Relationship Between Fecal Pellet Counts and Snowshoe Hare Density in Western Wyoming

ABSTRACT Snowshoe hares (Lepus americanus) are an important prey species for Canada lynx (Lynx canadensis) and are considered critical for lynx population persistence. Determination of snowshoe hare distribution and abundance is needed by land management agencies for lynx conservation. An accepted approach for estimating snowshoe hare abundance is the use of fecal-pellet plot counts. Locally derived regression equations are preferred for accurate calibration of pellet counts to snowshoe hare density due to local differences in pellet deposition and decomposition. We used linear regression to examine correlations between snowshoe hare density, as determined by mark–recapture estimates, and pellet plot counts on both uncleared plots and annually cleared plots on the Bridger-Teton National Forest, western Wyoming, USA. We found significant correlations between snowshoe hare density estimates and fecal pellet counts for both uncleared and annually cleared pellet counts; however, the relationship was stronger (higher r) when using pellet counts from annually cleared plots. In addition, we found that adjusting the buffer size by omitting hard habitat edges (not used by hares) around trapping grids improved correlations between snowshoe hare density and fecal pellet counts for both uncleared plots and annually cleared plots. Though precision is sacrificed when using uncleared plots, they may be useful as a coarse index of habitat use by snowshoe hares. Our derived regression equations may be useful to identify important foraging habitat for Canada lynx in western Wyoming. Land managers responsible for conserving snowshoe hare habitat in western Wyoming may use these equations to monitor changes in hare populations among habitats and during prescribed management actions.     

Estimating roe deer abundance from pellet group counts in Spain: An assessment of methods suitable for Mediterranean woodlands

Despite of the generalized expansion of wild ungulates in Europe, roe deer (Capreolus capreolus) is experiencing contrasted population trends; it is expanding in some regions while declining in others likely due to the expansion of other deer species. In both extremes, reliable methods to estimate population abundance are required. We evaluated different methods of estimating deer abundance in Mediterranean woodlands based on pellet group counts. Distance Sampling applied to pellet counts and a new easier and cost-effective method based on strip-variable transect counts (FST) were assessed comparing their estimates (pellet group density) with the abundance indices obtained from traditionally used reference methods (faecal standing crop) in 61 localities (n = 183 surveys). The average roe deer density estimated from faecal standing crop was 5.56 ± 0.75 (range 0.01–20.74) deer per 100 ha. Distance Sampling and FST estimates correlated with reference methods. As a first conclusion it may be noted that all indirect methods used here can be used to estimate roe deer abundance. The selection of a given method based on pellet counts to estimate roe deer population abundance should take into account the specific objectives of the research, resources available, and the timescale in which the information is required. Among them, Distance Sampling may be used when human resources and skills are enough but FST is a rapid and efficient alternative to estimate pellet group density when they are not.     

Estimating the density of kudu (Tragelaphus strepsiceros) in subtropical thicket using line transect surveys of dung and DISTANCE software

Many ecotourism reserves in the Eastern Cape Province of South Africa have introduced large carnivores which prey on ungulates such as kudu. Kudu occupy thick vegetation and helicopter‐based counts are not appropriate. In this study we tested line transect counts of faecal pellets in conjunction with DISTANCE analysis as a method for assessing the abundance of kudu. Transects were undertaken in three regions of two game reserves and the results compared with helicopter based game counts (for two regions) and a known kudu population in the third region (an enclosed breeding centre). Estimates of kudu abundance were two to three times greater than the helicopter counts, but within the known number of kudu in the breeding centre. The increased accuracy in the breeding centre was probably because the transects covered a greater percentage of the available habitat (0.07%) than in the reserves (approximately 0.007%). We suggest that DISTANCE software and line transects counts of pellet groups can be used for kudu and probably for other ungulates in thicket‐type vegetations. Accuracy will depend on the percentage of the available habitat that is surveyed and on the accuracy of the defecation and decay rates.     

Landscape structure affects food quality of sika deer (<Emphasis Type="Italic">Cervus nippon</Emphasis>) evidenced by fecal nitrogen levels

Evaluating the quality of wildlife habitat is essential for understanding and predicting population dynamics in heterogeneous environments. We used fecal nitrogen levels as an indicator of habitat quality of sika deer (Cervus nippon) and explored important landscape elements influencing nitrogen levels, taking deer density into account. We established 92 plots differing in deer density and landscape structure on the Boso Peninsula, central Japan, and collected fecal samples along a 1-km transect at each plot. The regression models involving two independent variables, i.e., deer density and the length of forest edge within an area of 100 or 200 m from the transect, were selected based on the Akaike’s Information Criterion (AIC). Levels of fecal nitrogen were positively correlated with the length of the forest edge and negatively correlated with population density of deer. The area of 100 or 200 m from the transect most likely reflected the behavioral scale of the deer. Coverage of palatable understory vegetation increased with proximity to forest edge and decreased with deer density. Variability in the level of fecal nitrogen could thus be explained by food availability in the landscape. These results suggest that landscape alterations increase the carrying capacity of sika deer and thereby increase impacts upon the ecosystem.     

Estimating abundance of Sitka black-tailed deer using DNA from fecal pellets

Densely vegetated environments have hindered collection of basic population parameters on forest-dwelling ungulates. Our objective was to develop a mark–recapture technique that used DNA from fecal pellets to overcome constraints associated with estimating abundance of ungulates in landscapes where direct observation is difficult. We tested our technique on Sitka black-tailed deer (Odocoileus hemionus sitkensis) in the temperate coastal rainforest of Southeast Alaska. During 2006–2008, we sampled fecal pellets of deer along trail transects in 3 intensively logged watersheds on Prince of Wales Island, Alaska. We extracted DNA from the surface of fecal pellets and used microsatellite markers to identify individual deer. With genotypes of individual deer, we estimated abundance of deer with moderate precision (±20%) using mark–recapture models. Combining all study sites, we identified a 30% (SE = 5.1%) decline in abundance during our 3-year study, which we attributed to 3 consecutive severe winters. We determined that deer densities in managed land logged >30 years ago (7 deer/km², SE = 1.3) supported fewer deer compared to both managed land logged <30 years ago (10 deer/km², SE = 1.5) and unmanaged land (12 deer/km², SE = 1.4). Our study provides the first estimates of abundance (based on individually identified deer) for Sitka black-tailed deer and the first estimates of abundance of an unenclosed ungulate population using DNA from fecal pellets. Our tool enables managers to accurately and precisely estimate the abundance of deer in densely vegetated habitats using a non-invasive approach. © 2011 The Wildlife Society.     

Towards a standardized index of European rabbit abundance in Iberian Mediterranean habitats

European rabbits Oryctolagus cuniculus are a keystone species in Iberian Mediterranean ecosystems. However, the reliability of methods for estimating rabbit abundance, particularly when at low numbers, is not well understood. Further, better standardization of these methodologies would allow abundance estimates to be more reliably compared between areas and periods. Consequently, we compared several frequently used methods of estimating rabbit abundance and assessed their advantages and disadvantages. During the summers of 2008 and 2009, in 11 localities of central-southern Spain we undertook (a) driving transect counts of rabbits, either at dusk or at night, (b) linear transects on foot recording rabbit signs, (c) cleared-plot pellet counts at permanent plots, and (d) standing crop counts, both with and without habitat stratification. Density estimated at night from driving transects using the Distance Sampling method (the reference method against which all other indices were compared) varied from 0 to 2.69 rabbits ha⁻¹. Most pellet-count indices were significantly related to the reference method. In particular, cleared-plot pellet counts in permanent plots corrected for pellet persistence showed the best correlation with the reference method. In contrast, latrine counts were not related to the reference method index, and we recommend against their use. A standard methodology based on cleared-plot pellets counts could be used to monitor rabbit abundance on a large scale.     

How accurate are single site transect data for monitoring butterfly trends? Spatial and temporal issues identified in monitoring Lasiommata megera

Multiple transect counts following Butterfly Monitoring Scheme (UKBMS) guidelines and Jolly–Seber estimates of population size were used to monitor the abundance of second generation Lasiommata megera on a single site in southern England. The two methods resulted in different patterns of emergence being detected. The proportion of the population (estimated by Jolly–Seber) recorded with transect counts depended on the time of day and weather with afternoon transect counts best recording the trend in abundance over the flight period, but even then counts recorded a variable fraction of the population (6.2–51.3%). Increasing the frequency with which transect counts are carried out per week reduced variation and increased the fit of transect counts to Jolly–Seber generated population estimates. However, indices of abundance generated from randomly selected transect counts for L. megera within sampling weeks varied 4-fold and indices for other butterfly species were also highly variable. For L. megera, transect count variability is attributed to non-representative placement of the transect route and changes in the behaviour and spatial distribution in relation to population size and season. We suggest that transect counts need to be fully validated before the data are used to monitor changes of butterfly populations at individual sites.     

Comparative performance of four survey methods for assessing Lilian’s Lovebird abundance in Liwonde National Park,Malawi

Monitoring abundance of threatened species is important for conservation planning. Lilian’s Lovebird Agapornis lilianae is a near-threatened small parrot found in mopane Colophospermum mopane woodland. Its population has not been investigated in any part of its range. We investigated the abundance and density of the Lilian’s Lovebird in Liwonde National Park, Malawi. Both distance sampling (line and point transects) methods and total counts (waterhole and flyway counts) were applied. The point count method gave very low numbers and was discontinued after the first year. Line transects conducted during the wet season had the highest density estimates of 17 ± 4.8 lovebirds km?2 of mopane woodland. However, number of observations per transect in each year were low. Waterhole counts had the lowest density estimates (10 ± 3.5 lovebirds km?2). Flyway counts gave an intermediate estimate (13 ± 3.0 lovebirds km?2). The total population of Lilian’s Lovebirds in Liwonde National Park is therefore estimated to be about 4 000 individuals. The use of line transect counts at the end of the rainy season is recommended for continued monitoring of Lilian’s Lovebirds abundance in Liwonde National Park.     

Using Pellet Counts to Estimate Snowshoe Hare Numbers in Minnesota

Abstract: We calibrated snowshoe hare (Lepus americanus) numbers with pellet counts in Minnesota, USA, to understand the relationship between hare numbers and pellets in the central portion of the hare range. We found a strong and significant correlation between hare numbers and pellet counts using either linear or functional regression with either annual or semiannual pellet counts. Equations we developed using linear or functional regression predicted >1 hare/ha at similar pellet-density thresholds. These equations can be used to efficiently identify habitats that support hare numbers necessary for Canada lynx (Lynx canadensis) persistence in Minnesota.     

Techniques for assessing the abundance of Brown Hares Lepus europaeus

Over the last few decades, there have been significant declines in Brown Hare Lepus europaeus numbers throughout Europe, leading to concern for their status in many countries. In Britain, there were no quantified data on the extent of this decline, on current population levels, or any baseline against which to monitor future population changes. The need for a quantified national hare survey led to this evaluation of the techniques available to assess hare numbers. Published information on counting hares is reviewed, and various techniques compared by applying them to a number of sites in southern England. Three basic approaches are available: counts of inactive hares, counts of active hares and indirect methods. Counts of inactive hares include total clearance, wide belt and line transect counts. Total clearance counts give an absolute figure, but are labour intensive and can only be applied to restricted areas. Wide-belt assessments are difficult to apply in certain habitats and even in open areas tend to produce a substantial over-estimate. Line transect counts are easy to undertake and are not labour intensive but should only be applied to large areas, or data from several small areas combined. Counts based on active hares are more problematical, because it is difficult to determine what proportion of the population is inactive at any one time. Spotlight counts based on variable circular plots are the most accurate but difficult to apply widely, and twilight counts are very subjective in their interpretation, especially when surveying small areas or areas with a large proportion of concealing habitats. Of the indirect methods, dung pellet counts can be valuable in specific areas but are difficult to apply across a range of habitats. We concluded that, of the various techniques considered, line transect counts have the greatest potential for a national survey, but need to be stratified so that enough transects are undertaken within each habitat stratum to obtain a reliable mean population estimate for each stratum.     

The disappearance of muntjac (Muntiacus reevesi) and roe deer (Capreolus capreolus) pellet groups in a pine forest of lowland England

Reliable knowledge of the disappearance rate of faecal pellets is essential for converting pellet density to deer density when using standing-crop pellet-group counts. Disappearance of muntjac and roe deer pellet groups was monitored in four growth stages of a pine forest of lowland England over a 15-month period. Time to disappearance of the pellet groups (days) of both species significantly differed between habitats and months; it was shorter in late summer to early autumn and in habitats with more ground vegetation. Muntjac pellet groups disappeared more quickly than roe deer pellet groups. Time to disappearance of roe deer pellet groups was negatively correlated with air and grass temperature in pre-thicket and pre-fell habitats, while time to disappearance of muntjac pellet groups was negatively correlated with frequency of rainfall and positively correlated with the run of wind (air passage over a site within a 24-h period measured in km) in pre-thicket habitats. It is the time of the standing-crop pellet-group counts and the disappearance rate of pellet groups deposited in different months and habitats that determine the appropriate method for conversion of pellet-group density to deer density.     

Methodology matters when estimating deer abundance: a global systematic review and recommendations for improvements

Deer (Cervidae) are key components of many ecosystems and estimating deer abundance or density is important to understanding these roles. Many field methods have been used to estimate deer abundance and density, but the factors determining where, when, and why a method was used, and its usefulness, have not been investigated. We systematically reviewed journal articles published during 2004–2018 to evaluate spatio-temporal trends in study objectives, methodologies, and deer abundance and density estimates, and determine how they varied with biophysical and anthropogenic attributes. We also reviewed the precision and bias of deer abundance estimation methods. We found 3,870 deer abundance and density estimates. Most estimates (58%) were for white-tailed deer (Odocoileus virginianus), red deer (Cervus elaphus), and roe deer (Capreolus capreolus). The 6 key methods used to estimate abundance and density were pedestrian sign (track or fecal) counts, pedestrian direct counts, vehicular direct counts, aerial direct counts, motion-sensitive cameras, and harvest data. There were regional differences in the use of these methods, but a general pattern was a temporal shift from using harvest data, pedestrian direct counts, and aerial direct counts to using pedestrian sign counts and motion-sensitive cameras. Only 32% of estimates were accompanied by a measure of precision. The most precise estimates were from vehicular spotlight counts and from capture–recapture analysis of images from motion-sensitive cameras. For aerial direct counts, capture–recapture methods provided the most precise estimates. Bias was robustly assessed in only 16 studies. Most abundance estimates were negatively biased, but capture–recapture methods were the least biased. The usefulness of deer abundance and density estimates would be substantially improved by 1) reporting key methodological details, 2) robustly assessing bias, 3) reporting the precision of estimates, 4) using methods that increase and estimate detection probability, and 5) staying up to date on new methods. The automation of image analysis using machine learning should increase the accuracy and precision of abundance estimates from direct aerial counts (visible and thermal infrared, including from unmanned aerial vehicles [drones]) and motion-sensitive cameras, and substantially reduce the time and cost burdens of manual image analysis.     

Estimating red deer abundance in a wide range of management situations in Mediterranean habitats

When human interventions interfere with the natural regulation of wildlife populations by favouring some species, overabundance can emerge. We evaluated different methods of estimating red deer abundance in a wide range of population densities from southern Spain. Distance sampling estimates were used as the reference method across 22 localities and were compared with two kilometric abundance indices (KAIs), four indices based on pellet group counts and two browsing indices (BWIs). The average red deer density estimated by distance sampling was 19.51±3.19 deer per 100 ha, showing a wide range across the study area (0.04–66.77). Distance sampling estimates correlated with the KAIs, pellet group-based index and the BWI. The agreement with distance sampling improved when groups were used instead of individuals in the KAIs, when the minimum pellet group size was fixed at 20 pellets in the dropping counts, and when only highly palatable species were used in the BWI. Thus, several direct and indirect methods can estimate red deer abundance in Mediterranean habitats from Southern Spain with appropriate modifications.     

Methods of estimating ungulate populations in tropical forests

Pellet group counts, drive counts and track counts were used to estimate population abundances of one small and four large species of duiker (Cephalophus sp.) in a moist evergreen forest in northeastern Zaire. Procedures to develop estimates based on line transect counts of pellet groups are described. The Fourier Series estimator proved to be useful for estimating densities of pellet groups. Comparisons were made between population abundance in heavily and lightly hunted areas, and between small and large species. The three census methods were consistent in showing no significant difference between animal abundance in the hunted populations or between abundances of the smaller species relative to the larger species. All methods showed potential as population indices for assessing trends of rare and elusive species in forest environments. Drive counts and pellet group counts may also be useful for estimating densities.     

Functional dietary response of Asian black bears to changes in sika deer density

Omnivores are generally opportunistic foragers and have a flexible dietary response to resource abundance and availability. Their populations may consist of individuals that differ from each other in terms of their trophic positions, which implies that the dietary response to resource fluctuations differs within a population. We investigated how changes in the abundance of sika deer (Cervus nippon) affected dietary variation and body condition in the Asian black bear (Ursus thibetanus). We used fecal analysis, nitrogen stable isotopes (δ¹⁵N), and body measurements to determine whether the variation in dietary meat content of Asian black bears is positively related to variations in the density of the sika deer population, whether male bears have a higher trophic position compared to females, and whether dietary meat content is positively related with body mass or body condition of bears. We found a positive correlation between the occurrence of deer remains in bear feces and deer density, suggesting that bears change their diet in response to temporal changes in deer density. Male bears had higher δ¹⁵N values than females, and neither values varied when deer density decreased. Males selectively consumed deer after a reduction in deer density, whereas females consistently consumed more plant-based diet. The δ¹⁵N values were positively related with body mass of adult (>4 yr) bears but had no relationship with body condition of bears of either sex or any age class. Deer seem to be an important food source for large adult males, which have an advantage in mating. Thus, increasing herbivore abundance and availability altered the foraging strategy of Asian black bears, but the importance of herbivore on bear diet differs within a population.     

Using spotlight observations to predict resource selection and abundance for white-tailed deer

Spotlight surveys for white-tailed deer (Odocoileus virginianus) can yield large presence-only datasets applicable to a variety of resource selection modeling procedures. By understanding how populations distribute according to a given resource for a reference area, density and abundance can be predicted across new areas assuming the relationship between habitat quality (measured by an index of selection) and species distribution are equivalent. Habitat-based density estimators have been applied to wildlife species and are useful for addressing conservation and management concerns. Although achieving reliable population estimates is a primary goal for spotlighting studies, presence-only models have yet to be applied to spotlight data for estimating habitat selection and abundance for deer. From 2012 to 2017, we conducted spring spotlight surveys in each of 99 counties in Iowa, USA, and collected spatial locations for 20,149 groups of deer (n = 71,323 individuals). We used a resource selection function (RSF) based on deer locations to predict the relative probability of use for deer at the population level and to estimate statewide abundance. The number of deer observed statewide increased significantly with increasing RSF value for all years and the mean RSF value along survey transects explained 59% of the variability in county-level deer counts, indicating that a functional response between habitat quality and deer distribution existed at landscape scales. We applied our RSF to a habitat-based density estimator (extrapolation) and zero-inflated Poisson (ZIP) and negative binomial (ZINB) count models to predict statewide abundance from spotlight counts. Population estimates for 2012 were variable, indicating that atypical weather conditions may affect spotlight counts and population estimates in some years. For 2013–2017, we predicted a mean population of 439,129 (95% CI ∼ ± 55,926), 440,360 (∼ ± 43,676), and 465,959 (∼ ± 51,242) deer across years for extrapolation, ZIP, and ZINB models, respectively. Estimates from all models were not significantly different than estimates from an existing deer population accounting model in Iowa for 2013 and 2016, and differed by <76,000 deer for all models from 2013–2017. Extrapolation and ZIP models performed similarly and differed by <2,897 deer across all years, whereas ZINB models showed inconsistencies in model convergence and precision of estimates. Our results indicate that presence-only models are capable of producing reliable and precise estimates of resource selection and abundance for deer at broad landscape scales in Iowa and provide a tool for estimating deer abundance in a spatially explicit manner. © 2019 The Wildlife Society.     

Population estimation and monitoring of an endangered lagomorph

We conducted the most intensive estimate of the endangered Lower Keys marsh rabbit (Sylvilagus palustris hefneri) metapopulation to date using pellet surveys and capture–recapture methodology. We livetrapped 83 rabbits, evaluated 5 closed population models, and selected the model that best represented the data. We considered the variation in behavioral response model the best model and correlated (r² = 0.913) its patch population estimates to patch pellet densities. From the prediction equation, we generated a range-wide metapopulation estimate of 317 rabbits, a western clade population of 257 rabbits, an eastern clade population of 25 rabbits, and translocated marsh rabbit populations of 35 and zero on Little Pine and Water keys, respectively. A subset of patches whose marsh rabbit subpopulations were last estimated in 1993 exhibited a 46% decline in abundance over 15 yr. Due to the low estimate of the eastern clade population, special effort should be initiated to avoid loss of genetic diversity. The prediction equation suffers from limited data at high pellet densities, patches with ≥5 pellets/m². Future studies should investigate if the slope of the regression is indeed near 1 by sampling patches across the range of pellet densities, especially those with ≥5 pellets/m². The equation provides managers a quick, efficient, and noninvasive method to estimate marsh rabbit abundance from pellet counts but the confidence of predicted rabbit densities from high pellet density patches is low. © 2011 The Wildlife Society     

An Evaluation of Survey Methods for Estimating Northern Bobwhite Abundance in Southern Texas

Abstract: Distance sampling has been identified as a reliable and well-suited method for estimating northern bobwhite (Colinus virginianus) density. However, distance sampling using walked transects requires intense sampling to obtain precise estimates, thus making the technique impractical for large acreages. Researchers have addressed this limitation by either resorting to the use of indices (e.g., morning covey-call surveys) or incorporating the use of aerial surveys with distance sampling. Both approaches remain relatively untested. Our objectives were to 1) compare density estimates among morning covey-call surveys, helicopter transects, and walked transects; 2) test a critical assumption of distance sampling pertinent to helicopter surveys (i.e., all objects on line are detected); and 3) evaluate the underlying premise of morning covey-call surveys (i.e., that the no. of calling coveys correlates with bobwhite density). Our study was conducted on 3 study sites in Brooks County, Texas, USA, during October to December, 2001 to 2005. Comparisons between walked transects and morning covey-call surveys involved the entire 5-year data set, whereas helicopter transects involved only the latter 2 years. Density estimates obtained from helicopter transects were similar to walked transect estimates for both years. We documented a detection probability on the helicopter transect line of 70 ± 10.2% (% ± SE; n = 20 coveys). Morning covey-call surveys yielded similar density estimates to walked transect estimates during only 2 of 5 years, when walked transect estimates were the least accurate and precise. We detected a positive relationship (R² = 0.51; 95% CI for slope: 29.5–53.1; n = 63 observations) between covey density and number of coveys heard calling. We conclude that helicopter transects appear to be a viable alternative to walked transects for estimating density of bobwhites. Morning covey-call surveys appear to be a poor method to estimate absolute abundance and to depict general population trajectories.     

Spatial and temporal habitat use and selection by red deer: The use of direct and indirect methods

Given the importance of red deer Cervus elaphus for hunting and conservation purposes, understanding the interactions between this species and its habitats in the Mediterranean region is a crucial step for the sustainable management of this species. Aiming to compare pellet group counts and direct observations methods to study the habitat use and selection by red deer, the results obtained by both methods were compared, and their advantages and disadvantages were discussed. To understand the temporal patterns of habitat use and selection, the survey was conducted at three different seasons, birth period, rut season and winter. The habitat use and selection were studied in relation to land cover, watercourse, roads, ecotone zones and other topographic features (altitude, slope and aspect), using generalized linear models and selection ratios. The similarity of the results provided by pellet group counts and direct observations indicate that both methods may constitute useful tools to study the habitat use and selection by red deer. Globally, red deer seemed to select habitats that provide simultaneously food and some cover, as shown by its preference for shrublands, independently of the sampling season. The positive selection of ecotone zones embodies the need for open spaces. Males and females showed a similar use of shrubland, but selected patches with different characteristics therein. The spatial and temporal patterns exhibited by our results suggest that red deer balance their habitat requirements in respect to each phase of their reproductive cycle. Pellet group counts and direct observations seem to be useful methods to analyze habitat use and selection, and may provide helpful knowledge to the management and conservation of red deer.