LONGEVITY OF THE NORTHERN SHORT-TAIL SHREW ( BLARINA BREVICAUDA ) AT RICE CREEK FIELD STATION, SUNY OSWEGO Sara Ressing Department of Biological Sciences Long-term longitudinal studies can provide information on habitat quality over time. The Short-tailed shrew ( Blarina brevicauda ) is carnivorous, abundant in most habitats and lives 18 months or less. Ageing criteria based on weight or reproductive condition provide unreliable r esults since shrews are nearly adult weight at emergence from the nest and can begin reproduction shortly thereafter. The only reliable ageing criterion is microscopic evaluation of wear on cheek teeth of preserved specimens: not applicable to live animals. We used field measurements of incisors of marked indi viduals trapped repeatedly over a 7 month period to see if incisor length could be reliably related to known age. We live trapped short-tailed shrews ( Blarina brevicauda ) at SUNY Oswegos Rice Creek Field Station every 1-2 weeks, MayNovember 2007. Individuals were marked with PIT tags and released. We trapped 62 individuals a total of 263 times (max. captures/individual = 14; max. interval between first and last capture: 193 days). Tooth wear is measurable over longer interv als of time, and incisor length can be used to place individuals into 3 age classes. I. Introduction The northern short-tailed shrew is the most abundant small mammal at Rice Creek Field Station. They are known to be relatively short lived with starvation, exposure, predation, and old age the primary causes of mortality. I ndividuals in captivity ha ve lived for over 30 months and wild caught specimens have been shown to live at least 15 months (Pearson, 1945). Most long term longitudinal studies of shrew populations (e.g. Getz et al., 2004) lack aging criteria, a fundamental demographic component, due to the difficulty of accurately determining the age of living shrews. Gene ral criteria for an ideal age determination technique for short-tailed shrews include: independence from irregular nutritional and physiological variations; clear separations into age classes without subjective judgment; suitability for living animals of all ages; a nd easy application (Larson & Taber, 1980). Criteria of this caliber are thus far absent from the literature regarding age identification in the northern short-tailed shrew ( Blarina brevicauda ). The most reliable criterion requires microscopic evaluation of wear on the cheek teeth of preserved specimens: a method not applicable to live animals (Pearson, 1945; Pr uitt, 1954; Choate 1968; Strait & Smith 2006). Here we discuss the value of using length of the pigmented portion of the upper incisor, a measurement that is easy to take in the field, as an appropriate aging criterion. We test the
S. Ressing 8 reliability of incisor pigment length as an indicator of age, and apply this measurement to a living population of B. brevicauda at Rice Creek Field Station, Oswego, New York. II. Materials and Methods A museum study of preserved material was first conducted to assess the accuracy of using incisor pigmentation as an indicator of age. Th e skulls of specimens (n=102) used in this study were collected throughout the central Ne w York area, preserved by Dr. J. A. Lackey, and held at SUNY Oswegos Rice Creek Biological Field Station, Oswego, New York. The upper mandibles of these skulls were inspected under a dissecting microscope, examining the occlusion of the three molars and third premolar (Fig. 1). Wear classes were established using criteria published by Pruitt (1954) and Pearson (1945) based on wear on the occlusion surfaces of the molars. Measurements of the length of the pigmented portion of the right upper incisor were taken using calipers accurate to 0.01 mm without reference to molar wear class. Incisors were measured twice, from beginning of pigmentation to the tip of the tooth. The repeated measures of incisor pigmentation were analyzed for experimenter consistency using Pearsons correlation. A representative photographic record of the dentition of the upper mandible, as well as a lateral view of the upper incisor was taken for each wear class (Fig. 2). After establishing and testing the aging criteria, we applied the aging method in a mark and recapture study of living individuals. Shrews were live trapped at SUNY Oswegos Rice Creek Field Station every 1-2 weeks from May-November 2007. Due to the mainly nocturnal summer activity cycle of B. brevicauda Sherman live traps were set at dusk and checked 3-4 hours later. Individuals we re marked with Biomark 8.5mm X 2.12 mm passive integrated transponders (PIT tags) and released. Animals were handled at night by headlamp, and immobilized in rip-stop nylon cones. Basic data were recorded on each animal at the time of each capture, including weight, reproductive status, total body length, tail length, and right hind foot length. Inciso r pigment length was measured using a set of calipers. Fig. 1: Dorsal view of B. brevicauda upper jaw. Dental formula P3M 1M2M3
Longevity of the Northern Short-Tail Shrew ( Blarina brevicauda ) 9 Fig. 2: Age Wear Classes based on Pearson (1945) and Pruitt (1954). Photographs show the dentition of the upper mandible and lateral view of the upper incisor at each wear class.
S. Ressing 10 II esults I. R ip between incisor pigment length and wear class based on wear of the olars was highly significant (r= 0.768, p= 0.000, n=102, 5) establis hed wear classes with young adults enc cant cha ere young adults, and 6.4% were old adult anim y from 40% to 30.4% (Chi-squared, P=0.0104); and using animal proAgeThe relationsh occlusal surface of the m Pearsons Correlation); however there was some overlap between wear classes (Fig. 3). Observer consistency was very high for inci sor pigment length remeasure (r = .950, p = 0.000, n=102, Pearsons Correlation). Table 1 shows range of incisor pigment length for age groups. Age classes were assigned based on Pearsons (194 ompassing classes one and two; adults expect ed to have teeth consistent with wear classes three and four, and old adults would be considered in wear class five and six. In the field study, 62 individual shrews were trapped a total of 263 times. A regression of tooth wear over time using only the first and last measurements showed signifi nge for the shrews of the upper field (P = 0.0001; R2 = 37%) but not for the lower field (P = 0.903; R2 = 0%) (Fig. 4). A comparison of total change in incisor pigment length and days between first and last capture (Fig. 5) shows considerable variability over shorter periods of time, but measurable decrease in incisor length over longer periods of time. Average change in one month was less than one millimeter, however after two months, the average change, 0.21 mm was substantial enough to be measured using calipers Standard deviation in changes in incisor pigment length (SD=0.3 mm) is not large enough to move individuals from one age class to another. In Fig. 6, age profiles over the trapping period are shown. On average, 64% of individuals captured were adults, 29.6% w als based on the criteria outlined in Table 1. Fig. 7 shows the longevity of animals marked at the upper and lower field. The maximum number of capt ures per individual was 14, and the largest interval between first and last capture was 193 days. Forty-eight percent of marked animals were not subsequently r ecaptured. The average number of captures per individual was 3.5. Efforts were made to reduce trap mortality in the shrews. The use of cardboard inserts reduced trap mortalit tein as bait in the trap reduced trap mortality from 28.8% to 12.9% (Chi-squared, P=0.0010); but only very frequent trap checks (<4 hours) reduced trap mortality to an acceptable level of 3%. These results were re ported in a poster presented by Chepko-Sade and Gerald Zoanetti at the American Soci ety of Mammalogists meetings in 2001, Table 1: Age categories based on incisor pigment length in B. brevicauda Category Pigmented Part of Incisors (mm) Young Adult >2.0 Adult 1.0 2.0 Old Adult <1.0
Longevity of the Northern Short-Tail Shrew ( Blarina brevicauda ) 11 Fig. 3: Degree of incisor wear is highly correla ted with degree of wear on the cheek teeth Wear ClassLength of Pigmentd Portion of Upper Incisor (mm) 6 5 4 3 2 1 2.5 2.0 1.5 1.0 0.5 0.0 Incisor Length vs Wear Class (r = -0.768, p = 0.000, n=102). 140 120 10080 604020 0 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 Time periodChange in tooth length Lower Fieldf Lower Fieldm Upper Fieldf Upper Fieldm GridSexScatterplot of Change in tooth length vs Time period Fig. 4: Regression of tooth length over time shows a significant change for individuals in the upper field (Upper Field: P = 0.0001; R2 = 37%, n=37), but not for the lower field (Lower Field: P = 0.903; R2 = 0%; n=28).
S. Ressing 12 Tooth Attrition Over Time-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 -55 45 145 245 345 445 545DaysTooth Loss (mm) Fig. 5: Reliable measures of w ear may take 18+ months. Total t ooth loss over capture interval is depicted. The red line shows the projected ch ange in tooth length, with .3mm standard deviation shown by dotted lines. Age profile for 2007 0.0% 20.0% 40.0% 60.0% 80.0% 100.0%January M a y J une July A ugust Sept e mber October N o ve mb e r A v e ra g e Young Adult Adult Old Fig. 6: Graphed age profile indicates the progression of aging as spring young mature, and adults from the previous spring die off. Over the trapping period 64% of individuals captured were adult, 29.6% were young a dult, and 6.4% were old adult animals.
Longevity of the Northern Short-Tail Shrew ( Blarina brevicauda ) 13 28-May17-Jul5-Sep25-Oct14-Dec 985153000022595 985153000022601 985153000022603 985153000022607 985153000022608 985153000022610 985153000022614 985153000022621 985153000022622 985153000022623 985153000022624 985153000022625 985153000022635 985153000022637 985153000022640 985153000022643 985153000022644 985153000022650 985153000022653 985153000022654 985153000022655 985153000022658 985153000022661 985153000022667 985153000022673 985153000022674 985153000022676 985153000022680 985153000022684 985153000022693 985153000022696 985153000022699 45756F030E 985153000002586Upper Field Longevity PIT Tag 28-May17-Jul5-Sep25-Oct14-Dec 985120013872742 985120028903494 985153000002286 985153000002294 985153000002355 985153000002406 985153000002447 985153000002462 985153000002489 985153000002492 985153000002512 985153000002521 985153000002614 985153000002629 985153000002679 985153000002699 985153000022502 985153000022504 985153000022508 985153000022530 985153000022535 985153000022549 985153000022563 985153000022565 985153000022571 985153000022573 985153000022580 985153000022585Lower Field Longevity PIT Tag Fig. 7: Persistence of short tailed shrew on the upper and lower field grids. Date of the first and most recent capture for each individual is shown. The largest interval between first and last capture was 193 days. Blue bars are males, pink ar e females. IV. Discussion Incisor pigment length is an accurate and reliabl e indicator of age in short-tailed shrews and can be used to place individuals into three age classes as shown in Table 1. As individuals
S. Ressing 14 age, their teeth wear down which is confir med by decreases in the amount of pigment measured on the upper incisors. The practical application of using these criteria for aging animals in the field is clear. Individuals can be placed in age groups (Fig. 6) to create a demographic profile for a living population for comparison with results of previous studies based on dead individuals (Pearson, 1945). This allows the periodic examination of the age profile of the same population at different times without the impact of removing large numbers of individuals from the population to ascertain age profiles based on cheek teeth attrition. Mortality for this trapping session was greatly reduced compared to mortality recorded in previous seasons (ChepkoSade, unpublished data). B. brevicauda weaken and die quickly in Sherman traps due to their fast me tabolism and the stress of captivity. Frequent trap checks reduced mortality the greatest amount, but the inclusion of cardboard inserts and animal protein in the traps also had an effect. Due to small sample sizes and high varia tion between successive measurements of the same individual, further trapping is needed to alleviate the spread in the data. The project will be continued over the summer in order to further quantify the rate of tooth attrition over time so that individuals may be more pr ecisely aged rather than just assigned to age classes. This information will allow us to st udy the demographics of this population in more detail. V. Acknowledgements Dr. B. Diane Chepko-Sade, Dr. J. A. Lackey, and Dr. Andrew Nelson. Field Assistants: Matthew Volny, Wendy Paterson, and Je nna McAdoo Funding received from Student Faculty Collaborative challenge Grant and Rice Creek Associates Grant. VI. References Choate, J. R. (1968). Dental Abnormalities in the Short-tailed Shrew, Blarina brevicauda Journal of Mammalogy 49(2), 251-258. Getz, L. L., Hofmann, J. E., McGuire, B., Oli, M. K. (2004). Population Dynamics of the Northern Short-tailed Shrew, Blarina brevicauda Insights from a 25-year study. Canadian Journal of Zoology 82, 1679-1686. Larson, J. S. & Taber, R. D. (1980). Criteria of Sex and Age. In S. D. Schemnitz (Ed.), Wildlife Management Techniques Manual (4th ed., pp. 143-202). Washington: The Wildlife Society, Inc. Pearson, O. P. (1945). Longevity of the Short-tailed Shrew. American Midland Naturalist, 34(2), 531-546. Pruitt, W. O., Jr. (1954). Notes on the Shortta il Shrew (Blarina brevicauda kirtlandi) in Northern Lower Michigan. American Midland Naturalist, 52 (1), 236-241. Strait, S. G. & Smith, S. C. (2006). Elemental Analysis of Soricine Enamel: Pigmentation Variation and Distribution in Molars of Blarina brevicauda. Journal of Mammalogy, 87(4), 700-705.