A Modification of Jacobson et al.’s (1997) Individual Branch-Antlered Male Method for Censusing White-Tailed Deer (original) (raw)

2011, Wildlife Society Bulletin

Jacobson et al.’s (1997) individual branch-antlered male (IBAM) method is a popular camera technique for estimating white-tailed deer (Odocoileus virginianus) abundance. Demographic ratios are estimated from raw photographic occurrences (RPO) of males, females, and fawns. Point abundance estimates of each group are estimated by using said ratios to extrapolate from a count of uniquely identifiable males. In 2009, using camera-trap data from the Mianus River Gorge Preserve (NY), we modified the IBAM technique to 1) generate measures of uncertainty for parameter estimates via bootstrapping camera stations, and 2) address the concern that RPO ratios may be biased if groups of animals differ in their probability of being photographed (e.g., trap success [TS]). For each sex–age group, we evaluated RPO as a function of TS using linear regression to generate photographic counts standardized by TS (standardized photographic occurrences [SPO]). We generated estimates of sex–age ratios and abundances using both RPO and SPO. To evaluate the accuracy of using SPO in conjunction with the IBAM method, we independently estimated the abundance of a marked group of female deer using a Poisson log normal (PNE) mark–resight estimator. Abundance estimates across sex–age classes were most similar between PNE and IBAM when SPO demographic ratios were used. Owing to the greater TS of females, using SPO discounted the relative abundance of females and, thus, lowered the female:male ratios and raised the fawn:female ratio. Uncertainty was broad across all approaches, yet accounting for TS reduced the confounding variability owing to differences in detection probability and generated more accurate parameter estimates.

A Method for Evaluating Density of Roe Deer, Capreolus capreolus (Linnaeus, 1758), in a Forested Area in Bulgaria Based on Camera Trapping and Independent Photo Screening

We performed an experimental survey of roe deer (Capreolus capreolus) in the Chepino Game Hunting Station (Southwestern Bulgaria) in spring 2014 using a camera-trap network. We established a network with a density of one camera per 2 ha of forest. Traps remained activated for five days in one sampling plot of 80 ha. Camera traps triggered by animal movements were set to take successive pictures with ten second time lapses. Camera trap records were examined by three independent groups of researchers and allowed for a very high rate of individual recognition (up to 82% of individuals pictured were classified by sex and age class). We identified a minimum of 29 roe deer individuals corresponding to a density of 36 individuals/km2, with a male/female ratio of 0.71, and a fawn/doe ratio of 1.33. This density was surprisingly high as compared to the known Bulgarian standards, and indicated a good conservative management of the roe deer population in the Chepino Region. Further, our estimates were confirmed by performing a capture-mark-recapture study of roe antlered bucks which were easy recognisable. We found a detection probability of 0.91 and a population density of 36.25 deer/km2. Therefore, camera networks could be used as a reliable monitoring method to estimate roe deer population density and to get a reliable population structure in areas where alternative monitoring methods are not possible or are too expensive. We recommend this method to be adopted by game reserves in Bulgaria in order to improve knowledge about roe deer population demography and for improving the management of its populations.

Elk calf mortality patterns in the Blue Range Wolf Recovery Area: New Mexico

This year (2011) was the first of a 3-year study investigating elk calf survival and mortality patterns in the Gila National Forest of western New Mexico. Crews captured 37 elk calves from May 22 through June 19, 2011. Calves were captured by hand and equipped with an ear tag transmitter. As of November 2011 we observed 28 mortalities; 12 were attributed to black bear predation, 7 were coyote mortalities, 3 were mountain lion kills, 3 were killed by unknown predators, and 3 were unknown mortalities. When applicable, field necropsies were performed to search for subcutaneous hemorrhaging. Bite and scratch marks, along with tracks, scat and other site evidence were used to identify the predator species responsible. We monitored for the presence of Mexican wolves at mortality locations to help determine if wolf predation may have occurred. No radio-collared wolves were found in the immediate vicinity of any predated calf when we had the ability to scan for packs. However, diversionary ...

Simulated Effects of Releasing Pen-raised Deer into the Wild to Alter Population-level Antler Size

The ability to develop large antlers in penned deer (Odocoileus sp.) has increased interest in releasing pen-raised deer to increase antler size of wild populations. We used a model based on population genetic theory with random removal as the form of population control and either 10% emigration and 10% immigration to represent a free-ranging population (Free Range) or with no egress or ingress to represent a fenced property (Fenced). We compared results with a livestock model with no egress or ingress and selective removal of smaller antlered males as the form of population control (Best Case). We modeled release of fawns with an antler distribution averaging 200 gross Boone and Crockett (B&C) score at 5 rates (1%, 5%, 10%, 25%, and 50% replacement of existing population of 2,000) and report the change from a population average of 127.5. The impact of releasing pen-raised deer into native populations was minimal below 25% replacement rate. Replacing 5% of a free-ranging population with 100 pen-raised deer increased B&C score by 0.8, whereas replacing 25% with 500 pen-raised deer increased score by 12. Releasing pen-raised deer into a fenced property was 50% more effective; a 25% replacement increased score by 18. The Best Case Model increased score by 33 at 25% replacement. The cost for each unit increase in score was US$115,000 in a free-ranging population, US$75,000 in a fenced population, and US$33,000 in the best case. Our results suggest that altering genetic composition of white-tailed deer populations is not feasible for free-ranging populations and very costly within fenced populations.

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