Original Article A Modification of Jacobson et al.’s (1997) Individual Branch-Antlered Male Method for Censusing White-Tailed Deer MARK WECKEL, 1 Mianus River Gorge Preserve, 167 Mianus River Road, Bedford, NY 10506, USA; Division of Vertebrate Zoology, American Museum of Natural History, Central Park W at 79th Street, New York, NY 10024, USA; The Graduate Center, The City University of New York, 365 Fifth Avenue, New York, NY 10016, USA ROBERT F. ROCKWELL, Division of Vertebrate Zoology, American Museum of Natural History, Central Park W at 79th Street, New York, NY 10024, USA FRANK SECRET, John Jay High School, 60 N Salem Road, Cross River, NY 10518, USA; Wildlife Technician Program, Mianus River Gorge Preserve, Bedford, NY 10506, USA ABSTRACT 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. ß 2011 The Wildlife Society. KEY WORDS abundance, camera traps, census technique, detection, Odocoileus virginianus, sex ratios, trap success, white-tailed deer. Population estimation techniques, such as aerial inventories, thermal infrared sensing, or spot-light surveys, provide useful metrics for monitoring white-tailed deer (Odocoileus virgin- ianus) abundance (Fafarman and DeYoung 1986, Naugle et al. 1996), but may not be appropriate for the scale of smaller management areas characteristic of fragmented sub- urban and urban environments. Here, deer management can be highly localized (McDonald et al. 1998, Porter et al. 2004) and wildlife professionals need accurate abundance estimates specific to individual properties to plan harvest goals and track population trends. This is especially important where lethal means to reduce overpopulated suburban deer herds are subject to political pressure and public accountability. Jacobson et al.’s (1997) individual branch-antlered male (IBAM) abundance estimator is a popular method suitable to this scale. The method uses camera-trap data to enumerate a minimum number of uniquely identifiable adult males and to estimate sex and age-class ratios (hereafter, demographic ratios). The abundance of all males, females, and fawns is calculated by way of extrapolation. However, there are 2 major drawbacks to the IBAM estimator that limit its broad application. First, the method does not provide error terms for parameter estimates (Curtis et al. 2009). Without a measure of precision, comparing abundance across time and place is limited. Second, the method estimates the relative abundance of males, females, and fawns using raw photographic occurrences (RPO), which assumes that the different groups have equal detection probabilities (McCoy 2010, O’Brien 2011). Failing to meet this assumption will bias abundance estimates in favor of those groups whose individuals are more frequently photographed. Received: 22 December 2010; Accepted: 28 June 2011; Published: 3 October 2011 1 E-mail: mweckel@mianus.org Wildlife Society Bulletin 35(4):445–451; 2011; DOI: 10.1002/wsb.64 Weckel et al.  Using Cameras Traps to Census Deer 445