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Fawns per 100 Does
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Fawn to doe ratios (FDRs) collected in late summer give information on fawn recruitment and survival. FDRs from Summer Deer Observation (SDO) surveys were summarized using groups of county Deer Management Units (DMUs) to show regional patterns over time. County DMUs were grouped based on location, habitat characteristics, and deer demography.
For additional Information….
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FDRs are used for monitoring deer population status because they provide information about fawn production and survival which are driven by the nutritional condition of the population. Fawn production is strongly influenced by food availability which is in turn affected by the size of the deer population and the quality of the habitat. In addition, survival of newborn fawns is often related to predation and the nutritional status of the doe.
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Collection and analysis methods
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The SDO survey is conducted by DNR employees and affiliates who keep records of the number of does, fawns, and bucks seen in August and September. The sum of the fawns divided by the sum of the does from SDO is the calculation for a county group’s FDR and provides an index to current reproductive rates. Historically, FDRs from SDO have been estimated annually for 9 county groupings.
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County group FDRs from SDO are shown as average number of fawns per 100 does annually with a 3-year running average to assess trend. Average FDRs vary across Wisconsin, generally lower in forested regions than in farmland regions and higher after mild winters in the north. Low FDRs in some counties may reflect higher levels of predation on newborn fawns and populations that are closer to carrying capacity. The county group FDR metric is no longer an input into the formula that is used to estimate annual deer population size by DMU but it still may be helpful to assess trends in FDR at a regional level. FDRs by DMU are derived from SDO and other surveys to provide the necessary inputs to the population model and are covered in the section of this website called ‘Fawn to Doe Ratio (DMU)’.
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Limitations and precautions
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No unbiased method has been developed to measure the number of fawns per doe in late summer deer populations. However, trends in roadside observations of does and fawns, especially in forested regions, have tended to match expectations based on other measures of nutritional condition of the herd and severity of winter weather. The precision and repeatability of FDRs are functions of the number of does and fawns observed, when the observations are made, and the skill level and interest of the observers. This county group FDR metric does not directly provide data for the deer population models.
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County group FDRs from SDO surveys continue to be a useful way to track regional trends in deer recruitment. Any future needs are exploratory to aid in understanding what mechanisms may be driving the observed trends.
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Additional background materials related to this metric
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FDR reports are available for viewing on the Wisconsin DNR website dnr.wi.gov keyword “wildlife reports”. DMU-level FDRs are covered on a separate page on this website ‘Fawn to Doe Ratio (DMU)’.
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