Tamias Striatus Research Articles

The impact of potential predation upon the foraging behaviour of eastern chipmunks

Predation risk may have a profound impact upon foraging behaviour. I studied how potential exposure to predation affected the foraging behaviour of eastern chipmunks (Tamias striatus). I measured the time taken to approach a patch ("approach time"), the period of residency in the patch ("patch residence time"), the degree of vigilance, and the size of the load of seeds taken by chipmunks foraging at patches (food trays) in both open and forested sites. Chipmunks have shorter approach times to trays in the open than to trays amongst forest cover. Although the load size taken did not differ between the two sites, chipmunks had increased patch residence time in open patches versus covered patches, as a result of increased vigilance. As load size did not increase with patch residence time in the open patches, foraging in the open provides a lower gain rate than foraging in closed habitats. Chipmunks may require both patch types to maximize their cache of seeds for over-winter survival. Increased vigilance while foraging in open sites may decrease the risk of predation and allow chipmunks to utilize these patches. Thus, the loss in gain rate while foraging in open patches may be offset by the ability to use exposed patches to increase long-term survival.

Scatter-hoarding by a larder-hoarding rodent: intraspecific variation in the hoarding behaviour of the eastern chipmunk, Tamias striatus

Abstract. The adaptive significance of alternative patterns of dispersing hoarded food was examined by determining which factors influence the occurrence of scatter-hoarding in the eastern chipmunk a species that typically larder-hoards food to its burrow. A standardized food-provisioning test was used to determine the incidence of scatter-hoarding in relation to age, sex, reproductive condition, time of year, patch position and social context. Juveniles and females with young scatter-hoarded significantly more often than did other classes. Newly emerged juveniles scatter-hoarded both before and after they acquired a permanent burrow of their own, but decreased their frequency of scatter-hoarding as they grew older and more capable of defending their burrow. Females with young in the burrow did not appear to use scatter-hoarding to avoid revealing the location of the burrow, but may have been avoiding the risk that their young would consume all their hoarded food. The incidence of scatter-hoarding was not affected by the distance of the patch from the burrow nor by the number of competing sciurids at the patch. However, scatter-hoarding was more often performed by individuals that were harassed at the patch. This may have been a response to leaving the patch with an incomplete load; experimental exclusion of animals before they had completed loading demonstrated that possessing a small load increased the tendency to scatter-hoard. For juveniles and non-breeding adults, scatter-hoarding permitted more rapid removal of food from a patch than did larder-hoarding, but for females with young, scatter-hoarding trips took longer than larder-hoarding would have, largely because such females often made more than one hoard per trip. These results do not support the hypotheses that scatter-hoarding is a vestigial behaviour pattern of no adaptive significance or that is is simply a response to lack of larder space. They do, however, support the hypotheses that scatter-hoarding reduces pilferage of hoarded food by individuals unable to defend a larder and that it increases the rate at which subordinate individuals can sequester food from ephemeral patches.

Context-specific alarm calls of the eastern chipmunk, Tamias striatus

The structure and context of alarm calls produced by chipmunks (Tamias striatus) at a field site in southern Quebec were recorded during opportunistic field observations and experimentally simulated hawk attacks. Chipmunks produced three call types in the presence of predators. Chipping consisted of a series of high frequency notes with a rapid downward frequency slope (9.6 to 2.8 kHz) and was given in the presence of mammalian predators by chipmunks perched on a raised vantage point. Chucking consisted of a series of lower frequency notes also sloping downwards (2.5 to 0.4 kHz), given in the presence of avian predators by perched animals. The trill was a lower amplitude, multi-note call usually given only once by animals before reaching a refuge while fleeing from either type of predator. The average trill contained 6–11 downward sloping notes (7.3 to 0.8 kHz). The alarm call types of eastern chipmunks appear to be similar to those reported for western chipmunks. However, they differ in the clear separation of the calls for aerial and terrestrial predators. Chipmunks differ from most other terrestrial sciurids in giving repeated calls for aerial as well as terrestrial predators and in using a call just before reaching a secure refuge.

The effect of competitors and distance on central place foraging eastern chipmunks, Tamias striatus

Abstract. Loading functions, travel times, and load sizes of nine eastern chipmunks, Tamias striatus, collecting sunflower seeds from uniform spatial arrays were examined in the presence and absence of conspecific competitors at different distances from their burrows. Seed collection times increased with the number of seeds collected, resulting in negatively accelerated loading functions. For a given number of seeds, collection times increased in the presence of competitors, due primarily to time spent alert or engaged in interactions with other individuals. Seed collection times decreased with distance from the burrow. In the presence of competitors, travel speed was faster. There were large individual differences in loading functions but not in travel times. The qualitative predictions of the central place foraging model were supported: load sizes increased with distance from the central place and decreased in the presence of competitors. The usual methods of quantitative testing were impossible because loading functions and travel times varied with individual, distance and competitor presence. Calculations based on the seed collecting times of each individual in each situation, however, showed that observed rates of food delivery to the burrow were higher than those that would have been achieved by taking smaller loads. Calculations based on an extrapolation of the relationship between seed collection time and seed number for each individual in each situation suggested that observed rates of food delivery were lower than those that would have been achieved by taking larger loads. Thus, chipmunks appeared to take loads that were smaller than those needed to maximize their rate of food delivery.

Interference competition in central place foragers: the effect of imposed waiting on patch-use decisions of eastern chipmunks, Tamias striatus

When central place foragers compete aggressively for patchy resources, subordinates may be preventedfrom collecting food until a dominant has departed with its load. Extensions of central place foraging models predict that animals forced to wait at a patch should increase their load sizes and patch times aswell as their tendency to search for and switch to alternative patches. We tested these predictions usingeastern chipmunks, Tamias striatus, hoarding sunflower seeds collected from seed/vermiculite mixturesin trays placed 5-8 m from their burrows. By using her hand to prevent access to the patch, the experimentersubjected animals to progressively increasing waiting times at two seed densities; another series of trialsat the same seed densities monitored a similar number of trips without imposed waiting. As predicted, patch times and load sizes were higher in sessions with imposed waiting than in control sessions. Loadsizes increased with trial number in experimental sessions but decreased or remained the same in controlsessions. Chipmunks spent more of their time searching for alternative patches during trials with imposed waiting than during controls. They also started searching for alternative patches at lower levels of imposed waiting when using poor than when using rich patches. These results indicate that the effects of interference on foraging decisions and on spatial overlap between individuals can be predicted by simple economic models. Furthermore, the results suggest how resource-defense tactics can be predicted by the economic effects of interference on the foraging efficiency of the opponent.

The placement, recovery, and loss of scatter hoards by eastern chipmunks,Tamias striatus

The placement, recovery, and loss of scatter hoards by eastern chipmunks,Tamias striatus

Corridor use and the elements of corridor quality: Chipmunks and fencerows in a farmland mosaic

An important issue in developing practical conservation actions and in understanding how corridors function is that of identifying what constitutes a high quality corridor for a particular species or assemblage. We studied the use of fencerow corridors by the eastern chipmunk Tamias striatus to identify the elements of corridor quality for an animal species. Chipmunks were trapped in four woods and 18 fencerows of varying width, habitat and linear continuity, in farmland near Ottawa, Canada. There were many recorded movements by individuals within and between fencerows and woods. Chipmunks used fencerows in at least two main ways, and the elements of corridor quality were found to differ for these two modes of use. Resident individuals lived within and along many fencerows, thus promoting continuity of the resident population between woods. They favoured fencerows with tall trees and a woodland structure; neither fencerow width nor linear continuity accounted for additional variation in the number of residents after habitat attributes were included in a stepwise regression model. Transient chipmunks, those trapped once only in a fencerow, apparently used the fencerow network as a pathway through farmland. Linear continuity of fencerows was the most important correlate of the number of transients, with habitat attributes explaining additional variance in a regression model. Fencerows with grassy vegetation alone were never used by chipmunks and, like the surrounding farmland, appear to be inhospitable habitat. The different ways that individuals may use corridors, and the differing elements of corridor quality, have implications for models of corridor use and metapopulation function, and for practical corridor management and restoration.

Variable Acorn Crops: Responses of White-Tailed Deer and other Mast Consumers

We examined movements and behavior of female white-tailed deer ( Odocoileus virginianus ) relative to the acorn mast-fall from 1986 through 1989 in a mature deciduous forest in Front Royal, Virginia. Ten white-tailed deer with radiotransmitters increased their home range to incorporate acorn-producing areas during mast-fall. Consumption of acorns by deer constituted ca. 50% of foraging time during peak mast-fall; average consumption rate was 0.75 acorns/min searching. Although the number of acorns eaten by deer was correlated with mast-fall, a prolonged time was spent searching for acorns after mast-fall. Deer consumed 70% of marked acorns placed out during mast-fall, while medium-sized animals (e.g., Tamias striatus, Sciurus niger, Sciurus carolinensis ) consumed 61% of acorns placed out later in autumn. We hypothesize that high densities of deer may limit populations of more mast-dependent species, particularly at low acorn-crop densities.

Experimental infection of the eastern chipmunk (Tamias striatus) with the Lyme disease spirochete (Borrelia burgdorferi).

Lyme disease, caused by the spirochete Borrelia burgdorferi, is endemic in the northeast, north-central, and Pacific coastal states of the United States. The eastern chipmunk (Tamias striatus) is found throughout the disease-enzootic regions except along the Pacific coast, and may serve as an important reservoir host in some locations. To characterize their potential as a host, 11 adult chipmunks were inoculated with 10(5) spirochetes from strains of B. burgdorferi isolated from Peromyscus leucopus and Ixodes scapularis in a hyperendemic area of Westchester County, New York (USA). All inoculated chipmunks became infected. Spirochetemias were detected by isolating spirochetes in Barbour-Stoenner-Kelly media in eight of eight chipmunks, and lasted for 2 to 5 days. Spirochetes were isolated from the ears of all animals, starting at 1 wk and for < or = 4 mo, and from various internal organs at 133 days post-inoculation. Laboratory-reared larval I. scapularis ticks became infected with spirochetes after feeding on two of the inoculated chipmunks.

Acorn Preference and Habitat Use in Eastern Chipmunks

-We used field and laboratory trials to examine the effects of size and species of acorn on food choice by eastern chipmunks (Tamius striatus) from central New York. Initial trials suggested that chipmunks preferred the low tannin, white oak (W; Quercus alba) acorns over the high tannin, red oak acorn (R; Q. rubra). However, the smaller size of the W acorns, and therefore greater ease of handling, possibly confounded the affects of tannin content on acorn choice. Additional field and laboratory experiments confirmed that chipmunks preferred smaller acorns, but W acorns were still preferred to equal-sized R acorns. Frequency of live capture of chipmunks during the period of acorn drop (midSeptember to mid-November) at the field site was related directly to the total basal area (P -0.02) but not number of W trees. Capture frequency was also correlated negatively with the number (P = 0.04) but not basal area of R trees in the canopy. Our results suggest that chipmunks prefer to eat W acorns and that chipmunk activity is in part influenced by this preference. Heavy chipmunk harvesting of the preferred W acorns may be influencing the successional patterns in the forest at our study site.

Load Size Variation in the Eastern Chipmunk, Tamias striatus: The Importance of Distance from Burrow and Canopy Cover

AbstractWe examined the degree to which chipmunks foraging from dishes containing sunflower seeds varied cheek pouch load size according to both travel time (distance from burrows) and predation hazard (canopy cover). Results showed that larger loads were taken under cover at some distance from burrows than were taken from closer or more open sites. Distance effects appeared to reflect the influence of traveling times on quitting harvest rates as predicted by central place foraging models. Quitting harvest rates also appeared to be higher under low than under dense canopy cover; this trend was most pronounced at some distance from burrows suggesting that foraging decisions were made relative to both energetics and predator avoidance. Chipmunks appeared to employ a patch exploitation strategy that minimized the hazard:gain ratio.

The Effect of Profitability on Caching by the Eastern Chipmunk (Tamias striatus)

-TO test the prediction that tendency to cache food from a distance depends on profitability, fixed amounts of three foods, apple pieces, sunflower seeds and almonds, were offered at various distances to caches (burrows) of eastern chipmunks (Tamias striatus). For each food type, I determined the percentage of food cached as a function of distance between the food patch and the cache, an index of foraging cost. Chipmunks cached most of the less profitable apple pieces when distance to the cache was small, and the percentage cached decreased with distance. On the other hand, chipmunks cached the more profitable sunflower seeds and almonds equally from all distances.

Role of the eastern chipmunk as a host for immature Ixodes dammini (Acari: Ixodidae) in northwestern Illinois.

Infestation of the eastern chipmunk, Tamias striatus L., by immature Ixodes dammini Spielman, Clifford, Piesman and Corwin was studied in Castle Rock State Park in northwestern Illinois during June-October 1991. Mean larval density peaked in August, while nymphal density declined steadily through the study period. Prevalence of tick infestation was high throughout the trapping period. Tick distribution on chipmunks was aggregated in most of the sampling periods. Levels of I. dammini infestation recorded on chipmunks in this survey are higher than previous results recorded in the northeastern and midwestern United States. Chipmunks had significantly higher levels of nymphal I. dammini infestation than white-footed mice (Peromyscus leucopus Rafinesque). A major role of the eastern chipmunk as a host for immature I. dammini in upland forest habitat in northwestern Illinois can be established. In bottomland and ecotone habitats where chipmunks were scarce, P. leucopus contributed most to the feeding of larval ticks.

Spatial-Genetic Structure in the Eastern Chipmunk, Tamias striatus

Spatial autocorrelation is used to identify the pattern of allozyme variation in populations of the eastern chipmunk (Tamias striatus). A nonrandom pattern of autocorrelation was detected when distances several hundred times the distance across an average home range were considered. A population sufficiently large to survey demographics and the mating system (across several dozen home ranges) was deemed too small for genetic studies. The size of the genetic neighborhood of the chipmunk was estimated from a correlogram. These results are interpreted to mean that it is possible to identify the size of the genetic neighborhood by use of spatial autocorrelation and that it is an appropriate preliminary analysis for identifying the limits of dispersal and gene flow.

Mammals of the Elm Creek Local Fauna, Late Pleistocene of Beaver County, Oklahoma

-Twelve mammalian taxa are identified (four to genus only) from the 1 1,410year-old Elm Creek local fauna. The water shrew Sorex palustris probably lived along margins of cold water streams of glacial meltwater. The chipmunk, Tamias striatus, probably inhabited broad-leafed woodlands marginal to the cold water streams. Other small mammals of the fauna are typical prairie or grassland forms. The ground squirrel, Spermophilus franklin ii, is now found to the north and west of Elm Creek. Remains of mammoth, horse and camel were recorded. The small mammals that lived at Elm Creek ca. 11,000 years ago principally were prairie forms. The boreal forest mammals recorded from northern Kansas and Nebraska at about this time did not extend as far south as the Oklahoma Panhandle in the terminal Pleistocene. A summary of eight late Pleistocene local faunas from Meade County, Kansas, and the panhandles of Oklahoma and Texas show cool-prairie environment, not cold climate or coniferous forest.

The influence of apparent predation risk on the foraging behaviour of eastern chipmunks (Tamias striatus)

The hypothesis that foraging behaviour is affected by the presence of a predator was tested in the field by presenting a stuffed marten (Martes americanus) to foraging eastern chipmunks (Tamias striatus). With a stuffed predator present, chipmunks approached the seed source more slowly. The closer the marten was to the seed tray, the smaller the loads collected by the chipmunks and the fewer the seeds consumed at the tray.

Defensive Behavior of Eastern Chipmunks Against Aedes triseriatus (Diptera: Culicidae)

Eastern chipmunks (Tamias striatus L.) were placed in Plexiglas cages with 0, 2, 5, 10, or 20 female Aedes triseriatus Say mosquitoes for 2 h. Previously published studies demonstrated little effective mosquito defensive behavior because of pause behavior by the chipmunks. By recording chipmunk behavior on videotape, pause behavior was reduced, and the chipmunks exhibited effective mosquito defense. The chipmunks defended themselves actively by attacking mosquitoes in flight, biting, head shaking, body turning, face grooming, hindfoot scratching, and flicking the tail. These defensive behaviors were correlated positively with the number of mosquitoes exposed to the chipmunks and with the number of mosquitoes killed.

Exploration versus exploitation: a field study of time allocation to environmental tracking by foraging chipmunks

When food sources change unpredictably in time and space, animals may improve their foraging rate if they devote some of their foraging time to locating and assessing the quality of alternative sites, even after they have already discovered and begun to use one site. To test the hypothesis that the amount of time allocated to exploration would increase as the quality of the presently exploited patch decreased, experiments were performed on five wild eastern chipmunks, Tamias striatus, hoarding sunflower seeds from artificial patches. When seed density was high, chipmunks returned promptly to the patch as soon as they had deposited each load. As seed density was reduced, chipmunks spent progressively more time exploring before returning to the patch. When seed density again increased, exploration times declined. Our experimental design also permitted a test of central place foraging theory. As predicted, chipmunks had longer collecting bouts but took smaller numbers of seeds per load when seed density was low than when it was high.

Survey for Ixodes spp. and Borrelia burgdorferi in southeastern Wisconsin and northeastern Illinois

Forested areas adjacent to Milwaukee, Wis., and Chicago, Ill., were investigated for rodents and ticks infected with Borrelia burgdorferi, the causative agent of Lyme disease. White-footed mice (Peromyscus leucopus or Peromyscus maniculatus), meadow voles (Microtus pennsylvanicus), and eastern chipmunks (Tamias striatus) were captured; and specimens from these animals were cultured for B. burgdorferi to define whether the midwestern Lyme disease area currently encompasses these large metropolitan centers. During 1988, B. burgdorferi was successfully cultured from the tissues of two M. pennyslvanicus voles captured from the Chicago area. However, no Ixodes spp. ticks were captured. None of 274 animals captured from sites I3 and 12 additional sites in Wisconsin and Illinois during the summer of 1989 were infected with B. burgdorferi or Ixodes spp. In addition, no ticks were recovered when the underbrush in 11 contiguous areas was flagged. Apparently, B. burgdorferi is rarely found in these areas because of the absence of the appropriate tick vectors. Further studies are needed to monitor the dispersal of B. burgdorferi-infected Ixodes dammini into this heavily populated midwestern region.

Genic homogeneity among temporal populations of the eastern chipmunk (Tamias striatus)

A population of eastern chipmunks (Tamias striatus) was surveyed for allozyme variation over two distinct reproductive seasons each year during 1987 and 1988. Individuals were placed into resident, recruit, and disappearing individual categories for the allozyme analysis. The resident population declined by 43% during the period of the study. Individuals in the recruit and emigrant categories accounted for about 50% of the population each season and the number in each of these categories varied widely from season to season. No inbreeding, based on genotype frequencies, was observed within the resident population. No significant genic heterogeneity was observed among temporally separated populations of chipmunks in the resident, recruit, or disappearing individual categories. The high levels of additions and losses from the population and the complex age-structure of chipmunk populations were likely the major contributors to the lack of inbreeding and seasonal differentiation. These results are contrasted with the more widely studied microtine systems.