Schnabel Method Research Articles

Stock status of coconut crab (Birgus latro) in Daeo, Morotai Island District, North Maluku, Indonesia

Abstract. Serosero RH, Sulistiono, Butet NA, Riani E. 2021. Stock status of coconut crab (Birgus latro) in Daeo, Morotai Island District, North Maluku, Indonesia. Biodiversitas 22: 626-634. The populations of coconut crabs (Birgus latro) in nature continue to decline due to their simple capture for human consumption. This study aimed to determine the status of coconut crab stock in Daeo, Morotai Island Regency, North Maluku, Indonesia including estimations of growth parameters and population size. This research was conducted from October 2016 to September 2017. Growth parameters were estimated based on 12 monthly length-frequency samples. Data analysis was carried out using the ELEFAN I method on the FiSAT II program for estimating growth parameters, and the Schnabel method for estimating population size. The results showed that the level of exploitation of male and female coconut crabs in Daeo was high (E > 0.5). The asymptotic length L∞ for males was 56.96 mm thoracic length (TL) and that of females 52.50 mm TL. The growth coefficient K for males was 0.14 and that for females 0.16. Length to is -1.026 (male) and -0.913 (female). The results generated using the Schnabel method suggested that the population size of the coconut crab in Daeo was 7,466 to 73,948 individuals considering a confidence interval of 95%. The recapture of tagged coconut crabs was merely 0. 82%.

Using Closed-Captures Population Analyses to Estimate Channel Catfish Relative Abundance

Channel catfish (Ictalurus punctatus) is an important recreational species in the Great Plains, and understanding the reliability of population data is critical to proper management. We therefore compared estimates of the abundance of channel catfish > 200 mm within a 6.2 river kilometer (RKM) reach of the Missouri River, Nebraska, using estimates derived from the Schnabel batch-marking methodology, closed-captures analyses using capture histories of uniquely marked individuals, and a method for extrapolating relative abundance (C/f) to absolute abundance using mean capture probabilities. Estimated abundance of channel catfish derived using the Schnabel method was 23,949 fish (18,011–39,120; 95% confidence interval). Closed-captures analyses yielded an estimated abundance of 25,817 channel catfish (24,885–26,785; 95% confidence interval). The estimated abundance of channel catfish extrapolated from C/f was 26,121 (24,755–28,056; 95% confidence interval). The smaller confidence intervals around estimates derived using uniquely marked individuals suggest the closed-captures method may result in more robust estimates than those derived using batch-marking techniques or C/f. However, all three methods produced similar estimates of channel catfish abundance. Our results confirm the hypothesis that C/f is proportional to abundance in this study, suggesting an index of relative abundance may be useful when sampling resources are limited.

Short Communication: Habitat and population characteristics of the endemic Java Tree Frog (Rhacophorus margaritifer) in Ranca Upas, West Java, Indonesia

Abstract. Nilawati TS, Hernawati, Taufik RA. 2019. Short Communication: Habitat and population characteristics of the endemic Java Tree Frog (Rhacophorus margaritifer) in Ranca Upas, West Java, Indonesia. Biodiversitas 20: 1644-1649. The Java tree frog (Rhacophorus margaritifer) is one of the endemic frogs of Indonesia. Ranca Upas forest, West Java, Indonesia is one of the habitats of this species which is threatened by the extension of the ​​campground and tourism area. The aim of this study was to identify the habitat and population characteristics of Rhacophorus margaritifer in Ranca Upas forest. Data was collected through Capture-Mark-Release-Recapture method in every 100 m distance of a 300 m transect, along the river. The captured frogs were tagged using modified shoelaces. Habitat characteristics were analyzed descriptively and quantitatively, population number was estimated by the Schnabel method, and population distribution was calculated using the Morisita distribution index. The results showed that R. margaritifer habitat was at an altitude of 1630-1670 m asl with 16.6 oC average air temperature and 90.8% air humidity. The habitat was near river with clear water and mud substrate at 14.8 oC water temperature, 0.068 m/s water velocity, and neutral acidity. Furthermore, three species of plants, namely Strobilanthes crispus, Curculigo capitulata, and Cyathea sp. were identified to be very often used by R. margaritifer. Population abundance of R. margaritifer was estimated to be 286 individuals, with 5 individuals /100m2 density and it showed a clumped disp.ersion. Average size of frogs found in the study area was 40 mm Snout to Vent Length (SVL) and the range was 36 to 65 mm. This showed that the location is dominated by young frogs and the study area is a good habitat for R. margaritifer.

Growth and population assessment of the queen conch <i>Strombus gigas</i> (Mesogastropoda: Strombidae) by capture mark-recapture sampling in a natural protected area of the Mexican Caribbean

<span>La Ensenada de Xel-Ha es usada como parque para ecoturismo y representa un santuario para la conservación del caracol rosado. El incremento en la presión de la pesca ha llevado a la inclusión de esta especie en CITES. Mucho del conocimiento acerca del crecimiento del caracol rosado ha sido generado a través de la acuicultura, encierros oceánicos o usando estimaciones derivadas de las dinámicas poblacionales. En este estudio estimamos la tasa de crecimiento de <em>Strombus gigas</em> juvenil en un área natural protegida, por métodos directos durante el período de abril 2009 a enero 2011. Los datos fueron obtenidos por muestras de captura-marca-recaptura. Un total de 1 418 individuos fueron marcados y el crecimiento de 714 caracoles fue analizado. La talla de la población y la densidad relativa fue estimada usando el método de Schnabel. La densidad promedio relativa fue estimada en 0.1694±0.0996ind. m-2, mientras que la densidad más alta fue estimada para septiembre 2010 con 0.3074ind. m-2 . La tasa de crecimiento más alta (0.27±0.10mm día-1) fue detectada en juveniles con una talla inicial entre 100-149mm, seguida por juveniles <100mm, con un incremento de 0.24±0.05mm día-1. La tasa de crecimiento disminuyó para individuos con una talla inicial entre 150-199mm (0.18±0.09mm día-1) y para organismos >200mm (0.08 ± 0.07mm día-1). La variabilidad en la tasas de crecimiento fue alta en individuos entre 100-149mm y mostró diferencias estacionales; con la tasa de crecimiento más alta en mayo 2010. El reclutamiento de juveniles más alto se dio en octubre 2009 y en febrero 2010. La población de Xel-Ha ha crecido en tamaño y se pudo encontrar más adultos y juveniles que en estudios anteriores, lo que demuestra que el Parque de Xel-Há está funcionando como un santuario para la conservación del caracol rosado del Caribe en la Riviera Maya de México. La tasa de crecimiento de juveniles en Xel-Ha es alta y presenta grandes variaciones en los individuos, lo cual refleja las condiciones naturales de la alimentación y la agregación. Las diferencias estacionales en las tasas de crecimiento pueden estar asociadas con la calidad del agua y la disponibilidad de nutrimentos para la producción primaria. Concluimos que el método directo es útil parar monitorear el crecimiento en juveniles de <em>S. gigas</em> y que el crecimiento en condiciones naturales es mayor que en sistemas de acuicultura. Esta información puede ser aplicada al manejo de pesquerías así como también en programas de rehabilitación y acuicultura.</span>

Four-probe methods for measuring the resistivity of samples in the form of rectangular parallelepipeds

The problem of measuring the resistivity of isotropic samples of finite dimensions in the form of rectangular parallelepipeds using the four-probe technique was considered. Two variants of contact arrangements were studied: (1) four collinear probes are positioned on one side of a sample symmetrically with respect to the other sides, and (2) two probes on one side of a sample and two on the opposite side are placed precisely in opposite positions and symmetrically with respect to the other sides of the sample (the Schnabel method). Solutions of the problem of the electric field potential distribution in a sample for different positions of the current contacts were found. The solutions were obtained in the form of double series and methods of their summation are presented. The obtained results are extended to the case of measuring the resistivity of anisotropic samples when the resistivity tensor has two independent components. The results of using the developed technique for measuring the resistivity of such a highly anisotropic material as highly oriented pyrolitic graphite using the Schnabel method are presented.

陆桥岛屿环境下社鼠种群数量的估算方法

We live-trapped two Niviventer confucianus populations from March to November of 2010 in Thousand Island Lake region using the capture-mark-recapture(CMR) method.We used Jolly-Seber method,modified Lincoln index method,Schnabel method and minimum number of animals alive(MNA) method to estimate population sizes of Niviventer confucianus,and discussed the applicability of these estimators in white-bellied rats on land-bridge island.Our results showed that there was no significant difference between Jolly-Seber method and modified Lincoln index method.We considered that modified Lincoln index method was more suitable for estimating the population quantity of Niviventer confucianus in the land-bridge island.The study can provide basic data for the future study of population ecology of rodent in the land-bridge island.

A comparison of Mediterranean Gecko (Hemidactylus turcicus) populations in two temperate zone urban habitats

Urban ecosystems represent unique habitats that might be more or less suitable than natural systems for many species. The Mediterranean Gecko, Hemidactylus turcicus is a synanthropic species that has successfully colonized many urban and suburban areas outside its natural range. In the United States, H. turcicus has been found predominantly in southern states on exterior surfaces of buildings. We compared population density, demographics, and extent of dispersal of populations of H. turcicus at two anthropogenic sites in a temperate region of the United States. The University of Central Oklahoma (UCO) had higher building density and greater cover by anthropogenic surfaces and the Oklahoma City Zoo (ZOO) had lower building density and greater cover by vegetation. Mark and recapture sampling was conducted at UCO from 2006 to 2007 and during 2008 at ZOO. The sizes of the populations at the two sites were estimated using the Schnabel method and population densities were calculated using those estimates. Age class of captured animals, sex of adults, and gravid status of adult females were determined at both sites. We assumed that greater exterior wall surface area of individual buildings at UCO and greater land cover by anthropogenic surfaces might 1) reduce population density and 2) facilitate dispersal there relative to the ZOO. Population sizes and density in animals per ha of land and building cover and demographics were similar at the two sites. Population density per ha of building exterior wall area was higher at ZOO than at UCO. The higher density of animals on buildings, lower proportion of subadults in the population and lower maximum dispersal distance at ZOO suggest that successful diffusion dispersal might be limited at that site relative to UCO.

KEBAN BARAJ GÖLÜ KEREVİT (Astacus leptodactylus Eschscholtz, 1823) POPULASYON BÜYÜKLÜĞÜNÜN ARAŞTIRILMASI

birey/m 2 , Keban bolgesinde 1.37 birey/m 2 ve Cemisgezek bolgelerinde 1.40 birey/m 2 olarak Abstract: The investigation of the crayfish (Astacus leptodactylus Eschscholtz, 1823) population amplitude in Keban dam lake In this study, the crayfish (Astacus leptodactylus Eschscholtz, 1823) population amplitude in Keban Dam Lake was investigated. For prediction of population amplitude marking and many counting method (Schnabel Method) was used. The study was carried out in the stations deter- mined in Agin, Keban and Cemisgezek regions of Keban Dam Lake. The catching amount of unit effort was calculated as 0.93 individual crayfish/pinter/7 days. The crayfish densities were predicted as 1.82 individual/m 2 in Agin region and 2.08 individual/m 2 in Keban and Cemis- gezek regions. Total stocks were determined as 2198560 individuals in Agin region, 2672800 individuals in Keban region and 4799142 individuals in Cemisgezek region, due to weight 58482 kg in Agin region, 71096 kg in Keban region and 127657 in Cemisgezek region. The densities of catchable length of crayfish (≥ 9 cm) were determined as 1.17 individual/m 2 in Agin region, 1.37 individual/m 2 in Keban region and 1.40 individual/m 2 in Cemisgezek region.

Anoles of St. Vincent (Squamata: Polychrotidae): Population Densities and Structural Habitat Use

We examined population densities and structural microhabitat use by Anolis griseus and A. trinitatis at eight sites on the leeward (western) coast of St. Vincent, West Indies. Estimates of population density based on the Schnabel method varied according to habitat complexity and ranged to 5,208/ha for A. griseus (a higher estimate at one site was not considered due to conditions that compromised the accuracy of estimates) and to 27,923/ha for A. trinitatis. Our highest estimate for both species at one site (32,867/ha) was the highest yet recorded for any site on a two-species Lesser Antillean island. For both species, larger individuals tended to perch higher and on perches of larger diameter than smaller lizards, with adult male A. griseus using the highest and largest diameter perches. However, considerable overlap in perch use among other size classes of A. griseus and all size classes of A. trinitatis suggests that structural habitat partitioning is not rigid in these two species. Although A. griseus was most abundant at densely shaded sites, A. trinitatis was essentially ubiquitous, supporting the predictions that these anoles were ecologically versatile and abundance and microhabitat use would reflect available vegetative structure.

ESTIMATION OF NOBLE CRAYFISH (ASTACUS ASTACUS L.) POPULATION SIZE IN THE VELIKA PAKLENICA STREAM (CROATIA)

Astacus astacus is one of four native European crayfish species living in Croatian freshwaters. It is naturally distributed in rivers belonging to the Black Sea Basin. To some rivers of the Adriatic Sea Basin, however, it had been introduced by man. According to the information from local people it is most likely that A. astacus has been introduced into the Velika Paklenica Stream during the first half of the 20 th century. Our study stream, draining the Velebit Mountain, is situated in Paklenica National Park, Middle Adriatic. The fieldwork of our study was performed during July 2000 and 2002, respectively. To estimate the population size we used mark-recapture techniques (Jolly-Seber Method, Schnabel Method and Schumacher and Eschmeyer Method). Crayfish were trapped with baited LiNi traps that were set along the stream banks at 10 m intervals and left there overnight. Caught animals were individually marked by piercing holes into the uropods and telson and then released. In July 2000 we caught 233 crayfish in total, from which 70 specimens were trapped more than once. In July 2002 we caught 296 crayfish, from which 86 were trapped more than once. Differences in the population size between the two years are discussed.

Lake Sturgeon Abundance and Harvest in Black Lake, Michigan, 1975–1999

Abstract The population of lake sturgeon Acipenser fulvescens in Black Lake, Michigan, has supported a popular winter spear fishery since 1948, but status of the population had not been assessed since the mid-1970s. We sampled the population during May–Jul 1997 with 20.3- and 25.4-cm-stretch-measure gill nets with the objective of estimating population size using the Schnabel method. We also examined harvest data from voluntary registration of speared fish spanning the years 1975–1999 to evaluate the impact that harvest may have had on the population. During 24 sample periods, we tagged and measured 192 lake sturgeon between 75 and 193 cm total length and removed the marginal pectoral fin ray from a subsample of those fish to estimate age. We also recaptured 14 lake sturgeon during the 24 sample periods. Captured fish ranged in age from 9 to 64 years. The estimated size of the 90 cm and larger lake sturgeon population was 1,241 fish. Based on the length frequency of the catch, there were 549 harvestable-s...

Assessment of pine weevil numbers on clear-cut and forest sites with shelter boards and pitfall traps

Field experiments were conducted in 1991 and 1992 on clear-cut and forest sites in four forest areas in southern Sweden with the aim to test possibilities for estimating pine weevil (Coleoptera: Curculionidae) population sizes. More pine weevils (Hylobius abietis andH. pinastri) were caught in baited pitfall traps than under shelter boards. The proportions ofH. pinastri in the totalHylobius catch were higher under shelter boards than in pitfall traps, indicating a difference between the species in behaviour towards the trap types. Numbers ofH. abietis found on forest sites were lower than those on fresh clear-cut sites, but not those on one year old or older clear cut sites. In mark-recapture experiments the recapture rates ofH. abietis ranged from zero to 73%; they were zero on fresh clear-cut sites. Recapture rate was not correlated to dispersal distance. Estimates of population size (Schnabel method) were in magnitudes of 150 to 5000H. abietis per hectare. The estimates did not reveal consistent differences between forest and one-year old or older clear cuttings. Dispersal distances were on average 6.0 m in 1991 and 5.4 m in 1992. Only in one area in 1992 the dispersal distances were significantly different between forest and clear-cut site.

Distribution Patterns of Raptors in Relation to Density of Meadow Voles

-Densities of overwintering Red-tailed Hawks (Buteo jamaicensis) and Rough-legged Hawks (Buteo lagopus) were examined in relation to densities of meadow voles (Microtus pennsylvanicus) on six habitat types. Generally, densities of both raptor species were greater in habitats that had higher densities of meadow voles. However, not all habitats with high numbers of voles had high numbers of the raptors. The amount and distribution of cover also appeared to influence the distribution of the raptors. Hence, patches that support high densities of prey may not be foraging sites for predators because other factors may reduce availability of prey. Optimal foraging theory predicts that animals should maximize their net rate of energy intake (Krebs 1973, Pyke et al. 1977). For example, when the food of a predator is distributed unevenly in space, the predator would be expected to spend more time on those patches yielding greatest net gain of energy (MacArthur and Pianka 1966, Krebs 1973, Smith and Sweatman 1974, Zach and Falls 1976a, Pyke et al. 1977, Bobisud and Voxman 1979, Waage 1979). Several studies have shown that predators do concentrate their search efforts in areas of high prey density (Goss-Custard 1970, Simons and Alcock 1971, Smith and Dawkins 1971, Hassel and May 1974, Smith 1974, Smith and Sweatman 1974, Hartwick 1976, Zach and Falls 1976a, b, c). Royama (1970, 1971) hypothesized that predators learn to use the most profitable patches where is defined in terms of biomass of prey taken by a predator per unit of hunting time, rather than strictly on the basis of prey density. Few field studies, however, have investigated whether predators concentrate their foraging efforts on the most sites. In the present study, we examined the profitability hypothesis of Royama (1970) by measuring responses of raptors to different densities of meadow voles (Microtus pennsylvanicus). On Toronto International Airport, meadow voles constitute more than 85% of prey items in the diets of overwintering Red-tailed Hawks (Buteo jamaicensis) and Rough-legged Hawks (B. lagopus; Baker 1977). From November to March these hawks devote most of the day to foraging and might be expected to be most numerous in areas where voles are abundant. STUDY AREA AND METHODS Toronto International Airport is on the western perimeter of Metropolitan Toronto, Ontario (79?37'W, 43?41'N). In addition to buildings and paved areas, it includes about 1,200 ha of farmland and assorted grasslands. The airport is surrounded by industrial and urban areas and by flat old-field communities that are largely devoid of trees and shrubs. On the basis of acce s roads and runways, we chose a study area of 827 ha so as to permit a total census of the raptors on the study area. The study area was divided into six habitat types according to vegetation composition and type of land management. Shortgrass habitats (407 ha) were mowed and treated with herbicides regularly by airport personnel so that the average vegetation height was about 10 cm and the dominant plant species was bluegrass (Poa sp.). Agricultural land (273 ha) was classified into four habitat types. Pastures (49 ha) were grazed by cattle except in winter. By early fall, little cover remained on pastures except around clumps of weeds avoided by the cattle. Plowed fields (100 ha) were farmed during summer, then were plowed in early fall and left fallow over winter. Winter wheat (69 ha) was sown in September, and harvested the following July. There was little cover on winter wheat fields over winter. Straw habitats (55 ha) occurred only in 1974-75 when straw from the harvested winter wheat was left in rows in the fields over winter. The straw p ovided good winter cover for voles. Old fields (147 ha) were largely abandoned farm fields (70%) and unmanaged areas near streams and lowlands (30%). They were densely covered by perennial grasses, forbs and hawthorn (Crataegus spp.) seedlings. More detailed description of these habitat types is in Steele (1977). Vole populations were estimated on the basis of livetrapping plots using standard capture/mark/recapture methods (Davis 1956). Estimates were based on the Schnabel (1938) method, using Overton's (1965) modification for known removals. The minimum number of voles known to be alive (MNA) was also tabulated (Krebs 1966). One live-trapping plot was set on each habitat type, with no plot less than 50 m from the habitat boundary, and no plot within 400 m of any other. Each plot was a 0.4-ha grid with one trap set every 10 m for a total of 55 traps per plot. Each plot was trapped every three months and at each sample period the traps

Census Methods for Eastern Gray Squirrels

Six methods were used to estimate abundance of eastern gray squirrels (Sciurus carolinensis) on 31.5 ha of deciduous forest in southwestern Pennsylvania. Among 3 methods based on multiple capture data, the Schnabel method gave the least variable estimates. The frequency-of-capture method yielded highly variable estimates, and the data did not fit well the probability distributions normally used for this method. Erratic estimates were also obtained from the Jolly method using 171 recaptures. The plot-removal method needed further study. However, time-area counts required fewer man-hours than did plot removal to achieve accuracy within 15 percent at the 90 percent confidence level. Response-to-call method showed no potential as an index to abundance of gray squirrels. None of the methods was judged satisfactory for extensive application for squirrel management. J. WILDL. MANAGE. 42(3):550-657 The main objective of this study was to compare reliability and practicality of 6 census methods for eastern gray squirrels. Abundance of tree squirrels has been estimated by many methods, but most of these have not been evaluated adequately. Mark-recapture methods are the most commonly used for squirrels. They are not always practical and are subject to error if assumptions on which the models are based are not met. With observational methods, such as time-area counts and flush counts, squirrels are counted during a given time along a transect or in a plot. Uhlig (1955) reported that counting leaf nests gave reliable estimates. However, this method has little potential where leaf nests are uncommon, as in the area where our study was done. Plot removal is a newer observational method which had not been field tested on squirrels. Another observational technique which has had limited use to census squirrels is to stimulate squirrels to make a vocal response and then count the number responding. Various other techniques have been based on number of squirrels caught or observed per unit of effort. Trap success depends on many factors other than population density; Friley (1955) found this method unreliable. Hunter success has been used as a census method, often with marking to obtain a Lincoln Index (Nixon et al. 1975). However, post factum estimates from harvest data have limited value for management of squirrels. A. Woolf, R. Sapalio, and A. Olsen assisted in this study, which was supported by a research grant from Rachelwood Wildlife Research Preserve. D. Heller, The Ohio State University, allowed us to use some of his data from a concurrent study on eastern gray squirrels.

Estimating and Testing Differences between Population Levels by the Schnabel Estimation Method

In the Schnabel method of estimating number of animals, the number of recaptures has been assumed to follow a Poisson distribution. This approximation is useful in testing differences in population levels when the Schnabel method is used for estimation, since the distribution of recaptures from one population, conditional on the total number of recaptures from both populations, is approximately binomial with parameters n and p, where p is a function of the parameters of the two Poisson distributions. Tests based on this conditional binomial distribution are described. Confidence limits of the population numbers have been considered and a stop rule developed for the Schnabel experiment used at the second stage of a paired comparison. The Schnabel method (Schnabel 1938) of estimating numbers of animals from tagrecapture data is widely used in fish and game population studies. This method is popular because (1) computations are simple, (2) daily estimates are a feature of this method, enabling the field worker to see his results as the work progresses, and (3) the method is flexible and can reasonably be expected to provide useful results over a wide range of capture conditions. However, there is some hesitancy about using the Schnabel method, since the variances of these estimates are difficult to estimate. In addition, it has not been made clear whether tests of differences between estimated populations can safely be based on such estimates of variance, as is also true for confidence intervals about an estimate. Simple straightforward tests of differences in population level, as well as confidence limits for the population estimate, are possible by using the knowledge that the number recaptured has approximately a Poisson distribution (Chapman 1954). To estimate population size by the Schnabel method, let x x-= number of recaptures, (1) A(n,M,), (2) 1=1

A Population Study of the Gray Fox

An attempt was made to analyze some of the component forces of some gray fox populations in northern Florida. The size of the populations studied was determined by the use of an age-ratio-reduction method. In this method the size of the population was indirectly derived by determining the magnitude of the effect on the age ratio of sterilizing a known number of females. A knowledge of the degree of reduction of the age ratio caused by sterilizing these females allowed the calculation of the entire female population. Application of the sex ratio permitted an estimation of the size of the entire fox population. It was possible to estimate the size of these same populations by several variations of the recapture method (Lincoln Index and Schnabel method) and the removal method. The recapture methods usually gave higher estimates than the age-ratio-reduction method. The estimates of the age-ratio-reduction method indicated a density of slightly less than 3 to 4 foxes per square mile. From recapture distances, a probable approximate diameter of two miles was estimated for the size of the home range of the gray fox in this region. Groups of foxes of family composition were captured in areas isolated from captures of other foxes and were termed family aggregations. Twenty-one family aggregations were found. The diameters of these family aggregations were in close agreement with the recapture data concerning the estimate of the size of the home range. This study explores the possibility of estimating the size of a gray fox (Urocyon cinereoargenteus floridanus) population by altering the breeding capacity of a known number of females and determining the effect on the age ratio of the population. The size of the population is deduced from the magnitude of this effect. The study also includes investigations of reproduction, mortality, and movement. The census method is similar to the methods used by Allen (1942), Kelker (1940;1945), and Riordan (1948) in estimating the sizes of populations of game animals that were selectively hunted according to sex. Their method was to compare preand postopen season sex ratios after which they computed the size of the populations by the use of knowledge of the number of male and/or female animals killed. Kelker's formulae estimated population sizes for each sex and fawns separately. The age ratio was used to determine the number of fawns, but the observed change takes place in the adults rather than in the young as in the method presented here. The recapture method (Jackson, 1939) derives an estimate from the proportion of marked individuals in the population. In contrast to the recapture method, the age-ratio-reduction method presented here does not require the recapture of a large number of the pre1 A portion of the author's doctoral dissertation presented to the Division of Vertebrate Ecology, Johns Hopkins University, School of Hygiene and Public Health.