res~a n ~ in contact with the bedsJte substrata, or both. If a deer is ~ in erect ~ reeumbency with its limbs t u ~ e d tightly beneath the body (do.ed proture), the effective surface area is smaller than if the

limbs are extended and the carriage of the body relaxed, diq~llcinl it late.dly {open poeture). The dosed pmture is common when the enwronment presents a ~ thermal sink, as on cold mornings of early ~ m m e r or during ~bzero weather of late winter; ot~en the head is ttw,ked alonl~de the flank area, the~by min|mi~inlg the body surfaces exposed to both the bedsite and the atmosphere. The open posture of deer is more common to thermal environ-

mental conditions when heat dissipation rather than conservation may predominate; more of the body surfaces are exposed to the thermal environment, and in full expression of this pmture the animal may lie for short periods with its neck and head extended along the ground. T h a e postures are t u o c ~ also with heliothermie behaviour by deer d u r i ~ early summer morninIs, when they lie in direct m a i ~ t with .the hair layer piloerected, possibly fagilitIfiq penetration of heat through the hair layer to the body mrfaee,. Selectivity of bedmte s u l w n t a can alto daaeate or increase potential mnductive heat ~ I h a ~ seen captive white-tailed deer paw mow from t h w bedmte and then recline directly on the ffoxn lalffice; relatively drier bedsite I r c I t Ire ~ _ ~ _ d ~ m g thaw, when l m well-drained tiles are ot~Mmsaturated with water; mounds of dcgaying veltqation, warmer thin the surroundi~ Fotmd, are used o n ~ sum-

raer eve.inge: and __,9~__u61u¢ dm.p. expmzd soil ,mrfaces on hot summer days. Since ~ may vary widely in ~ ~ that altgt both th~ rate and total conductive heat ~ in ~ and qxice that aim alter the duration e( l y i ~ agtivity, sad the t d e c ~ n o f bed~ue IUbstmtI, are impcwtaat to the thermal ~o~.omy of white4alltd daer. The e t c t that dilkrem~ in ~ ~

of winter and intoner ~

tad w,erat phrtidoO-

eal and bchaviom-al r e t p o m ~ by white4alled deer may have on total conductive heat loss is evaluated for a recumbent adult animal of 490 N body weight. Lying in the dosed posture on a sofid surface, the effective surface areas transferring heat through direct

Differences of thermal properties of white-tailed deer pelage s.,.w,, w,.~,

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Fig. 4. Conductive heat transfer predicted for a recumbent 490 N (50 kg) white-tailed deer in summer and winter pelage when the hair layer is without (0 N m- z) and with (490 N m- z) compression that may result from differences in position, of the body during lying activity. Surface areas of the body reloons effective in heat transfer were expressed as fractions of the surface areas for each body region (see text). Cooling of the lower legs simulating vasoconstriction, decreases total conductive heat transfer to the substrata both for the compressed (upper edge of stippled area} and the uncompressed pelage (lower edge). Total conductive heat transfer across each seasonal pelage is expressed as a percentage of the respective seasonal fasting heat production (FHP) reported by Silver et aL (1969} for a white-tailed deer of this body mass in (A) summer pelage (131 W) and (B) winter pelage (88 W). contact with the bedsite substrata are estimated from the regional surface areas predicted from regression equations reported by Stevens (1972) and also by Moen (1973). The fractional areas of each body region of the trunk, the upper, middle and lower forelegs, arid the upper, middle and lower hindlegs are respectively 0.11, 0, 0.12, 0.25, 0.09, 0.13 and 0.30. Body surfaces in contact with other body surfaces are subtracted from the respective regional surface areas. Although the proportions of each regional body surface in contact with the substrata are difficult to determine, measurements made on tame recumbent white-tailed deer and inspection of photographs of animals in a variety of postures suggest that these estimates are reasonable approximations. In this posture, the total effective surface area in contact with the substrata is estimated at 0.20 m z (equivalent to 12~ of the whole-animal surface area). Conductive heat transfer was computed for each effective body region by utilizing the values summarized in Tables 1, 2 and 3. Total conductive heat transfer across each seasonal pelage increases linearly with increases in the temperature difference between the thermally effective surfaces of the recumbent white-tailed deer and its bedsite substrata (Fig. 4). At a given difference in temperature between the body surfaces and bedsite, however, the total conductive heat transfer of the uncompressed hair layer is about 2.58 times as great for the summer pelage as for the winter pelage. Compression of the hair layer of either seasonal pelage increases total conductive heat transfer, although the effect is only about one-sixth as great for the winter as for the summer pelage. Vasomotor responses have not been documented in white-tailed deer, however the thermal significance of both regional temperature and volume distribution of blood through peripheral tissues should be similar to observations of several domestic species (Blaxter, 1962). Vasoconstriction of the peripheral vasculature of the lower legs of white-tailed deer in either seasonal pelage conserves body heat that would be lost if higher differences in temperature were maintained (stippled areas of Fig. 4).

In winter, a temperature difference of 35 K is likely and heat transfer to the substrata approximates 40% of the winter fasting heat production (FHP) reported by Silver et aL (1969) (if all tissue surfaces are mainrained at 308 K and the substrata is at 273 K). A decline in temperature of only the lower forelegs and lower hindlegs from 308 to 290 K, in this example, reduces the predicted conductive heat transfer from about 40 to 20 W (about 20°,/oof the winter FLIP). A reduction in temperature of other body surfaces in contact with the substrata and/or a decrease in the effective surface area would further reduce conductive heat transfer. White-tailed deer in summer pelage are unlikely to experience temperature differences as high as 35 K, although 17 K is probably common. If this characterizes jdl thermally effective surfaces, heat transfer across the uncompressed pelage hair layer approaches 40~ of the summer FHP. However, a reduction of the temperature difference of the lower limbs from 17 to 10 K decreases the predicted heat loss from about 50 to 25 W (about 20°/0 of the summer FLIP) because these regions are poorly insulated. The effect that vasomotor responses may have on total conductive heat transfer during lying activity is, therefore, comparable to" the effect of selecting bedsite substrata that result in a smaller difference in temperature, or the effect of 4he warming of the substrata surface by heat transferred from the animal body, both resulting in reduced heat loss. Thus, whlte-taii~l deer may regulate total conductive heat transfer during recumbency at similar levels of the respective seasonal FlIP through bchavioural and physiological responses and change in the thermal resistance of the pelage, thereby ameliorating the energetic requirements of inhabiting the strongly seasonal northern temperate zone. The pattern of changes in bchaviour and activity of white-tailed deer in different thermal environments will be given elsewhere (Jacobsen, in preparation). Acknowledoements---! thank W. P. Armstrong and F. L Jacobsen for help in obtaining the animals, preparing pelage samples, and with many of the measurements. The

158

NADINE K. J^coB.~r~

assistance of A. N. Moen in providing the thermal conductivity apparatus and financial support is gratefully acknowiedged. Chief Comerniskey of the Seneca Army Depot facilitated collections of wild deer used in this study. This work was funded through Pittman-Rohertson WR-4 and the New York Department of Environmental Conservation. REFERENCES ASTM Subcommittee C16.30. (1974) What property do we measure? Heat transmission measurements in thermal insulation, ASTM STP 544, pp. 5-12. American Society for Testing & Materials, Philadelphia. BENIqL~'T3"J. W. (1964) Thermal insulation of cattle coats. Aust. Soc. Anita. Prod. S, 160-166. BIRKEBAKR. C. (1966) Heat transfer in biological systems. In International Review of General and Experimental Zoology (Edited by F~TS W. J. L. & HAatmON R. J.) YoL 2, pp. 269-344. Academic Press, New York. BLAXT~ K. L (1962) The Energy Metabolism of Ruminants. Thomas, Springfield. CENA K. & MOtqlr~it4 J. L (1975a) Transfer processes m animal coats. I. Radiative transfer. Proc. R. Soc. Lond. B 188, 377-393. CENA K. & MON,rairt J. L. (1975b) Transfer pr _oce~___ces_in animal c o a t II. Conduction and convection. Proc. R. Soc. Lond. B. I l L 395--411. CEqA K. & MO~,m,,~ J. L. (1975c) Transfer proces,~t in animal coats. IlL Water vapour diffusion. Proc. R. Soc. Lond. B. I U , 413-423. COWAN M c T . & RADDt A. G. (1972) Pelage and molt in the black-tailed deer (Odncoileus hemionus). Can. J. Zool. ~0, 639--647. DAvm L. B. JR & B ~ R. C. (1975) Convective energy tramfer in fur. In F.co/ogica/Studies (Edited by GATI~ D. M. & SoemL R. B.) Vol. 12, pp. 525-548. Springer, New York. DAWSONT. J. & BltOWN G. D. (1970) A comparison of the inuthttive and reflective properties of the fur of desert kanllarOm. ¢omp. Biochem. Physiol. 37, 23-38. EVANS K. E, (1971) Energetim of sharp-tailed 8rouse (Pedk~cetes phashmellus) during winter in western South Dakota. Ph.D. dissertation, Cornell University, Ithaca, New York.

GEIOElt R. (1965) The Climate Near the Ground. 4th edn (rev.) Translated by Scripta Technica, Inc. Harvard University Press, Cambridge, MueachusettsHAMM~L. H. T. (1955) Thermal properties of fur. Ant J. Physiol. IS:l, 369-376. HART J. S. (1956) Seasonal changes in insulation of the fur. Can. J. Zool. 34, 53-57. JACOS.~m N. K. (1973) Physiolosy, behavior, end thermal transactions of white-tailed deer. Ph.D. dissertation, Corneil University, Ithaca, New York. KltelTH F. (1965) Principles of Heat Transfer. International Textbook Co, Scranton. LEwrz C. P. & HA~T J. S. (1960) The effect of wind and moisture on heat loss through the fur of newborn caribou. Can. J. Zooi. ~ , 679-688. MOEN A. N. (1973) Wildlife Ecology. W. H. Freeman, San Francisco. M o o ~ 1. (1955) The thermal insulation of caribou pelts. Textile Res. J. 25, 832--837. MotaglSON P. (1966) lnsulative flexibility of the guanaco. J. Mammal. 47, 18-23. SCHOLAN~ P. F, WALTt~S V., HOCg R. & IRVtNO L. (1950) Body insulation of some arctic and tropical mammals and birds. Biol. Bull. 99, 225-236. SE~ERINOHAUSC. W. & CHEATUM E. L. (1956) Life and times of the white-tailed deer. In The Deer of North America (Edited by TAYLOa W. P.) pp. 57-186. Stackpole Company, Harrisburg, and the Wildlife Management Institute, Washin$ton, DC. SIEGELS. (1956) Nonparametric Statistics for the Behavioral Sciences. McGraw-Hill, New York. SILVER H, COLOVOSN. F., HOLTER J. B. & HAYES H. H. (1969) Fasting metabolism of white-tailed deer. J. Wtldl. Man~e. 33, 490-498. STEEL g. G. D. & TOp.mE J. H. (1960) Principles and Procedures of Statistic& McGraw-Hill, New York. ST~Vl~NS D. S. (1972) Thermal energy exchange and the maintenance of homeothermy in white-tailed deer. Ph.D. dissertation, Cot'nell University. Ithaca, New York.

Key Word lndex--Odocolleus viginianus; white-tailed deer; thermal conductivity; coat thickness: seasonal thermal resistance of pelage.