Females and Young
Response to Males
Response to males has been reported under "Attention to Females," since it seems impractical to attempt an illustration of one without the other.
In general, during the rut the female bighorn plays the part of the pursued, with passive compliance the culmination of the pursuit.
Out-of-season overtures from rams are likely to be met by a head-on presentation of lowered horns, which is usually accepted by the ram as final.
Occasionally a ewe will digress from what appears to be a normal passivity and evince a positive aggressiveness toward a ram.
Some evidence indicates a possibility that as the mating season tempo increases ewes not in oestrus with lambs still nursing try to hide out to avoid unnecessary harassment from the younger rams.
We have no data determining the length of the bighorn oestrus cycle or the length of time a ewe is responsive to the mating season, but the records of captive animals at the Desert Game Range show that the bighorn ewe can and does conceive during her second year. Gestation is believed to take from 170 to 180 days (Aldous, 1957, p. 57).
Selection of Lambing Area
The selection of a lambing area in Death Valley apparently presents an individual problem to each ewe each year she bears a lamb. Low-density vegetation and sheep population seem in general to preclude effectively the gathering of ewe and lamb bands that we found so common on the Desert Game Range in 1953. (Under "Food" and under "Water," see "A Factor in Bighorn Distribution and Survival." See also, "Introduction.")
One possible exception to this generality was recorded on June 30, 1960, at Quartz Spring in the Cottonwood Mountains. It may be significant that the habitat in which it occurred is as nearly comparable to the Desert Game Range habitat as could be found in the Death Valley regionan elevation of 5,200 feet in one of the few areas in the monument where Joshua trees lead up into the piñon belt. Here at 4 p.m. we found two yearlings "babysitting" with 12 lambs while their 12 mothers browsed the mountainside at varying distances. We were with them that night until dark and the next day until noon, when the exigencies of the burro research impelled us into another area. It is a single incident and the only one even suggesting the existence of a lambing area in Death Valley.
Pluvial and floral instability may prevent the annual return of even one ewe to the same lambing area, as indicated by our population record of Indian Pass since 1955.
We have been able to make but one prolonged observation of lambing in Death Valley, but that fact in itself suggests its unpredictability, the lack of permanent lambing areas, and an apparent tendency of ewes to remain solitary for at least a week or two both before and after parturition.
Our first observations of lambing were made at the Desert Game Range in 1953 when the captive ewe at Corn Creek Headquarters gave birth to her fourth lamb, as described by O. V. Deming (1955). Actual parturition was not observed, but immediate prenatal and postnatal developments were carefully studied and photographed and have served as a field indicator to the present time.
Number of Young
The number of young is often confused by the tendency of lambs to run in pairs (Deming, 1955, p. 136), but we have no record of bighorn twins being born in the Death Valley region.
Birth of Young
The birth of young has not been observed during this study. However, we were able to maintain full-time observations on a pregnant ewe in the Furnace Creek area for 3 weeks before lambing and for 10 weeks afterward. This was in addition to the study of a captive ewe at the Desert Game Range in 1953.
Positive field determination of pregnancy is generally difficult and sometimes impossible, but the pregnant ewe at Furnace Creek, identified throughout this report as Old Mama, left no doubt of her condition when her unborn lamb was observed vigorously kicking from within, first on January 7, then on the 16th, and with disturbing violence on the 18th when she was on her way to the solitude of Pyramid Peak. On two or three occasions she leaped up from siesta and moved restlessly about as though trying to counteract the lamb's activities in some way.
Although she was apparently still about 10 days from parturition, her udder had been developing for over a week, but her genitals were not beginning to swell. She was restless and quite evidently trying to leave the band. She had the sagging potbelly with the sunken appearance in front of the hips which suggests pregnancy instead of overeating.
When Old Mama returned on February 2, she was still potbellied, sagging more than ever in front of the hips. By February 19, 1956, this condition was still pronounced: "Ewe still potbellied. If seen for first time now, she would be mistaken for pregnant ewe, not as a mother of a 3- to 4-week-old lamb."
Prior to this observation, a bloody residue of vaginal excretion had defaced the white rump patch somewhat; on February 25 she began to show signs of afterbirth complications; and on February 28 "a raw, red protuberance from her vagina" became evident. Later in the day, a "chunk of meat about size of first joint of finger" was found at her day-bed site. On March 1 it was noted that the "ewe seems to have no ill effects from chunk of meat dropped from vulva 2 days ago. One urination at 11:45. Action normal, urine clear."
Growth, Behavior, and Care of Young
Growth, behavior, and care of young has been unavoidably disussed to a considerable extent under "Play." A review of that section will complement the following material:
Care of the young is usually treated separately, but in the case of bighorn lambs the very nature of the care received slants the growth and behavior immediately toward self-sufficiency and independence, and so the two factors will be considered at the same time. The following data were recorded during the observations of Old Mama and her lamb in Furnace Creek, but they are so typical in nature that they are included here as a generality.
The lamb's first postnatal experience with its new world is with its mother's mouththe soothing warmth of the cleansing tongue, the warm breath, and the low, gutteral grunts of reassurance as the lamb staggers to its wobbly legs and falls back to earth. In its efforts to retain this assurance, the lamb reaches up, searching uncertainly for the source of its comfort, and eventually, if all goes well, begins to nurse.
The mother nurses the lamb a few seconds at a time, touches its rump with her nose, steps over its head with a hindleg, and walks away. As time passes, the nursing periods become farther and farther apart as other food becomes more important to the growth of the lamb. (See table 9.)
TABLE 9.Observations on nursing new lamb
The muzzle contact remains important. For the first days the lamb spends most of its time doing three things: Nursing, sleeping, and hovering around its mother's head in its first wavering patterns of emulation.
The mother nuzzles the lamb as it wobbles up to her but turns away when this inhibits her ingestion of food at a critical time. In its efforts to determine what its mother is doing, the lamb staggers out into the brush, gets its legs entangled, and falls over. Its first lesson in self-sufficiency begins then, because the mother ignores it and eventually it must thrash its own way out and back to its feet.
By the end of the first week the lamb puts its nose to the ground beside its mother's and its jaw begins an empty chewing. The ewe raises her head with a spray of Bebbia in her teeth and, as she chews it up and swallows it, the lamb looks up and chews. Again the ewe reaches down and again the lamb nuzzles in, but this time when the ewe raises her head with food in her mouth the lamb looks up and chewson its first twig of Bebbia. Browsing has begun.
While the lamb is still less than a week old, two ravens flying over head fill the mother with apprehension, and she eats nothing for 15 minutes, until the ravens are gone.
When an overeager observer approaches too close, the lamb immediately takes its place against the offside flank of its mother and, assisted by touch, follows it as one dancer follows another. At 2 weeks of age, it is learning to paw out its own bed, eats everything its mother does, tries to defecate when she does, is very curious about her cud chewing, and tries repeatedly to get some from her mouth for itself.
Lacking another lamb to play with, it tries to play with its mother, who for the most part ignores it even when it jumps up and down on her side while she rests.
The independence of attitude and action so necessary to desert bighorn survival is now beginning to be noticeable. The lamb now makes no effort to keep up with its mother in traveling. It walks along steadily, catching up with the ewe only when she stops to wait. If its mother calls, however, or if it gets lost, it runs to find her.
At 3 weeks of age its rump patch is beginning to look more like its mother's changing from a dirty yellowish brown to whitish yellow, and white by 6 weeks.
It is beginning to browse incessantly when not resting. Sometimes even when resting it lies down close enough to plants to eat without getting up. We've never observed this in adults.
We wonder if its "eating" gravel now and then is experimental or mineral ingestion.
The mother and lamb are browsing over a distance of 3 to 5 miles per day and climbing from 1-1/2 to 212 miles to bed every night. The lamb is always friskier at the end of the climb than at any other time. We watch it make its first 1-mile climb when it is no more than 48 hours old, and at the end of the climb it makes a wobbly run and jumps up on a flat boulder about a foot high, tries to kick its heels in the air, and falls off the boulder, gets up at once, and begins vigorous nursing.
The mother seems to pay little attention to the welfare of its lamb, but on one occasion she climbed a cliff which the lamb failed to negotiate, falling back to the base: "Ewe crossed quickly to more accessible spot when she saw lamb fall, leaned over and watched lamb intently until it crossed the falls and gained the top of the cliff beside her."
The mother seems anxious to be always well up the mountain for bedding by sundown. On February 22 at 4:48, the ewe suddenly looked up, looked around, looked up at Pyramid Peak as though surprised at how late it was, and made the most rapid exit and climb for bedding to date.
At 4 weeks of age the lamb is learning rapidly, eating or sampling everything it can get into its mouth. It shows great curiosity about telephone poles, runs its nose up and down, slowly tilting its head back while its eyes run up the length of the pole.
At 6 weeks of age it finds a playmate. A new band of five strange bighorn have come into the wash and apparently have "chosen" Old Mama as their leader. The lamb, being hungry, tries to nurse the new comers one at a time, even the ram, until its mother comes and feeds it.
On March 27, 1956, we notice that one eye of Old Mama's lamb is badly swollen, and the next day it is swollen shut. It lies down as much as possible and eats practically nothing. Keeping up with the band is a great effort. Its mother, Old Mama, seems totally unconcerned.
Temptation is great to try to do something for the lamb, but we must watch without interference and may learn something of resistance to infection, recuperative powers, etc., as a part of survival.
The next day the lamb's eye is open but it is a very sick animal, lying down as much as it can and still keep up with the band. It scrambled slowly up out of the wash with them just below Pyramid Wash to get away from too many Easter week visitors.
On March 30, 1956, we lost the Furnace Creek band for several hours, during which time they crossed the highway on their way to the Big Curve, and one of the lambs was struck by a car. Eventually this was reported to me by a visitor who first asked what those animals were in Furnace Creek Wash. I told him. He said, "One was hit by a car just now." Another visitor had asked him for a gun with which to kill the animal to put it out of its misery, he told us, but he had no gun and didn't know if one had been found. The accident, he said, had happened "above where all the red rocks were."
I hurried to see what had happened. No sheep anywhere. No blood on the road. No body.
I finally found the band in the far curve of the wash above the Big Dip and went out to see who was missing. Old Mama's lamb! Old Mama herself was placidly feeding as though she had never even had a lamb. The other lamb was browsing contentedly nearby. Devoted mother and inseparable playmate both gorging themselves on Stephanomeria. Evidently one of their number being killed by an auto leaves no disturbing effect! Or did they not see the lamb struck and therefore not know what had happened? Or again, was the lamb all right somewhere and they knew it?
With this thought in mind, I went back to the Big Dip and the "red rocks" (where presumably the lamb was struck) and began to trail the band up the wash to their present location. About 200 yards above the Big Dip a rustle in the brush attracted my attention from my close scrutiny of the tracks at my feet, and there stood the lamb, lame in the right front leg, but otherwise unscathed!
For 2 hours the lamb rested, eating a little, sometimes on its feet, looking for Mama. The band was still up the wash in a curve but coming down, with Old Mama now looking for her lamb.
While they were 50 feet away, the lamb managed a hobbling run to Mama and nursed 10 seconds. The other lamb, seeing the cripple from a distance, rushed, gamboling, toward it, and being a little ram tried to mount it, knocking it over on its side. The band began to climb and by dark was up the mountain half a mile, the little cripple plugging along with amazing stamina, the other lamb once more sticking close by.
The next day it rained. The band vanished on Pyramid Peak, and we did not see the lamb until April 3. Old Mama's lamb was still with them, its pelage rough, still limping, but eating fairly well. There still seemed to be no concern for the handicapped condition of the lamb. At 11 a.m., the band began an unusually rapid trek south, traveling to within 200 yards of Deadman's Curve before stopping, a distance of nearly 2 miles. They paid no attention to the sick lamb, who hobbled painfully, doggedly, silently along, sometimes out of sight, once nearly a quarter of a mile behind.
At the curve the lamb was finally eating a Bebbia plant when the young ram came up and without warning charged the lame lamb, hurling it through the air 4 feet into a rock bed on its lame side. It took the lamb a few seconds of struggle to regain its feet. It stood with its lame right front leg in the air for a few moments, shook its head, sneezed, then went back to feeding, ignoring the ram but 2 feet away.
Ten minutes after the lamb had caught up with them at the curve, they started back to Travertine Point at the same fast clip, the crippled lamb again trailing desperately along behind.
On April 8 we note that "as evidence of improved health of the lamb, it has been, during siesta, getting to its feet now and then to pester Old Mama with playful butting, pawing, and that curious effect of seeming to try to take her cud away from her."
The other lamb was about a week older, and possibly because it was a ram lamb, it had been showing button horns since it was 8 weeks old. Both lambs were now chewing their cuds.
We could not find the band on April 9.
That evening at sundown when they went up to bed, the lamb was like a small dog "following" a hunter. It was all over the mountainside, choosing the steepest, roughest terrain it could find. It was apparently feeling much better, no limp, no cough, although its coat was still rough.
On April 11, 1956, the lamb rested almost all day. At 2:45 two ravens, one at a time, dived at it, which its mother ignored, but it leaped up and ran to Old Mama. There it forgot its fears and nursed 15 seconds, the first time that day, the longest in many.
We did not find them again until April 16 and 17, 1956. Old Mama and her lamb were in Furnace Creek Wash both days: Monday from 12 until 2, Tuesday from 11 until 1.
They did not appear until nearly noon, both days at the foot of the curve below Big Dip. The ewe looked gaunt on arrival and fell immediately to voracious feeding, moving but a few feet from one plant to the other. Stephanomeria and Bebbia again, with only occasional Hymenoclea and Franseria. She seemed to stay in the farthest reach of the curve, as though to insure less disturbance. The lamb, while it looked less gaunt than its mother, was quiet and browsed constantly also, with one nursing of about 8 seconds each day.
Old Mama seemed to watch the mountains more and more in the course of her last 2 days with us and never came near us or allowed us to come near her.
On both the 16th and 17th the lamb was actually the first to take to the ridge on the way out. It seemed almost prearranged. Old Mama would start feeding toward the edge of the wash, and as she approached within about 50 feet of it the lamb ran past her and on up the mountains perhaps 50 feet above her. While she did not seem to hurry, Old Mama nevertheless followed the lamb up the mountain on both her last days here, after having been in the wash for but 3 hours each day.
We never saw her and her lamb together again. When she returned to the wash 7 months later on November 17, 1956, she was alone. Nine out of 10 Death Valley ewes who have lambs in the spring are likely to be alone again before the year is gone. (See "Chief Causes of Mortality.")
We have observed lambs through the Death Valley summer at Willow Creek, Nevares Spring, and Navel Spring. At these elevations, survival through a summer is a serious business, with no time or energy for playgetting enough to eat and to drink takes all there is.
How long a bighorn ewe will nurse her lamb appears to depend on the individual and the circumstances in each situation. We have seen 7-month-old lambs nursing, while on the other hand Little Fuzzy had already been weaned for some time when he died at an age of about 1 month. But the bulk of our evidence suggests that Death Valley lambs are seldom weaned before they are 4 months old.
Some lambs, probably those raised alone by a solitary ewe, seem to prefer staying with their mothers throughout their first year and sometimes the second. A very common Death Valley "band" is a ewe, a yearling, and a nursing lamb.
But lambs brought up in groups tend to show an increasing preference for companionship of their own age. "Babysitting," with all the younger lambs left in the care of one or two older members of the band, becomes common. In all cases, however, an increasing individual independence marks the first year of the lamb's life. The following notations are cited as a fairly typical observation of this phase of development:
The growth and behavior of lambs seems important enough to this report to review, in toto, the following field notes:
They ate for half an hour, then the ewe and yearling ram started to leave. The lamb did not leave, but continued eating, then went back to Old Spring, drank 3 minutes more and ate at Old Spring for 5 minutes. The ewe and yearling waited for it a short distance above the springs. The ewe nibbled on desertholly a few times, the yearling did not.
The ewe then led up to the rugged rocks above Old Spring and was joined by the others, who acted as though they would have liked to lie down if there had been a level or comfortable place. The lamb found a small shelf, lay down, but didn't stay long. It made no attempt to nurse during this entire time.
This day's observations, during which the official temperature was 113°, provide several significant points to review:
1. The length of time spent, first in drinking, then feeding, and finally in resting was so far above average that great thirst, hunger, and fatigue are indicated, suggesting that a relatively long time had elapsed without water and that a great distance had been traveled. This suggests abandonment of a former home area, and their physical condition suggests a causative factor of either food or water failure.
2. These sheep all appeared to be in the last stages of starvation and exhaustion. I remarked to Buddy that "Here are the poorest sheep we have ever seen anywhere, and this can't be just dehydration." Yet within half an hour the most remarkable recovery we have ever witnessed had been accomplished. The ewe and the yearling by that time showed no sign of malnutrition and exhaustion, and the lamb had recovered to a great extent.
3. The fact that the lamb had drunk 5 minutes longer and eaten with greater persistence than the others and still showed a slower recovery may be pointing toward the area of mortality, the limiting factor in the survival of the bighorn which has eluded us for so long.
4. The lamb was the effective leader of the band of three in that it was the first to water and the last to stop drinking; after drinking it sought out its own feeding grounds, forcing the ewe to follow it in browsing; the ewe and yearling went up the mountain at one point but the lamb went calmly to Old Spring, drank and ate for some time while the ewe and yearling waited; during the first part of siesta the lamb preceded the others from shade to shade with the ewe eventually coming to find it; the lamb broke siesta and led them back for browsing in the wash before they all went into the shade for more rest; when last seen at dusk the lamb was once more in the lead by about 100 feet.
5. The ewe's familiarity with the area leaves no doubt that she had been here before, but the fact that we had not identified her before certainly indicates the inclusion of more than one spring in her home area and bears out last summer's observations that some ewes seem to have only one spring as the focal point of a home area, while others may have several.
The next morning at 7:15 a band of 15 came into water.
The separation of lambs from their mother by rams during the rut-run has been discussed under "Reproduction." It is mentioned again here in emphasis of the need for independence at an early age.
Our 10-day Death Valley Buttes observations of a band of 14, including 6 lambs, gave us our only data in the growth and behavior of a group of lambs, and much of it has been previously discussed under "Play" and in other sections of this report. Some points are worth summarizing in the present connection:
How much and when lambs play and learn from each other and their elders is substantially controlled by weather and available food and water supplies.
The adult animals are for the most part content for the young (up to yearling ewes and 2- to 3-year-old rams) to carry on their own play activities. The difference in play behavior by age class and sex apparently arises from the probability of ewes being pregnant by the end of their second summer. We have no record of young ewes over a year old engaging in play activity to any considerable degree, but rams up to 3 years appear to be especially prone to play.
That adult ewes do not entirely give up their authority was indicated on February 10, 1958:
So we have followed the development of the young up to the time when it appears that the female may reach adulthood through the onset of her first oestrual cycle, which may be at any time during her second year. The young male seems to retain his juvenile attachments, at least to some extent, through his third year, at which time he is likely to abandon his off-season activities with mixed bands and join the "bachelor" rams in their supreme indifference to the growth, behavior, and care of the young.