THE 2001 DEER PELLET GROUP SURVEYS

Transcription

1 MICHIGAN DEPARTMENT OF NATURAL RESOURCES Wildlife Report No THE 2001 DEER PELLET GROUP SURVEYS by Harry R. Hill ABSTRACT During the spring of 2001, a deer pellet group survey was conducted in most of the Upper Peninsula (UP) and selected units of the northern Lower Peninsula (NLP) (Fig. 1). The selected units in the NLP were chosen to monitor deer numbers in the tuberculosis area (DMU 452) and areas to the west and south. The UP is partitioned into six units for purposes of the pellet group survey. The western UP is divided into the high, medium, and low snowfall units. The high snowfall unit consists of deer management units (DMUs) 007, 042, and 066. The medium snowfall unit is comprised of DMUs 036 and 052. The low snowfall unit consists of 022 and 055. The eastern UP is divided into DMU 021 and DMUs (comprised of DMUs 017 and 049). The pellet group survey was not conducted in DMU 48 in the northeastern UP. INTRODUCTION Free-ranging wildlife populations are difficult to sample. The animals abilities to run and to hide not only make them difficult to capture, but also make them very difficult to observe. Therefore, wildlife biologists have determined that the best method for judging the density of white-tailed deer (Odocoileus virginianus) is to make counts of some sign that the deer leave. Deer droppings or pellet groups seem to be best suited for systematic appraisal. This technique is simply a formalized extension of methods used by experienced hunters to gauge the abundance of animals. RATIONALE The information about the density of deer pellet groups is primarily useful as an index to the abundance of deer. Bennett, English, and McCain (1940) originally used estimates of pellet group density to compare deer use on different areas. However, it may have seemed unsatisfactory to talk about pellet groups when they were actually interested in deer. Therefore, biologists defined a simple relationship between the number of pellet groups on an area and the number of deer necessary to produce those groups. This relationship was then used to mathematically convert pellet groups per acre into deer per square mile or deer per section. In order to estimate a deer population, we need to know (1) the rate that pellet groups are produced, (2) the number of pellet groups present, and (3) the period during which they were deposited. Studies with penned deer indicated that deer defecate on the average about 13.4 times in a 24-hour period. Thus, the total pellet groups on an area divided by 13.4 provides an estimate of the number of deer-days of use. Then if we can determine the period over which groups were deposited, we can estimate the number of deer present (McCain 1948). A contribution of Federal Aid in Wildlife Restoration, Michigan Project W-127-R. Printed by Authority of: P.A. 451 of 1994 Total Number of Copies Printed: Cost per Copy:.....$ Total Cost:....$.61 Michigan Department of Natural Resources IC (08/14/2001)

2 The period of time over which the groups have been deposited is defined to begin after leaf fall in the autumn and to end on the average date that the sample plots were searched. Usually, the leaves in any particular area are knocked from the trees during a relatively short period because of heavy winds, rain, snow, or a combination of these. Fallen leaves form a mat that hides groups dropped earlier. Thus, only those groups dropped after leaf fall are visible. Leaf fall is noted for each part of the state by the local wildlife biologists. However, in some areas the leaf cover is sparse, leaving it up to the biologists to separate the new pellet groups from the old. The actual relationship between deer density and pellet group density is much more complex. It is affected by many factors, including weather, diet, and composition of the deer herd. Since the exact form of this relationship is unknown, the new figure which is calculated is not an exact number of deer, but it is, at least, an improved population index (Overton 1969). However, experiments have shown that the simple relationship is a reasonable approximation of the true relationship between pellet group density and actual deer density (Eberhardt and VanEtten 1956). SAMPLE The northern deer range in Michigan encompasses an area of over 30,000 square miles. Since it is virtually impossible, and far too expensive, to search the entire area, a sampling plan must be formulated. The area is classified by the field biologists into three categories of deer abundance. Then the three categories (strata) are separately sampled. The number of samples allocated to each category depends on the area included in the category and the variability observed within the strata. The survey is primarily designed to produce estimates for areas greater than the size of two counties. This sampling design is called stratified sampling. Stratified sampling does not introduce any personal bias into the survey but does provide more precise estimates with less effort. Stratification is merely a method of assuring that the greatest effort is spent where it will do the most good. The entire deer range is divided into over 30,000 first stage sampling units or sections. Typically, sections are one square mile. Due to land survey corrections and lake shores, some sections may contain less than one square mile of land area. This survey design assumes that only sections that contain more than one-half square mile of land area are available for sampling. Therefore, the number of sections in a district may not agree exactly with the district s land area. The sections to be sampled are determined by random selection. Each section within a stratum within a district has the same chance of being selected. Second stage samples are areas located in each randomly selected section. These are a series of five 1/50-acre rectangular plots (12 x 72.6 ). The five plots together make up a course. The midpoint of each end of the plot is marked with a wooden stake. COMPUTATIONS The survey estimates the average number of deer pellet groups to be found on any randomly selected course in a district. In Table 3, the average groups per course are changed to groups per section and then this estimate is converted to total deer. Dividing the average groups per course by five gives the average groups per plot (a course consists of five plots). This value is multiplied by 50 to calculate average groups per acre (the plots are 1/50-acre) and then multiplied by 640 acres per section to estimate the number of groups per section. This is converted to the number of deer by dividing the groups by the deposition rate to give deer-days and then by the number of days to give the average number of deer present for the period. These figures are termed unadjusted deer in district. The calculations are shown in a simplified formula at the bottom of the table. The unadjusted figure is an estimate of the average overwinter deer population. 2

3 Fewer deer than the unadjusted estimate (Table 3) are actually present in the spring. Deer that die during the deposition period also contribute pellet groups. For example, four deer which each live for one month will contribute about the same number of pellet groups as two deer which each live for two months or one deer which lives for four months. To correct for this, we subtract the pellet groups deposited by deer that do not survive the entire pellet deposition period. Deer killed during the regular firearm deer season dropped pellet groups for about a month before being shot, and these groups were included in the total estimate of pellet groups. Their contributions must be deducted for the period they were present. This same process is used for other losses to calculate the spring herd estimate. Then the estimated number of deer lost during the deposition period, not their contributions, are added to the estimated spring herd to get the previous fall s herd estimate. Table 5 contains these calculations. This does not account for deer illegally killed and removed during the pellet deposition period. The illegal removal is unknown, but perhaps sizable. This means that the actual fall population is somewhat larger than the figure given, and the spring population is somewhat smaller. The estimates of legal deer kill are from annual mail surveys (Frawley 2000). In years when losses are expected to be high, dead deer surveys are undertaken to quantitatively estimate these overwinter losses. The estimates are summarized in Table 1 and Figure 1. The estimated spring deer densities by stratum for each unit are found in Table 2. SOURCES AND CONTROL OF ERROR The number of deer is not constant from section to section across the state. Likewise, the number of pellet groups also varies from one course to another. The amount and direction of these variations are due to chance and are termed sampling errors. The deer pellet group survey, like all sampling techniques, is subject to many sources of error in addition to chance or sampling errors. These non-random errors or biases arise in counting and aging the pellet groups, in estimating deer defecation rates and leaf fall dates, and in sampling error. Ryel (1959), Eberhardt (1960), and VanEtten and Bennett (1965) discuss these problems in some detail. It appears that the actual determination of (1) the number of pellet groups present on a sample plot and (2) their relative age, is responsible for a large share of the variations in survey results. Errors in estimating the defecation rate and in estimating the leaf fall date does not appear to contribute major errors to the final estimate. Ideally, to reduce counting errors and misidentification of pellet age to a minimum, a few experienced individuals should search all of the courses each year. This is not possible because of the effort involved and the time limits imposed. Therefore, a recheck system is used. On the 1956, 1957, and 1958 pellet group surveys, all plots were originally searched by one person. As a recheck, 20 percent of the courses were randomly selected and searched a second time by an experienced biologist. Discrepancies between the original counts and the rechecks resulted in increasing the estimates of the total deer population by 30 percent in the northern Lower Peninsula in 1956, by 1 percent in this area in 1957, and by 16 percent in the Upper Peninsula in 1957 (Eberhardt 1957). A system of concurrent rechecks is used on the surveys. This involves making independent counts on all plots by members of two-person crews and then arriving at a composite count. Crew members start at opposite ends of the plot and count pellet groups on the half plot to their right. Metal disks are used to mark all groups found. Searchers then switch sides and check their partner s work. The biologists on the crews are responsible for classifying pellets into age categories and making final decisions on the number of groups present. Where a crew has only one biologist (the usual case), there is no real check on his/her identification of old and new groups. We have not found consistent characteristics to distinguish pellet groups dropped prior to leaf fall from those dropped after leaf fall. This means that we must use the relationship of the groups to fallen leaves and ground 3

4 vegetation whenever possible. Where this is not feasible, as in grasslands, oak stands, conifer swamps, etc., we must depend on the searcher s ability to make correct judgments on the age of questionable groups. Some notion of the magnitude of these errors can be obtained by comparing the ratios of old to new pellet groups between districts within the various strata. Unfortunately, such comparisons are complicated by changes in weather, changes in deer use, and changes in deer foods among the various districts and between years. Thus, we cannot be sure that any differences that we find are due to human error alone. STATISTICAL CALCULATIONS Table 6 contains the summaries of the statistical analyses by district, giving stratum averages ( x j ), district average ( x st ), and stratum standard deviation s j. Computations for each district were made as suggested by Cochran (1953) for stratified random sampling: x = w x w x w x st n n where the wj ' s are the proportion of the total number of sections in each stratum and the x j ' s are the stratum averages ( ) = st 1 ( 1 ) + 2 ( 2 ) + + n ( n ) vx w vx w vx w v x where the w s ' are as above and j vx ( j ) ' sare variances of stratum averages = s 2 j. n In a similar fashion, estimates of the averages and variances were made for the Upper Peninsula. Here the w ' s j ' become the proportion of the Upper Peninsula occupied by each district, the xj ' s are the district averages, and the vx ( )' stheir corresponding variances. With a systematic sub-sample, the model is equivalent to a simple random sample with one element per sample. Therefore, there is no estimate provided for a component of variation from plot to plot within each first stage sampling unit (section). Cochran indicates the variance estimate based on the first stage sampling unit, as derived from the second stage samples, is a valid approximation as long as n/n is small (less than.05 is suggested). Here n refers to the number of sections selected out of the total possible, N, in each stratum. Equal Rights for Natural Resources Users The Michigan Department of Natural Resources (MDNR) provides equal opportunities for employment and access to Michigan s natural resources. Both State and Federal laws prohibit discrimination on the basis of race, color, national origin, religion, disability, age, sex, height, weight or marital status under the Civil Rights Acts of 1964 as amended (MI PA 453 and MI PA 220, Title V of the Rehabilitation Act of 1973 as amended, and the Americans with Disabilities Act). If you believe that you have been discriminated against in any program, activity, or facility, or if you desire additional information, please write the MDNR, Human Resources, P.O. Box 30028, Lansing, MI , or the Michigan Department of Civil Rights, State of Michigan Plaza Building, th Street, Detroit, MI 48226, or the Office for Diversity and Civil Rights, U.S. Fish and Wildlife Service, 4040 North Fairfax Drive, Arlington, VA For information or assistance on this publication, contact: MDNR, Wildlife Division, P.O. Box 30444, Lansing, MI , This publication is available in alternative formats upon request. TTY: Michigan Relay Center

5 LITERATURE CITED Bennett, L. J., P. F. English, and R. McCain A study of deer populations by use of pellet-group counts. J. Wildl. Mgmt. 4(4): Cochran, W. G Sampling techniques. John Wiley and Sons, Inc., New York. Eberhardt, L. L The 1956 and 1957 pellet-group surveys. Game Div. Rept. No. 2133, Michigan Dept. Conserv., Lansing. 37pp Estimation of vital characteristics of Michigan deer herds. Game Div. Rept. No. 2282, Michigan Dept. Conserv., Lansing. 192pp.. R. C. VanEtten Evaluation of the pellet-group count as a deer census method. J. Wildl. Mgmt. 20(1): Frawley, B. J Michigan Deer Harvest Survey Report Seasons. Wildlife Report No Michigan Dept. Natural Resources, Lansing. 27pp. McCain, R A method for measuring deer range use. Trans. N. Am. Wildl. Conf. 13: Overton, W. S Estimating the numbers of animals in wildlife populations, pp in Giles, R. J. (ed.), Wildlife Management Techniques, Third Edition:Revised. Ryel, L.A Deer pellet-group surveys on an area of known herd size. Game Div. Rept. No. 2252, Michigan Dept. Conserv., Lansing. 26pp. VanEtten, R. C., and C. L. Bennett, Jr Some sources of error in using pellet group counts for censusing deer. J. Wildl. Mgmt. 29(4):

6 Figure 1 HOUGHTON KEWEENAW HighSnowfall Unit ONTONAGON BARAGA MARQUETTE GOGEBIC MediumSnowfall IRON Unit DICKINSON LowSnowfall Unit MENOMINEE Legend Boundary for Pellet Survey Units County Boundary State Boundary or Great Lakes Shoreline N Miles ALGER DELTA 2001 Pellet Survey Units SCHOOLCRAFT DMU 21 MASON OCEANA DMU 48 LEELANAU BENZIE MANISTEE MUSKEGON LAKE NEWAYGO OTTAWA LUCE CHIPPEWA DMU MACKINAC GRAND TRAVERSE Coastal Unit EMMET CHARLEVOIX ANTRIM WEXFORD MISSAUKEE CHEBOYGAN OTSEGO West Unit KALKASKA CRAWFORD ROSCOMMON OSCEOLA CLARE GLADWIN MECOSTA ISABELLA MONTCALM GRATIOT PRESQUE ISLE DMU ALPENA 452 MONTMORENCY OSCODA OGEMAW South Unit MIDLAND BAY SAGINAW KENT IONIA CLINTON SHIAWASSEE Core Area ARENAC ALCONA IOSCO GENESEE TUSCOLA HURON LAPEER SANILAC ST.CLAIR MACOMB Kilometers ALLEGAN BARRY EATON INGHAM LIVINGSTON OAKLAND VAN BUREN KALAMAZOO CALHOUN JACKSON WASHTENAW WAYNE MONROE BERRIEN CASS ST.JOSEPH BRANCH HILLSDALE LENAWEE DEER PER SECTION: FALL 2000 AND SPRING 2001 Fall Spring Fall Spring Unit Unit High Snowfall DMU 452* Medium Snowfall West Low Snowfall South DMU Coastal DMUs 17& *DMU 452 includes the entire five-county area. 6

7 Table 1 SUMMARY OF ESTIMATES Units Sections Unadjusted Deer Legal Kill [1] Other Losses [2] Deer Population Fall 2000[3] Estimates Spring 2001 High Snowfall 4,251 51,895 13,668 10,969 69,055 44,418 Medium Snowfall 3, ,464 24,993 28, , ,669 Low Snowfall 2, ,942 34,439 39, ,382 96,497 DMU 21 1,739 54,032 9,473 10,085 66,969 47,411 DMUs ,084 55,935 11,353 12,887 71,930 47,690 DMU 452 3,024 81,062 30,730 15, ,074 69,983 West 3,773 84,826 26,996 7, ,473 76,579 South 4, ,248 64, , , ,811 Coastal 4, ,059 60,784 36, ,452 91,814 [1] Legal kill (all seasons including block permits and deer management assistance permits). [2] Does not include illegal kill completely removed from the field. [3] Fall population estimate prior to October 1, Figures include adjustments for early seasons, archery, regular firearm, muzzleloader, block permits, and deer management assistance permits. Due to rounding, the figures in this table may not sum exactly to the totals. Table 2 ESTIMATED SPRING POPULATION DENSITY BY STRATUM (Deer Per Square Mile) Stratum High Snowfall Medium Snowfall Low Snowfall DMU 21 DMUs I II III Average Stratum DMU 452* West Unit South Unit Coastal Unit I II III Average *Weighted average of 562-square mile core area and surrounding 2,462-square mile area. 7

8 Table 3 UNADJUSTED POPULATION ESTIMATES[1] (Average Overwinter Population) Units Days From Leaf Fall Avg. Pellet Groups/Course Average Deer/Section Sections In Unit Unadjusted Deer in Unit High Snowfall ,251 51,895 Medium Snowfall , ,464 Low Snowfall , ,942 DMU ,739 54,032 DMUs ,084 55,935 DMU ,024 81,062 West ,773 84,826 South , ,248 Coastal , ,059 Upper Peninsula deer per section = (Avg. Pellet Groups/Course) x 50 x 640 (days from leaf fall) x x is average pellet groups deposited per deer day in the U.P. Northern Lower Peninsula deer per section = (Avg. Pellet Groups/Course) x 50 x 640 (days from leaf fall) x x is average pellet groups deposited per deer day in the N.L.P. 50x640 5 is a constant which converts the counts from per course to per section. [1] Unadjusted means that deer dying during the pellet deposition period have not been taken into account. 8

9 Table 4 STATISTICAL ANALYSIS OF DEER PELLET GROUPS PER COURSE Unit Stratum Sections Number of Samples Average Standard Deviation High Snowfall I II III 3, Unit Average 5.29 Standard Error 1.15 Medium Snowfall I II 1, III 1, Unit Average Standard Error 1.98 Low Snowfall I 1, II 1, III Unit Average Standard Error 2.30 DMU 21 I II III 1, Unit Average Standard Error 2.50 DMUs I II III 1, Unit Average Standard Error 1.95 DMU 452 I II 1, III 1, Unit Average Standard Error 1.13 West I II III 2, Unit Average 8.50 Standard Error

10 Table 4 (Continued) STATISTICAL ANALYSIS OF DEER PELLET GROUPS PER COURSE Unit Stratum Sections Number of Samples Average Standard Deviation South I II 2, III 1, Unit Average Standard Error 1.87 Coastal I II 1, III 3, Unit Average 9.23 Standard Error 1.39 Table 5 ADJUSTMENTS FOR DEER REMOVALS High Snowfall Unit Deposition period 206 days Archery season--about 2,482 deer contributing for 21 days Firearm season--about 10,438 deer contributing for 30 days Muzzleloader season--about 681 deer contributing for 47 days about 3,510 deer contributing for 43 days about 7,459 deer contributing for 133 days 51, , ,816 [1]Block and deer management assistance permit harvests are prorated into each season. [2]Does not include illegal kill completely removed from the field Adjusted Spring Population 44,418 Hunting Removal for all Seasons 13,668 Other Losses 10, Fall Population 69,055 10

11 Table 5 (Continued) ADJUSTMENTS FOR DEER REMOVALS Deposition period days Medium Snowfall Unit Archery season--about 4,484 deer contributing for 21 days Firearm season--about 19,034 deer contributing for 30 days Muzzleloader season--about 1,332 deer contributing for 47 days about 9,136 deer contributing for 43 days about 19,414 deer contributing for 133 days 122, , ,994-13, Adjusted Spring Population 103,669 Hunting Removal for all Seasons 24,993 Other Losses 28, Fall Population 157,212 Low Snowfall Unit Deposition period days Archery season--about 5,133 deer contributing for 21 days Firearm season--about 26,690 deer contributing for 30 days Muzzleloader season--about 2,373 deer contributing for 47 days about 12,623 deer contributing for 43 days about 26,823 deer contributing for 133 days 122, , ,798-18,389 [1]Block and deer management assistance permit harvests are prorated into each season. [2]Does not include illegal kill completely removed from the field Adjusted Spring Population 96,497 Hunting Removal for all Seasons 34,439 Other Losses 39, Fall Population 170,382 11

12 Table 5 (Continued) ADJUSTMENTS FOR DEER REMOVALS DMU 21 Deposition period 200 days Archery season--about 1,536 deer contributing for 21 days Firearm season--about 7,060 deer contributing for 30 days Muzzleloader season about 816 deer contributing for 47 days about 3,328 deer contributing for 43 days about 6,757 deer contributing for 133 days 54, , , Adjusted Spring Population 47,411 Hunting Removal for all Seasons 9,473 Other Losses 10, Fall Population 66,969 DMUs Deposition period days Archery season--about 2,695 deer contributing for 21 days Firearm season--about 7,896 deer contributing for 30 days Muzzleloader season--about 693 deer contributing for 47 days [2Fall and early winter losses-- about 4,253 deer contributing for 43 days about 8,634 deer contributing for 133 days 55, , ,713 [1]Block and deer management assistance permit harvests are prorated into each season. [2]Does not include illegal kill completely removed from the field Adjusted Spring Population 47,690 Hunting Removal for all Seasons 11,353 Other Losses 12, Fall Population 71,930 12

13 Table 5 (Continued) ADJUSTMENTS FOR DEER REMOVALS DMU 452 Deposition period 179 days Archery season--about 3,368 deer contributing for 15 days Firearm season--about 21,354 deer contributing for 24 days Muzzleloader season about 1,151 deer contributing for 48 days Late season--about 2,443 deer contributing for 60 days about 8,141 deer contributing for 37 days about 7,220 deer contributing for 127 days 81, , ,683-5, Adjusted Spring Population 69,983 [3]Hunting Removal for all Seasons 30,730 Other Losses 15, Fall Population 116,074 [1]Block and deer management assistance permit harvests are prorated into each season. [2]Does not include illegal kill completely removed from the field. [3]Includes early season harvest of 2,286 deer. 13

14 Table 5 (Continued) ADJUSTMENTS FOR DEER REMOVALS West Unit Deposition period 181 days Archery season--about 5,580 deer contributing for 17 days Firearm season--about 19,021 deer contributing for 26 days Muzzleloader season about 1,287 deer contributing for 50 days Late season--about 878 deer contributing for 62 days about 2,606 deer contributing for 39 days about 5,292 deer contributing for 129 days 84, , , Adjusted Spring Population 76,579 Hunting Removal for all Seasons 26,996 Other Losses 7, Fall Population 111,473 South Unit Deposition period 173 days Archery season--about 16,081 deer contributing for 14 days Firearm season--about 40,384 deer contributing for 23 days Muzzleloader season about 3,060 deer contributing for 47 days Late season--about 3,649 deer contributing for 59 days about 17,100 deer contributing for 36 days about 8,422 deer contributing for 126 days 177,248-1,301-5, ,244-3,558-6,134 [1]Block and deer management assistance permit harvests are prorated into each season. [2]Does not include illegal kill completely removed from the field Adjusted Spring Population 158,811 Hunting Removal for all Seasons 64,012 Other Losses 25, Fall Population 248,345 14

15 Table 5 (Continued) ADJUSTMENTS FOR DEER REMOVALS Coastal Unit Deposition period 181 days Archery season about 15,462 deer contributing for 19 days Firearm season--about 39,818 deer contributing for 28 days Muzzleloader season about 2,098 deer contributing for 52 days Late season--about 2,629 deer contributing for 64 days about 27,641 deer contributing for 41 days about 9,213 deer contributing for 131 days 114,059-1,623-6, ,261-6,668 [1]Block and deer management assistance permit harvests are prorated into each season. [2]Does not include illegal kill completely removed from the field Adjusted Spring Population 91,814 Hunting Removal for all Seasons 60,784 Other Losses 36, Fall Population 189,452 15