Locomotion and Activity Phasing of Some Medium-Sized Mammals

American Society of Mammalogists

Locomotion and Activity Phasing of Some Medium-Sized MammalsAuthor(s): J. Lee KavanauSource: Journal of Mammalogy, Vol. 52, No. 2 (May, 1971), pp. 386-403Published by: American Society of MammalogistsStable URL: http://www.jstor.org/stable/1378681 .

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LOCOMOTION AND ACTIVITY PHASING OF SOME MEDIUM-SIZED MAMMALS

J. LEE KAVANAU

ABSTRACT.-Six carnivores and a monkey studied in the laboratory spent most of their active time treading a wheel. Some of the animals had essentially the same phasing of activity known or presumed in the wild, namely the pig-tail macaque (diurnal), ringtail (nocturnal), and bobcat (arrhythmic). The tayra and grison were diurnal, raising the possibility that the nocturnal activity reported in the field is a consequence of man's encroachments. The bimodal activity of the grison (and to a lesser extent the tayra), including a mid-day siesta, concurs with behavior under semicaptive field conditions. Both the bobcat and domestic cat were arrhythmic, with pronounced peaking of activity during artificial twilights. The red fox was primarily nocturnal with activity peaking during periods of twilight but, as in the field, daytime activity also occurred. The macaque, grison, and tayra were relatively insensitive to temporary abrupt changes in light intensity during their activity periods. The ringtail was more like nocturnal rodents, being fairly rigidly bound by conditions of illumination. The red fox and bobcat were inhibited by dim light and darkness. The bobcat was entrained to a 4-hour "day" by alternating dawns and dusks every 2 hours. Gaits ranged from the slow "deliberate" walk of the cats to occasional galloping by the red fox, ringtail, and cats. In addition to walking, the macaque and tayra engaged in acrobatics. All seven animals showed strong tendencies to tread in one direction, despite starting and stopping hundreds of times.

Running in activity wheels probably is the best method for assessing activity and rhythmicity of confined small mammals. In effect, a wheel provides an endless straight path along which animals can tread unhindered at their chosen gaits (Kavanau, 1970). This technique has been used heretofore with only one animal larger than the rat, namely the Tasmanian devil, Sarcophilus harrisii (Packer, 1966). I report here the initial findings of a study of seven medium-sized mammals representing five families and ranging in weight from a 1-kilogram ringtail to a 6.5-kilogram bobcat. These spent a large fraction of their active time treading a wheel as did small mammals (Kavanau, 1967, 1968, 1969).

MATERIALS AND METHODS

The study group consisted of single young adult females of the tayra (Eira barbara), red fox (Vulpes vulpes), bobcat (Felis rufus), and domestic cat (Felis catus); single adult females of the ringtail (Bassariscus astutus) and grison (Galictis vittatus); and a young adult male pig-tail macaque (Macaca nemestrina). Except for the ringtail and grison, all specimens were obtained as young and raised to young adulthood. The tayra and grison were captured in Ecuador, the bobcat, red fox, and ringtail in Texas, and the pig-tail macaque in Thailand. All but the macaque were maintained outdoors until studied. Food was given daily (see Crandall, 1964), with water present continually. Times of providing food during experiments were selected to disturb the animals minimally.

An activity wheel 122 centimeters in diameter and 29 centimeters wide was mounted on ball bearings in a frame of timbers and plywood (Fig. 1). It consisted of plywood

386



May 1971 KAVANAU-MAMMALIAN LOCOMOTION AND ACTIVITY

FIG. 1.-Activity wheel, cage, and incandescent lights (east light on). The communicat- ing aperture between the wheel and the cage is not visible.

discs joined along their circumferences by 1-centimeter wooden dowels at 3.8-centimeter spacings, with a strip of hardware cloth attached outside the dowel treading track. Revolutions and speed and direction of rotation were sensed by a tachometer generator and microswitch (Kavanau, 1963, 1966). The wheel was aligned along an east-west axis adjoining a cage (Fig. 1) containing a nest box, water, and tray of sand. The enclosure was in an air-conditioned room (temperature varied from 19 to 23?C and relative humidity from 40 to 60 per cent).

Twilights lasting roughly 1 hour (range, 0.015 to 39 lux = lumens per square meter) were simulated as described by Kavanau (1969). Daylight was simulated by one of two 100-watt incandescent bulbs mounted 20 centimeters below the top of the wheel at each end (Fig. 1). When running, an animal faced toward or away from the lighted bulb.

387



JOURNAL OF MAMMALOGY

Except during orientation tests, the incandescent bulb was supplemented by 240 watts of fluorescent ceiling lamps. With both sources energized, the range of daytime illuminance levels was from 210 lux (farthest possible position of the animal from the lights) to 3200 lux (nearest possible position). With a 100-watt bulb alone, it was from 140 to 2700 lux. Night light was provided by a G.E. no. 44 incandescent lamp mounted below each 100-watt bulb and energized at 0.65 to 6.5 volts (range, 1.5 X 10'- to 1 lux at 1 meter). Illuminance levels given in the figures and text below are at a distance of 1 meter-roughly the average displacement of the heads of the animals from the light sources. Experimental procedures, recording, programming, and so forth, were the same as described for small mammals (Kavanau, 1963, 1966, 1967, 1968, 1969).

In most cases the light cycle consisted of 12 hours of bright light (320 lux), 10 hours of dim light (0.014 lux), and 1 hour each of dusk and dawn (Table 1). Except for the tayra, the indoor beginning of dawn and end of dusk occurred within 1 to 2 hours of astronomical sunrise and sunset (beginning and ending of the contributions of the sun to the light level). The seven specimens adapted to the experimental situation-adopting their characteristic gaits and phasing of activity-in from 3 to 14 days. The data in Table 1 (except those for total days studied) are for the periods after adaptation occurred. Study periods subsequent to those represented in Table 1 were used to test the effects of abrupt changes in light level, alternating twilights, and influences of light position on orientation.

RESULTS

Activity Phases and Patterns

The macaque, tayra, and grison were diurnal (Table 1, Figs. 2 and 3). The macaque's activity extended over most of the day but was greatest during dawn and the post-dawn hours. There was a strong tendency to nap during midday. The grison became active about 2 hours after the end of dawn. Activity occurred in 2 to 4 bouts of more or less continuous locomotion separated by commensurate periods of rest. The activity pattern was bimodal, as the grison typically took a midday siesta of several hours (Figs. 2 and 3). The morning activity usually consisted of a single 3- to 5-hour bout. The afternoon activity was variable, sometimes split into several bouts (Fig. 2) or even omitted. Activity generally ceased during dusk. When I shortened the day 3 hours, to see if I could force the grison to be active during dawn, it "compensated" by shortening its activity period, and remained inactive during dawn. The tayra generally became active several hours after dawn, was active fairly continuously for 7 to 8 hours, and retired several hours before dusk. On some days, activity was interrupted by a short midday siesta. I was able to overlap the tayra's activity on the twilight periods by shortening the daylight period from 12 to 7 hours. It then became active during dawn and retired during dusk (Figs. 2 and 3, Table 1).

The grison and tayra probably would have been 100 per cent diurnal (day plus twilights) except for the small disturbances on providing food 1 to 3 hours after dusk. The macaque's food had to be given 1 to 2 hours before dusk, for this animal tended to become quite excited and active when disturbed at night. Its 5.1 per cent activity at night (Table 1) was sporadic and caused partly by unavoidable disturbances.

388 Vol. 52, No. 2



TABLE 1.-Comparative findings for activity indices and phasing for the periods of activity plotted in Figs. 2 and 3. The average distance "traveled" per 24 hours refers to the distance traveled along the periphery of the wheel. The red fox range of 95 to 232 minutes active per

24 hours excludes 12 nights (out of 29) at somewhat inhibitory low light levels, for which the range was 49 to 192 minutes.

Animal

Grison

Tayra

Pig-tail macaque

Domestic cat

Bobcat

Red fox

Ringtail

Days studied

These Total data

40 10

36 9

17 7

20 7

49 19

59 29

70 21

Hours of "daylight"

12

7

12

12

12

12

13

Total minutes active per 24 hours

Avg. Range

270 148-365

184 113-280

88 44-130

54 12-67

147 85-208

143 95-232

314 258-351

Per cent of total activity

Day Night Twilights

98 0.03 2.1

89 2.1 9.2

86 5.1 9.0

38 25 37

20 57 23

0.3 81 19

0 94 6.4

Speed (meters per second)

Avg. Max.

0.95 3.4

1.6 5.4

0.98 4.3

0.52 2.6

0.78 5.2

2.0 6.5

1.2 3.7

Average session length

(seconds)

5.4

10

2.5

8.1

3.2

15

17

Maximum Avg. distance unceasing "traveled"

activity per 24 hours (minutes) (kilometers)

40 15

48 18

9 5.2

15 1.7

26 6.9

24 17

19 21

zI

z4 01- C) 0~ 0 H

0

C)

H

H



JOURNAL OF MAMMALOGY Vol. 52, No. 2

'Running' 'Running' . . Eastward Not Westward

Running

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Speed of Periphery of Wheel (meters/second)

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,.*-S ; ','_t-P end of .' -r ,- dawn

FIG. 2.-Representative analogue records of locomotor activity for six mammals (records separated by dashed horizontal and vertical lines). Each dot gives the instantaneous direction of rotation and speed at the periphery of the wheel, as recorded every 4 seconds. Dots to the right of the centerline denote treading westward; to the left, eastward (see upper left labels). Central dots and vertical centerlines indicate a stationary wheel. Speed is indicated along the abscissae. Short horizontal lines crossing the centerline mark off the 1-hour intervals numbered along the ordinates. Time advances from bottom to top. The first 3 hours, in which no activity occurred, are omitted from the grison's record. The ringtail did not run at high speed during dusk on the night shown.

The ringtail was 100 per cent nocturnal (night plus twilights). It generally became active in mid-dusk to late dusk, was active most of the night, and retired from early to mid-dawn (Figs. 2 and 4). Food was provided during the day while the animal slept. The red fox was almost 100 per cent nocturnal

390

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-4-- 2101

. - 4- 3 5 4

Red Fox

2 3- 5

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8-

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May 1971 KAVANAU-MAMMALIAN LOCOMOTION AND ACTIVITY 39

Acrobatics (Sessions/Revolutions)

\ A-A I*-~~~~~~~~~~~?

Average Non-Stop Session Length

/ -

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of Wheel

_' Dawn Hour -- Dusk Hour

/ A\- 41 \ ~~~~~~~~~j

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Active Time -*ATayra -. Grison -* Pig-taill

Macaque-

Hour Intervals

FI[G. 3.-Plots of locomotor indices as a function of time of day for the three diumal animals during the experimental periods of Table 1. The small amnount of activity that occurred during the night (see text and Table 1) is not plotted.

2.5- 0

cr0.5-

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391




(night plus twilights) during the first part of the study (29 days of Table 1). Activity peaked during dusk, midnight, and dawn (Figs. 2 and 4). It occurred in 5 to 10 bouts lasting from 5 minutes to 2 hours. In the subsequent 3-week period of study, when some of the night light levels being tested were inhibitory (see Fig. 6), sporadic daytime activity began to occur. Much of this was 1 to 2 hours before dusk, sometimes overlapping the times of food re- plenishment. At first the daytime activity during this subsequent period amounted to only 4 per cent of the total but during the last few days (when the animal also began sleeping in the wheel) it increased to 19 per cent.

Both the bobcat and domestic cat were arrhythmic, with activity distributed in bouts and peaking during twilights (Table 1, Figs. 2 and 4). The bobcat's bouts averaged 21 minutes by night and 13 by day. Rest periods between bouts averaged 67 minutes by night and 161 by day; 71 per cent of the bouts occurred at night (including twilights). The activity of the domestic cat was scattered in a few bouts of 5 to 40 minutes.

Both cats spent most of their inactive time resting in the wheel, where exposure to light was at a maximum. Although replenishing the bobcat's food at various times during the day did not always awaken it, some of the daytime activity was brought on by this act. Some of the postdawn activity of the domestic cat also was brought on by the disturbance of providing food (at from 0.5 to 3 hours after dawn).

Gaits, Speed, and Session Lengths

The macaque alternated between walking on all fours (at about 1.5 meters per second) and swinging, hanging, standing, and jumping on and off the wheel axle. Acrobatics usually predominated in the morning and walking in the afternoon (Fig. 3). A period of sustained walking is seen in the fourth pre-dusk hour in Fig. 2. The average speed of movement of the periphery of the wheel (Table 1) represents both walking and acrobatics. The increase in the macaque's speed in the 3 predusk hours (Fig. 3) is essentially an artifact associated with providing food, but speed was on the increase, in any event, all through the afternoon.

The length of an activity session (usually averaging 2 to 30 seconds) was reckoned from the time the rotation rate of the wheel reached 10 per cent of full scale in a given direction on the recorder chart (Fig. 2, 10 per cent of 4 meters per second to the right or left) and triggered a limit switch, to the time it fell back below 10 per cent in the same direction. Since rocking of the wheel accompanies acrobatics, the macaque's average session length was very short (Table 1). For the same reason, the ratio of sessions to revolutions (that is, of rocking to steady advance) gives a good quantitative index of acrobatics (Fig. 3). The maximum period of unceasing activity (Table 1) is the longest period of continual movement of the wheel, regardless of speed or direction. For the macaque this was only 9 minutes.

392 Vol. 52, No. 2




Speed of Periphery of Wheel

o 2.04- QoQo.c>o, Dusk o2.0- Hour I 1.6-

?? Co<^ A ~ ~ ~ J A ^Dawn a, 1.2- ._A_A_ __ ,_AAA~ Hour-

0.8- *--

- *o Red Fox Active Time -R Bobcat 60

^ % \ %,a -A Ringtail <D -~ "

?./ \ -^'N~ " Domestic Cat E .400- $

.._ 2- V.~ Q -/^ o . . . . . \. . . ̂ . . . . . . . . . . . \ . .

o, . , , 0...f...?.....,...Hour Intervals Hour Intervals

FIG. 4.-Plots of locomotor indices as a function of time of day for the nocturnal and arrhythmic animals during the experimental periods of Table 1.

The grison and tayra customarily walked at a medium to rapid pace, with the latter occasionally trotting. The tayra engaged in acrobatics to a minor extent. Its maximum period of sustained activity (Table 1) was the longest in the group. Although the tayra's average session length for the 9 days of Table 1 was only 10 seconds, on some days it attained 25 to 30 seconds. The ringtail customarily trotted, but it occasionally galloped for brief periods during the night and often did so for longer periods during twilights (Fig. 2 and below). It had the longest average session length in the group (Table 1).

The fox had three gaits-a medium trot at 1.6 meters per second, a fast trot at 2.6 meters per second, and a gallop at up to 6.5 meters per second. For the most part it trotted fast, with frequent but short periods of galloping (Fig. 2). On some days it alternated continually between the three gaits, leading to a double-banded record for the two trots.

The bobcat walked "deliberately" at about 1 meter per second, but it occasionally galloped briefly at up to five times faster. Daytime walking tended to be faster but less sustained than at night. Although its average session length was only 3.2 seconds for the 19 days of Table 1, on some other days it was as high as 23 seconds. Slow walking also predominated for the domestic cat, with occasional brief galloping.

393




Orientation

All seven animals showed strong tendencies to tread unidirectionally (Figs. 2 and 5). For the periods covered in Table 1, the directional percentages were as follows. The macaque averaged 87 per cent west (maximum, 95) and the grison 97 west (maximum, 99). Subsequently the grison became variable, usually changing direction four or five times per day. The bobcat averaged 94 per cent east at night (maximum, 100) and 87 during twilights. For the domestic cat the figures were 97 east by day, 91 by night, and 87 by twilights (maximum for a 24-hour period, 100). The tayra often oriented at the 97 to 99 per cent level and the red fox at above 95 per cent (maximum, 99), but their directions were unpredictable from day to day. The ringtail consistently oriented to the west at the 99 per cent level.

Except for the ringtail, a change in the position of the light did not influence the choice of running direction, as it often does with small mammals (Kavanau, 1967, 1968, 1969). The first time the position of the light was changed (from east to west) the ringtail, which had oriented 99 per cent west consistently for weeks, reversed direction. However, it subsequently resumed the westward habit, regardless of the position of the light. Thus, the light source appears to have influenced orientation, but once its position became variable its influence on running direction waned and, finally, disappeared.

Responses to Changes in Illuminance Level

The three tropical, diurnal representatives (macaque, tayra, and grison) were more or less indifferent to temporary changes in daytime light level. Thus, when the level was changed abruptly every hour or half hour (range, darkness to 320 lux), the activity and orientation of the animals scarcely were influenced. The only notable effects were that the tayra walked more slowly and both the macaque and the tayra ceased acrobatics in extremely dim light and darkness. All three animals were liable to become active temporarily if disturbed at night (even in darkness).

The ringtail gave marked responses to abrupt alternations of the night light intensity (range, darkness to 0.12 lux-Fig. 5). Active time was affected to the greatest degree, consistently (that is, during each 1-hour cycle) being up to 71 per cent greater at the lower of the two levels. Average speed of trotting consistently was highest in darkness (Fig. 5). Orientational consistency was unaffected.

Unlike the ringtail and diurnal species, the red fox and bobcat were inhibited by darkness and extremely dim light (0.00005 lux-about 0.4 per cent of the light on a clear moonless night). Such dim light in alternate half hours even led to a reduction of bobcat activity in the in-between periods of brighter light (to about half the control level). The fox's active time and average session length increased with increasing light level up to the highest value tested (1 lux), whereas trotting speed appeared to peak at about 0.1 lux- roughly half the intensity of full moon (Fig. 6).

394 Vol. 52, No. 2



May 1971 KAVANAU--MAMMALIAN LOCOMOTION AND ACTIVITY

Speed Percent Ligh (m/sec) of Time SchedL

1.00 52 * .. : ':<-' - ,- -

0.96 58 . *' c

1.06 51 "' -r. /:- . "

0.99 65 - j"hr C

1.12 83 . '.:..:-.': *

1.01 48 *. - F c

1.17 80* -. -

1.22 79 .*, *I 1.09 51 c' -'. ,.

'

-__ ..i~ : 5.' ... .:.- *- -'o..

1.26 81 -i , *

1.19 49 - ,s, '- a c

1.26 83 ' r. ..- --x,.r-I

1.15 75 - . :. o 1.29 S7 .". . .: ':. * *

1.17 79 ; 0:

Half-Hour * Dark; o-3x104 Lux = Averages 1/10 Starlight

t jle

31-

1

FIG. 5.-Trotting record for the ringtail on a night when the light level was alternated each half hour between 3 X 10-4 lux and total darkness. Note the striking alternate effects of the light levels on speed and per cent of time active. The 30-minute periods are delineated by horizontal bars just to the left of the centerline and by vertical bars at the far right. Light scheduling is indicated at the far right next to the 30-minute marks. Average speed and per cent of time trotting each half hour are given at the far left. The light source was to the left (east), that is, the animal trotted facing away from it.

Performance differences for the bobcat at different light levels often were dominated by the influences of galloping. Generally there was more galloping (and, hence, more rocking and more and shorter activity sessions) at the higher of two test levels, because the animal often broke into a gallop at the time the light level increased abruptly, but not when it decreased. At two

395

l

)i

I




relatively bright night levels (0.2 and 0.5 lux), galloping was roughly equal. Under these conditions, session lengths consistently were 50 per cent greater at the brighter level, whereas speed, active time, and orientational consistency were unchanged.

Twilight Responses

In addition to the influences of twilights on activity phasing, there were effects on orientation and speed; orientation consistently tended to be lower than at other times and, except for the tayra and grison, locomotion faster (Fig. 2). However, the gradual changes in speed with changes in twilight light level that are evidenced by small mammals (Kavanau, 1962, 1967, 1968, 1969) did not occur. The high-speed running of the ringtail during twilights, particularly dawn, was the most spectacular of any animal studied (Figs. 2 and 4).

A critical test of twilight influences is to present a series of dawns and dusks during the normal activity period (usually with 30 or 60 minutes of daylight after dawn and nightlight after dusk). Responses to this regime show whether twilight influences are independent of the times when the twilights occur. If so, this light schedule might "turn activity on and off" alternately, as it often did in experiments with white-footed mice (Kavanau, 1968, 1969).

Although alternately presented twilights were without apparent consistent effects on the behavior of diurnal animals and the red fox, they markedly affected the ringtail. On the first "night" of alternately presented twilights it ceased activity during each of the four dawns, was inactive during the four following daylight periods, and became active again during each of the four dusks.

When alternating twilights are presented to a nocturnal or diurnal animal for several days in succession, they often lead to a reduction of activity and a disruption of rhythmicity. One would not necessarily expect the performance of an arrhythmic animal to deteriorate under these conditions and, in the case of the bobcat, it did not. Alternating twilights were presented to the animal continuously for 152 hours, with 1-hour periods of day and night light in between-equivalent to 38 4-hour "days." The bobcat entrained well to these short "days," being most active during dawn (38 per cent of total activity), least active in bright light (14 per cent), and intermediately active at night (28 per cent) and during dusk (21 per cent). Activity was greatest during dawn on 20 of the 38 "days" and least on 6 of them. During daylight, however, it was greatest on only 3 of the "days" but least on 17 of them.

Far from having an inhibitory effect on the bobcat, there was 64 per cent more activity per unit of time on the schedule of 4-hour "days" than on 24-hour days. That the entrained 4-hour rhythm had no superimposed 24-hour one was shown by plotting the results on the basis of a 24-hour cycle. Tests were not made with the domestic cat.

396 Vol. 52, No. 2




Speed of Periphery of Wheel

:-

a) 2.0- cn \ C) -

| 1.5- Average Session Length

0.4-

0.3- a)c

c 0.2-

0.1- Active Time

Red Fox 15-

E 10-

4- . 5- i

Log Lux

0 o -1 -2 -3 Full Moon Starlight

FIG. 6.-Plots of locomotor indices for the red fox showing effects of illuminance level. Sixteen nights are represented, on each of which the level of illuminance was alternated between two values every half hour. There were four schedules, each of which lasted four consecutive nights and is represented by a pair of connected solid circles. The solid circles of the connected pairs give average values of the activity indices at the two illuminance levels on the four 4-night schedules. The abscissa for the right-most points is -4.3.

397




Warm-ups

Inasmuch as the medium-sized mammals proceed mostly at relatively slow paces, they might not be expected to warm up gradually to top speed after periods of inactivity, as do small mammals (Kavanau, 1967, 1968, 1969). Warm-ups were, in fact, lacking for the monkey and negligible for the cats, although moderate for the ringtail and tayra. After a long rest the grison usually warmed up gradually over the first 0.5 to 2.5 hours of a bout (Fig. 2); the red fox sometimes warmed up.

DISCUSSION

Great individual behavioral differences may exist among the highly adaptable and opportunistic species of this study. Because only one individual of each species was used, and some were raised in captivity and others captured as adults, the above findings are not necessarily characteristic of these species (even under laboratory conditions). The results and their discussion should be viewed more as illustrative of the potentials of the approach than as establishing definitive characteristics or relationships.

Activity Phasing in the Laboratory and Field

I use the term "activity type" to refer to the dominant habit of an adult animal with regard to the phase of the light cycle during which most of the activity occurs-diurnal, nocturnal, arrhythmic, or crepuscular (Kavanau, 1969). The activity type displayed in the laboratory is not necessarily the same as that in the field. The field type is an expression of complex interactions of the organism with many habitat factors, including light, predator pressure, availability of food, latitude, and season. On the other hand, in otherwise constant environmental conditions in the laboratory, the light regime is the chief external factor influencing activity phasing (this is not to deny the possible influences of other factors, such as field experience, breeding condition, and time and frequency of feeding).

I have adopted the working hypothesis that the activity type in laboratory light that simulates natural conditions (twilights, bright day light, dim night light, and appropriate lengths of day and night) gives a better indication of the genetically determined state of adaptation of the visual system than the phasing in the field. I call the laboratory type the "visual activity type." If this is the same as that found in the wild-the "ecological activity type"-I refer to the activity type as "stabilized."

The finding of a stabilized activity type is a good indication that the visual

system is closely adapted to the current field habits of the animal. On the other hand, if the visual and ecological activity types differ, the visual system probably is not best adapted to these habits. In the latter case, the visual

system would be exposed to selection pressures away from the ancestral condition toward a condition more suited to present field behavior. The change

398 Vol. 52, No. 2




from past field habits might be recent (influenced primarily by man), with the visual system as yet unchanged from the most recent ancestral type, or old, with the visual system already deviating from the ancestral type. Large-eyed animals with duplex retinae present a special case. For them, good vision often is possible under a wide range of light levels, so that selection pressures on the visual system as a result of changes in activity phasing might be small.

It is tacit to the above working hypothesis that many mammals can adopt habits for which their visual systems are not best suited. Indeed, studies of the vertebrate eye suggest that diurnality and nocturnality can appear and disappear over relatively short periods, evolutionarily speaking, as mutations and selection pressures direct (Polyak, 1957; Walls, 1967). Short-term adaptability is illustrated by many cases of mammals that are diurnal or arrhythmic in regions where they are unmolested but become nocturnal in areas where they are disturbed by man. The group includes such diverse representatives as mink, otters, yellow mongooses, lesser oriental civets, coatis, African bushpigs, American badgers, agoutis, and water buffaloes (Kaufmann and Kaufmann, 1963; Walker, 1964; Astley Maberly, 1967; Rue, 1967; Brosset, 1968).

In my studies of white-footed mice (Peromyscus species) and eastern chip- munks (Tamias striatus), the indoor phasing of activity was the same as that in the field (Kavanau, 1967, 1968, 1969). On the other hand, least weasels (Mustela nivalis), which are arrhythmic in the field, were 99 per cent nocturnal (night plus twilights) in the laboratory. Following the working hypothesis (and keeping in mind that they have small eyes), this suggests that least weasels had a nocturnal recent ancestor and that their visual system is exposed to selection pressures toward the arrhythmic type.

Quantitative determinations of the ecological activity types of unmolested animals are virtually nonexistent. One must rely, instead, on qualitative field observations and quantitative estimates under semicaptive conditions, such as in large field enclosures. Pig-tail macaques are said to be mainly diurnal in the field (Walker, 1964), which is consistent with the finding of 95 per cent diurnality for my specimen. The behavior of this one specimen hints at a possible napping of pig-tails during the heat of midday in the wild.

The bobcat is active mainly after dark but ventures forth in daylight (even bright sunlight) more than most other wild cats (Young, 1958; Leopold, 1959). My findings (Table 1) fit this characterization and suggest that a high degree of crepuscularity is superimposed on a basically arrhythmic type.

Some of the findings for the domestic cat should be qualified. The greater amount of day than night activity (38 versus 25 per cent), as opposed to the finding for the bobcat (20 versus 57 per cent), probably is not valid. The domestic cat was a pet and was extremely sensitive to faint sounds outside the experimental room during the day. These kept her awake and meowing much of the bright-light period. In a subsequent 41-day outdoor study, the same animal was arrhythmic with pronounced peaking of activity during

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twilights but, unlike in the indoor study, only 20 per cent of the activity occurred during the day.

The finding of 100 per cent nocturnality for the ringtail agrees with the animals reputation (Leopold, 1959; Seymour, 1960). For tayras, however, reports conflict. Some workers reported them to be primarily nocturnal (Cabrera and Yepes, 1940) and others chiefly or solely diurnal (Enders, 1935; Kaufmann and Kaufmann, 1965; Brosset, 1968), whereas Gaumer (1917) found them to be active both at night and on overcast mornings. The single specimen studied by Brosset (1968) was most active in the early morning and afternoon. The finding of 98 per cent diurnality for my captive- raised specimen might help to resolve the conflict; tayras might be diurnal where unmolested but tend to become nocturnal where disturbed by man. It is significant in this regard that the other diurnal tayras either were wild, insular specimens or tame animals in semicaptive conditions, with no fear of man. The fact that my specimen was not inhibited by dim light or darkness suggests that, despite the diurnal preference of some tayras, these animals are well suited for nocturnal activity.

The grison is said to be chiefly diurnal (Dalquest and Roberts, 1951; Morris, 1965; Rue, 1967), although Walker (1964) reported activity during day and night. Inasmuch as my specimen was 100 per cent diurnal and responded much like the tayra, and because both are tropical mustelids with many similarities, the same comments likely apply to the activity types of both. The grisons of Kaufmann and Kaufmann (1965) were most active in the early morning and late afternoon and usually slept in burrows or other shelter during the heat of midday. This strengthens the case for the applicability of at least some aspects of laboratory activity patterns to field behavior because my specimen also was most active at these times and always took a midday nap.

The most relevant studies of red foxes are those of Osterholm (1964) and Tembrock (1958). Activity of their specimens was greatest before and after sunset and sunrise (unobstructed horizons and zero elevation of the sun above the surface of the earth), but there were large seasonal influences. Thus, red foxes in the field may be largely crepuscular in autumn, largely nocturnal in winter, and appreciably diurnal in the summer, at least at high latitudes. My findings (4 June to 1 August) suggest that red foxes tend strongly toward nocturnality, with their most intense activity during twilights. The emergence of increasing daytime activity during the last 3 weeks of the study correlates with the seeming independence from (or seasonal variations in the influences

of) light conditions in the field.

Distribution of Activity

The bout-like activity of the cats, red fox, and some other carnivores in the

laboratory (Crowcroft, 1954; Kavanau, 1969), as opposed to the more nearly continuous activity of the ringtail, tayra, pig-tail macaque, and most of the rodents studied (Kavanau, 1966, 1967, 1968), might be related to differences

Vol. 52, No. 2 400




in hunting and feeding habits in the field. One might expect that the larger the prey taken, the greater the degree of exertion required in predation, and the more food consumed per meal, the more likely that activity would be broken into bouts separated by periods of rest. Animals that lie in wait for prey also might be expected to be active intermittently. A relatively low level of activity and consequent intermittent activity of cats would be consistent with their hunting habits.

The relatively sustained activity of my grison, tayra, and ringtail is consistent with their feeding habits in the wild, namely the taking of small prey and a varied omnivorous diet. Bobcats subsist chiefly on rodents and rabbits, although they sometimes take much larger prey (Young, 1958; Leopold, 1959). Small rodents make up the bulk of the prey of red foxes (Hamilton, 1935; Osterholm, 1964), with occasional fruits rounding out the diet.

Activity and Illuminance Level

The influences of different illuminance levels and twilights on the seven animals gave fairly consistent pictures. During their activity periods, the three diurnal species were relatively unaffected by temporary changes in light level and seemed to be handicapped little in dim light. In addition they mostly ignored artificial twilights that occurred at inappropriate times.

Like nocturnal rodents (Kavanau, 1962, 1967, 1968), the ringtail was influenced strongly by all light tests, suggesting that it is more rigidly bound by conditions of illumination than the diurnal animals. I could not establish an "optimum" level with respect to the ringtail's activity indices, although they clearly were greater at extremely low light levels.

There is reason to question the general adaptedness of the red fox and bobcat for activity in extremely dim light and darkness, for locomotion was inhibited strongly at 0.00005 lux and below. Of course, except in caves and burrows, such dim light would be encountered infrequently in the wild. The peaking of the red fox's trotting speed at about half the light level of the full moon (Fig. 6) may be related to optimum conditions for nocturnal hunting. Thus, Osterholm (1964) found that the role of vision in hunting was commensurate with that of hearing on clear moonlit nights but decreased in dimmer light.

The red fox and the cats were influenced strongly by artificial twilights, being most active and galloping most then. The fox essentially ignored twilights occurring at inappropriate times, whereas the bobcat usually was influenced by them. Whereas the cats and fox did not appear to be as facultative as the three diurnal animals, light conditions were far more permissive for them than for the ringtail and small mammals (Kavanau, 1968, 1969).

The fact that twilights are prime times for hunting probably accounts for the tendency of many animals to be active during these periods. Twilights generally would be the best times for predation on small nocturnal animals, because visibility would be better than at night. Moreover, atmospheric re-

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fraction shortens the night and the shortest nights occur during the season when food usually is most abundant (and hoarding by rodents is at a peak).

The Visual System

Because a duplex retina allows ready adaptation to a wide range of illuminance levels, carnivores (except small or strictly nocturnal species) would be expected to have both rods and cones in their retinas. In particular, the seven animals of this study have sufficiently large eyes to accommodate a duplex retina without much sacrifice of visual acuity. Of the seven, some retinal histology is known only for the domestic cat (Prince et al., 1960; Glickstein, 1969). The area centralis contains largely cones. As in man, cones become fewer and rods greater in number toward the periphery of the retina. A similarity between the retinas of bobcats and domestic cats would be expected. The red fox may have a retina similar to the retina of the domestic dog, in which cones number about 5 per cent of the total number of rods and cones (Prince et al., 1960; Walls, 1967). I would expect the pig-tail macaque's retina to be almost identical to that of man. Nothing is known of the retinas of ringtails, tayras, or grisons.

ACKNOWLEDGMENTS

This study was supported by National Science Foundation grant GB 7750. I thank Dr. W. Ross Adey for the loan of the pig-tail macaque.

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DALQUEST, W. W., AND J. H. ROBERTS. 1951. Behavior of young grisons in captivity. Amer. Midland Nat., 46:359-366.

ENDERS, R. K. 1935. Mammalian life histories from Barro Colorado Island, Panama. Bull. Mus. Comp. Zool., 78:385-502.

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KAUFMANN, J. H., AND A. KAUFMANN. 1963. Some comments on the relationship between field and laboratory studies in behaviour, with special reference to coatis. Anim. Behaviour, 11:464-469.

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KAVANAU, J. L. 1962. Twilight transitions and biological rhythmicity. Nature, 194: 1293-1295.

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LEOPOLD, A. S. 1959. Wildlife of Mexico. Univ. California Press, Berkeley and Los Angeles, xiii + 568 pp.

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SEYMOUR, G. 1960. Furbearers of California. California Dept. Fish and Game, Sacra- mento, 55 pp.

TEMBROCK, G. 1958. Aktivitatsperiodik bei Vulpes und Alopex. Zool. Jahrb., Physiol., 68:297-324.

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Department of Zoology, University of California, Los Angeles, 90024. Accepted 31 August 1970.

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Locomotion and Activity Phasing of Some Medium-Sized Mammals

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