Reproductive Behavior in Merriam's Chipmunk (Tamias Merriami)
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Great Basin Naturalist Volume 55 Number 1 Article 11 1-16-1995 Reproductive behavior in Merriam's chipmunk (Tamias merriami) Stephen B. Compton Hemet, California J. R. Callahan University of New Mexico, Albuquerque, New Mexico Follow this and additional works at: https://scholarsarchive.byu.edu/gbn Recommended Citation Compton, Stephen B. and Callahan, J. R. (1995) "Reproductive behavior in Merriam's chipmunk (Tamias merriami)," Great Basin Naturalist: Vol. 55 : No. 1 , Article 11. Available at: https://scholarsarchive.byu.edu/gbn/vol55/iss1/11 This Note is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Great Basin Naturalist 55(1). © 1995, pp. 89-91 REPRODUCTIVE BEHAVIOR IN MERRIAM'S CHIPMUNK (TAMIAS MERRIAM!) Stephen B. Compton' and J. R. Callahan' Key won£': Tamias. Eutamias, Neotamias, chipmunk, copulation. olfactimt. The literature contains little information The observation was made 1 April 1994 in a regarding mating chases and copulation in any wooded residential area in Idyllwild, Riverside of the western chipmunks (Tamias, subgenus County, CA (elevation 1590 m), between 1000 Neatamias). Callahan (1981) reported mating and 1130 h. The hahitat is mixed-conifer forest chases far Merriam's (T. merriami) and dUSk)' dominated by incense cedar (Calocellrus chipmunks (T. obscurus), but noted (unpub <lecurrens), yellow pine (Pinus ponderosa), live lisbed) that both copulating pairs were partly oak (Quercus chrysolepis), and black oak (Q. concealed by foliage. Larson (1981) described keUoggii), will, a sparse understory of chapar two copulations for Merriam's cbipmunk, but ral shrubs. When the observer arrived at 1000 a careful reading suggests that one of these h, six to seven Merriam's chipmunks, many of was a mounting attempt hy an immature male them males. were running over, around, and and tbe other was observed from a consider through a large woodpile while performing able distance. Best and Granai (1994) found nO conspicuous leaping maneuvers. No agonistic references on this subject other than Callahan interaction wa.o;; observed. It was not possible at (1981) and Larson (1981). this stage to identifY the female(s) or to tell in There has been some speculation and dif which direction the "chase" was headed. The ference of opinion regarding reproductive iso overall effect was somewhere between a lating mechanisms in parapatric species of Sciurus-like mating chase (e.g., Thompson western chipmunks. Blankenship and Brand 1977), io which several males follow one (1987) reported differences in vocal behavior female, and a lek, involving male display. The between Tamias merriami and T. obscwrus at chase covered an area 13-15 m in diameter Black Mountain (Riverside County, CAl and but centered on the woodpile and a nearby noted a possible role in reproductive isolation. heap ofsmaller pine branches. One of us QRC), however, had previously con After about 20 min, one chipmunk aater ducted a more extensive study ofvex.'aI behavior identified as female) ran up on one ofthe piled in these two cryptic species at Black Mountain brauches. A second chipmunk approached and from 1975 to 1980. Vocalizing individuals were they ran around for a few seconds. The female collected to conArm species identity, aod sono stopped on a brancb and the other chipmunk, grams were prepared and measured; yet no a male, ran up beside her. His entire right side statistically significant vocal differences were was in contact with her left side for ahout 1 sec, found (Callahan 1981, and in preparation). during which he made a nnzzling motion witb Ecological, olfactory, and mechanical barriers the right side ofhis face on the rear left portion to hybridization also have been suggested ofher face. The expected nasal/genital contact (Callahan 1977, 1981, Patterson 1984). These was not observed, but the pair had been out of hypotheses cannot be tested without more sight for a short time previously and this could data on chipmunk reproductive behavior. have occurred. The female then jumped to Accordingly, this note provides the first another branch, which was 5 em in diameter detailed description ofwestern chipmuok cop and 20 em above the ground, sloping at a 25' ulation that bas been publisbed, to the best of angle so that the female was facing downhill. our knowledge. Comparative data for other Copnlation then occurred only 2 m from the western chipmunk species would be ofinterest. observer (who was inside a parked vehicle). lSelld reprint requests tn Un" 3140, Uemct. CA 9&546. 'Museum ofSoolhweslern Bivklgy, UnjV{."t'liity of New Mexico, Albuquerque, NM 87131. 89 90 GREAT BASIN NATURALIST [Volume 55 The female crouched on the branch as if breeding season. Scent marking is prevalent in resting. The malc jumpcd to that branch and sciurids, but usually this means marking the quickly grasped the female from the rear with ground or a branch, not marking another ani his forelimbs around her pectoral region. The mal. The "nuzzling" and "brushing" behavior female's tail was deflected to the side and of the male Merriam's chipmunk, before and slightly raiscd, and the male's tail was cxtend during copulation, suggests that he was scent cd to the rear. Copulation consisted of fouf marking the female. series of pelvic thrusts. Each series (except the Conspecific marking has been described flJr last) lasted about 4 sec and comprised an esti various mammals, such as rabbits (Mykytowycz matcd 12-24 thrusts, at a rate of 3-6 per sec. 1965), but not for sciurids. Gurnell (1987) describes "face-wiping" behavior by various Each series of rapid thrusts was followed bv• a short resting period, during which the male trce squirrels, but only in the context of sub stopped thrusting and brushed his facc strate marking and (in Paraxerus) self-groom (mouth, nose, and chin) from side to side 2--4 ing; his description of copulation in Sciurus times against the hack of the female's neck. and Tarniasciurus says nothing about the male The fourth and last series of thrusts was short marking the female. With reference to olfacto er than the first three. The male then released ry communication in ground squirrels, Halpin his grip on the female, dismounted, and ran (1984) wrote that "there is no experimental off into the woodpile. The femalc, who had evidence that conspecific marking ... actually remained motionless during the act, remained occur[s] among the sciurids." on the branch about 1 sec and then also ran to Our observation indicates that conspecific the woodpile. The entire copulation lasted marking does occur in Merriam's chipmunk as about 18 sec. a component ofreproductive behavior. Without Although several male chipmunks partici experimental data, it is not possible to deter pated in the chase, none of them approached mine the significance of this marking. Pair the copulating pair. No chipmunks were heard bonding comes to mind, but there is no good vocalizing during the mating chase or copula evidence of long-term pair bonding in tion. We did not note any pre-mating vocal dis Merriam's or any other species of western play or Lockrufe by the cstrous femalc chipmunk, despite many years of field obser (Callahan 1981), but we wcre not present on vation. Other possibilities include the follow the days when the display (if any) would have ing: (1) the marking induces some required taken place. The Tami"s vocal display has physiological state in the female; (2) the mark been reported for a few species of chipmunks ing tells other males that the female has by Callahan (1981), Blake (1992), and others. already mated (hefore the copulation plug It is not clear whether this vocal display is forms and the message becomes redundant); universal or occurs only at low population or (3) the marking reinforces a short-term pair densities, when the female benefits by attract bond to ensure that subsequent copulations (if ing more distant males. any) on the day of estrus will be with the same No further copulations were seen, but as male. Larson (1981) indicated that the same many as seven male chipmunks continued to estrous female sometimes copulates more than run around the same woodpile for another hour, once. The level ofactivity appeared to decrease, and Mortality from all causes is higher for male there were none of the prodigious leaps seen than for female chipmunks (Smith 1978), per earlier. The group then gradually dispersed as haps due in part to the dispersal and exposure individuals headed for an adjacent area where associated with thc breeding season (Callahan 1981). After incurring the risk of predation other chipmunks were heard giving occasional "chipper" vocalizations (not the long series of and expending considerable energy on the mating chase, it should be to the male's advan chips that characterizes the Lockrufe). tage to ensure that his genes are passed to all The behavior described above suggests that the female's offspring ofthe season. scent glands playa key role in reproductive be havior ofthis species. Larson (1981) and others LITERATURE CITED have noted that male chipmunks have scent glands near the chin and angle of the jaw (oral BEST, T. L., AND N. J. GRANAI. 1994. Tamias merriami. glands) that become enlarged during the Mammalian Species 476; 1-9. 1995J NOTES 91 BLAKR. R. H. 1992. Estn>lIs calls in captive Asian chip £.....\RSON, E. A. 1981. Merriam's chipmunk on Palo Escrito munks, 'R~ ~~'US. jOllmal of Mammalogy 73: ill the:: Santa Lucia Mountains of California. Purt L 597-603. Regimen with recorded episodes of uatundi.slic be· BL\NnNSHI~ D.